The Cost Effectiveness of Digital

Subtraction Angiography in the Diagnosis

of Cerebrovascular Disease

May 1985

NTIS order #PB85-241115
HEALTH TECHNOLOGY CASE STUDY 34

The Cost Effectiveness of

Digital Subtraction Angiography

in the Diagnosis of

Cerebrovascular Disease

MAY 1985

This case study was performed as part of OTA’s Assessment of

Medical Technology and Costs of the Medicare Program

Prepared for OTA by:

Matthew Menken, M.D.

Gordon H. DeFriese, Ph.D.

Thomas R. Oliver, M.H.A.

Irwin Litt, M.D.

The Health Services Research Center

University of North Carolina at Chapel Hill

This Case Study was submitted in final version for OTA editing in October 1983.

OTA Case Studies are documents containing information on a specific medical

technology or area of application that supplements formal OTA assessments. The

material is not normally of as immediate policy interest as that in an OTA Report,

nor does it present options for Congress to consider.

CONGRESS OF THE UNITED STATES

OfRce d Technology Assessment

Washington, D C 20510
Recommended Citation:

Menken, Matthew, et al., The Cost Effectiveness of Digital Subtraction Angiography in

the Diagnosis of Cerebrovascular Disease (Health Technology Case Study 34), OTAHCS-34, Washington, DC: U.S. Congress, Office of Technology Assessment, May 1985.

This case study was performed as part of OTA’s assessment of Medical Technology and

Costs of the Medicare Program.

Library of Congress Catalog Card Number 85-600542

For sale by the Superintendent of Documents

U.S. Government Printing Office, Washington, DC 20402
Preface

The Cost Effectiveness of Digital Subtraction

Angiography in the Diagnosis of Cerebrovascular

Disease is Case Study 34 in OTA’s Health Technology Case Study Series. This case study has

been prepared in connection with OTA’s project

on Medical Technology and Costs of the Medicare

Program, which was requested by the House

Committee on Energy and Commerce and its Subcommittee on Health and the Environment and

the Senate Committee on Finance, Subcommittee on Health. A listing of other case studies in

the series is included at the end of this preface.

OTA case studies are designed to fulfill two

functions. The primary purpose is to provide

OTA with specific information that can be used

in forming general conclusions regarding broader

policy issues, The first 19 cases in the Health Technology Case Study Series, for example, were conducted in conjunction with OTA’s overall project

on The Implications of Cost-Effectiveness Analysis of Medical Technology. By examining the 19

cases as a group and looking for common problems or strengths in the techniques of cost-effectiveness or cost-benefit analysis, OTA was able

to better analyze the potential contribution that

those techniques might make to the management

of medical technology and health care costs and

quality.

The second function of the case studies is to

provide useful information on the specific technologies covered. The design and the funding levels of most of the case studies are such that they

should be read primarily in the context of the associated overall OTA projects. Nevertheless, in

many instances, the case studies do represent extensive reviews of the literature on the efficacy,

safety, and costs of the specific technologies and

as such can stand on their own as a useful contribution to the field.

Case studies are prepared in some instances because they have been specifically requested by

congressional committees and in others because

they have been selected through an extensive review process involving OTA staff and consultations with the congressional staffs, advisory panel

to the associated overall project, the Health Program Advisory Committee, and other experts in

various fields. Selection criteria were developed

to ensure that case studies provide the following:

● examples of types of technologies by function (preventive, diagnostic, therapeutic, and

rehabilitative);

examples of types of technologies by physical

nature (drugs, devices, and procedures);

examples of technologies in different stages

of development and diffusion (new, emerging, and established);

examples from different areas of medicine

(e.g., general medical practice, pediatrics,

radiology, and surgery);

examples addressing medical problems that

are important because of their high frequency or significant impacts (e. g., cost);

examples of technologies with associated high

costs either because of high volume (for lowcost technologies) or high individual costs;

examples that could provide information material relating to the broader policy and methodological issues being examined in the

particular overall project; and

examples with sufficient scientific literature.

Case studies are either prepared by OTA staff,

commissioned by OTA and performed under contract by experts (generally in academia), or written by OTA staff on the basis of contractors’

papers.

OTA subjects each case study to an extensive

review process. Initial drafts of cases are reviewed

by OTA staff and by members of the advisory

panel to the associated project. For commissioned

cases, comments are provided to authors, along

with OTA’s suggestions for revisions. Subsequent

drafts are sent by OTA to numerous experts for

review and comment. Each case is seen by at least

30 reviewers, and sometimes by 80 or more outside reviewers. These individuals may be from

relevant Government agencies, professional societies, consumer and public interest groups, medical practice, and academic medicine. Academicians such as economists, sociologists, decision

analysts, biologists, and so forth, as appropriate,

also review the cases.

Although cases are not statements of official

OTA position, the review process is designed to

satisfy OTA’s concern with each case study’s

scientific quality and objectivity. During the various stages of the review and revision process,

therefore, OTA encourages, and to the extent

possible requires, authors to present balanced information and recognize divergent points of view.

. . . Ill
Health Technology Case Study Seriesa

Case Study Case study title; author(s); Case Study Case study title; author(s);

Series No. OTA publication numberb

Series No. OTA publication numberb

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

Formal Analysis, Policy Formulation, and End-Stage Renal

Disease;

Richard A. Rettig (OTA-BP-H-9(1))C

The Feasibility of Economic Evaluation of Diagnostic Procedures: The Case of CT Scanning;

Judith L. Wagner (OTA-BP-H-9(2))

Screening for Colon Cancer: A Technology Assessment;

David M. Eddy (OTA-BP-H-9(3))

Cost Effectiveness of Automated Multichannel Chemistry

Analyzers;

Milton C. Weinstein and Laurie A. Pearlman

(OTA-BP-H-9(4))

Periodontal Disease: Assessing the Effectiveness and Costs of

the Keyes Technique;

Richard M. Scheffler and Sheldon Rovin

(OTA-BP-H9(5))

The Cost Effectiveness of Bone Marrow Transplant Therapy

and Its Policy Implications;

Stuart O. Schweitzer and C. C. Scalzi (OTA-BP-H-9(6))

Allocating Costs and Benefits in Disease Prevention Programs:

An Application to Cervical Cancer Screening;

Bryan R. Luce (Office of Technology Assessment)

(OTA-BP-H-9(7))

The Cost Effectiveness of Upper Gastrointestinal Endoscopy;

Jonathan A. Showstack and Steven A. Schroeder

(OTA-BP-H-9(8))

The Artificial Heart: Cost, Risks, and Benefits;

Deborah P. Lubeck and John P. Bunker

(O-I-A-BP-H-9(9))

The Costs and Effectiveness of Neonatal Intensive Care;

Peter Budetti, Peggy McManus, Nancy Barrand, and

Lu Ann Heinen (OTA-BP-H-9(1O))

Benefit and Cost Analysis of Medical Interventions: The Case

of Cimetidine and Peptic Ulcer Disease;

Harvey V. Fineberg and Laurie A. Pearlman

(OTA-BP-H-9(11))

Assessing Selected Respiratory Therapy Modalities: Trends and

Relative Costs in the Washington, D.C. Area;

Richard M. Scheffler and Morgan Delaney

(OTA-BP-H-9(12))

Cardiac Radionuclide Imaging and Cost Effectiveness;

William B. Stason and Eric Fortess (OTA-BP-H-9(13))

Cost Benefit/Cost Effectiveness of Medical Technologies: A

Case Study of Orthopedic Joint Implants;

Judith D. Bentkover and Philip G. Drew (OTA-BP-H-9(14))

Elective Hysterectomy: Costs, Risks, and Benefits;

Carol Korenbrot, Ann B. Flood, Michael Higgins,

Noralou Roos, and John P. Bunker (OTA-BP-H-9(15))

The Costs and Effectiveness of Nurse Practitioners;

Lauren LeRoy and Sharon Solkowitz (OTA-BP-H-9(16))

Surgery for Breast Cancer;

Karen Schachter Weingrod and Duncan Neuhauser

(OTA-BP-H-9(17))

18

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

The Efficacy and Cost Effectiveness of Psychotherapy;

Leonard Saxe (Office of Technology Assessment)

(OTA-BP-H-9(18))d

Assessment of Four Common X-Ray Procedures;

Judith L. Wagner (OTA-BP-H-9(19))’

Mandatory Passive Restraint Systems in Automobiles: Issues

and Evidence;

Kenneth E. Warner (OTA-BP-H-15(20))f

Selected Telecommunications Devices for Hearing-Impaired

Persons;

Virginia W. Stern and Martha Ross Redden

(OTA-BP-H-16(21))g

The Effectiveness and Costs of Alcoholism Treatment;

Leonard Saxe, Denise Dougherty, Katharine Esty,

and Michelle Fine (OTA-HCS-22)

The Safety, Efficacy, and Cost Effectiveness of Therapeutic

Apheresis;

John C. Langenbrunner (Office of Technology Assessment)

(OTA-HCS-23)

Variation in Length of Hospital Stay: Their Relationship to

Health Outcomes;

Mark R. Chassin (OTA-HCS-24)

Technology and Learning Disabilities;

Candis Cousins and Leonard Duhl (OTA-HCS-25)

Assistive Devices for Severe Speech Impairments;

Judith Randal (Office of Technology Assessment)

(OTA-HCS-26)

Nuclear Magnetic Resonance Imaging Technology: A Clinical,

Industrial, and Policy Analysis;

Earl P. Steinberg and Alan Cohen (OTA-HCS-27)

Intensive Care Units (ICUs): Clinical Outcomes, Costs, and

Decisionmaking;

Robert A. Berenson (OTA-HCS-28)

The Boston Elbow;

Sandra J. Tanenbaum (OTA-HCS-29)

The Market for Wheelchairs: Innovations and Federal Policy;

Donald S. Shepard and Sarita L. Karen (OTA-HCS-30)

The Contact Lens Industry: Structure, Competition, and Public

Policy;

Leonard G. Schifrin with William J. Rich (OTA-HCS-31)

The Hemodialysis Equipment and Disposable Industry;

Anthony A. Romeo (OTA-HCS-32)

Technologies for Managing Urinary Incontinence;

(OTA-HCS-33)

The Cost Effectiveness of Digital Subtraction Angiography in

the Diagnosis of Cerebrovascular Disease;

Matthew Menken, Gordon H. DeFriese, Thomas R. Oliver,

and Irwin Litt (OTA-HCS-34)

aAvailable for sale by the Superintendent of Documents, I J.S, Government dBackgound paper #3 t. The imp]icat;o~ of C’ost-Effectiveness Analysls of

Printing Office, Washington, DC, 20402, and by the National Technical Medical Technology,

Information Service, 5285 Port Royal Rd., Springfield, VA, 22161. Call ‘Background Paper #5 to The Implications of C’ost-Effectiveness Analysis of

OTA’S Publishing Office (224-8996) for availability and ordering infor- Medical Technology.

mation. fBackWound paper #1 to OTA’S May 1982 report Technology and Handiboriglna] publication numbers appear in parentheses. capped People.

c

The first 17 cases in the series wem 17 separately issued cases in Background gBackground Pa~r #2 to Technology and FIandicapped People.

Paper #2: Case Studies of Medical Technologies, prepared in conjunction

with OTA’S August 198J report The implications of Cost-Effectiveness Analvsis ot Medical Technology.

iv
OTA Project Staff for Case Study #34

Roger Herdman, Assistant Director, OTA

Health and Life Sciences Division

Clyde J. Behney, Health Program Manager

Anne Kesselman Burns, Project Director

Katherine E. Locke, Research Assistant

Pamela J. Simerly,l Research Assistant

Edward Seibert,2 Research Assistant

Brad Larson,3 Research Assistant

Virginia Cwalina, Administrative Assistant

Beckie I. Erickson, P. C./Word Processor Specialist

Brenda Miller,4 P. C./Word Processor Specialist

Diann Hohenthaner,5 Secretary

Carol Guntow,6 Clerical Assistant

‘Until September 1984

‘September 1984

‘S]nce March 1985

‘Until January 1985.

‘S]nce February 1985

‘S]nce October 1984
Medical Technology and Costs of the Medicare Program Advisory Panel*

Stuart Altman, Panel Chair

Dean, Florence Heller School, Brandeis University

Frank Baker

Vice President

Washington State Hospital Association

Robert Blendon

Senior Vice President

The Robert Wood Johnson Foundation

Jerry Cromwell

President

Health Economics Research

Chestnut Hill, MA

Karen Davis

Chair, Department of Health Policy and

Management

School of Hygiene and Public Health

Johns Hopkins University

Robert Derzon

Vice President

Lewin & Associates

Washington, DC

Howard Frazier

Director

Center for the Analysis of Health Practices

Harvard School of Public Health

Clifton Gaus

President, Foundation for Health Services

Research

Washington, DC

Jack Hadley

Director

Center for Health Policy Studies

Georgetown University

Kate Ireland

Chairman, Board of Governors

Frontier Nursing Service

Wendover, KY

Judith Lave

Professor

Department of Health Economics

University of Pittsburgh

Mary Marshall

Delegate

Virginia House of Delegates

Walter McNerney

Professor of Health Policy

J. L. Kellogg Graduate School of Management

Northwestern University

Morton Miller

Immediate Past President

National Health Council

New York, NY

James Mongan

Executive Director

Truman Medical Center

Kansas City, MO

Seymour Perry

Deputy Director

Institute for Health Policy Analysis

Georgetown University Medical Center

Robert Sigmond

Director, Community Programs for

Affordable Health Care

Advisor on Hospital Affairs Blue Cross/Blue

Shield Associations

Anne Somers

Professor

Department of Environmental and

Community and Family Medicine

UMDNJ—Rutgers Medical School

Paul Torrens

School of Public Health

University of California, Los Angeles

Keith Weikel

Group Vice President

AMI

McLean, VA

*The affiliations of the panel members reflect their positions during the assessment (June 1982-July 1984).

vi
Contents

Page

CHAPTER 1: INTRODUCTION AND

SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . 3

Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Summary and Conclusions . . . . . . . . . . . . . . 4

Organization of the Case Study . . . . . . . . . . 6

CHAPTER 2: STROKE AS A CLINICAL

PROBLEM . . . . . . . . . . . . . . . . . . . . . . . . . . 9

The Extent of the Problem . . . . . . . . . . . . . . 9

Treatment of Stroke . . . . . . . . . . . . . . . . . . . . 10

CHAPTER 3: INTRODUCTION TO

DIGITAL SUBTRACTION

ANGIOGRAPHY . . . . . . . . . . . . . . . . . . . . 15

Technological Development . . . . . . . . . . . . . . 15

Contemporary Methods and Clinical

Applications . . . . . . . . . . . . . . . . . . . . . . . . . 15

Clinical Efficacy and Effectiveness

of DSA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

The Safety (Associated Patient Risks)

of DSA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

CHAPTER 4: THE COSTS OF DIGITAL

SUBTRACTION ANGIOGRAPHY . . . . . 25

Purchase and Utilization Costs . . . . . . . . . . . 25

Patient Costs and Charges . . . . . . . . . . . . . . . 26

Implicit and Intangible Costs . . . . . . . . . . . . 26

Diffusion and Social Costs . . . . . . . . . . . . . . 27

CHAPTER 5: THE COST EFFECTIVENESS

OF DIGITAL SUBTRACTION

ANGIOGRAPHY . . . . . . . . . . . . . . . . . . . . 31

Review of Existing Studies of the Cost

Effectiveness of DSA . . . . . . . . . . . . . . . . . 31

New Technology and Patterns of

Medical Practice: Critical

Assumptions Underlying an Analysis

of Cost Effectiveness. . . . . . . . . . . . . . . . . . . . 33

Quantitative Estimates of the Cost

Effectiveness of DSA . . . . . . . . . . . . . . . . . . . 36

APPENDIX A: ACKNOWLEDGMENTS

AND HEALTH PROGRAM

ADVISORY COMMITTEE . . . . . . . . . . . 45

APPENDIX B: GLOSSARY OF TERMS

AND ACRONYMS. . . . . . . . . . . . . . . . . . . 48

REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Tables

Table No. Page

2-1.

