GUIDELINEFOR RADIATION PROTECTION ANDPERFORMANCE EVALUATION OF
PET-CT IMAGINGFORUM FOR NUCLEAR COOPERATION IN ASIA (FNCA)
5 MARCH 20111

Contributors
Dr. Noriah Jamal - Malaysia
Dr. Muhd Noor Muhd Yunus - Malaysia
Dato’ Dr. Rehir Dahalan - Malaysia
Prof. Dr. Ahmad Zakaria - Malaysia
Prof. Dr. Chen Shengzu - China
Dr. Hideo Murayama - Japan
Mr. Tran Ngoc Toan - Vietnam
Asso. Prof. Dr. Rujaporn Chanachai -Thailand
Mr. Alexis Tiongson De Leon - The Philippines
Prof. Dr. Kwan-Hoong Ng - Malaysia
Asso. Prof. Dr. Wan Ahmad Kamil - Malaysia
Mr. Ng Aik Hao - Malaysia
Mr. Mohd Aminuddin Said - Malaysia
Mr. Zunaide Kayun - Malaysia
Mr. Adnan Khalid – Malaysia - Malaysia
Dato’ Dr. Mohd Ali Khader - Malaysia

Acknowledgement
We wish to acknowledge the contribution made by Professor Dato’ Dr Humairah Abdul
Samad Cheung, President (2010-2012), College of Radiology, Academy of Medicine
Malaysia, in the final editing of this Guideline.

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GUIDELINE FOR RADIATION PROTECTION AND PERFORMANCEEVALUATION OF PET-CT IMAGINGCONTENTS
Page
1Introduction
1.1
Scope and Objectives of this Document
1.2
Care of Patients undergoing PET-CT Procedures

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2

Radiation Protection in PET-CT Imaging
2.1
Principles of Safe Radiation Protection
2.1.1 General Principles
2.1.2 The Justification of Practice2.1.3 The Optimisation of Protection
2.1.4 Occupational Dose Limits
2.2
Medical Exposures
2.2.1 The Justification of Practice2.2.2 Optimisation
2.2.3 Dose Limits
2.3
Radiation Shielding for PET-CT Facility Design
2.3.1 Shielding Requirements
2.3.2 Shielding Assessment
2.3.3 Radiation Warning Sign
2.3.4 Personnel present during PET-CT Examination
2.3.5 Markings on CT X-ray Generators and Tube Assemblies

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Acceptance Testing
3.1
When Acceptance Testing of PET-CT Scanner should be performed
3.2
Standard of Acceptance Testing of PET Scanner
3.3
Standard of Acceptance Testing of CT Scanner

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4

Performance Characteristics of PET-CT
4.1
Quality Control Procedures
4.2
Qualifications and Responsibilities of a Nuclear Medicine Medical
Physicist (NMMP)
4.2.1 Qualifications
4.2.2 Responsibilities
4.3
Performance Evaluation of PET Scanner
4.3.1 Performance Characteristics to be monitored
4.4
Performance Evaluation of CT Scanner
4.4.1 Performance Characteristics to be monitored
4.4.2 CT Baseline Values
4.4.3 Diagnostic Reference Levels

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4.5

Specific Tests for PET-CT
4.5.1 Overall Performance
4.5.2 Patient Radiation Dose in CT
4.5.3 Organ Doses in PET

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5

Documentation
5.1
QC Report and Follow-up Procedures
5.2
Record Keeping

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6

References

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7

Appendices
Appendix A:
Appendix B:
Appendix C:
Appendix D:

Terminology
Performance Evaluation Tests, Tolerances and Checklists for CT
Performance Evaluation Tests, Tolerances and Checklists for PET
Daily and Quarterly QC Tests for PET-CT

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1

Introduction

1. 1

Scope and Objectives of this Document

Positron Emission Tomography-Computed Tomography (PET-CT) system is a new imaging
tool in nuclear medicine. The primary goal of PET-CT imaging is to produce highly accurate
fusion images with proper registration of both CT and PET images on the same platform. An
additional goal is to produce images with the lowest reasonable radiation dose consistent
with the clinical use of the equipment.
Even though the systems can be operated to acquire either CT images or PET images, they
are mainly operated to acquire both, combining two medical imaging technologies: CT for
anatomical imaging and PET for functional imaging. This brings the advantages and also thecomplexities of both systems while providing anatomical and functional information throughfusion images.
Therefore, PET-CT scanner should be tested on installation and monitored by a Nuclear
Medicine Medical Physicist (NMMP) to ensure proper functioning within the manufacturers’
specifications and accepted performance standards.
The scope of this document is to present a guideline on radiation protection related to the useof a PET-CT scanner and the performance evaluation of this imaging device.
The objectives of this guideline are to:a. provide adequate safety measures to protect patients, occupationally exposed
personnel and the public from unnecessary radiation exposure from PET-CT
imagingb. improve and maintain the quality of clinical data acquired using PET-CT scannerc. ensure that minimum standard of PET-CT scanner performance is achieved.
This guideline should be read in conjunction with all related rules and regulations enforced.
It is important that the performance level of the scanner is established during acceptancetesting, and that performance standards are maintained over time by an appropriate quality
control programme. Inadequate performance and quality control procedures may cause an
unnecessary increase in dose to the patient and staff, and a decrease in the diagnostic value ofthe examination.

