FR2493148A3 - ABSORBABLE RADIOACTIVE PARTICLES FOR SELECTIVE RADIOGRAPHIC METHOD FOR DETECTION OF CORONARY STENOSES - Google Patents

Abstract

THE PROCESS CONSISTS OF INJECTING INTO THE SUBJECT'S BLOOD A CERTAIN NUMBER OF PARTICLES 25 EMITTING GAMMA RAYS WITH AN ENERGY LESS THAN 300 KEV, IN SELECTIVELY FILTERING THE RADIATION EMANTING FROM THE SUBJECT'S BODY THROUGH A SCREEN CONTAINING 31 OPIONING REGIONS AND REGIONS TRANSPARENT TO RADIATION 23 IN A SELECTED CONFIGURATION AND TO DETECT THE RADIATION PASSING IN A STRAIGHT LINE THROUGH TRANSPARENT REGIONS TO DETERMINE SUCCESSIVE LOCATIONS IN A THREE-DIMENSIONAL SPACE ACCORDING TO THE TIME OF EACH PARTICLE AND DETERMINATION FROM THESE PARTICLE THE BLOOD FLOW RATE, WHICH ALLOWS TO DETERMINE THE IMPORTANCE, SIEGE AND SEVERITY OF STENOTIC INJURIES IN VESSELS.

Description

Coronary heart disease is the main

  pale cause of death in the United States and in the world

  western. Coronary heart disease is responsible

  two thirds of the deaths of individuals of the male sex

  culin during the period of life (30 to 64 years) where family and social responsibilities are the greatest. About a third of individuals who die from coronary heart disease die immediately after occlusion of the coronary arteries; a third die in

  the next few hours, and only a third be-

  are in need of hospital therapy. Among the individuals

  due to their first myocardial infarction, more than half have never had any signs or symptoms

  coronary heart disease.

  In recent years, surgery

  of bypass grafting has been shown to be

  be a therapeutic modality with very broad possibilities

  application skills. Because more than 70% o of shorthand

  its coronary arteries occur in the first four centimeters of the coronary arterial system, one can bypass a high percentage of coronary lesions

  with a low mortality rate and a high death rate

  sobstruction. Extensive epidemiological studies have

  brings out the factors (hypercholesterolemia, hyper-

  blood pressure, obesity and smoking) which are statistically correlated with an increased frequency of heart disease

  coronary. But although a patient may have integrated

  stop leaving the higher risk group by changing its

  kind of life in an appropriate way, these clues can-

  may not, for any given patient, provide information regarding the existence of stenotic lesions of the coronary arteries or serve as a basis for decisions

  clinical regarding therapeutic intervention.

  The use of electrical tension tests has been suggested.

  trocardiographic as a means of screening individuals

  who have significant coronary lesions. This-

  during a major prospective study during

  in which the subjects were subjected to repeated tests

  However, the sensitivity of this test was found to be too low (only 30%) to be satisfactory.

  Currently, coronary arteriography gives

  do more useful information. about the condition of the ar-

  coronary tères than any other technique. However, in a large cooperative study, the frequency of significant complications was 2% and the mortality rate was 0.23%. In addition to the dangers, the process is painful, expensive and time consuming. For this reason, coronary angiography is not performed on individuals who do not have

  symptom and it is not suitable for performing an exa-

  systematic study of large populations.

  US Patent No. 4,111,191 issued September 5, 1978 to Robert F. Shaw has been described under the heading "Apparatus and Method for examining blood vessels of interest by tracking position with respect to time of particles introduced therein" l (Apparatus and method for examining blood vessels of interest by locating the position over time of particles introduced therein) an embodiment of an apparatus for detecting the extent, location and severity of lesions

  stenotics of the coronary arteries while operating ex-

  body. This apparatus and the corresponding process

  use techniques that operate on pairs of si-

  reverse directions detected outside the

body.

  In accordance with the embodiment of the present

  te invention which has been represented, we detect stenotic arteriosclerotic lesions of the coronary arteries in

  injecting a number of radioactive emitting particles

  gamma yons in and out of a subject's circulating blood

  tecting gamma radiation emitted through coded openings to determine the speed of blood flow

in his coronary vessels.