3-1.

3-2.

3-3.

3-4.

5-1.

5-2.

5-3.

5-4.

5-5.

5-6.

5-7.

Death Rates for Cerebrovascular

Diseases by Age Groups,

United States, 1980 . . . . . . . . . . . . . . . . . 9

Attempted Applications of DSA

Reported in the Literature . . . . . . . . . . . 17

Comparative Advantages of DSA

and Conventional Arteriography . . . . . 18

Levels At Which Diagnostic

Technologies May Be Assessed . . . . . . . 19

DSA Radiation Exposure Estimates

for Cerebrovascular Studies . . . . . . . . . 20

Data Used for Cost-Effectiveness

Analysis of DSA. . . . . . . . . . . . . . . . . . . 32

Estimated Charges for

DSA Examinations . . . . . . . . . . . . . . . . . 38

Estimates of the Cost Effectiveness

of DSA (with fixed charges for

arteriography) . . . . . . . . . . . . . . . . . . . . . 38

Estimates of the Cost Effectiveness

of DSA (with variable charges for

arteriography) . . . . . . . . . . . . . . . . . . . . . 39

Estimates of Cost Effectiveness

of DSA for Expanded Population

At Risk With Variable Yield Rates

for Positive Findings . . . . . . . . . . . . . . . . 40

Estimates of the Cost Effectiveness

of DSA for a Population At Risk

With Variable DSA Yield Rates and

Variable Arteriography Charges . . . . . . 41

Estimates of the Cost Effectiveness

of DSA for a Population At Risk

Expanded Four-Fold With Variable

Yield Rates for Baseline Findings . . . . . 42

Figures

Figure No. Page

3-1.

5-1.

5-2.

Diagram of a Digital Subtraction

Angiography (DSA) System . . . . . . . . . 16

Clinical Alternatives Without

DSA Available.. . . . . . . . . . . . . . . . . . . . 33

Clinical Alternatives With

DSA Available . . . . . . . . . . . . . . . . . . . . . 33

vii
OTA Note

These case studies are authored works commissioned by OTA. Each author

is responsible for the conclusions of specific case studies. These cases are not statements of official OTA position. OTA does not make recommendations or endorse

particular technologies. During the various stages of review and revision, therefore, OTA encouraged the authors to present balanced information and to recognize divergent points of view.

. . . Vlll
1.

Introduction and Summary
1.

Introduction and Summary

BACKGROUND

Digital subtraction angiography (DSA) is a

new, and rapidly developing, technology in the

field of diagnostic radiology. DSA is one of several computer-assisted radiologic tools for diagnosing conditions associated with the internal

structure of blood vessels. The technique usually

involves injecting contrast medium into the veins

and measuring over time the changing concentration of contrast medium passing through the

vascular structures of interest. 1 Through the use

of a computer, the images before the contrast injection are “subtracted” from those after injection

to give a numerical representation of the arterial

structure under study. This relatively noninvasive2 technique can be performed on an outpatient

basis with very low risk of morbidity compared

to conventional and (invasive) techniques such as

arteriography. 3

DSA has been shown to have important clinical uses in diagnostic studies of the carotid, renal, intracranial, and peripheral arteries, the aorta

and in pulmonary studies. There are reasonable

expectations that this procedure will develop to

the point where it will have wide applicability in

the diagnosis of coronary artery disease in the next

several years.

Since 1980, when prototype commercial systems were introduced in the United States, improvements in the design and capacity of available DSA equipment have established the clinical

efficacy and effectiveness of this procedure for cer-

‘With respect to cembrovascular diagnostic studies, both intravenous and intra-arterial DSA have been employed. However, in

this case study the notation “DSA” is used to signify intravenous

applications only. The focus is limited to intravenous DSA, because

it is the method employed in the evaluation of the extracranial circulation, especially the carotid arteries, in most cases as of October

1983, when this case study was submitted to OTA for final editing.

2A relatively noninvasive technique is a technique that involves

puncturing or atheterizing a vein, which carries considerably lower

morbidity than techniques that involve puncturing or catheterizing

an artery, such as conventional arteriography.

‘See the glossary of terms for definitions of selected medical terms

(app. B).

tain purposes. These improvements have also

raised the possibility of applications in dozens of

additional areas of diagnostic radiology.

The rapidity with which this technology has

been developed and diffused throughout the medical care system in the United States raises important public policy questions about the cost implications of the procedure, especially its relative cost

effectiveness when compared to other diagnostic

radiology technologies it may replace. It is likely

that the fact that this technique is relatively noninvasive will increase its importance and frequency

of use as a preliminary examination procedure for

the diagnosis of certain types of diseases. For these

reasons, it is important to know under what conditions it may be expected to yield cost savings

over currently available technologies.

In this case study, a single category of clinical

problems where DSA is in use on a broad scale—

cerebrovascular disease—is selected as the context within which the cost effectiveness of DSA

is explored.4 This case study does not present new

primary data from a prospective study of DSA

use in the diagnosis and management of cerebrovascular disease. Rather, the data derived from

the very few studies that already exist are used

to test certain assumptions about the cost effectiveness of this new technology compared to conventional arteriography. Furthermore, because the

data available to explore these questions are not

precisely what would be required to conduct the

appropriate test, the calculations presented in this

case study will not be completely satisfactory to

those with expertise in cost-effectiveness analysis.

The intention of this study, however, is to present a careful description of the current and potential application of DSA within the area of diag4A majority of the DSA procedures performed are examinations

of the carotid arteries. The diagnosis of carotid artery disease (a

common manilkstation of cerebrovascular disease) is important since

it is a major cause of stroke.

3
4

nostic radiology concerned with cerebrovascular

disease and to suggest the implications of the technology for patterns of clinical practice and patient

care costs under different assumptions. The diagnosis and treatment of stroke, as well as the problems of identifying patients at high risk for stroke,

represent clinical activities with broad implications for American health care resource allocaSUMMARY AND CONCLUSIONS

DSA is clearly a major technological advance

in the field of diagnostic imaging radiography.

Further refinements of the basic technology in the

next several years are expected to enhance its present utility in the diagnosis of cerebrovascular disease, a major cause of death in the United States.

There are several technologies of varying degrees of invasiveness already in widespread use

in the diagnosis and treatment of cerebrovascular

disease. DSA presents a new alternative to conventional arteriography for establishing the presence or absence of carotid artery stenosis (narrowing). Although the technique is more sensitive

and specific than some noninvasive tests (i. e.,

ultrasonography) for the diagnosis of arterial

stenosis, and more effective than real-time ultrasound for the diagnosis of ulcers, DSA remains

somewhat less accurate than conventional arteriography, especially for the evaluation of ulcerative lesions. However, as technological improvements take place, the speed and spatial resolution

of DSA images of the cerebral vascular system

are expected to eventually approach the accuracy

of arteriography. Physician acceptance of DSA

as a substitute for arteriography is expected to occur rapidly and to reach a level beyond 80 percent replacement (64), except perhaps in some

teaching medical centers. In these centers, diagnostic evaluations are often duplicative.

For those patients who are now being examined by arteriography, it is relatively simple to

formulate a reasonable estimate of the number

who may subsequently receive only a DSA examination. It is more difficult to estimate the number of patients at risk of cerebrovascular disease

in the general population who might be screened

tion. Because of the importance of stroke as a

leading cause of death, and because of the high

cost of acute medical care, rehabilitation, and

long-term care requirements for stroke victims,

the investigation of new techniques for clinical

management of this set of problems merits serious attention by health care providers and policymakers alike.

through the use of DSA, but who would not be

considered candidates for arteriography or

surgery.

This case study outlines a number of assumptions about the way in which DSA might be integrated with current patterns of practice in primary care and neurological specialties. In the

United States, 87 percent of the patients served

by neurologists are referred by other (usually

primary care) physicians. The management of

patients with a clinical diagnosis of transient

ischemic attack (TIA), one of the most common

clinical indicators of cerebrovascular disease and

possibly a forthcoming stroke, is determined by

the physician who has first contact with the patient following such an event. Because a physician will almost never witness a TIA, most TIAs

are diagnosed on the basis of the history and physical examination of the patient some time after

the TIA has occurred. Since TIAs are presumed

signs of a possible forthcoming stroke, they usually precipitate the patient’s contact with the medical care provider.

There is considerable ambiguity and confusion

among physicians (in neurology and in primary

care specialties) over the most appropriate management strategies for patients with a history of

TIAs (105). Moreover, there is a significant risk

that some patients will be misdiagnosed as having had a TIA. It is important to recognize that

TIA is a clinical diagnosis; it is not a diagnosis

formulated on the basis of a radiographic test or

procedure. When arterial stenosis is discovered

with a DSA exam, the physician may conclude

that a patient’s dizzy spell, temporary numbness

in a hand or foot, or an unusual ocular problem
5

was a TIA. The problem with this pattern of decisionmaking and medical practice is that asymptomatic atherosclerosis is prevalent in the general

population. A temporary neurological problem

and arterial stenosis often coexist, and yet may

be totally unrelated to one another. Causality is

established through clinical judgment alone.

At present, conventional arteriography is the

most accurate technology for testing the hypothesis of carotid artery stenosis. Because of the risk

of morbidity and the special circumstances under

which this procedure is done (usually requiring

hospitalization of the patient), there are many factors operating to constrain the overuse of conventional arteriography. The introduction of DSA

makes available a less costly, relatively low risk,

highly accurate, and useful source of the same

diagnostic information now available through

arteriography.

The introduction of any new medical technology is usually followed by a period of experimentation during which individual physicians explore

the utility and accuracy of the new technology,

while continuing to use those techniques with

which they are familiar, Such a pattern may be

expected with DSA. In the near future, DSA may

be expected to duplicate or supplement the diagnostic information provided by other noninvasive

tests, and arteriography, the test currently used

in the diagnosis of arterial stenosis. Later, the

other noninvasive tests may be expected to be

used less frequently. As the accuracy of DSA becomes accepted as a sufficient basis for surgical

decisionmaking, the utilization of conventional

arteriography for the diagnosis of carotid artery

stenosis may be expected to significantly decline

as well.

An important variable in determining the costs

of DSA is the level of use of each DSA facility

(whether in a hospital or non-hospital setting)–

that is, its operational efficiency. Moreover, it is

necessary to measure the subsequent use of conventional arteriography and other imaging facilities. For example, if the use of arteriography declines substantially, but the equipment, facilities,

and personnel are maintained, then the costs of

DSA will only add to the total costs of diagnostic imaging services taken as a whole. Similarly,

if DSA equipment diffuses widely, and is not utilized efficiently, then the high fixed costs of the

technology will exceed any expected benefits.

As with all types of technology, there is an efficient level of use that includes regionalization

and the sharing of facilities. However, there are

important features of many diagnostic technologies, like DSA and arteriography, that present

special problems with respect to their cost impact.

Unlike therapeutic technologies, which are directed toward known manifestations of disease,

diagnostic technologies have been developed to

aid in the search for clinical evidence to define

and explain conditions of presently unknown

origin. Some of these technologies have been developed for the diagnosis of particular diseases,

but later have been found to have wider applications (5). It is the general pattern of clinical use

of these technologies (which can entail rather

open-ended exploratory uses of a wide variety of

technologies), combined with their technical sophistication and accessibility, that determines their

eventual cost effectiveness.

The estimation of the cost effectiveness of DSA

must be undertaken in a broad context. In this

cost-effectiveness analysis, concern is with the

measurement of the incremental cost of a unit of

benefit under average conditions of use. In the

field of medical practice, it is “average conditions

of use” that make the estimation of cost effectiveness so problematic.

This case study suggests that DSA is likely to

be cost effective if its pattern of use is a substitute for, rather than a supplement to, conventional arteriography in the diagnosis of carotid

artery disease. Preliminary accuracy and sensitivity data for DSA suggest the prospects for this

pattern of acceptance and use are rather high.

However, under average conditions of use, the

availability of DSA is likely to result in a much

larger number of patients evaluated for possible

carotid artery disease. In fact, seven times the

number of patients now receiving conventional

arteriography would, it is estimated, receive DSA

examinations in connection with the diagnosis of

carotid artery disease, and it is likely that many

of these patients will also receive more than a

single DSA exam during the same episode of care.
6

Because DSA offers an alternative to conventional arteriography that has a lower risk of morbidity and can be done on an outpatient basis,

it can be expected that many patients (once they

know about its availability) will want the procedure performed. These patients and their families are likely to value the procedure highly for

its ability to reduce the worry and uncertainty

associated with certain diagnostic conditions.

Given the demonstrated high quality, sensitivity and specificity of DSA images for the study

of carotid artery disease, the relatively low risk

of morbidity and the lack of need for hospitalization, it is likely that an increasing number of

patients will have DSA studies ordered by their

primary care physicians prior to consultation with

a necrologic specialist. Whereas conventional

arteriography was almost never performed without benefit of a necrologic opinion, DSA will frequently become part of the primary physician’s

initial evaluation protocol. Since DSA results are

of such high quality and presumably easier to interpret, it is likely that necrologic consultants will

be bypassed more frequently by primary physicians in their decisions to refer patients for surgical therapy when carotid artery disease is diagnosed. The use of DSA by primary care physicians

in diagnosing carotid artery disease is likely to increase the volume of unnecessary surgical therapy for patients undergoing DSA examinations,

These trends warrant careful attention over the

next several years.