1.2

Care of Patients undergoing PET-CT Procedures

1.2.1 Nuclear Medicine (NM) physicians, radiologists, NMMPs, NM technologists,
radiographers and all supervising physicians have a responsibility to minimise radiation doseto individual patients, staff, and society as a whole, while maintaining the necessary
diagnostic image quality. This concept is known as “As Low As Reasonably Achievable(ALARA).”5

1.2.2 All PET-CT facilities should have in place policies and procedures, in accordancewith the ALARA principle, which should be adhered to. Examination protocols should take
into account patient body habitus, such as height and/or weight, body mass index or lateralwidth. A NMMP should be consulted when necessary.
1.2.3 The dose reduction devices that are available on imaging equipment should be active.
If not, manual techniques should be used to moderate the exposure while maintaining thenecessary diagnostic output. The radiation dose should be periodically measured by a NMMP
in accordance with the appropriate standards.

6

2. Radiation Protection in PET-CT Imaging
2.1

Principles of Safe Radiation Protection

2.1.1

General Principles

2.1.1.1 Radiation protection is based on principles defined by the International Commission
on Radiological Protection (ICRP). Three general principles apply to safe radiation
practice, namely justification of practice, optimization of protection and individual dose
limits.
2.1.2

The Justification of Practice2.1.2.1 No practice shall be adopted unless its introduction produces a positive net benefit to
the exposed individuals.
2.1.3

The Optimisation of Protection

2.1.3.1 In relation to a particular practice, the magnitude of individual dose, the number ofpeople exposed, and the likelihood of incurring exposure, shall be kept ALARA, economic
and social factors being taken into account.
2.1.3.2 ALARA should be an over-riding principle in all aspects of radiation protection whenusing ionising radiation for imaging purposes. As a result, all practices where ionisingradiation emitting devices are used for imaging purposes shall be designed so as to reduce toa reasonable level,a.
the undesired exposure of individuals from radiation,b.
the risk of equipment failure leading to an uncontrolled exposure,c.
the occurrence of errors when in use.

2.1.4

Occupational Dose Limits

2.1.4.1 The effective and equivalent dose to individuals shall not exceed the limits defined in
the International Atomic Energy Agency (IAEA) Basic Safety Standards.
2.1.4.2 These objectives are in general achieved by a combination of engineering design
features of the equipment, facility and administrative procedures.

2.2

Medical Exposures

2.2.1

The Justification of Practice2.2.1.1 A patient may be exposed to radiation for medical imaging purposes with thepatient's approval when in the professional judgement of the nuclear medicine

7physician or other authorised medical practitioner, the proposed usage of radiation will beof net benefit to the patient.
2.2.2

Optimisation

2.2.2.1 Optimization of the protection of the patient should take place by proper protection
design, operation and quality assurance. In addition, protecting the patient requires
optimization of the imaging procedure as a whole to deliver adequate dose to the diseased
tissues and to reduce unwanted radiation dose to other tissues in accordance with the
ALARA principle, economic and social factors being taken into consideration.
2.2.3

Dose Limits

2.2.3.1 Dose limits do not apply to medical exposures, since the total benefit of the exposure
is directed to the individual exposed, and because of the individual medical requirementsof each patient.
S
ECTION 1—GENERAL REQUIREMENTS
2.3
Radiation Shielding for PET-CT Facility Design
2.3.1

Shielding Requirements

2.3.1.1 Special care must be exercised regarding radiation shielding requirements for PETCT facility design. Appropriate shielding must be provided for patient injection/uptake
rooms, PET-CT imaging suites, and any other areas where PET radiopharmaceuticals areprepared, used, or stored.
2.3.1.2 Due to the high energy of annihilation radiation used in PET, the amount of shielding
materials needed to protect adjacent areas is typically much larger than that for conventional
CT scanners or other diagnostic imaging modalities including conventional nuclear medicine
imaging.
2.3.1.3 A NMMP should be consulted early in facility design planning stages so thatshielding requirements can be determined and structural design issues, created from using thelarger amounts of shielding can be assessed. The design and shielding information should be
forwarded to the appropriate authority for licensing purposes.
2.3.1.4 Appropriate radiation shielding should be provided for the doors, walls, floor andceiling of the room in which the PET-CT scanner is installed and for any protective barrier
intended for use as a shield for the operators, to ensure that the radiation dose to any
personnel is as low as reasonably achievable.
2.3.1.5 Where a fixed protective shield is provided for use by the operator it must, in the caseof new installations, be clearly and durably marked with the lead equivalent and the kVp ofthe X-ray beam at which the lead equivalent was measured.

