Composing a reference heart beat signal

A method and apparatus for composing a reference heart beat by synchonously summing heart beat signals detected by a high resolution radioactivity distribution detection system for non-invasive measurement of cardiac performance. A plurality of sensing devices form an array for detecting radioactive events emitted from a heart under study. A processor sums heart beat images of a continuous series of detected events and generates a reference heart beat by synchronizing the regrouping of the beat images as a function of the peaks at volumetric end diastole and the image troughs at volumetric end systole. The reference heart beat represents a statistical standard heart beat for the heart under study and defines a base signal for quantative measurements and qualitative analysis of the condition of the subject heart.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to nuclear medicine and, more particularly, 
is directed towards nuclear cardiology. 
2. Description of the Prior Art 
Electrocardiograph machines monitor electrical signals given off by the 
muscles of the heart as they pump blood around the body. These electrical 
signals, in combination with signals generated by a radioactivity 
distribution detection system, form a basis for non-invasive measurements 
of cardiac performance. A spike or R-wave in the signal monitored by the 
electrocardiograph is used to define the beginning of each heart beat. A 
series of measurements taken on a plurality of heart beats are added to 
provide sufficient statistical basis for valid cardiac diagnosis. Such 
non-invasive nuclear cardiac measurement techniques are costly and time 
consuming in that they require, in addition to a radiation detection 
apparatus, an electrocardiograph machine and the placement of associates 
electrodes on the body. Erratic electrical signals generated by the heart 
muscles and monitored by the electrocardiograph result in confusing 
diagnostic measurements. 
SUMMARY OF THE INVENTION 
A primary object of the invention is to provide a method and apparatus for 
composing a reference heart beat with which an actual heart beat can be 
compared for diagnostic purposes. Radioactive events emitted from a heart 
under study following administration of a diagnostic amount of a 
radioactive substance are sensed by a plurality of sensing devices that 
form an array. A processor synchronously sums and averages a series of 
heart beat image signals that are produced from a continuous series of 
sensed events and generates a reference heart beat. The processor 
synchronously regroups the heart beat image signals as a function of the 
maximum and minimum points of each heart beat cycle, the maximum and 
minimum points occurring at the ends of diastole and systole movements, 
respectfully. The reference heart beat, which defines a standard heart 
beat of the subject under study, provides sufficient statistical basis for 
quantative measurements and qualitative analysis of cardiac condition. 
Other objects of the present invention will in part be obvious and will in 
part appear hereinafter. 
The invention accordingly comprises the apparatuses processes, together 
with their parts, steps, elements and interrelationships that are 
exemplified in the following disclosure, the scope of which will be 
indicated in the appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referred now to the drawings, FIG. 1 shows a radioactivity distribution 
detection system 10 for non-invasive measurements of cardiac performance 
of a biological specimen following administration of a diagnostic amount 
of a radioactive material by composing a reference heart beat that defines 
a statistical base for such measurements. System 10 includes a plurality 
of crystal assemblies 12 disposed in an array 14 for sensing radioactive 
events emitted from a heart under study and a processor 20 for generating 
data signals defining cardiac condition. Processor 20 generates the 
reference heart beat signal by synchronously summing a series of heart 
beat image signals produced from a continuous series of sensed events. The 
heart beat image signals are summed as a function of the maxima and minima 
for each heart beat image, the maxima and minima occurring at the ends of 
diastole and systole movements, respectively. The reference heart beat 
signal defines a standard heart beat of the subject under study, and 
provides sufficient statistical basis for quantative measurements and 
qualitative analysis of cardiac condition. That is, the reference heart 
beat signal is a data base for subsequent measurements and analysis. 
Each crystal assembly 12 has four scintillators 16, each scintillator is at 
a unique address location in array 14 and, when activated by sensing 
radioactivity, emits a light signal. The light emitted by any one 
scintillator 16 is detected by a plurality of detectors 18, for example 
photomultiplier tubes, that are superimposed on crystal assemblies 12. A 
unique set of photomultiplier tubes 18 is disposed over one scintillator 
16 in each of four adjacent crystal assemblies 12. Data signals generated 
by a photomultiplier tube 18 monitoring an activated scintillator 16 in a 
particular crystal assembly 12 and the photomultiplier tubes monitoring 
the adjacent scintillators of the particular crystal assembly are 
processed in processor 20 to provide a presentation of cardiac condition. 