ORGANIZATION OF THE CASE STUDY

Chapter 2 presents an overview of cerebrovascular disease generally, and stroke specifically, as

clinical problems. After discussing the direct and

indirect costs of stroke, the theory of preventive

therapy is introduced, using TIAs as an example.

Numbness of a foot or a hand, blindness in one

eye or double vision, are all “early warning”

signals of stroke and should lead to further neurological examination. Chapter 2 concludes that

new medical techniques are needed to help in the

early diagnosis of stroke.

Chapter 3 provides an indepth look at the technology, DSA. It describes the development,

growth and operation of DSA and compares DSA

to arteriography. Efficacy and safety are highlighted as two explicit advantages of DSA. The

evaluation of aortic arch abnormalities, aortic

coarctation, and vascular bypass grafts are some

of the clinical applications

chapter 3.

of DSA discussed i n

Chapter 4 looks at the costs of DSA. There are

many costs involved in acquiring a new technology. Chapter 4 initially analyzes two main types

of costs: capital costs (computers, X-ray equipment and facilities) and operating costs (personnel and supplies). Next, direct implicit and intangible costs, costs related to diffusion, and social

costs are all discussed.

The purpose of chapter 5 is to study the cost

effectiveness of DSA. “Cost per procedure” and

“cost per lesion” are compared with the same data

found for arteriography. Conclusions are then

made concerning the increase in future use of DSA

in the diagnosis of cerebrovascular disease.
.

2.

Stroke as a Clinical Problem
.

2.

Stroke as a Clinical Problem

THE EXTENT OF THE PROBLEM

Stroke (completed cerebral infarction) is the

third most common cause of death in the United

States. In addition to its importance as a cause

of mortality, stroke and associated disorders

affecting the central nervous system account for

a significant burden of illness treated by the medical care system. A major cause of stroke is carotid

artery disease (a common manifestation of cerebrovascular disease), which is often diagnosed

through digital subtraction angiography (DSA)

examination.

Several studies have reported that the incidence

of stroke has declined over the last several years

in the United States (40,41,79,95). Future projections of the need for diagnostic or therapeutic

technologies for treating stroke need to take these

trends into account. However, the age-specific

death rates from these conditions, taken as a

whole, have continued to be significantly higher

for persons beyond the age of 55 than for younger

persons (see table 2-1). Likewise, the volume of

diagnostic procedures used in the care of persons

suspected of having cerebrovascular disease is

higher among those older age groups.

Table 2-1 .—Death Rates for Cerebrovascular Diseases

by Age Groups, United States, 1980 (number of deaths

per 100,000 resident population)

Total, all ages, adjusted . . . . . . . . . . . . . . . . . . . . 41.5

Total, all ages, crude . . . . . . . . . . . . . . . . . . . . . . . 76.6

Under 1 year . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.8

1-14 years . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.3

15-24 years . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2

25-34 years . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.7

35-44 years . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.6

45-54 years . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . 26,1

55-64 years . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67.8

65-74 years . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 222.4

75-84 years . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 834.7

85 years and older , . . . . . . . . . . . . . . . . . .......2,094.0

SOURCE: U.S Department of Health and Human Services, National Center for

Health Statistics, Hea/th, Lhifed States, 1982, table 19, p 67

Cerebrovascular disease in general has been

estimated to have an annual incidence of 195 per

100,000 population per year (62). The Office of

Graduate Medical Education of the U.S. Department of Health and Human Services (DHHS) convened a special panel of experts to consider the

number of neurological care physicians needed to

care for this volume of illness on an annual basis

(42). This panel concluded that 967 hours of

neurological specialty care would be required annually per 100,000 population. This level of medical specialty care would also be provided by types

of health personnel other than neurologists—

physiatrists (specialists in rehabilitation medicine),

physical therapists, speech pathologists, occupational therapists, and others (42).

Cerebrovascular disease occupies a significant

portion of the practice of primary care physicians

as well. Although stroke is not among the top 25

outpatient diagnostic encounters recorded by

family physicians, cerebrovascular disease (ICD-9

Code 336: “Acute, but ill-defined, cerebrovascular

disease”) is the second most common diagnosis

for hospital patients of office-based general practice and family physicians in the United States

(43). It has been estimated that 13 percent of all

hospital patients have a primary and/or secondary necrologic diagnosis (113), and that at least

50 percent of these diagnoses are for cerebrovascular disorders (46). This situation reflects the frequency with which stroke patients require longterm institutional care.

The costs of stroke are enormous. In 1975, the

direct and indirect costs of stroke were estimated

to be approximately $9.5 billion annually (103).

Because many patients with a stroke have losses

of intellect and locomotion that require long-term

institutionalization, prevention of stroke is a major health care objective at this time.

9
10

TREATMENT OF STROKE

Once a completed stroke has occurred, no

known treatment can repair damaged tissue to restore function. Thus, preventive care is essential

in the management of patients with cerebrovascular disorders. Since completely effective preventive therapy—the elimination of hypertension and

atherosclerosis—is not available at this time,

“half-way” preventive therapies are currently

employed. These include general medical measures, such as control of hypertension and cardiac

arrhythmias, if present, as well as surgical measures, such as endarterectomy (the surgical removal

of cholesterol plaque from the inner surfaces of

arteries) or cerebral bypass surgery.

The dominant theory underlying preventive

therapies for stroke is the identification of strokeprone individuals who have had transient ischemic attacks (TIAs). A TIA is a reversible episode

of cerebrovascular insufficiency that usually lasts

less than one hour, and always lasts (by definition) less than 24 hours. These “warning spells”

have an incidence of 30 per 100,000 total population per year (62). The interval between episodic

attacks varies from several hours to several

months or longer. While the episodes often follow a stereotyped pattern in a given patient, their

modes of occurrence vary. It is most commonly

thought that they arise from the passage of microemboli of fibrin-platelets or cholesterol into the

cerebral circulation.

Although TIAs area form of physiologic disturbance, they are generally grouped on an anatomic

basis by clinicians according to the visible symptoms. TIAs include those of carotid artery origin,

those of vertebral and basilar artery origin, and

those of indeterminate origins. It should be noted

that a physician rarely witnesses a TIA and is dependent for clinical diagnosis upon the patient’s

recall and medical history. The hallmark of a TIA

is the localized disturbance of brain function that

is associated with specific physiologic symptoms.

A hand or foot may become numb, or one side

of the body may show such symptoms. One eye

may become blind, or partly blind, or double vision (diplopia) may occur. Vertigo and dizziness,

disturbances of speech and language, and episodes

of leg weakness, are other symptoms that may

reflect the occurrence of a TIA.

When a TIA is suspected, a clinician performs

a complete physical neurological examination and

searches for evidence of heart disease or disease

of the carotid/vertebrobasilar systems. A murmur (bruit), audible with a stethoscope, over a

major artery in the neck is often a sign of turbulent

blood flow resulting from atherosclerosis of the

underlying vessel. This sign is a good bedside indicator of arterial narrowing (stenosis), but both

the presence or absence of a bruit may be misleading. For example, it is known that as a vessel

becomes progressively narrowed, the loudness of

a bruit may actually diminish, so that when disease is severe and advanced, no bruit maybe audible. Other bedside signs include a difference of

greater than 15 percent between the blood pressures recorded in both arms, absence of a palpable

branch of the external carotid artery, or the

visualization of embolic material in the retinal circulation with an ophthalmoscope.

To supplement bedside testing, a number of

“noninvasive” tests (requiring neither arterial nor

venous punctures) are currently employed to

assess the extracranial circulation. Ophthalmodynamometry enables physicians to record the

blood pressure in the ophthalmic artery, the first

major intracranial branch of the carotid artery

itself. A computed tomography (CT) scan may

demonstrate a stroke in the brain. Such a test suggests that the clinical impression of TIA was in

error, and that a completed cerebral infarction,

or stroke, has actually occurred. Strokes may be

ischemic (reduced CT density), hemorrhagic (increased CT density), or both. Thermography may

show a diminished temperature over the medial

forehead, which may indicate carotid artery disease. Real-time ultrasound (also known as a Bscan, a test which measures the anatomical structure of vessels), and a Doppler device (an imaging device for measuring the flow velocity of

blood through the arteries), may provide evidence

of the extent of arterial lumen compromise and

disturbance of blood flow.
11

If the physician decides that the patient is at

significant risk for a stroke, and that surgery may

be indicated to relieve arterial obstruction, an

arteriogram (also called an angiogram) has always

heretofore been indicated. This is an “invasive”

test requiring direct arterial puncture. The overall complication rate of this test is 1.7 to 3.7 percent. The radiation exposure is approximately 20

REM per arteriogram (24). Apart from risk of

associated morbidity, the conventional arteriogram is uncomfortable for the patient and usually requires a period of inpatient hospitalization

to observe the patient for possible complications

arising from the procedure. Most practicing physicians recommend consultation with a neurologist

and/or surgeon for the majority of patients who

are possible candidates for arteriography to determine: a) that symptoms are due to TIA; b) that

a significant risk of stroke remains if no therapy

is provided; and c) that surgery is feasible if

arteriography demonstrates a significant lesion.

Because of careful screening, carotid lesions are

usually demonstrated in 75 to 80 percent of all

patients having arteriograms following carotid

TIAs (24).

For patients who are not surgical candidates

(before or after arteriography), anticoagulant drug

therapy is usually considered. Another possible

therapy includes medications that inhibit platelet

aggregation (e.g., aspirin or dipyridamole). Available data suggest that TIAs maybe prevented with

long-term medical prophylaxis, especially in men,

but the effectiveness of this therapy to prevent

strokes due to extracranial vascular disease remains uncertain (103,104).
3.

Introduction to Digital

Subtraction Angiography
Introduction to Digital

Subtraction Angiography

Digital subtraction angiography (DSA) is a new

radiographic technology used in diagnosing vascular disease. DSA is employed to obtain images

of arteries in various parts of the body and is

highly effective in contrasting arterial structures

with their surrounding bone and soft tissue (3).

DSA has proven especially useful in the identification of vascular abnormalities, including occlusions, stenoses, ulcerated plaques, and aneurysms

(21,58,107).

The potential importance of DSA in the diagnosis of cerebrovascular disease is suggested by

Reuter’s (87) observation that as much as oneTECHNOLOGICAL DEVELOPMENT

The development of DSA was a result of the

research of medical physics groups at the University of Wisconsin, the University of Arizona, and

the Kinderklinik in Kiel, West Germany during

the early 1970s (21,58,74). Fundamental advances

in intravenous arteriography, which had been intermittently used since the 1930s, were made possible by the introduction of cesium iodine image

intensifiers and advances in digital electronic

methods of storing and manipulating information

(21). By 1978, the feasibility of DSA for human

subjects was demonstrated, and prototype commercial DSA systems were introduced in 1980 at

the Universities of Arizona and Wisconsin, the

Cleveland Clinic, and South Bay Hospital in

Redondo Beach, California (57,58,74). There are

quarter of the combined volume of neuroradiology and angiography services in some medical

centers is now directed toward evaluating carotid

and cerebral atherosclerosis, including stroke. The

Cooperative Study of Transient Ischemic Attacks

(TIAs) (102) reported an average of 5.4 definite

TIAs per 100 acute beds per year in the participating medical centers. Estimates of the use of

arteriography procedures for these hospitalized

patients range between 87 and 97 percent (23).

DSA will either supplement or replace a large portion of the arteriographic procedures.

now nearly 20 manufacturers of DSA systems and

many more in the process of developing new systems (18).

The size of the market for DSA equipment is

somewhat difficult to estimate because of the uncertain future of demonstrated uses of DSA in coronary angiography. A spokesperson for one of

the major manufacturers of DSA equipment

shared two projections of investment banking

firms for all types of DSA units for the period

from 1982 through 1986. One firm projected total

sales of 5,160 units, while the other firm projected

sales of 9,800 units for the same period. There

were estimated to be about 600 DSA units of all

types in operational status as of January 1983.

CONTEMPORARY METHODS AND CLINICAL APPLICATIONS

With respect to cerebrovascular diagnostic in the evaluation of the extracranial circulation,

studies, both intravenous and intra-arterial DSA especially the carotid arteries, in most cases.1

have been employed. However, in this case study

the notation “DSA” is used to signify intravenous

applications only. The focus is limited to intra- ‘As of October 1983, when this case study was submitted to OTA

venous DSA, because it is the method employed for final editing.

15
16

DSA systems work in the manner depicted in

figure 3-1 as follows: a contrast medium is injected

intravenously; X-ray detection of the contrast

medium produces 1 to 30 exposures per second

(before and after the injection of contrast medium); and arterial images are converted from

analog to digital form and transmitted to a computer-storage complex (55). The digitalized image information makes it possible to “subtract”

the precontrast images from those obtained after

contrast injection so as to visualize arterial structures without direct arterial puncture and injection. The data can be recalled for viewing on a

video screen, and successive images created

through subtraction techniques which allow the

contrast of the arterial structures to be visualized

for the detection of abnormalities.

The purpose of the subtraction process used in

DSA is to eliminate (or factor out) the bone and

soft tissue images that would otherwise be superimposed on the artery under study (12,58). The

serial images show changes in the contrast appearance over time (temporal subtraction) and at varying X-ray intensities (energy subtraction) (12,57).

Most DSA examinations require 25 to 45 minutes to perform (63,99,112), if there are no technical complications (e.g., difficulties with catheterization), and can be performed on an outpatient

basis. This is a considerable advantage in safety

and cost over most standard arteriographic examinations, which require at least overnight

observation of the patient in the hospital to detect

post-procedure arterial obstruction or hemorrhage

(24,33). However, a small number of the latter

have been safely performed on an ambulatory

basis in recent years (45).

DSA has a wide range of clinical applications

in addition to its use in carotid artery studies.

Mistretta and his colleagues (74) at the University of Wisconsin have substituted DSA for standard arteriography in the evaluation of aortic arch

anomalies, aortic coarctation, and vascular bypass grafts. Digital subtraction techniques have

also been used for imaging of the abdominal, cardiac, pulmonary, carotid, intracerebral, and

peripheral vessels. Table 3-1 provides an overview

of the range of attempted applications of DSA imaging technology reported in the literature. BeFigure 3-1 .—Diagram of a Digital Subtraction Angiography (DSA) System

I

I

I

I

I

/

I

I

I

I

I

I

I

I

I

I

I

I

I

;

I

I

I

I

SOURCE: Office of Technology Assessment. Adapted with permission of the General Electric Co, from G. S. Keyes, N. J, Pelc, S, J. Riederer, et al., Digita/ F/uorography

A Teclmology (@date (Milwaukee, Wl: General Electric Co., 1981),
17

Table 3-1 .—Attempted Applications of DSA Reported in the Literaturea

Anatomical regions studied

Principal author of study Carotid Thoracic Cardiac Abdominal Intracranial Pulmonary Peripheral Aorta Renal Other

Weinstein, et al. (1981)b

. . . . . . X . . . . . . .