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2.3.1.6 Where a viewing window is used as part of the protective shield the lead equivalentand the kVp of the X-ray beam at which the lead equivalent was measured must, in the caseof new installations, be clearly and durably marked on the viewing window.
2.3.2

Shielding Assessment

2.3.2.1 Specifications for radiation shielding of protective barriers and the design details ofrooms used for PET-CT scanner should be determined and documented by the NMMP before
building works start.
2.3.3 Radiation Warning Sign
2.3.3.1 A radiation warning sign complying with the IAEA safety standards regulation must
be displayed on the outside of the entry doors to any room housing a PET-CT scanner.
2.3.3.2 A radiation warning light must be positioned at the entry doors to a room housing a
PET-CT scanner.
2.3.3.3 Where a radiation warning light is provided, it should illuminate whenever the
X-ray tube is placed in the preparation mode before exposure or when exposure is inprogress. The light must remain illuminated for the duration of the exposure and must bear
the words ‘RADIATION - DO NOT ENTER’ or similar instruction. Immediate
illumination should be ensured.
2.3.4

Personnel present during PET-CT Examinations

2.3.4.1 The NM technologist or radiographer should ensure that no personnel, other than thepatient, remains in the PET-CT room during an exposure.
2.3.4.2 The only personnel who should be present in the room during scanning are those:a.
whose presence during the procedure is necessary, orb.
who are responsible for the care of the patient, orc.
who are receiving instruction from the personnel conducting the procedure.
2.3.5

Markings on CT X-ray Generators and Tube Assemblies

2.3.5.1 X-ray generators and tube assemblies must be permanently marked and the markings
must be clearly visible.
2.3.5.2 X-ray generators must bear the following markings:a.
the name or trademark of the manufacturer;b.
the type or model number; andc.
the serial number or registration number.
2.3.5.3 X-ray tube assemblies must bear the following markings on the outer side of
the tube housing:a.
the name or trademark of the manufacturer of the X-ray tube insert;

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b.
c.
d.
e.
f.

the type or model number of the X-ray tube insert;
the serial number of the X-ray tube insert;
the name or trademark of the manufacturer of the X-ray tube housing;
the type or model number of the X-ray tube housing; andthe serial number of the X-ray tube housing.

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3

Acceptance Testing

3.1

What Acceptance Testing of PET-CT Scanner should be performed

3.1.1 Acceptance testing of PET-CT scanner shall be performed upon installation andshould be completed before clinical use.
3.2

Standard of Acceptance Testing of PET Scanner

3.2.1 Acceptance testing and data analysis of the PET scanner should be done according to
the procedures in the appropriate National Electrical Manufacturers Association (NEMA)
publication.
3.3Standard of Acceptance Testing of CT Scanner

3.3.1 Acceptance testing and data analysis of the CT scanner should be done according toAppendix B.

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4

Performance Characteristics of PET-CT

4.1 Quality Control Procedures
4.1.1 Quality Control (QC) procedures approved by a NMMP must be instituted andmaintained properly. The procedures should ensure that consistent, optimum-quality images
are produced while the exposure of patients, staff and the public to radiation satisfies the
ALARA principle.
4.1.2 The QC procedures should include checks and test measurements on all parts of theimaging system, as indicated in this guideline.
4.1.3 The NMMP must design quality control procedures that include regular testingprocedures to ensure proper operation on a daily basis. Quarterly testing with a 3D phantom
for uniformity, resolution, and contrast is recommended.
4.1.4 The QC activities for PET-CT should be reviewed regularly.
4.1.5 The test results must be reviewed by the NMMP and documented in an annual survey
report.
4.1.6 Each facility is required to submit a summary of the quality control and frequency of
testing currently being done on each PET-CT unit to the appropriate authority.

4.2
Qualifications and Responsibilities of a Nuclear Medicine Medical Physicist(NMMP)
4.2.1

Qualifications

4.2.1.1 A NMMP is an individual who is competent (as defined by the appropriate authority)
in applying knowledge in the physics of nuclear medicine.
4.2.1.2 The NMMP may be assisted by properly trained individuals in obtaining QC data.
However, the ultimate responsibility is on the NMMP.
4.2.2

Responsibilities

4.2.2.1 The NMMP must be familiar with the principles of imaging physics and radiation
protection, laws and regulations pertaining to the use of the equipment being tested, thefunction, clinical usage, and performance specifications of the imaging equipment, andcalibration processes and limitations of the instruments and the techniques used for
performance testing.

124.2.2.2 The NMMP has to ensure that instruments used for routine radiation dosimetry or
equipment performance monitoring should have a current calibration certificate that is
traceable to an appropriate national standard.