In the illustrated embodiment, radioactivity distribution system 10 
includes a detector assembly 24 having a collimator 26, array 14 of 
crystal assemblies 12, and photomultiplier tubes 18. By way of example, 
collimator 26 is a multi-plane focused collimator characterized by at 
least two different focal lengths. A subject under diagnosis (not shown) 
is positioned on a programmable XY platform 28 that is in spaced 
relationship to detector 24. Equilibration of an injected radioactively 
tagged tracer in a blood pool is used as a reference beacon to position 
array 14 over the precordium. Command signals generated by a computer 30 
in response to sensing of the tracer in the blood pool actuate a driver 
control 32 which operates to move platform 28 to the desired position. 
Individual scintillation events in detector assembly 24 are sensed and the 
coordinate position of each event is determined. 
Array 14 is mounted in spaced registration with collimator 26 which 
includes a plurality of tapered collimator bores 74. Each scintillator 16 
is disposed in registration with one taped collimator bore 74. Each 
collimator bore 74 is used to limit the field of view of each scintillator 
16 to a unique spatial segment of the specimen being diagnosed. In this 
manner, a two dimensional image of the heart under diagnosis is obtained. 
The two dimensional image is made up of a specified number of picture 
elements that correspond to the number of unique spatial segments isolated 
by multi-bore collimator 26. The shape and volume of each separate spatial 
segment in the specimen is defined by the geometry of each collimator bore 
74. A description of the detailed electronic circuitry for providing an 
image of the organ under diagnosis is found in U.S. Pat. Nos. 4,044,332 
and 4,048,501, which are incorporated herein by reference. 
Each scintillator 16 in array 14 has a unique address that is identified by 
a particular row and column location. Generally, one photomultiplier tube 
18 is associated with four scintillators, one scintillator in each of four 
crystal assemblies 12 in adjacent rows and columns. One photomultiplier 
tube 18 is associated with two scintillators 16 at the edges of array 14 
and one photomultiplier tube 18 is associated with one scintillator 16 at 
the corners of array 14. Data signals generated by photomultipliers 18 are 
processed in front-end electronics 34 which includes a decode logic unit 
38 and a decode coincidence logic unit 42. The data signals at the outputs 
of photomultipliers 18 are decoded in decode logic 38. In addition, the 
signals at the outputs of photomultipliers 18 are applied to decode 
coincidence logic unit 42 which provides an indication that data signals 
have been detected from at least three adjacent photomultipliers. 
The structure of each crystal assembly 12 is such that light from one 
scintillator 16 is coupled to four photomultiplier tubes 18. That is, most 
of the light from a scintillation in one scintillator 16 location in one 
crystal assembly 12 is sensed by one photomultiplier tube 18 that is 
superimpossed on the activated scintillator. A smaller amount of light 
from the activated scintillator 16 is sensed by the two photomultiplier 
tubes 18 which are superimposed on the two scintillators that are adjacent 
the activated scintillator in the same crystal assembly 12. An even lesser 
amount of light from the activated scintillator 16 is sensed by the one 
photomultiplier tube 18 which is superimposed on the remaining 
scintillator 16 in the same crystal assembly. In this way, three 
photomultiplier tubes 18 determine the position of the activated 
scintillator 16 by the light emitted therefrom by pulse height weighting. 
All acceptable data sensed by scintillators 16 in array 14 is accumulated 
and stored in a buffer memory 68. The XY address of each scintillator 16 
is determined by the output signals generated by corresponding 
photomultiplier tubes 18 associated therewith. In memory 68, each sensed 
scintillator 16 event is accumulated to previously sensed events having 
the same address location. The number of events stored at a given address 
is the number of recorded disintegrations having originated within the 
monitored subject at a point, the XY location of which corresponds to the 
given address. Following the accumulation period, the accumulated data in 
raw digital form is fed to computer 30 and stored in corresponding address 
locations. The data in computer 30 in normalized into Gray scale coded 
signals as a function of the greatest number of detected events at any one 
address and fed to a halftone conversion unit 70. Signals generated by 
halftone conversion unit 70 are applied to a display 72 for controlling 
the number of dot picture elements per unit area at the XY display 
locations that correspond to the address locations. 
As previously indicated, sensed events at each unique address are 
accumulated in memory 68. That is, the number of scintillation events for 
each XY location in array 14 is accumulated in a corresponding XY location 
in memory 68. Upon completion of the accumulation step, the data 
accumulated in memory 68 is fed to computer 30, memory 68 is cleared and 
is readied for reception of new data. The events accumulated during one 
accumulation period represents one heart beat image, and a series of 
accumulated events defines a series of heart beat images. Operation of the 
system is directed from a control panel 76 having a series of 
interconnected switching devices that are connected to computer 30 via a 
programmer 78. A manual data input 80, for example a keyboard, is provided 
for logging any pertinent data in a display 72. 