Crummy, et al. (1980). . . . . . . . . X . . . . . . . . .

Levy, et al. (1982). . . . . . . . . . . X . . . . . . . . .

Brody, et al. (1982). . . . . . . . . . . X . . . . . . . . .

Turnipseed (1982). . . . . . . . . . . . X . . . . . . . . .

Buonocore, et al. (1981). . . . . . . . . . . . . . . . . .

Mistretta, et al. (1981). . . . . X . . . . . . . . .

Hillman, et al. (1981). . . . . . . . . . . . . . . . . . . .

Johnson (1982) . . . . . . . . . . . . . . . . . . . . . . . . .

Kruger, et al. (1981 )........ .. X.. . . . . . . .

Meaney, et al. (1980 )....... .. X.. .. .X...

Pond, et al. (1982 )....... . . . .. X.. . . . . . . .

Chilcote. et al. (1981).. . . . . . .. X.. . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . x x. . . . ... .X.... . . . . . . . . . .x.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

aDoe~ not necess~ily imply routine clinical use at this time

bFull cltatlons found In References Sect!on

SOURCE Off Ice of Technology Assessment

cause of problems with spatial and contrast

resolution, virtually all examinations of the coronary arteries, which cannot be adequately visualized with intravenous DSA at the present time,

require arteriography.

Because DSA functions as both a screening procedure for at-risk or asymptomatic patients and

as an evaluative procedure for reconstructive surgery (74,108), estimates of the probable volume

of use based only on the latter type of use are

bound to be conservative. DSA makes a unique

contribution to the field of diagnostic radiology

(3), serving as a bridging technique between

totally noninvasive tests and conventional arteriography, at times replacing the latter. Turnipseed

and his colleagues (107) clarified the respective

uses of the techniques available to the radiologist

and clinician for diagnostic imaging:

Arteriography has played an important role

in the surgical management of peripheral vascular disease because of its ability to precisely

define the location and severity of arterial lesions. However, its clinical use has been limited

by the risks of arterial catheterization, hospitalization cost, and poor patient acceptance. Arteriography is now commonly used to confirm a

diagnosis of vascular disease and to plan appropriate surgical management in patients with

symptoms and physical findings of arterial insufficiency.

Because arteriography has not been practical

for routine diagnostic screening, a variety of

noninvasive screening tests have been developed

as diagnostic aids. These noninvasive methods

allow more objective evaluation of larger patient

populations and are attractive because of safety,

cost efficiency, patient acceptance, and the accuracy in detecting hemodynamically significant

occlusive lesions. These techniques have been

used primarily for diagnostic screening and postoperative assessment.

Although noninvasive methods are useful,

they have limited capabilities and some serious

shortcomings. Many noninvasive tests are indirect and restricted by technical limitations to

evaluation of isolated arterial segments. Most

cannot define or distinguish minor stenosis and

ulceration from normal vessels and have difficulty in assessing remote areas of the circulation

(intracranial, cardiac, and visceral systems).

Noninvasive equipment is expensive, often very

specialized, and requires personnel with specific

technical and interpretive skills (107).

DSA, therefore, has the potential of significantly

improving the radiologist’s and clinician’s capabilities in diagnostic screening and postoperative

assessment.

Furthermore, DSA is likely to limit the use of

older noninvasive tests (e. g., periorbital ultrasonography and thermography), because of

greater sensitivity and specificity for diagnostic

purposes. However, the evaluation of DSA as a

diagnostic technology for the study of carotid

artery disease must note the increasing development and diffusion of ultrasound-based methods

for diagnosing extracranial occlusive vascular dis-
18

ease. These technologies have developed very rapidly and newer methods are likely in the future.

Because of the safety of these tests, their popularity in clinical practice is not likely to be

displaced by DSA in complex or poorly understood clinical situations. However, it may be expected that, where the diagnosis of a carotid TIA

seems highly likely on clinical grounds alone, the

physician may select DSA as the initial diagnostic test.

Of the large and growing number of noninvasive tests, ultrasound imaging has proved to be

the most versatile and reliable in clinical practice.

A combination of B-mode real-time imaging, with

a Doppler scanning device (often called “duplex

scanning”), has become increasingly prevalent.

Using this method, an image of the carotid vessel

is obtained with the B-scan, and then the blood

flow pattern at a given anatomic location is determined with the Doppler signal. This method is

advantageous in noninvasive diagnosis in skilled

hands, but it takes considerable experience for an

operator to become sufficiently expert in the use

of this tool to produce reliable and reproducible

information of clinical value. However, in part

because these techniques have proved popular

with practicing clinicians, and in part because they

are affordable in office-based practice, industry

is likely to respond to the demand for this technology with more accurate and more easily performed duplex scanning in the near future.

By way of comparison, the indirect noninvasive

tests (e.g., periorbital ultrasonography), which

monitor the cerebral and orbital circulations

beyond (downstream from) a carotid lesion, have

been shown in most practice settings to have a

lower sensitivity and specificity than DSA and/or

arteriography and are employed much less frequently at this time than was the case only a few

years ago. This trend is likely to be accentuated

in the coming years.

As described above, DSA is also likely to limit

the use of, or substitute for, arteriography under

many clinical circumstances. In addition, it will

be employed in situations where arteriography is

inapplicable, thus increasing the total volume of

arterial examinations. For example, some patients

for whom arteriography is risky—such as elderly

patients, who are at greater risk for stroke from

cerebral arteriography--can have their carotid

arteries examined easily and with reduced risk of

complication using DSA. Also, DSA may be performed repeatedly on the same individual in order to monitor postoperative or therapeutic progress, without significant morbidity and with good

patient compliance. The comparative advantages

of DSA and standard arteriography have been

summarized in table 3-2.

It is clear that DSA examinations are not a simple substitute for arteriograms. Instead, for those

conditions for which DSA and arteriography are

both applicable, the lower radiation and complication rates of DSA, the outpatient site of

testing, the reduced time required for the procedure, and patient acceptance (83,112) may result

in a use rate of DSA many times greater than that

of arteriography. In addition, DSA may be used

as a substitute for or a supplement to other noninvasive tests. Two studies of DSA cost effectiveness estimate that for patients with suspected

TIAs, clinicians order DSA examinations (where

this technology is available) at approximately

twice the current rate of arteriographic studies

(24,33). However, at present there are no empirical bases for future estimates of DSA utilization.

Table 3.2.—Comparative Advantages of DSA

and Conventional Arteriography

Advantages of standard

Advantages of DSA arteriography

Decreased morbidity Increased spatial resolutiona

Decreased patient Feasibility of selective

discomfort injections

Decreased hospitalization Less degradation of patient

time motion

Decreased procedure time Visualization of smaller

Decreased film cost blood vessels

Increased contrast

resolution b

Usefulness in patients

with limited arterial

access

Lower cost per

examination

asPafjal ~e~olut~on: extent to which radiographic image makes it possible to

detect and distinguish anatomically contiguous structures.

bcontrast reso/u//on: extent to which computer can detect subtle differences

in amount of contrast medium present

SOURCE: M. F. Steighorst, C. M. Strother, C. A. Mistretta, et al., “Digital Subtraction Arrgiography: A Clinical Overview, ” Applied F?adlo/ogy

10(6):45-49, 1931.
19

CLINICAL EFFICACY AND EFFECTIVENESS OF DSA

The claimed advantages and disadvantages of

DSA derive, in large part, from the efficacy and

safety of the technology. A substantial volume

of evidence regarding the efficacy and safety of

DSA is now available through clinical testing of

DSA in several medical centers.

Banta and Behney (8) define technological efficacy as “the probability of benefit to individuals

in a defined population from a medical technology applied for a given medical problem under

ideal conditions of use” (emphasis added). Effectiveness is the probability of benefit under average conditions of use. The literature to date on

DSA generally addresses clinical efficacy and

safety, not effectiveness. Most studies have been

conducted in institutions engaged in clinical research under carefully monitored conditions (21).

An exception is the experience documented at

Scottsdale Memorial Hospital in Arizona (63). It

is not clear whether experimental and early clinical data from academic medical centers, such as

the Universities of Wisconsin and Arizona—each

with several years of pioneering experience in

DSA use—can be employed reliably to predict the

effectiveness and safety of DSA by radiologists

and clinicians in community hospitals, clinics, and

group practices and the resulting patterns of DSA

use.

Measurement of the efficacy of DSA is multidimensional, as depicted in table 3-3 (adapted

from Fryback [38]), because benefits can be

discerned at the levels of: 1) physical image; 2)

the detection, accuracy, and sensitivity of tests;

3) diagnostic decisionmaking; 4) therapeutic decisionmaking (or “management efficacy”); 5) patient outcome; and 6) social utility (38). Implicit

in this scheme is the belief that increasing diagnostic accuracy is not an end in itself, but rather

an instrumental value. The overall efficacy of

DSA, then, lies in its contributions to better patient outcomes and ultimately to improved social

welfare (31,38),

Most of the clinical evaluations of DSA have

taken place at levels 1 and 2 of the Fryback model,

namely, with a focus on image quality or on diagnostic sensitivity, specificity, and accuracy. “Sensitivity” may be defined as the proportion of

positive tests in all patients with disease; “specificity” is the proportion of all negative tests in patients without disease; and “accuracy” is the ratio

of correct diagnoses to all diagnoses.

Investigations of the efficacy of DSA have not

yet concentrated on the effects of DSA throughout the medical care system. The literature generally does not address differences in physician

diagnosis, selection of treatment alternatives, patient outcomes, or social welfare attributable to

DSA. The majority of studies consider the accuracy of DSA for diagnosis in comparison to

other diagnostic techniques, usually conventional

Table 3-3.—Levels At Which Diagnostic Technologies May Be Assessed

Level of the measurement Typical output measures

Level 1: Image efficacy . . . . . . . . . . .

Level 2: Image and

observer efficacy . . . . . . . . . . . . . . .

Level 3: Diagnostic efficacy . . . . . . .

Level 4: Management efficacy

(therapeutic decisionmaking) . . . .

Level 5: Patient outcome efficacy . .

Level 6: Societal efficacy

quality of image resolution

percentage yield of abnormal cases; percentage

correct diagnoses; sensitivity; specificity

change in order of clinician’s diagnostic

considerations

percentage change in therapeutic protocol;

percentage change to appropriate therapy

survival rates; percentage cures; morbidity measures;

reduced worry of patient and family

(or utility) . . . . . . . . . .’. . . . . . . . . . . dollars added to GNP; age-adjusted survival rates

SOURCE: Off Ice of Technology Assessment, Adapted from D G, Fry back, “A Conceptual Model for Output Measures in Cost.

Effectiveness Evaluation of Diagnostic Imaging, ” paper presented at the Symposium International de Evaluation

Cout. Eff!caclte en Neuroradiologie, Bordeaux, France, May 14.15, 1982.
20

arteriography. For images of good diagnostic ing the scan procedure. The quality of images can

quality (approximately 85 percent), the sensitivity be affected by swallowing, breathing, peristalsis

(95 percent), specificity (99 percent), and accuracy (movement of esophagus), or other physical mo-

(97 percent) of DSA appear to be very good tions, depending on the vessels to be visualized

(19,112). (112). Other causes of failure are inadequate vein general, the principal reason for inadequate nous access, leakage of dye, and faulty injection.

visual resolution is movement of the patient durTHE SAFETY (ASSOCIATED PATlENT RISKS) OF DSA

OTA defines the “safety” of a medical technology to be:

. . . the judgment of the acceptability of relative

risk in a specified situation;

while “risk” is defined as:

. . . the probability of an adverse or untoward

outcome occurring and the severity of the resultant harm to health of individuals in a defined

population associated with use of a medical technology applied for a given medical problem

under specified conditions for use (8).

Using these definitions, the safety of DSA may

be measured and compared to the present methods of diagnostic imaging for vascular diseases.

As noted by Patterson (81), the efficacy and safety

of neurosurgical and related technologies are only

estimated informally, because of measurement difficulties, different conditions of use, and the experimental nature of some technologies. This appears to be the case for DSA. There are no

rigorous epidemiological or randomized clinical

studies that document either the direct or indirect

safety effects. This seems to be due to the fact that

most clinicians are impressed with the apparent

low risk of DSA relative to benefit, as compared

with alternatives.

The amount of radiation from DSA is so small

that clinical decisionmaking generally does not

take radiation into consideration. Radiation doses

for DSA reported in carotid studies are given in

table 3-4. Radiation exposure varies depending on

the subtraction method selected for the exam and

the number of views required for diagnosis (21,

24,56).

Complications from DSA are minimal compared to standard arteriography. Both peripheral

and central intravenous injections are likely to be

less risky than arterial punctures required for

arteriography. In particular, arteriographic procedures may cause stroke due to dislodging embolic material (19), dissecting the arterial walls,

or rupturing aneurysms (54), whereas this does

not occur with DSA.

A survey of radiologists at 514 hospitals showed

that about 2 to 3 percent of all patients undergoTable 3-4.—DSA Radiation Exposure Estimates for Cerebrovascular Studies

Estimated radiation

Principal author of study Area of study exposure per imagea

Crummy, et al. (1980)b Extracranial arteries 100-150 mRc

Chilcote, et al. (1981) Carotid arteries 230 mR

Brody, et al. (1982) Carotid arteries 130 mR

Detmer, et al. (1982) Extracranial arteries 3.6 Rd

aNurnber of images per study may vary considerably depending on anatomical site, operators, or Patient characteristics.

bFull citations found in References Section.

cmR . milliroentgen(I Roentgen (R) = the unit of radiation exposure equivalent to 2.08 x 10° iOfI pairs in one cc. of air. The

measure of radiation exposure in human tissue conventionally used is the “Rad, ” the absorbed dose of 100 ergs/gin of tis.

sue. One Rad is equivalent to 1.02 Roentgen, the difference between two units of measure being considered negligible,)

dR . Rad. (Detmer, et ai, (24), the source for data on a complete DSA study (including multiple ima9eS), note that a conventional arteriographic study would expose the patient to approximately 20 Rads of radiation.)

SOURCE: Office of Technology Assessment,
.

21

ing a total of 118,591 arteriographic exams—

transfemoral, transaxillary, translumbar—suffered complications which required additional

therapy or prolonged the patient’s hospital stay

(54). These complications included 30 deaths (0.03

percent of all exams). Another study indicated

that of 1,328 patients who were suspected of having TIAs and had arteriograms, 13 percent had

temporary complications and 0.65 percent suffered permanent neurological complications (102).