4.3 Performance Evaluation of PET Scanner
4.3.1

PET Characteristics to be Monitored

4.3.1.1 The performance evaluation procedures should include as a minimum, thoserecommended by the manufacturer. The following characteristics shall be evaluated for theequipment to which they apply on at least an annual basis:a. Spatial resolution
b. Count rate performance (count rate versus activity), including count loss
correction. Specific measurements of the following are recommended
i. Total coincidences
ii. Random coincidencesiii. Scatter coincidences
iv. Net true coincidences
v. Noise equivalent count ratec. Sensitivity (kcps/kBq)d. Scatter Fraction (SF)e. Image quality, accuracy of attenuation and scatter corrections
4.3.1.2 Performance Evaluation Tests, Tolerances and Checklists for PET equipment are
shown in Appendix C.

4.4 Performance Evaluation of CT Scanner
4.4.1

Characteristics to be Monitored

4.4.1.1 The performance of each CT unit must be monitored at least annually. Thisevaluation should include, but not be limited to:a.
Alignment light accuracyb.
Alignment of table to gantryc.
Multiple-row detector assembly and available scan modesd.
Slice localisation from scanned projection radiograph (localisation image)e.
Table increment accuracyf.
Slice thickness
g.
Image qualityi.
Spatial resolution
ii. Low-contrast resolution
iii. Image uniformity
iv. Noisev.
Artefact evaluation

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h.
i.
j.

k.

l.

4.4.2

CT number accuracy and linearity
Display devicesi.
Image display monitor(s)ii. Hardcopy display unit(s), if available
Dosimetryi.
CT Dose Index (CTDI)
ii. Patient radiation dose for representative examinations
iii. Review of pediatric dose reduction protocols
iv. Monitoring of pediatric specific (typically weight-based) doses
Safety evaluationi.
Visual inspection
ii. Work load assessmentiii. Scatter radiation measurements
iv. Audible and visual signalsv.
Posting requirements
Other tests as required by state and/or local regulations

CT Baseline Values

4.4.2.1 Baseline values for noise, mean CT number, uniformity, slice thickness, high contrast
resolution and CTDI should be established at the start of operation and following any
maintenance likely to affect these parameters.
4.4.2.2 Values for parameters in clause 4.4.2.1 should be defined using the appropriate
image quality phantoms for all field sizes.
4.4.2.3 Deviations from baseline values should not exceed those given in Table 1.
4.4.3

Diagnostic Reference Levels

4.4.3.1 Dose exposure evaluation of CT procedures should be conducted as part of the QA
programme.
4.4.3.2 Dose levels that consistently exceed those in Table 2 should be investigatedand justified.

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Table 1 Acceptable Deviations from CT Baseline Levels
Parameter

Deviation

Noise± 10% or 0.2 HU* (whichever is greater)

Mean CT number± 4 HU

Uniformity± 2 HU

Slice thickness± 1.0 mm for thicknesses > 2.0 mm or± 50% for thicknesses ≤ 2.0 mm

Dose index± 20%

High-contrast resolution± 15% modulation

Couch positioning± 2.0 mm

* HU = Hounsfield unit

Table 2 Some Diagnostic Guidance Levels for CT Procedures
Examination

CTDIw, (mGy)

Routine Head

60

Dose Length Product(mGy /cm)
1050

Routine Chest

30

650

Routine Abdomen

35

780

Routine Pelvis

35

570

Pediatric

25

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Specific Tests for PET-CT
4.4.4

Overall Performance

4.5.1.1 The performance of either the PET or the CT system can affect the overall
performance of dual-modality imaging. Each system should be tested individually, as statedpreviously, and together to examine co-registration. For this purpose, specially designed
phantoms shall be scanned on both the PET and CT systems.
4.5.1.2 Accuracy of co-registration should be determined by established procedure.

4.4.5

Patient Radiation Dose in CT

4.5.2.1 Patient radiation dose represented by CTDI shall be evaluated at least annually.
4.5.2.2 Doses to adult and pediatric patients from CT examinations (e.g., head, thorax,
abdomen, pelvis, and whole-body) shall be assessed. These results shall be compared withappropriate guidelines or recommendations when they are available. Appropriate steps
should be taken if the reference doses are not consistent with the recommendations.
4.4.6

Organ Doses in PET

4.5.3.1 The activity of radiopharmaceuticals used must be optimum so that the dose to apatient is optimum without compromising the quality of the image.