Programmable XY platform 28 comprises a table 82 that is mounted to a 
slidable member 84. A rack, 86 which engages a pinion 88 of a driver 90, 
is mounted to member 84. Member 84 is slidably received in guideways 92, 
94 that are provided in parallel guides 96, 98, respectively, rack 86 
being in parallel spaced relationship with guides 96, 98. Guideway 92 
extends along the longitudinal axis of guide 96 and guideway 94 extends 
along the longitudinal axis of guide 98. Guides 96 and 98 are formed also 
with a pair of transverse guideways 100, 102 and 104 and 104, 106, 
respectively. Guideway 100 is in registration with guideway 104 and 
guideway 102 is in registration with guideway 106. Fixed guides 108 and 
110 are slidably received in guideways 100, 102 and 104, 106, 
respectively. Fixed guides 108 and 110 are in parallel spaced relationship 
to one another and in perpendicular spaced relationship with guides 96, 
98. A rack 112, which engages a pinion 114 or a driver 116, is mounted to 
guides 96, 98 in parallel spaced relationship with guides 108, 110. It 
will be realized from the foregoing description that table 82, member 84 
and rack 86 are slidable in a first direction within guideways 92, 94; and 
guides 96, 98 and rack 112 are slidable in a second direction within 
guideways 100, 102 and 104, 106; the first and second directions being 
mutually perpendicular to one another. For convenience, by way of example, 
the first and second directions will be referred to as the X and Y 
directions, respectively. That is, driver 90 moves table 82 in the X 
direction and driver 116 moves table 82 in the Y direction. Drivers 90 and 
116, for example stepping motors, are controlled by signals generated by 
driver control 32 in response to command signals from computer 30. It is 
to be understood that platform 28 is movable also in the Z axis by means 
of jack screws 118, for example. 
As previously indicated, the precordial region of the subject under 
diagnosis is positioned under array 14 by moving platform 28. The desired 
location of the subject with respect to array 14 is determined by the 
blood pool containing the radioactively tagged tracer that is equilibrated 
in the blood without leaking into the intravascular spaces. As shown 
schematically in FIG. 2, after the step of positioning the subject is 
completed, a continuous series of events are detected by scintillators 16 
and accumulated in memory 68 to events having the same XY locations in 
array 14. The series of detected events represents a continuous series of 
heart beat images or frames of heart beats. In the illustrated embodiment, 
by way of example, the continuous series of frames is detected for a 
period of ninety seconds at a rate of twenty frames per second. The 
eighteen hundred frames obtained during the ninety second period are 
synchronously averaged in processor 20 to provide a standard heart beat 
image which defines a data base for measurement and analysis of cardiac 
performance. 
In the preferred embodiment, a region of array 14, which is positioned over 
either the left and/or right ventricle, is isolated in memory 68. 
Processor 20 generates a histogram of the sensed events which represents 
the number of counts over the isolated area versus time. Since the events 
are sensed while in a state of equilibrium, fluctuations in the number of 
counts are proportional to fluctuations in the blood pool and correspond 
to a volumetric measurement. Therefore, the points of successive maxima 
and minima count levels delineate the cardiac profile at end diastole and 
end systole, respectively. In the illustrative embodiment, maxima and 
minima are defined as the points where the first derivative changes sign 
with a magnitude greater than that of two standard deviations of 
statistical noise. 
The standard of reference heart beat, which is a representative equilibrium 
heart beat, with increased statistics, but intact temporal resolution, is 
obtained by synchronously summing the image heart beats in processor 20 
using the volumetric maxima and minima. Arrhythmic heart beats, which are 
determined from analysis of the periodicity of the beats, are included or 
excluded from the synchronous summation of beats that provides the 
representative equilibrium heart beat. The representative beat is composed 
from a contiguous set of images that describe an average beat of the 
heart. Using the representative heart beat as a statistical base, 
processor 20 generates data signals defining a quantative measurement of 
the heart function, for example, ejection fraction, ventricular volume 
curve, or regurgitant fraction. These data signals are based upon the 
proportionality of scintillation counts to the blood volume they perfuse. 
Also, processor 20 generates data signals defining qualitative assessments 
of heart wall motion. Such assessments are derived from an endless loop 
cinematic video display of the equilibrium representative cycle images. 
Since certain changes may be made in the foregoing disclosure without 
departing from the scope of the invention herein involved, it is intended 
that all matter contained in the above description and depicted in the 
accompanying drawings be construed in an illustrative and not in a 
limiting sense.