Johnson (56) concludes that:

“(t)he complexity, expense, and a certain morbidity and mortality associated with this radiographic procedure [arteriography] compel a set

of indications virtually as strict as that for surgery.”

Certain complications can arise in DSA exams

due to leakage of contrast medium outside the

vein, venous reflux (contrast medium going into

vein the wrong direction), or patient reaction to

the contrast medium (21,57,108,112). Various

clinical studies have documented only a small

number of such problems—all were transient—

of several thousand patients examined (19,21,

57,112).

The safety as well as the clinical efficacy of DSA

will depend to a considerable extent on the quality

of the particular equipment being used (a factor

which also affects diagnostic accuracy and specificity); the compatibility of new DSA equipment

with existing facilities; the techniques used; and

the experience of the physicians and allied health

personnel performing and interpreting these diagnostic images. Several investigators have noted

some variability in imaging capabilities of DSA

under different technical conditions and have

evaluated the physical requirements of the imaging systems with regard to assuring high quality

standards (6,67).
4.

The Costs of Digital

Subtraction Angiography
4.

The Costs of Digital

Subtraction Angiography

The costs of acquiring digital subtraction angi- many forms. This chapter attempts to summarize

ography (DSA), building or modifying an existing existing experience with respect to the costs of

physical facility to house the equipment, and ini- DSA in the United States.

tiating the service in an operational mode are of

PURCHASE AND UTILIZATION COSTS

A technology such as DSA requires both capital and operating expenditures. Capital outlays

are necessary in most instances for the equipment

itself and for the physical space within which to

operate the equipment. Unfortunately, it is difficult to estimate the rate of amortization of DSA

equipment at this stage in the development and

implementation of the technology.

Freedman (33) estimated that the investment in

a DSA computer, X-ray equipment, and room will

range from $400,000 to $800,000. The costs a hospital or clinic may incur depend on whether the

radiographic/fluoroscopic equipment is already

present. If so, most hospitals can add a digital

computer to their radiography rooms for an average cost of $250,000. The price range for these

“add-on” systems in January 1982 was $135,000

to $350,000 (61). In the future, considerable savings are expected from combining the data processing and storage requirements of the various

kinds of computer-assisted radiographic techniques, such as the use of a single computer to

retrieve and store information from more than one

DSA machine (1,29).

Operating costs include fixed personnel costs

and variable supply costs. Personnel costs, although fixed for a given facility, vary considerably among facilities depending both on the facility’s caseload and the configuration of DSA in

relation to other radiologic technologies. For example, a physician is required to be physically

present in or around a DSA unit to supervise the

injection of the contrast agent, but this physician

can also service a second adjacent room where

another DSA or computed tomography (CT) scan

unit is operating. There are circumstances where

a physician could supervise a third room as well,

possibly a room equipped with a real-time ultrasound unit. 1 Thus, a rotating physician can effectively supervise several radiological procedures

in different, but adjacent, rooms simultaneously,

therefore reducing the fixed personnel costs of all

of these procedures.

With a caseload of six to eight cases per day

(1,500 to 2,000 annually), it is commonly estimated that two full-time technicians (requiring a

total of $50,000 in salary and fringe benefits annually) will be required to operate a DSA efficiently (33). A secretary is required to make appointments, complete insurance forms, and to

perform other activities. Because this secretary is

likely to participate in other activities, such as

scheduling patients for other radiologic examinations, this fixed personnel cost is factored into a

miscellaneous category (of about $50,000 annually) which includes insurance, administrative

costs, utilities, etc.

Supply costs were estimated in 1982 to average approximately $100 per DSA examination,

allowing for 20 percent waste and repeating the

study (33). Since that time, special DSA procedure kits have been developed which cost approximately $60 each. Allowing for a 10 percent waste

factor, current supply costs should range between

‘See ch. 2 for a description of real-time ultrasound.

25
26

$65 to $75 per case. Some variation in costs is

associated with the way in which the contrast

medium is injected. A peripheral injection usually requires a supply cost of approximately $80

per case; when the catheter is placed in the

superior or inferior vena cava, these costs are approximately $100. Among the more expensive

items that contribute to variable costs are the catheter ($18), floppy disk for the computer ($10), and

the contrast agent (150 cc. at $15) (33).

It is useful to summarize these cost data by way

of a breakeven analysis. If it is assumed that

variable (supply) costs are $80 per case (with

PATlENT COSTS AND CHARGES

The total expenditures associated with performing a procedure such as DSA also include institutional and professional charges billed to the patient or the insurance carrier. Reports of billed

charges in the literature (24,33,61) average between $175 and $300 for institutional providers.

These figures incorporate fixed overhead costs,

variable supply costs, and the volume of DSA

procedures performed. As the volume increases,

the cost per procedure may decrease, although the

actual charges to the patient may not.

On a national level, third-party insurer responses to DSA are difficult to summarize. As an

example, however, in 1983 physicians and hospitals in New Jersey were paid at the rate of $500

per DSA examination. The basis on which this

figure was determined is not clear, but informal

conversations with individuals directly involved

with setting the charge suggest that the figure was

derived by examining the costs of inpatient arteIMPLICIT AND INTANGIBLE COSTS

peripheral injection of contrast agent), and there

is a caseload of eight patients per day, 250 days

per year, the total variable costs would be

$160,000 per year. If this figure is added to an annual fixed cost of $400,000, a figure within the

range of actual experience in late 1982 (33), the

total annual costs of operating a DSA unit on a

per case basis can then be calculated. Using these

figures, one can estimate a total annual cost of

$560,000 assuming a total of 250 working days

per year. With an annual caseload of 2,000 patients (250 days X 8 patients per day), this yields

a breakeven cost of $280 per case.

riography, a more expensive procedure that produces similar information. Detmer and colleagues

(24) assumed a charge of $1,120 for inpatient

arteriography in their study, including the cost

of hospitalization and professional fees. In New

Jersey, however, the arteriography charge appears

to be substantially higher, perhaps in the neighborhood of $2,300 per arteriogram.

Despite the seemingly arbitrary current rates

of DSA reimbursement, it is clear that third-party

payers view DSA as a potential cost-saving tool.

Not only does DSA eliminate the necessity for

hospitalization of the patient, but there is the possibility that with time and experience, as well as

further technological advances, this procedure will

substantially replace a large portion of the current demand for inpatient cerebrovascular arteriography. A reduction in inpatient arteriography

will lead to overall lower costs for each patient

examined.

The costs as delineated above are likely to Another significant problem with this type of

change. Thus, a long-range evaluation of the cost evaluation is that the future level of use of coneffectiveness of DSA as compared to alternative ventional arteriography is uncertain. Currently,

imaging technologies is very difficult. This is an arteriography is available in most U.S. hospitals.

inherent problem of evaluating the costs and ben- If DSA substantially reduces the need for arteriefits of an evolving technology. ography, as is contemplated, the costs of main-
27

taining the fixed arteriography facilities will rapidly increase on a per-arteriogram basis. These

unit cost increases may be partially offset by the

integration of DSA and arteriography units, or

by the closure and consolidation of arteriographic

facilities among inpatient care institutions. The

adoption of Medicare’s diagnosis-related group

(DRG) and other prospective payment systems is

likely to further stimulate this consolidation

process.

On the other hand, arteriography use may remain high despite the widespread introduction of

DSA. The digital subtraction processes used in intravenous DSA are now being applied to conventional arterial studies; the improvements in computer data processing and image quality may

allow the study of previously inaccessible vascular

structures. Thus, a prospective cost analysis cannot treat arteriography as a “steady-state” technology, nor its current level of utilization as a

stable pattern. The cost-effectiveness analysis of

DIFFUSION AND SOCIAL COSTS

Diffusion of a technology may lower per procedure expenditures, depending on economies of

scale in production and further innovations of the

technology. Similarly, the per procedure costs of

DSA may decrease in association with its increase

in availability. This could further result in reduction of the economic and social impact of stroke

(3,103).

However, technology diffusion also has the potential for enormous aggregate costs as well as

savings. Any assessment of DSA must consider

not only how the costs of DSA compare with

arteriography, but the extent to which DSA leads

to increases in the total volume of diagnostic

studies performed. Thus, the evaluation of the

economic impact of DSA should include the

change in expenditures per examination as well

as the increase (or decrease) in total examinations

performed.

It seems certain that the demand for DSA technology by many clinical specialists will be very

high. Neurosurgeons, cardiologists, vascular surgeons, neurologists, and other physicians will

DSA in chapter 5 incorporates flexible levels of

arteriography use to reflect this uncertainty.

The costs of DSA equipment may change dramatically as well. Presumably, the high costs of

research and development (R&D) are incorporated into the early models. These R&D costs

should decrease over time, and with economies

of scale in production, lower the cost, and hence

the price, of the equipment. One possible offsetting factor, though, is that manufacturers maybe

able to make continual qualitative improvements

in the technology and thereby maintain a high

price. If present equipment becomes obsolete, this

will stimulate either the purchase of new equipment before the existing units are fully depreciated

or the upgrading of existing equipment through

the purchase of additional components. It is likely

that DSA is not yet a mature technology—either

in technical development or in its medical applications—and will experience significant changes

similar to the CT scan in years ahead.

make frequent use of DSA. Also, general practitioners and family physicians learn of diagnostic

imaging breakthroughs in primary care journals

(29) and may refer their patients for those imaging studies.

If diffusion of DSA is unconstrained, utilization of DSA will undergo rapid growth. This will

occur because: 1) the lower complexity and risks

of DSA will make it useful for large numbers of

patients who would not ordinarily undergo arteriography; 2) the applications of DSA are increasing; 3) the numbers of specialists who would use

DSA (and are being trained in its use) are growing, and they are more widely dispersed geographically; and 4) the ambulatory nature of DSA

makes it available to a greater number and variety of health care institutions, including group

practices, multispecialty clinics, and hospitals.

Restraints on the diffusion of DSA can come

from at least two sources, health planning agencies and third-party payers for medical care. A

1980 OTA study found that health planners were

primarily oriented toward health “needs,” usually
28

consider only capital costs, and never explicitly

weigh costs and benefits in certificate-of-need recommendations (as reported in 8). The economic

(or political) reason for this behavior is that there

is no mechanism for effecting a direct budget constraint in the health planning process (8). It is

therefore disadvantageous for a local agency to

deny specified medical needs and benefits when

the costs of adopting the new technology are

spread throughout the insurance system.

Similarly, the enthusiasm of technology manufacturers, providers, and insured patients for the

expanded use of DSA is not likely to be offset by

the reimbursement procedures of third-party payers. Medicare and Blue Cross/Blue Shield, as examples, make coverage decisions based on: 1) efficacy, 2) safety, 3) state of development, and 4)

acceptance by the medical community (8,44,51).

Billed charges are not a criterion for deciding

whether to cover a new procedure. Charges become relevant only with respect to decisions regarding the level of payment.

Since fee schedules generally reward the use of

technology-intensive services (68), “it may be

more advantageous to a physician to order and

read diagnostic tests than to expend the time he

spends with a patient performing a physical examination” (23). It has been demonstrated that

a physician can triple his/her income merely by

ordering a higher volume of tests for the same

number of patients (93).

Greenberg and Derzon (44) note these and other

difficulties with medical payment policies, and offer four general options: 1) restrict coverage of

“unproven” procedures, presumably those whose

efficacy has not been demonstrated in controlled,

randomized clinical trials; 2) introduce cost effectiveness criteria; 3) educate physicians in appropriate uses of technology; and 4) educate consumers. The introduction of these criteria for

insurance coverage, particularly cost effectiveness,

is not likely to have a substantial impact by itself

(8). For reasons already stated, there are strong

forces operating against the control of technology development and diffusion in the case of

DSA.
5.

The Cost Effectiveness of

Digital Subtraction Angiography
5.

The Cost Effectiveness of

Digital Subtraction Angiography

The final objective of a thorough cost and

quality assessment of any new medical technology is to ascertain the degree of relationship between the incremental costs of the new procedure

and the extent to which the prevention and/or

treatment (cure) of the relevant diseases has

occurred or is likely to occur. In this case study

of digital subtraction angiography (DSA), the

focus of inquiry is somewhat more limited. Although it would be ideal to be able to compare

all technologies of all types relevant to cerebrovascular disease on the basis of their contribution

to improvements in patient morbidity, mortality,

disability, longevity, and productivity, the information needed for such an analysis simply does

not exist. Thus, the conventional approach to cost

REVIEW OF EXISTING STUDIES OF

COST EFFECTIVENESS OF DSA

Two cost effectiveness studies of DSA have

been performed (24,33). Each compared conventional arteriography with DSA in the evaluation

of patients with transient ischemic attacks (TIAs).

Freedman (33) limited his analysis to the cost of

studies of the carotid arteries. The primary unit

of analysis in both studies was the “cost per identified lesion”; Detmer and colleagues (24) also included a measure of “radiation dose per lesion

found.” The key assumption, monetary values,

and findings from each study are listed in table

5-1.

In these studies, the population to be studied

with DSA is assumed to be approximately twice

as large as the population currently examined with

arteriography. These estimates are derived from

a cooperative study of TIAs conducted in five academic medical centers (102). Freedman (33) notes

that the incidence of TIAs reported in the cooperative study appears to be low. He argues that

effectiveness analysis for a diagnostic imaging

technology is to compare the “cost per procedure”

and the “cost per lesion found” between the new

technology and one or more existing technologies

(24,33).

In the case of carotid artery disease, a “significant lesion” is usually defined as arterial stenosis

of 50 percent or greater. This is the approach

taken in this analysis of the cost effectiveness of

DSA. In other words, this analysis seeks to measure the “cost per unit of effectiveness” of DSA in

comparison with conventional arteriography, a

competing alternative technology with common

objectives (8). It also reviews the existing cost effectiveness analyses.

THE

incidence can range up to four or five times that

level in a community with a large elderly population. It would appear, then, that the population

at risk has tremendous implications for the overall costs of DSA imaging as a technological alternative to conventional arteriography.

Yield rates (the numbers of lesions found per

population screened) are also widely variable,

even for arteriography. Eisenberg and Nicklin (28)

observed that abnormalities found in arteriographic studies ranged from 22-42 percent to 100

percent for TIA patients. This variability is due

to the inclusion or exclusion of ulcerative lesions,

differences in the populations screened, local differences in patterns of practice in certain medical

specialties, and whether the findings were reported

in the clinical or radiological literature. Detmer

and colleagues (24) base their estimated yield of

75 percent for arteriography on the actual yield

of that technology at the University of Wiscon31
32

Table 5-1 .—Data Used for Cost-Effectiveness Analysis of DSA

Assumptions Detmer, et al. (1982)a Freedman (1982)a

1.