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5 Documentation
5.1

QC Report and Follow-up Procedures

5.1.1 The NMMP shall report the findings to the physician(s) or the responsible
professional(s) in charge of obtaining or providing necessary service to the equipment.
5.1.2 The Head of Department should take immediate action by direct verbal
communication if there is imminent danger to patients or staff using the equipment due tounsafe conditions.
5.2

Record Keeping

5.2.1 A record of maintenance and QC test results should be kept for each component of
the PET-CT system. Information on any defects found and their repair must be included.
5.2.2 Records should include necessary information to allow retrospective dose assessment.
5.2.3 All QC records, including faults, modifications and maintenance, must be madeavailable to the appropriate authority on request.
5.2.4 Written survey reports shall be provided in a timely manner consistent with theimportance of any adverse findings.

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6

References

American Association of Physicists in Medicine Task Group 108 report “PET and PET-CT
Shielding Requirements,” in conjunction with the National Council on Radiation Protection
Report 147, should be used as a reference in determining PET-CT shielding requirements.
American Association of Physicists in Medicine (AAPM). Specification and Acceptance
Testing of Computed Tomography Scanners. College Park, Md: American Association of
Physicists in Medicine; AAPM Report 39, 1993.
American College of Radiology. ACR technical standard for medical nuclear physics
performance monitoring of PET-CT imaging equipment. In: Simmons G, Dahlborn M, eds.
Practice Guidelines and Technical Standards, 2008. Reston, VA: American College ofRadiology; 2008:1155-1159.
American College of Radiology. Nuclear medicine/PET accreditation program requirements.
Available at: http://www.acr.org/s_acr/bin.asp?CID51744&DID5 12152&DOC5FILE.PDF.
Australian Radiation Protection and Nuclear Safety Agency & National Occupational Health& Safety Commission. Recommendations for Limiting Exposure to Ionizing Radiation (1995)(Guidance Note [NOHSC:3022(1995]). ARPANSA, Yallambie, Victoria. 2002.
Australian Radiation Protection and Nuclear Safety Agency & National Occupational Health& Safety Commission. National Standard for Limiting Exposure to Ionizing Radiation[NOHSC:1013(1995)], Radiation Protection Series Publication No. 1, ARPANSA,
Yallambie, Victoria. 2002.
Brambilla M, Secco C, Dominietto M. et al. Performance characteristics obtained for a new
3-dimensional lutetium oxyorthosilicate-based whole-body PET/CT scanner with the
National Electrical Manufacturers Association NU 2-2001 standard. J Nucl Med
2005;46:2083-2091.
MacFarlane C R. ACR Accreditation of Nuclear Medicine and PET Imaging Departments. J
Nucl Med Technol 2006; 34:18–24.
FERENCES AND
European Commission (EU). European Guideline on Quality Criteria for Computed
Tomography, Report EUR 16262 EN. 1999.
International Atomic Energy Agency (IAEA). Quality Assurance for PET and PET/CT
Systems:IAEA Human Health Series No. 1. Vienna, 2009.
Mawlawi O, Podoloff D A, Kohlmyer S. et al. Performance characteristics of a newly
developed PET/CT scanner using NEMA standards in 2D and 3D modes. J Nucl Med
2004;45:1734-1742.

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National Council on Radiation Protection and Measurements (NCRP). Structural Shielding
Design for Medical X-Ray Imaging Facilities. NCRP. Bethesda, Md; 147; 2004.
National Electrical Manufacturers Association. NEMA NU 2-2007 Performance
Measurements of Positron Emission Tomographs (PETs). 2007.
National Electrical Manufacturers Association. NEMA NU 2-2008 Performance
Measurements of Positron Emission Tomographs. Available at: http://www.nema.
org/media/pr/20070627b.cfm. Accessed July 26, 2008.
Surti S, Kuhn A, Werner M E. et al. Performance of Philips Gemini TF PET/CT scanner withspecial consideration for its time-of-flight imaging capabilities. J Nucl Med 2007;48:471480.
Townsend D W and Beyer T. A combined PET/CT scanner: the path to true fusion. Br J
Radiol 2002;75:S24-S30.
Townsend D W, Carney J P, Yap J T. et al. PET/CT today and tomorrow. J Nucl Med
2004;45:4S-14S.

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Appendix A – Terminology
absorbed dose. Energy delivered from radiation per unit mass of absorbing material,measured in Gray (Gy) or mGy. One Gray equals one joule per kilogram.
acceptance testing. Testing prior to delivery of a system.
air KERMA. Kinetic Energy Release per Unit Mass (KERMA) measured in a mass of air.
Analog-to-Digital Converter (ADC). These devices convert continuous electrical voltages
to discrete integer numbers in a defined range. When a digital image is acquired in an analog
form, an ADC converts the electrical signal that represents the x and y positions for a
detected photon to a matrix location in the ranges of, for example, 1–64 or 1–128.
annihilation photons. When a positron is emitted, it travels a short distance in tissue, losing
energy. It eventually combines with an electron and the two annihilate (disappear), with themass being converted into energy in the form of two gamma rays (511 keV) that travel in
opposite directions.
asymmetric energy window. Normally, the energy window is centred on the main peak(s)of the radionuclide being imaged. To reduce scatter, an off-centre energy window, shifted up
on the peak, is sometimes used. This is referred to as an asymmetric window.
axial Field-Of-View (FOV). The maximum length parallel to the long axis of a positronemission tomograph along which the instrument generates transaxial tomographic images.
back-projection. This is the process used in reconstruction, which allocates counts in thereconstructed image at each voxel proportional to the number of recorded counts on the
projection, defined by the geometry of detection. In the simplest case assuming a parallel
hole collimator, each voxel will be allocated counts from a projection pixel, defined by a line
drawn at right angles to the projection that passes through the voxel.
Bismuth Germanate Oxide (BGO). This is a detector material commonly used in PET
cameras. It has a higher density than NaI and is therefore well suited to detection of the highenergy (511 keV) annihilation photons.
Centre Of Rotation (COR). This defines the point that should correspond to the exact
centre around which the detectors rotate; it should correspond exactly to the centre of the
projections recorded at all angles. Any error in this point will lead to loss of resolution.
coincidence detection. In order to detect the two gamma rays emitted from a positronannihilation event, two detectors are used and a valid event is recorded when both detectors
record an interaction at the same time (or within a very short time of each other). The
detectors operate in electronic coincidence. This term is used with detectors in dedicated PET
systems as well as in gamma camera based PET systems.

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convolution. Convolution is the filtering procedure undertaken in the spatial domain. It
involves replacing each pixel value by a weighted sum of the neighboring values and thevalue itself. The result will depend on the weighting values, usually resulting in a smootherimage (e.g. nine points smooth).
CT. This abbreviation stands for computed tomography.
CT Dose Index. The integral of the dose profile along a line perpendicular to thetomographic plane from -7T to +7T (where T is the nominal slice thickness), divided by the
product of the nominal slice thickness and the number of tomograms (N) produced in a single
scan.
CT number. The number used to represent the mean X-ray attenuation associated with eachelemental area of the CT image. It is normally expressed in Hounsfield units.
cut-off/critical frequency. The shape of a filter is defined by some mathematical function,with the value 1 at zero frequency and lower values at progressively higher frequencies. The
cut-off or critical frequency is a parameter that defines the shape of the function, a lower cutoff frequency defining a curve that drops to zero faster, resulting in a smoother result. In thecase of the Butterworth filter the cut-off frequency defines the point when the amplitude
reaches half the maximum value.
electronic collimation. Since annihilation photons travel in opposite directions, the origin of
the annihilation can be defined by the straight line joining the points of detection of the two
photons without the need for conventional collimation.
energy spectrum. A plot of the number of gamma photons detected as a function of theenergy of the gamma rays. Such spectra are useful for setting energy windows with the pulse
height analyser and for observing the amount of scatter present.
energy window. Setting a lower and upper energy threshold, the energy window determines
which gamma ray energies are accepted and displayed.
FOV. This abbreviation stands for field of view.
Full Width at Half Maximum (FWHM). This term refers to resolution measurements (e.g.
spatial and energy resolutions). FWHM is usually measured from a profile through an imageof a line or point source, or, in the case of energy, from the energy spectrum of a single
gamma emitting radionuclide. The spread is due to resolution effects and is measured by thefull width of the profile at a point which is half the maximum height of the profile.
contrast resolution. The ability to resolve different objects in the displayed image, when the
difference in attenuation between the objects and the background is large compared to noise.
It is also known as spatial resolution.

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KERMA (K). Kinetic Energy Released in a material by ionising radiation and is determinedas the quotient of dEtr by dm, where dEtr is the sum of the initial kinetic energies of all the
charged ionising particles liberated by uncharged ionising particles in a material of mass dm(K = dEtr/dm). The unit of KERMA is the gray (Gy), or joule per kilogram.
KERMA rate. KERMA per unit time and is determined as the quotient of dK by dt, where
dK is the increment of kerma in the time interval dt.
lead equivalent. The thickness of lead causing the same attenuation of a beam of a specified
radiation quality as the material under consideration.
line source. A thin line (such as a capillary tube) filled with activity, which is used formeasuring resolution. The diameter of the line source should typically be 1 mm.
Lutetium Oxyorthosilicate (LSO). This is a new detector material currently being
considered for PET systems.
mean CT number. The mean value of the CT numbers of all pixels within a certain defined
region of interest.
NEMA (National Electrical Manufacturers Association). NEMA develops standard
specifications for imaging equipment including gamma cameras (SPECT) and PET. These
form the basis for specification and acceptance testing of equipment, and some tests, withmodification, can also be used for routine quality control.
noise. The variation of CT numbers from a mean value in a defined area in the image of a
uniform substance.
Noise Equivalent Count Rate (NEC). Noise Equivalent Count Rate used to estimate thenumbero f true count acquired per sec exempt of scatter, random and intrinsic contributions.
performance evaluation tests. Those tests which are undertaken either regularly, or after
maintenance or repairs, to detect whether any changes in the performance of the equipment
has occurred. They are also referred to as quality control (QC).
phantom. A test object that simulates the average composition of various structures.
Positron Emission Tomography (PET). Tomography based on detection of the dualannihilation photons that originate from positron emission. The technique involves detectionof the dual photons in coincidence (at the same time).
primary beam. Iionising radiation that emerges through the specified aperture of theprotective shielding of the X-ray tube and the collimating device.
projections (count profiles). This term refers to the counts recorded during tomographic
acquisition. The counts in a single row of the images recorded in SPECT at a given angle
represent a projection of the emitted counts. These can also be referred to as count profiles.