II.

Ill.

Iv.

Patient population

A. Definite TIAs . .

B. Possible TIAs. .

Yield rates:

A. DSA . . . . . . . . . .

B. Arteriography . .

Cost/procedure:

A. DSA . . . . . . . . . .

B. Arteriography . .

examined:

. . . . . . . . . . . . . . . . . . . . . . . 8.4 TIAs/100 beds

. . . . . . . . . . . . . . . . . . . . . . . 17.4 TIAs/100 beds

. . . . . . . . . . . . . . . . . . . . . . . High = 75 percent

Low = 25 percent

. . . . . . . . . . . . . . . . . . . . . . . High = 75 percent

Low = 25 percent

. . . . . . . . . . . . . . . . . . . . . . . $ 225

. . . . . . . . . . . . . . . . . . . . . . . $1,120

Cost effectiveness (cost/lesion found)

Population

5.4 TIAs/100 beds

16.8 TIAs/100 beds

High = 80 percent

Low = 40 percent

High = 80 percent

Low = 40 percent

$ 500

$1,200

examined

Screening protocols Low High

A.

B.

c.

D.

Arteriography only . . . . . . . . . . . . . . . . . . . . $1,492

DSA followed by arteriography if DSA is

positive. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . $1,438 $1,590

DSA, followed by arteriography in only 50

percent of positive DSA exams as a

confirmatory measure . . . . . . . . . . . . . . . . . $ 936 $1,065

(1) DSA, followed by arteriography in only

10 percent of positive DSA exams

(Freedman) . . . . . . . . . . . . . . . . . . . . . . . . –

(2) DSA, followed by arteriography in only

5 percent positive DSA exams

(Detmer. et al.) . . . . . . . . . . . . . . . . . . . . . $ 376 $ 512

Low High

$1,500

$1,825 $2,033

$1,225 $1,433

$ 775 $ 950

—

aFull citations found in References Section.

SOURCE Office of Technology Assessment

sin Hospital; they assume that DSA accuracy is

equal to that figure (adjusted for a 5-percent rate

of technical failure of DSA). Detmer and his colleagues (24) noted, however, that DSA does not

currently approach that level of accuracy for

ulcerative lesions. The generalizability of this rate

is quite limited, and the estimated yield rates for

DSA means that the Detmer and the Freedman

studies must be carefully interpreted. The same

conditions will limit the accuracy of this cost effectiveness analysis of DSA in the diagnosis of

cerebrovascular disease.

The validity of the estimated costs of DSA and

arteriography are also subject to scrutiny. Detmer

and colleagues (24) present no cost findings at all,

but simply list the billed charges for these procedures at the University of Wisconsin Hospital.

Further, costs in their analysis do not include professional fees (approximately $150) (33). Freedman (33) does not provide detailed estimates of

the fixed and variable costs of DSA imaging, but

only gives “point estimates, ” rather than ranges,

of cost effectiveness.

Interpretation of these studies is further complicated by the fact that the estimates are derived

from operational costs in two large and innovative radiology practices, one of which is part of

an academic medical center. These practices may

reflect a very different cost experience from community hospitals and ambulatory sites, particularly with respect to the allocation of overhead

costs.
33

NEW TECHNOLOGY AND PATTERNS OF MEDICAL PRACTICE:

CRITICAL ASSUMPTIONS UNDERLYING AN ANALYSIS OF

COST EFFECTIVENESS

In order to investigate the cost effectiveness of

a new diagnostic tool such as DSA, it is important to attempt to understand its potential role

in the care of patients with TIAs or patients who

may have had a completed stroke. It is essential

that predicted changes in the process of health care

delivery and its outcome be identified. Thus, a

cost effectiveness analysis of DSA should proceed

from a conceptual model of how this technology

will “fit” with existing technologies and patterns

of practice relevant to the disease(s) of focal interest.

The hypothesis made in this case study of the

impact of DSA on existing patterns of medical

practice and technology use in the diagnosis and

treatment of cerebrovascular disease is illustrated

in figures 5-1 and 5-2. Prior to the introduction

of DSA, as figure 5-1 depicts, the physician who

encountered a patient with a TIA or a stroke had

several diagnostic procedural options to consider.

For a number of reasons, the physician may have

decided that no tests were indicated, perhaps because of coexistent medical problems that made

invasive testing and surgical therapy unwarranted. In other circumstances, the physician may

have moved to noninvasive testing followed by

arteriography, or arteriography could have been

employed as the initial test. The interplay of technologies illustrated in figure 5-1 is based on three

important assumptions:

1. No surgical therapy is currently performed

without arteriography.

2. Arteriography maybe the initial diagnostic

test.

3. Arteriography may be the only diagnostic

test.

A possible fourth assumption, and one that is

certainly true in many medical centers, is that

radiologists and other physicians are reluctant to

undertake tests with significant morbidity risks

(e.g., arteriography) without the opinion of a

neurologist to determine that the patient’s symptoms are due to TIA and therefore warrant the

use of arteriography and/or surgical therapy.

Figure 5-1.— Clinical Alternatives Without

DSA Available

TIA

SOURCE: Off Ice of Technology Assessment

TIA

therapy therapy therapy

SOURCE: Office of Technology Assessment.

As DSA becomes increasingly available, the

patterns of care associated with TIA are likely to

undergo significant changes. It may be hypothesized that arteriography will less often be the initial diagnostic test, even in the case of patients

with a history of definite TIA. As indicated in figure 5-2, DSA may become the initial test of

choice, or it may follow noninvasive testing of

other types. On the output side, DSA maybe the

final test before medical or surgical therapy, or

it may lead to arteriography prior to medical/surgical intervention. The important assumptions

underlying the hypothesized patterns of patient

care diagramed in figure 5-2 are:

1. The sensitivity and specificity of DSA are

generally much greater than for other noninvasive procedures under ordinary conditions of use.
34

2.

3.

4.

The accuracy of DSA is somewhat less than

arteriography, but DSA is much safer and

less uncomfortable for the patient.

Arteriography is almost never performed

(except in certain academic medical centers)

without prior DSA examination, where the

latter test is readily available.

Surgery may be undertaken without arteriography in selected cases.

Support for some of these assumptions is provided by Little and colleagues (65):

In a previous study (19), . . . there was excellent correlation between the conventional

angiogram and the intravenous [DSA] when the

carotid bifurcation was well visualized (i.e., sensitivity, 95 percent; specificity, 99 percent; accuracy, 97 percent). When the carotid bifurcation was not well visualized by intravenous

[DSA], there was a substantial chance of misinterpretation of the study results. The most

common cause of misregistration was the patient’s swallowing. Overall, the intravenous

digital subtraction angiogram was found to accurately demonstrate the carotid bifurcations in

71 percent of the arteries evaluated. In the present study, 96 percent of the carotid bifurcations

were adequately visualized.

Although conventional angiography was usually recommended in patients treated surgically,

intravenous [DSA] obviated the need for conventional studies in the evaluation of many patients. Some patients having extracranial and intracranial studies underwent carotid artery

surgery without the need for further investigations.

The sponsors of the first outpatient ambulatory

neurodiagnostic center in the State of New Jersey

indicate anecdotally (45) that DSA has proven to

be a significant advance in the evaluation of patients with cerebrovascular disease. According to

Michael L. Gruber, M. D., a neurologist with this

group:

. . . Our experience indicates that of those patients who have surgically amenable abnormalities of the carotid bifurcations, no further studies

are indicated in the majority (approximately 80

percent). In other words, the surgeon will operate on the basis of the digital subtraction angiogram. In the other 20 percent of cases, further

study is required . . . because of technical problems with the DSA; because (the test revealed)

total occlusion on the DSA; (in such cases the)

standard procedure is to follow this with a conventional angiogram; and lastly the reluctance

on the part of some surgeons to accept this new

modality of investigation (45).

As a further indication of the extent to which

DSA may substitute for conventional angiography

as the diagnostic test establishing the need for

carotid artery surgical therapy, Little and colleagues (64) summarized the experience with DSA

at the Cleveland Clinic:

DSA examinations frequently obviated the

need for conventional angiography. Some patients having satisfactory extracranial and intracranial studies underwent carotid endarterectomy without further contrast studies. The

number of patients undergoing carotid surgery

without conventional arteriography continues to

increase.

Because DSA has not yet gained widespread use

as a diagnostic procedure, the data do not exist

by which to accurately predict the patterns of use

which will develop for the diagnosis and treatment of cerebrovascular disease. It is possible,

however, to speculate on some of the ways in

which DSA might be used, given current patterns

of practice in disciplines such as neurology and

primary care specialities. The following six assumptions are made as the basis of a cost effectiveness analysis of DSA:

1.

2.

The technical proficiency of DSA is expected

to rapidly improve as a result of the intense

competition among the major imaging equipment manufacturers.

As the speed and spatial resolution of DSA

studies improve and the quality of ancillary

technology improves, more and more patients will have only a DSA procedure before

undergoing cerebrovascular surgery.

Detmer and colleagues (24) estimated that if no

more than 5 percent of positive DSA examinations were followed by conventional arteriography for confirmation purposes, a savings of approximately $1,100 per discovered lesion would

result.

3. It is unlikely that only one DSA study will

be performed per discovered lesion. It seems

more likely that a minimum of two DSA ex-
35

aminations (one before and one after therapy) will become the pattern of care.

This would especially be the case for all surgically

treated patients, since the postoperative DSA examination would serve as a new “baseline” for the

future. Among medically treated patients, it seems

reasonable to assume that many will receive repeat examinations at yearly intervals to determine

whether the pathology has progressed and to learn

whether the stenosis of the carotid arteries has become more serious. Hence, only among patients

where the DSA exam did not find a lesion can one

assume that a single examination will suffice.

4. The population of patients receiving DSA examinations in the future is likely to be much

larger than the current number who receive

in-hospital arteriography.

Freedman (33), and Detmer and colleagues (24)

both estimate the number of patients who will receive DSA examinations as twice the number presently having conventional arteriography. The

1977 Cooperative Study of TIA (102) reported an

average of 5,4 definite TIAs per 100 acute care

beds per year (the highest rate being 8.8 TIAs per

100 beds per year). Freedman (33) and Detmer (24)

assumed that 95 percent of the higher prevalence

estimate (or 8.5 per 100 beds) would receive

arteriograms. Thus, previous studies and their

assumptions suggest that as many as 17.4 DSA

examinations per 100 acute care beds will be performed annually in U.S. hospitals.

Because DSA is an ambulatory care procedure,

however, the “burden of illness” in the total population may be a more reasonable guide for the

estimation of potential utilization, rather than the

frequency of relevant diagnoses per 100 acute hospital beds. Available data (62) suggest that the incidence of TIA is 30 per 100,000 population per

year with an average episodic duration of 5 years,

or a prevalence of 150 per 100,000. Physicians are

likely to “follow” patients with recurrent TIAs

with repeated examinations, especially as the imaging quality improves.

In addition, virtually all patients with a completed stroke would likely receive a DSA examination. The incidence of stroke is 150 per 100,000

per year with an average duration of 4 years.

Since a completed stroke is considered to be a relative contraindication for surgical intervention, few

such patients now receive arteriography unless

subsequent TIAs occur, or the treating physician

finds evidence that a major stroke might subsequently occur after a minor stroke that has left

relatively little intellectual and motor impairment.

Since DSA is much safer than arteriography, it

is assumed that many stroke patients will receive

this examination. A DSA exam following a stroke

may help the physician determine prognosis for

family counseling, even though relatively few

demonstrated lesions in stroke patients will receive

surgical therapy.

If one assumes that 90 percent of new TIAs,

70 percent of new strokes, 30 percent of old TIAs,

and 10 percent of old strokes receive a DSA examination annually, then 237 (27 + 105 + 45 +

60) DSA examinations for carotid artery disease

per 100,000 population would seem a reasonable

estimate. This figure is much larger than one based

on hospital data from New Haven, Connecticut,

that was estimated at 33 per 100,000 population

(34).

5. The prevalence of asymptomatic extracranial

occlusive vascular disease will further increase the volume of DSA procedures performed.

It has been estimated that in asymptomatic individuals, there is a 22 percent prevalence of

arterial stenosis of the extracranial and major intracranial vasculature sufficiently severe to compromise the arterial lumen by at least 50 percent

(96,97). Many of these patients have abnormal

clinical signs on examination, even though no

symptoms were present before the exam. These

signs include bruits (murmurs) audible through

a stethoscope placed adjacent to a compromised

artery, diminished arterial pulsations, and an abnormally low blood pressure recorded distal to

(beyond) a stenotic vessel. Many of these patients

will likely receive a DSA examination, especially

prior to administration of general anesthesia for

a surgical procedure elsewhere in the body, because of a concern that a stroke might occur during surgery even in the absence of prior symptoms. Except under unusual circumstances (such

as prior to prolonged surgery) patients with
36

asymptomatic occlusive vascular disease do not

now receive arteriograms. With the ready availability of a safe and effective diagnostic tool such

as DSA, many asymptomatic patients with abnormal signs on clinical examination will likely

receive a diagnostic evaluation. It appears to be

a safe assumption that the indications for surgical therapy may be expanded to include asymptomatic patients with severe stenosis discovered

by DSA examinations. This will result in an overall increase in the number of surgically treated

lesions.

6. The increasing availability of DSA, its technical quality and its extremely low morbidity will significantly alter the pathway

through which patients with TIA are evaluated and/or referred by primary care physicians.

Because of the risk of complication associated with

conventional arteriography and the relatively

large radiation exposure (20 roentgens per examination for arteriography vs. 3.6 for DSA), patients are now carefully screened by their physicians before arteriography is scheduled. This

screening occurs in two ways: First, as shown in

figure 5-1 above, preliminary noninvasive tests

(e.g., ultrasonography) are often performed in order to reduce the likelihood of a “true negative”

arteriographic examination. Most experienced clinicians prefer to screen all but the most urgent

patients before performing an arteriogram. Thus,

patients for whom arteriography is the first and

only examination are a minority of those receiving this examination.

Second, the screening process includes a neurologist’s opinion that a patient’s symptoms are likely

QUANTITATIVE ESTIMATES OF THE

COST EFFECTIVENESS OF DSA

to come from extracranial occlusive vascular disease. Many primary care physicians diagnose TIA

for symptoms that necrologic specialists would

place in other categories. For example, dizziness

is a common symptom among the elderly, especially when one first arises from a seated or lying

position. Neurologists know that most dizzy patients do not suffer the types of stroke that would

signal the occurrence of TIAs even if they have

symptoms of dizziness and vertigo (without other

symptoms and signs). Furthermore, symptoms in

the extremities may represent focal seizures

(localized to one part of the body), and these may

be misdiagnosed as TIAs by the less experienced

non-neurologist. Many patients with acute confusional states, due to a variety of toxic and

metabolic causes, are also falsely labeled as having had TIAs. For these and other reasons, many

radiologists will not accept patients for arteriographic examinations of the extracranial vasculature unless a neurologist has been consulted.