22

The set of projections, recorded at different angles, form the data that are used for
tomographic reconstruction.
prompt counts. Count that represents coincidence events acquired in the standard
coincidence window of a positron emission tomograph. Prompt counts include true,
scattered and random coincidence events.
Quality Assurance (QA). The systematic process of checking to see whether a product orservice being developed is meeting specified requirements.
Quality Control (QC). A procedure or set of procedures intended to ensure that amanufactured product or performed service adheres to a defined set of performance criteria.
random coincidence. When two gammas originating from quite independent sources (e.g.
two separate positron emissions) are detected at the same time, the path defined by the pointsof detection does not correspond to a positron emission. This incorrectly located coincidence
event is referred to as a random event.
resolution. This refers to the ability of imaging systems to distinguish between two closely
spaced small sources. Usually expressed in terms of FWHM, which describes the spread of
the image obtained from a line or point source.
resolution recovery. This is the opposite of smoothing, and is achieved by filtering or
deconvolution. By use of an appropriate filter the loss of resolution due to some measurable
effect (e.g. due to a detector’s finite resolution) can be partially recovered. However, any
noise in the original image will normally be amplified.
ring artefacts. These are a common error in reconstructed images which are caused by alocalized non-uniformity in the detector.
scatter coincidence. When one or both photons originating from a positron event aredetected in coincidence, the path defined by the points of detection does not necessarily
correspond to the point of positron emission. This event is referred to as a scattercoincidence.
Scatter Fraction (SF). A dimensionless ratio of the scattered coincidence events to the sumof scattered and true coincidence events in a defined Region Of Interest (ROI) of the scanner
FOV.
scattered photon. A gamma ray which has changed direction at least once due to Compton
interaction and loss of energy in the material through which it is travelling.
scattered radiation. Ionising radiation produced from the interaction of electromagnetic
ionising radiation with matter. It has a lower energy than, or different direction from, that of
the original incident ionising radiation.
sensitivity. Fraction of the emitted gamma rays which pass through the collimator(collimator sensitivity) or are detected by the gamma camera (system sensitivity).

23

single event. In a PET system, when a photon is detected without a corresponding
coincident photon, this is referred to as a single event. Owing to the probability of detection,
there are many more single events detected than coincidences.
sinogram. The image formed by placing projection values in sequential rows (i.e. arranging
pixels corresponding to projection position versus projection angle) is called a sinogram. It isso called since the projections from a single point describe a perfect sine wave when plottedin this form.
slit phantom. A phantom consisting of a lead mask with thin slits cut into it. Typically theslits are 1 mm wide and 30 mm apart. They are used for measuring intrinsic FWHM
resolution and also linearity.
spatial frequency. Frequency normally refers to cyclic variations as a function of time
(units: s–1). However, if a curve represents variations in values over distance (units:
1/distance), the number of oscillations per unit distance is referred to as a spatial (rather than
temporal) frequency.
tomography. Literally this means ‘drawing a body slice’. Tomography involves
measurement from different angles around an object with the intention to ‘reconstruct’ animage of the internal distribution of some parameter (e.g. activity in PET).
transverse Field-Of-View (FOV). The maximum diameter circular region perpendicular tothe long axis of a positron emission tomograph within which objects might be imaged.
true coincidence. When two annihilation photons originating from a single positronannihilation are detected in coincidence (without being scattered), this is referred to as a truecoincidence.
uniformity. A measure of how uniform the observed counts across the FOV are when thedetector is irradiated by a uniform source. Integral uniformity is a measure of the maximum
count deviation ((max – min)/(max + min)) over a given FOV. Differential uniformity is ameasure of the maximum rate of change over a specified distance. Both shall be measured for
the UFOV and the CFOV.
voxel. If one considers a digitized 3-D volume rather than a digitized 2-D image, each digitalvalue within the volume can be considered to occupy a small volume element (e.g. a smallcube) or voxel. One therefore refers to planar projections as having pixels, but to eachreconstructed slice as having voxels, which also have a thickness corresponding to thespacing between adjacent slices.
X-ray tube potential difference. The peak value of the potential difference applied to the Xray tube, expressed as kilovolts peak (kVp).

24

Appendix B – Performance Evaluation Tests, Tolerances and Checklists for CT
The schedule of tests and tolerances specified in this section's tables have been adopted frominternational literature and the tolerances should be regarded as a minimum standard for therange of equipment considered and the frequency determined. Manufacturers’ tolerance
specifications may be used when they approximate the tabulated values.
No
Parameters.
1.
X-ray generator
i.

ii.
2.

3.

Accuracy of kVp

Accuracy of exposure time

Optimum Standard

Maximum deviation:≤ ± 5% or ± 5 kV
whichever is smaller

Frequency

Annually

Maximum deviation :≤ ± 10%

Radiation dosimetryi. Patient dosimetry (CTDI)≤ ± 20% of nominal

ii. Scout localisation image
Scan localisation≤ ± 20% of nominali.

Axial scan localisation
light accuracy≤ ± 2mmii. Isocenter alignment,
sagittal and coronal
localisation light accuracy≤ ± 5mmiii. Gantry (or table) tilt
accuracy≤ ± 30 of intended

iv. Table top increment≤ ± 2mm in 20 cmv.

≤ ± 2mm in 20 cm

Couch travel accuracy(spiral Scan)vi. Accuracy of scanprescription from scout
localisation image

Semi-annually

Annually≤ ± 1mm

25

4.

5.

Image scan width(Sensitivity profile)Single-slice CT

Multi-slice CT

According to
manufacturers’
specification

Radiation dose profile± 20% of intended or ± 1
mm whichever is:• greater for < 5 mm
slice.
• smaller for ≥ 5 mm
sliceSingle-slice CT

Multi-slice CT

6.

± 20% of intended or± 1 mm whichever is:• greater for < 5 mm
slice.
• smaller for ≥ 5 mm
slice

Image display

Visual display

Hard copy display

Annually

Annually

According to
manufacturer’s
specification(SMPTE pattern) Luminance andcontrast notsignificantly different
from hard copy
output.
 Geometric distortion
not exceeding ± 1mm
 5% and 95% patches
must be visible.
 No noticeable
artefect.







Luminance contrast
not significantly
different from visual
output.
Geometric distortion
not exceeding ± 1
mm
5% and 95% patches
must be visible.
No noticeable artefact
Optical density values
must be within thespecified range.

Daily

Monthly

Daily

Monthly

26

7.

8.

Image quality(CATPHAN-500 or
similar)i.

CT number uniformity± 5HU (Head Phantom)

ii.

Noise (% of μwater )≤ ± 0.5% (Head Phantom)

iii. Image artefact (transaxial scan
localisation images)

No significant artefact

iv. Low contrast resolution

5 mm

v.

1 mm holes (5lp/cm)

High contrast resolution

Quantitative accuracyi.

Accuracy of distancemeasurements (transaxial andscan localisation images)± 1 mmAnnuallyii.

CT number value•

Water: 0 ± 1.5 HUMonthly•

Other material ± 20 HU(or) 5% whichever isgreateriii. CT number constancy

Value and standard
deviation for water remains
relatively constant

iv. CT number dependence on scan ≤ ± 3HU
thickness

9.

Monthlyi.

CT number dependence on
phantom size

≤ ± 20HUii.

CT number dependence on
phantom position≤ ± 5HU

iii. CT number dependence onreconstruction algorithm≤ ± 3HU

Leakage radiation

0.1 mGy in one hour at 1
meter from focus

Daily

Semi-annually
Semi-annually
Annually
Annually

Acceptance test. Tubechange27

Appendix C – Annual Performance Evaluation Tests, Tolerances and Checklists for
PET
The schedule of tests and tolerances specified in the table below has been adopted frominternational literature and the tolerances should be regarded as a minimum standard for therange of equipment considered and the frequency determined. Manufacturers' tolerance
specifications may be used when they approximate the tabulated values.
No
1.
2.
3.
4.
5.
6.
7.
8.
9.

Parameter (s)Scatter fraction
Uniformity
Correction for count losses and random
Correction for attenuation and scatter
Spatial resolution
Count rate performance
Noise Equivalent Count (NEC) rate
PET sensitivity
Image quality analysis

Tolerance (%)
±10
±10
±10
±10
±10
±10
±10
± 10
± 10

28

Appendix D – Daily and Quarterly QC Tests for PET-CT
The tolerance is based on the manufacturers’ specifications

Daily:-

Reboot the system
Coincidence timing resolution
Test of PET-CT in clinical mode
Routine image quality PET-CT test
CT tube warm-up
CT air calibration
Uniformity
PET normalization (blank scan)-

Normalization
Well counter correction
Image quality analysis
2D/3D activity concentration calibration
PET-CT fusion accuracy

Quarterly:29