It maybe hypothesized that DSA may significantly alter the pathway through which patients

with suspected cerebrovascular disease are managed. It is possible that both primary care physicians and radiologists may become convinced that

the superior quality of DSA images and the lower

morbidity risk of the procedure itself can allow

some proportion of patients with suspected TIA

to be managed without neurology specialty consultation. However, the American Neurological

Society strongly suggests that appropriate neurological advice should be sought even in the most

straightforward of cases.

Measuring the cost effectiveness of DSA in the The data presented in the tables that follow repdiagnosis of patients with carotid artery disease resent the variability in cost effectiveness which

is a complex task. Because several factors which can be expected in the operation of DSA under

influence the acquisition, use, and efficacy of DSA different institutional and clinical circumstances.

are variable, a range of costs must be incorporated These data are largely based on secondary inforinto the analysis. mation in previous studies of DSA (see principally
37

24,33). These studies provide important indicators

of the specific cost parameters of DSA. Because

their methods are limited in scope, these studies

also pose certain limitations for these analyses.

Estimates of the cost effectiveness of DSA reported in this case study are based on the predicted patient charges necessary to cover the costs

of operation of a DSA unit. The use of billed

charges in the calculation of cost effectiveness indicators does not identify the actual flow of resources (revenues) to the production of DSA examinations, since patient or insurance payments

will most likely fall below the level of billed

charges. The primary concern here, however, is

comparing the relative amount of outlays for a

specific set of medical procedures—the diagnostic imaging of carotid artery disease—as a new

technology (DSA) is introduced into the field of

diagnostic radiology. Since data on the costs of

conventional carotid arteriography are unavailable in the literature, DSA charges have been estimated for comparison with charges for conventional arteriography reported by Freedman (33)

and Detmer and colleagues (24).

Another issue is the appropriateness of the cost

effectiveness indicators employed in this analysis. It may be argued that the indicator used in

prior studies, cost per lesion found, is an incomplete measure of the costs of cerebrovascular

diagnosis. Because arteriograms are assumed to

follow only positive DSA tests, the costs of further diagnostic evaluation following negative DSA

tests are missing.

Hypothetically, the costs associated with negative DSA results may be of two kinds: 1) costs

of arteriography or other testing ordered by conservative clinicians who want to confirm the negative DSA results, and 2) costs of patient disability

or death due to false negative DSA tests, where

the failure of DSA to show arterial disease prevented timely medical or surgical intervention.

Realistically, technical improvements in DSA imaging and physician experience with the technology should reduce followup testing of negative

DSA findings to insignificant levels. Indeed, it is

likely that positive DSA exams will be a sufficient

basis for making decisions regarding surgical intervention (45,64,65). Furthermore, clinical tests

of DSA show that when a good (i. e., diagnostically useful) image is produced (approximately

85 percent with an experienced radiologist), the

sensitivity of the procedure is close to 95 percent

in the examination of the carotid arteries (19). In

other words, only 5 percent of all patients with

actual arterial disease will have a negative DSA

finding.

It is reasonable, therefore, to assume that nearly

all the costs of carotid artery imaging are incorporated into the measures of “charges per lesion

found” and “charges per patient examined” as estimated in this case study. These measures are not

ideal, because they do not indicate the effectiveness of DSA in improving clinical therapy or patient outcomes, but they do estimate an important unit of analysis, the cost of diagnosing carotid

artery disease.

DSA charges must reflect: 1) fixed capital costs

of the DSA equipment and facility; 2) semi-fixed

costs for radiological personnel, equipment maintenance, administration, and utilities; 3) costs of

supplies; and 4) professional fees. Total annual

fixed costs are estimated by Freedman (33) to be

from $274,000 to $448,000. Table 5-2 shows the

charges which are necessary to cover the costs of

DSA operation at a volume of 1,500 and 2,000

cases per year at several levels of fixed costs for

a DSA facility.1 These charges range from $446

to $648 per examination.

The most important determinants of the cost

effectiveness of DSA, as calculated in tables 5-3

through 5-7, are charges and yield rates for DSA

exams and charges for arteriograms which may

be ordered to followup DSA findings. By varying the values of these three parameters, it is possible to conduct a sensitivity analysis of the cost

effectiveness of DSA under various clinical and

institutional patterns of operation.

Yield rates for DSA—the number of lesions

identified per 100 DSA exams performed—are

predicted to reach 80 percent for the examination

of patients who previously would have received

an arteriogram. This figure is comparable to the

‘This case study, following Freedman (33), assumes that patient

revenues will be approximately 80 percent of billed charges due to

bad debts and cost-based reimbursements.
38

Table 5-2.—Estimated Charges for DSA Examinations

supply CostsaTotal Breakeven Professional Total

Total annual fixed costsa

per exam Exams/year cost/exam chargebfees a

charges/exam

$274,000 . . . . . . . . . . . . . . . . . . . $100 1,500 $283 $353 $150 $503

2,000 237 296

$318,000 . . . . . . . . . . . . . . . . . . .

446

100 1,500 312 390 150 540

2,000 259 323 473

$360,000 . . . . . . . . . . . . . . . . . . . 100 1,500 340 425 150 575

2,000

$404,000 . . . . . . . . . . . . . . . . . . .

280 350 500

100 1,500 369 462 150 612

2,000 302 377 527

$448,000 . . . . . . . . . . . . . . . . . . . 100 1,500 399 498 150 648

2,000 324 405 555

aLe@S of fixed c~ts, supply costs, and profession~ fees are estimated on basis of information provided by Freedman (1982). Current SupPIY cOStS are estimated

in 1982 to avera@ approximately $100 per DSA examination, allowing for a 20 percent waste and repeat study factor.

bAlso following Freedman (1~), it is assumed that patient revenues willbe approximately 60 percent of billed charges due to bad debts and cost-based reimbursements. If receipts after bad debt md acceptance of assignment (of fees by third-pafiy payers) are expected to equal 60 percent of charges, the breakeven charge

equals 1.25 times costs.

SOURCE: Office of Technology Assessment, following G. S, Freedman, “Economic Analysis of Outpatient Digital Angiography,”App//ed Radio/ogy 11(3): 29-38, 1982.

Table 5-3.—Estimates of the Cost Effectiveness of DSA

(with fixed charges for arteriography)a

Cost-effectiveness indicators

DSA Lesions Arteriography Total Charge per Charge per

Protocol exams found exams charges billedb

lesion found patient examined

1 (arteriogram only) , . . . . . . . . . . . . . 0 80 100 $120,000 $1,500 $1,200

II (arteriogram if DSA positive). . . . . 100 80 80 (a) 140,600 1,758 1,406

(b) 153,500 1,919 1,535

(c) 160,800 2,010 1,608

III (arteriogram only for 50% of

positive DSAs) . . . . . . . . . . . . . . . . . 100 80 40 (a) 92,600 1,158 926

(b) 105,500 1,319 1,055

(C) 112,800 1,410 1,128

IV (arteriogram only for 10% of

positive DSAs . . . . . . . . . . . . . . . . . . 100 80 8 (a) 54,200 678 542

(b) 67,100 839 671

(c) 74,400 930 744

~A~erlography charge: $11200

bDSA charges: a) S446, b) $575, c) $648.

SOURCE: Office of Technology Assessment. Arteriography charge estimated by G. S. Freedman, “Economic Analysis of Outpatient Digital Angiography,” App/ied Radio/ogy

11(3): 29-38, 1982

yield of positive findings from conventional arteriography. The safety and efficacy of DSA in

patient diagnosis will allow or encourage a much

larger population to be examined than could be

done previously with arteriography, however. It

is estimated in the literature that the population

at risk for carotid artery diseases is two to three

times larger than that which can currently be

screened by arteriography (24,33,102). Earlier, the

argument for estimating the annual volume of

DSA procedures at or near 237 per 100,000 population was made. This figure is more than seven

times higher than the 33 per 100,000 estimated to

be receiving arteriography at the present time. For

this larger group, the yield of positive DSA findings is likely to be considerably less than the current yield of arteriography or DSA.

The yield rates of DSA for this expanded population are estimated to range from 25 percent upward (24,33). Tables 5-5 through 5-7 incorporate

yield ratios of 25, 50, and 80 percent in the new

populations to be screened with DSA.

Arteriography charges are set at $1,200 in

Freedman’s (33) study of the cost effectiveness of

DSA. This corresponds closely with the charge

of $1,120 at the University of Wisconsin reported

by Detmer and colleagues (24). Therefore, in the
39

Table 5-4.—Estimates of the Cost Effectiveness of DSA

(with variable charges for arteriography)a

Cost-effectiveness

indicators

Total Charges Charges

DSA Lesions Arteriography Arteriography charges per lesion per patient

Protocol exams found exams charge billed b

found examined

I (arteriogram only) . . . . . . . . . 0 80 100 $1,200 $120,000 $1,500 $1,200

II (arteriogram if DSA

positive) . . . . . . . . . . . . . . . . . 100 80 80 1,232 (a) 143,160 1,790 1,432

Ill (arteriogram only

of positive DSAs)

IV (arteriogram only

of positive DSAs)

(b) 156,060 1,951 1,561

(C) 163,360 2,042 1,634

for 50%

. . . . . . . . . 100 80 40 1,306 (a) 96,840

(b) 109,740

(c) 117,040

for 100/0

. . . . . . . . . 100 80 8 1,379 (a) 55,632

(b) 68,532

(C) 75,83 2

,211 968

,372 ,097

,463 ,170

695 556

685

. , 758

857

948

aThe variable charges for arferiography reflect the following assumptions:

1 Patient charges are set at a level such that actual patient receipts will just offset, or break even with, the costs of patient care at the current volume of procedures

If patient receipts, after bad debts and acceptance of assignment, average 60 percent of billed charges, then the estimated breakeven cost per arteriogram is $960

(0.60 x $1200 current charge)

2 The cerebrovascular studies in which DSA may effectively replace arteriography represent about one-quarter of the current volume of arteriograms.

3 Approximately 50 percent of the long-run costs of arieriographic facilities are fixed

Given these assumptions, the estimated breakeven charge per arteriogram at any new volume of arteriography is equal to”

Where the new volume of arteriography is equal to the current volume of arteriography minus one-quarter the percentage reduction in cerebrovascular arteriography

due to DSA substitution

bDSA charges a) $446, b)$575, c) $648

SOURCE: Office of Technology Assessment

calculations in tables 5-3 and 5-5, a fixed charge

of $1,200 for arteriograms is used in calculating

total imaging charges per patient examined and

per lesion found.

It is reasonable to assume the DSA will replace

a certain percentage of arteriography. As the volume of arteriograms changes, the charges necessary to cover the fixed capacity of arteriographic

facilities must also vary. Fineberg (31) notes that

only 5 to 15 percent of the costs of CT scanning

are variable with volume, and variable costs of

DSA appear to range from 25 to 35 percent of

total costs. For arteriography, high fixed costs

may be lowered considerably by the combination

of DSA and arteriographic facilities and personnel. Thus, tables 5-4, 5-6, and 5-7 assume that 30

percent of all costs of arteriography are fixed and

calculate the measures of cost effectiveness on the

basis of anticipated new (reduced) charges for

arteriograms.

It should be noted that utilization of arteriography may not decrease in terms of the absolute numbers of examinations performed. The use

of arteriography depends on the acceptance of

DSA by radiologists and clinicians as a substitute

imaging procedure. Data in table 5-7 show that

if the population examined for carotid artery disease expands to four times its current volume (i.e.,

from 100 to 400 DSA exams), it is very likely that

the demand for arteriography will rise (and its cost

per exam will fall). The clinical protocols developed by Freedman (33) are used in tables 5-3

through s-7 to estimate the “charges per lesion

found” and “charges per patient examined” as

DSA is partially substituted for arteriography in

the diagnosis of carotid artery disease. At this time
40

Table 5-5.—Estimates of Cost Effectiveness of DSA for Expanded Population At Riska

With Variable Yield Rates for Positive Findings

Cost-effectiveness

indicators

Total Charges Charges

DSA Lesions Arteriography charges

Protocol foundb

per lesion per patient

exams exams billed c

found examined

II (arteriogram if DSA

positive) . . . . . . . . . . . . . . . . . 200 A. 160 160

200 B. 130 130

200 c. 105 105

Ill (arteriogram only for 50%

of positive DSAs) . . . . . . . . . 200 A. 160 80

200 B. 130 65

200 c. 105 53

IV (arteriogram only for 10%

of positive DSAs) . . . . . . . . . 200 A. 160 16

200 B. 130 13

200 c. 105 11

(a) $281,200

(b) 307,000

(C) 321,600

(a) 245,200

(b) 271,000

(C) 285,600

(a) 215,200

(b) 241,000

(C) 255,600

(a) 185,200

(b) 211,000

(C) 225,600

(a) 167,200

(b) 193,000

(C) 207,600

(a) 152,800

(b) 178,600

(C) 193,200

(a) 108,400

(b) 134,200

(C) 148,800

(a) 104,800

(b) 130,600

(C) 145,200

(a) 102,400

(b) 128,200

(C) 142,800

$1,758

1,919

2,010

1,886

2,085

2,197

2,050

2,295

2,434

1,158

1,319

1,410

1,286

1,485

1,597

1,455

1,701

1,840

678

839

930

806

1,005

1,117

975

1,220

1,360

$1,406

1,535

1,608

1,226

1,355

1,428

1,076

1,205

1,278

926

1,055

1,128

836

965

1,038

764

893

966

542

671

744

524

653

726

512

641

714

aAssumes the ~op~ation at risk which can &j safely studied will double in size (24). This is regarded as a minimum level of additional volume Of DSA procedures Performed.

bDSA yield ratios:

(A) 60 percent (if volume of procedures is assumed at current level)

(B) 50 percent

(C) 25 percent (Yield ratios of those procedures beyond the current volume, e.g., 100 procedures in this example. Hence, yield ratios in (B) and (C) are calculated

at 60 percent for the first 100 procedures performed and at 50 percent and 25 percent, respectively, for all procedures performed beyond the initial 100,)

CDSA charges: a) $446, b) $575, c) $648. Arterlography char9e: $11200

SOURCE: Office of Technology Assessment.

there is no simple level of substitution that seems

most likely; instead, it appears that over time,

substitution of DSA for arteriography will in- ●

crease, but with no predictable upper limit.

Because the patterns of clinical use of DSA are

difficult to predict, it is also difficult to estimate

accurately the cost effectiveness of this new tech-

,

nology. Certain trends are evident from the data

presented in tables 5-3 through 5-7, however:

Ž As DSA substitutes for arteriography in the

diagnosis of carotid artery disease, the cost

effectiveness of DSA increases, and total

costs of diagnostic imaging are reduced.

As the yield of positive findings with DSA

decreases due to the application of this technology to a larger population of cases, the

costs per patient decline, but the cost per lesion found rises.

As the population examined for carotid lesions increases, total costs per diagnostic imaging are virtually certain to increase regardless of how effective DSA is or how much

it replaces arteriography. That is, the intro-
—

41

Table 5.6.—Estimates of the Cost Effectiveness of DSA for a Population At Riska

With Variable DSA Yield Rates and Variable Arteriography Charges

Cost-effectiveness

indicators

Total Charges Charges

DSA Lesions Arteriography Arteriography charges per lesion per patient

Protocol exams foundb

exams charge billed c

found examined

II (arteriogram only if DSA

positive) . . . . . . . . . . . . . . . . . 200 A. 160 160 $1,122 (a) $268,720

(b) 294,520

(C) 309,120

200 B. 130 130 1,158 (a) 239,740

(b) 265,540

(C) 280,140

200 c. 105 105 1,193 (a) 214,465

(b) 240,265

(C) 254,865

Ill (arteriogram only for 500/0

of positive DSAs) . . . . . . . . 200 A. 160 80 1,232 (a) 187,760

(b) 213,560

(C) 228,160

200 B. 130 65 1,258 (a) 170,970

(b) 196,770

(C) 211,370

200 C. 105 53 1,280 (a) 157,040

(b) 182,840

(c) 197,440

IV (arteriogram only for 100/0

of positive DSAs) . . . . . . . 200 A. 160 16 1,359 (a) 110,944

(b) 136,744

(c) 151,344

200 B. 130 13 1,367 (a) 106,971

(b) 132,771

(c) 147,371

200 c. 105 11 1,372 (a) 104,292

(b) 130,092

(C) 144,692

aA~~U~e~ ~he ~OP~~~iOn ~~ ~l~k ~hlCh can be safely ~tud{~ ~ill d~ub[e (n sl~e (24) This is regarded as a MlrllrnUrTl level of additional volume of DSA procedures performed

bDSA yield rat!os

(A) 80 percent (If volume of procedures IS assumed at current level)

(B) 50 percent

(C) 25 percent (Y!eld ratios of those procedures beyond the current volume, e g., 100 procedures in th!s example Hence, yield ratios In (B) and (C) are calculated

at 80 percent for the first 1 CO procedures performed and at 50 percent and 25 percent. respectively, for all Procedures Performed beyond the Initial 100 )

CDSA charges a) $446 b) $575, c) $648

SOURCE Off Ice of Technology Assessment

$1,680

1,840

1,932

1,844

2,043

2,155

2,043

2,288

2,427

1,174

1,335

1,426

1,315

1,514

1,626

1,496

1,741

1,880

693

855

946

823

1,021

1,134

993

1,239

1,378

$1,344

1,473

1,546

1,199

1,328

1,401

1,072

1,201

1,274

939

1,068

1,141

855

984

1,057

785

914

987

555

684

757

535

664

737

521

650

723

duction of DSA is likely to represent an ad- costs of DSA due to changes in costs (and

dition to the costs of health care in the treat- charges) of DSA and arteriographic facilities

ment of carotid artery diseases. are often small relative to the variations

● The variations in cost effectiveness and total caused by the patterns of DSA utilization.
42

Table 5-7.—Estimates of the Cost Effectiveness of DSA for a Population At Risk Expanded Four-Fold

With Variable Yield Rates for Baseline Findings (with fixed charges for arteriography)a

Cost-effectiveness

indicators

Total Charges Charges

DSA Lesions Arteriography Arteriography charges per lesion per patient

Protocol exams foundb

exams charge billedc

found examined

II (arteriogram only if DSA

is positive) . . . . . . . . . . . . . . . 700

700

700

Ill (arteriogram only for 50%

of positive DSAs) . . . . . . . . . 700

700

700

IV (arteriogram only for 10%

of positive DSAs) . . . . . . . . . 700

700

700

A. 560 560 $1,200

B. 380 380 1,200

C. 230 230 1,200

A. 560 280 1,200

B. 380 190 1,200

C. 230 115 1,200

A. 560 56 1,200

B. 380 38 1,200

C. 230 23 1,200

(a) $ 984,200

(b) 1,074,500

(C) 1,125,600

(a) 768,200

(b) 858,500

(c) 909,600

(a) 588,200

(b) 678,500

(c) 729,600

(a) 648,200

(b) 738,500

(c) 789,600

(a) 540,200

(b) 630,500

(c) 681,600

(a) 450,200

(b) 540,500

(c) 591,600

(a) 379,400

(b) 469,700

(c) 520,800

(a) 357,800

(b) 448,100

(c) 499,200

(a) 339,800

(b) 430,100

(c) 481.200

$1,758

1,919

2,010

2,022

2,259

2,394

2,557

2,950

3,172

1,158

1,319

1,410

1,422

1,659

1,794

1,957

2,350

2,572

678

839

930

942

1,179

1,314

1,477

1,870

2.092

$1,406

1,535

1,608

1,097

1,226

1,299

840

969

1,042

926

1,055

1,128

772

901

974

643

772

845

542

671

744

511

640

713

485

614

., 687

aThe fixed ~harg= for a~eriograplly~~rre~P~nd to ~“rrent Cflarges for the procedure in 1982.83 (33), assuming that arteriographic facilities are Operating at futl Capacity

or efficiency The . . Domlatlon . examined with DSA, then referred for arteriography, will expand by a factor of 2 to 6 This will require additional arteriographic facilities

which would also presumably operate at full capacity or efficiency in th; long run

bDSA yield ratios:

(A) 80 Dercent (if volume of procedures is assumed at current level)

(B) 50 percent

(C) 25 percent (Yield ratios of those procedures beyond the current volume, e.g , 100 procedures in this example. Hence, yield ratios in (B) and (C) are calculated

at 60 percent for the first 100 procedures performed and at 50 percent and 25 percent, respectively, for all procedures performed beyond the initial 100 )

CDSA charges a) W46, b) $575, c) $648

SOURCE Off Ice of Technology Assessment
Appendixes
Appendix A. — Acknowledgments and

Health Program Advisory Committee

The development of this case study was greatly aided by the advice of a number of people. The authors

and OTA staff would like to express their appreciation to the Medical Technology and Costs of the Medicare

Program Advisory Panel, to the Health Program Advisory Committee, and especially to the following individuals:

Harold Margulies Robert Moliter

Office of Health Technology Assessment General Electric Co,

National Center for Health Services Research Washington, DC

Rockville, MD Dermis Cotter

Rosanna Coffey Prospective Payment Assessment Commission

National Center for Health Services Research Washington, DC

Rockville, MD Murray Goldstein

Mimi Fahs National Institute of Neurological and

National Center for Health Services Research Communicative Disorders and Stroke

Rockville, MD

Walter L. Scott

National Center for Devices and

Health

Food and Drug Administration

Rockville, MD

Robert G. McCune

National Institutes of Health

Bethesda, MD

Radiological Pat Rubner

Blue Cross/Blue Shield Association

Chicago, IL

David Tannenbaum

Blue Cross/Blue Shield Association

National Electrical Manufacturers Association

Washington, DC

Monica Walters

Office of Medical Applications of Research

National Institutes of Health

Bethesda, MD

Brad Perry

Office of Research

Health Care Financing Administration

Baltimore, MD

Don Detmer

University of Wisconsin Medical Center

Madison, WI

Chicago, IL

Gerald Freedman

Temple Radiology Group

New Haven, CT

Richard Scheffler

School of Public Health

University of California at Berkeley

Berkeley, CA

William B. Stason

Harvard School of Public Health

Boston, MA

45
46

HEALTH PROGRAM ADVISORY COMMITTEE

Sidney S. Lee, Committee Chair

President, Milbank Memorial Fund

New York, NY

Stuart H. Altman*

Dean

Florence Heller School

Brandeis University

Waltham, MA

H. David Banta

Deputy Director

Pan American Health Organization

Washington, DC

Carroll L. Estes**

Chair

Department of Social and Behavioral Sciences

School of Nursing

University of California, San Francisco

San Francisco, CA

Rashi Fein

Professor

Department of Social Medicine and Health Policy

Harvard Medical School

Boston, MA

Harvey V. Fineberg

Dean

School of Public Health

Harvard University

Boston, MA

Melvin A. Glasser** *

Director

Health Security Action Council

Committee for National Health Insurance

Washington, DC

Patricia King

Professor

Georgetown Law Center

Washington, DC

Joyce C. Lashof

Dean

School of Public Health

University of California, Berkeley

Berkeley, CA

Alexander Leaf

Professor of Medicine

Harvard Medical School

Massachusetts General Hospital

Boston, MA

Margaret Mahoney*

President

The Commonwealth Fund

New York, NY

Frederick Mosteller

Professor and Chair

Department of Health Policy and Management

School of Public Health

Harvard University

Boston, MA

Norton Nelson

Professor

Department of Environmental Medicine

New York University Medical School

New York, NY

Robert Oseasohn

Associate Dean

University of Texas, San Antonio

San Antonio, TX

Nora Piore

Senior Advisor

The Commonwealth Fund

New York, NY

Mitchell Rabkin**

President

Beth Israel Hospital

Boston, MA

Dorothy P. Rice

Regents Lecturer

Department of Social and Behavioral Sciences

School of Nursing

University of California, San Francisco

San Francisco, CA

‘Until April 1983.

● ’Until March 1984.

● **Until October 1983,

‘Until August 1983.

● *Until April 1983.
47

Richard K. Riegelman Frederick C. Robbins

Associate Professor

George Washington

School of Medicine

Washington, DC

Walter L. Robb

President

University Institute of Medicine

Washington, DC

Rosemary Stevens

Professor

Vice President and General Manager Department of History and Sociology of Science

Medical Systems Operations University of Pennsylvania

General Electric Co. Philadelphia, PA

Milwaukee, WI
Appendix B. —Glossary of Terms and Acronyms

Glossary of Terms

Accuracy: The number of correct test results divided

by the total number of tests performed. Diagnostic

accuracy may vary with the prevalence of the disease in the population.

Aneurysm: A permanent abnormal blood-filled dilation of a blood vessel resulting from disease of the

vessel wall.

Arterial lumen: The cavity of a tubular organ.

Arteriography: Visualization of an artery using photographs made with X-rays after the injection of

radiopaque (impervious to the rays) material into

the bloodstream.

Atherosclerosis: A chronic disease characterized by the

deposition of fatty substances in the inner layer of

the arteries.

Bruit: A sound or murmur heard in an organ, especially an abnormal one.

Carotid bifurcation: The division into two branches

of the principal artery in the neck.

Cerebral infarction: An area of dead tissue in the cerebrum caused by a deficiency of blood due to functional constriction or actual obstruction of a blood

vessel.

Cerebrovascular disease: A disease affecting or pertaining to the blood vessels of the cerebrum or

brain.

Cholesterol: A steroid alcohol present in animal cells

and body fluids, important in physiological processes, and implicated experimentally as a factor in

arteriosclerosis.

Digital subtraction angiography (DSA): A radiologic

tool used for the diagnosis of conditions pertaining to the internal structure of blood vessels. The

procedure involves injecting a contrast medium into

the veins and then monitoring the change of the

medium as it passes through the veins. The computer subtracts the images before the injection from

the images after the injection to attain a numerical

representation of the arterial structure.

Diplopia: A vision disorder in which two images of

a single object are seen because of unequal action

of the eye muscles (also called “double vision”).

Doppler device: A radar-like device used to measure

the velocity of blood flow through the arteries.

Duplex scanning: The combination of the B-scan and

the Doppler device. Using this method both the image of the blood vessel and the flow pattern at a

given location can be determined.

Effectiveness: Same as efficacy except that it refers to

,,

. . . average or actual conditions of use. ”

Efficacy: The probability of benefit to individuals in

a defined population from a medical technology applied for a given medical problem under ideal conditions of use.

Endarterectomy: Surgical removal of the inner layer

of an artery when thickened and obstructed.

Energy subtraction: Using digital subtraction angiography to show changes in the contrast appearance

of the artery at varying X-ray intensities.

Fibrin: A white insoluble protein formed from fibrinogen during the clotting of blood.

Hemorrhagic: Of or pertaining to a copious discharge

of blood from the blood vessels,

Microemboli: A microscopic abnormal particle circulating in the blood.

Noninvasive technique: A diagnostic method that does

not involve the penetration (by surgery or hypodermic needle) of the skin.

Occlusion: The blocking off or obstruction of blood

flow through a vessel.

Periorbital ultrasonography: A diagnostic technique

using ultrasonic waves to examine the orbit or the

eye socket.

Peristalsis: Successive waves of involuntary contraction passing along the walls of the intestine or other

hollow muscular structure and forcing the contents

onward.

Platelet: A disk-shaped structure found in the blood

of all mammals. It is known for its role in blood

coagulation.

Prophylaxis: Measures designed to preserve health (as

of society) and prevent the spread of disease.

Real-time ultrasound (B-scan): A device used to measure the anatomical structure of vessels by vibrations

of the same physical nature of sound, but with frequencies above the range of human hearing.

Risk: A measure of the probability of an adverse or

untoward outcome and the severity of the resultant

harm to health of individuals in a defined population and associated with use of a medical technology applied for a given medical problem under

specified conditions of use.

Safety: A judgment of the acceptability of risk in a

specified situation.

Sensitivity: The number of positive test results divided

by the number of patients that actually have the

disease.

Specificity: The number of negative test results divided

by the number of patients that actually have the

disease.

Stenosis: A narrowing or constriction of a bodily

passage or orifice.

48
49

Stroke: A condition caused by sudden lesions in the Yield rates: The numbers of lesions found per popublood vessels of the brain. The lesions could be lation screened.

caused by hemorrhage, embolism or thrombosis.

This condition is often followed by permanent Glossary

neurological damage.

Temporal subtraction: Using digital subtraction angiography to show changes in the contrast appear- DSA

ance of the artery over time. DHHS --

Transient ischemic attacks: A deficiency of blood in

a part of the body, due to functional constriction TIA –

or actual obstruction of a blood vessel. CT scan —

Ulcerated plaques: Breaks in the yellowish plaque DRG –

which is formed within the intima and inner media R&D –

(innermost and middle coats of the blood vessels)

of large and medium-sized veins.

of Acronyms

digital subtraction angiography

Department of Health and Human

Services

transient ischemic attacks

computer axial tomography

diagnosis related group

research and development

.
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