  Due to the high peripheral resistance

  myocardial vascular tissue and the interval

  switchable self-regulating resistance changes

  available to the coronary circulation, it requires

  80-90% coronary noses to decrease appreciably

  the volume flow of coronary blood can be improved. This tendency for the volume flow of coronary blood to remain

  normal even in the presence of severe strictures is responsible

  ble of late onset or no symptoms

  , angina pectoris and electrocardiogram diagrams

  allowing me to make a diagnosis even in the presence of coronary stenosis and explains why the measurement

  of the volume flow of the blood provides only indications

  poor coronary artery disease.

  However, this tendency for the volume flow of blood to remain normal even in the presence of severe stenosis provides this distinguishing characteristic that the blood flowing in a segment of stenosed artery must have a high speed. In fact, to keep the volume flow constant, the average speed of the fluid in a

  stenosed artery segment must change in an exac-

  inversely proportional to the change in sur-

  cross-sectional faces between a normal blood vessel and a stenosed blood vessel. The more severe the coronary stenosis, the more the increases in

  speed of blood flow become important.

  In accordance with the embodiment of the pre-

  invention which has been represented, we introduce in

  the patient's body by intravenous injection of the

  discrete radioactive emitters gamma rays having dimensions sufficiently small to pass in the capillary networks and these particles are distributed

  in the volume of circulating blood. We follow the parties

  cules that appear in the volume of circulating blood-

24931 140

  tion. We follow the particles that appear in the re-

  gion of the heart in three dimensions, for example, through

  coded openings associated with gamma cameras, each

  that coded opening comprising transparent parts and parts opaque to radiation. A stereo collimator

  nopé, a collimator with parallel channels as well as the

  coded vertex used in the embodiment shown

  felt have all been described below. We analyze the

  recordings of particle positions as a function of

  time and, each time a particle follows an in-

  saying that it circulates in a coronary artery, we are told

  the speed of the blood as it flows through the ar

  tère by timing the passage time of the particle.

  From the data accumulated from multiple particle passages in the coronary circulation, we construct

  a representation of the cross section of the opening

  passage of the coronary arterial system.

  Other features of the invention appear

  will read the following description and

  examination of the appended drawings in which: - Figure 1 is a perspective view of a human heart showing the main coronary arteries; Figure 2 is a schematic view including a block diagram of the present invention which uses

  conventional detectors and collimators with channel pa-

  groups to observe particles or radioactive sources

  ves in three dimensions; Figure 2b is a schematic view including a block diagram of the present invention which uses conventional detectors and converging collimators

  in a camera system in which the magnification is

  depends on the distance between the source and the plane of the collima-

  guardian; Figure 3 is a schematic view including a block diagram of the present invention which uses a

  conventional detector and a coded opening containing a ta-

  unordered brush with square holes; Figure 4 is a schematic view including a block diagram of the present invention which uses a coded opening screen containing a single annular orifice;

  FIG. 5 is a synoptic table of the process

  showing the data analysis which can be used with the embodiments shown in Figures 2, 3 and 4; and

  Figures 6a and 6b are graphs showing

  respectively present the relative frequency of detection

  tion along the length of a coronary vessel and its cor-

  relationship with the cross-sectional area of the

  corresponding passageway of the vessel.

  As shown in Figure 1 which

  will be noted, it should be noted that there are three coro-

  principal naires. These three vessels branch somewhat irregularly to form an average of ten secondary vessels, as shown. Arteriosclerotic lesions are typically limited to the segments of the coronary vessels in the epicardium and rarely extend beyond the most proximal parts of the secondary vessels. The highest concentration of arteriosclerotic lesions is found in the first 2 to 3 centimeters of the left descending anterior artery 3, but the lesions are moreover distributed relatively

  randomly in the primary and secondary arteries nearby

  males. Seventy percent of all arterial lesions

  Coronary riosclerotics are found within 4 cen-

  proximal timers of the main coronary arteries.

  The average speed of the flow of blood in the coronary blood vessels of the epicardium is of the order of 20 cm / s. A 50% stenosis is generally considered to be significant. To be useful, the system should be able to distinguish normal vessels from stenotic lesions at 509 'and it should be able to

249 3148

  assess significant additional decreases

  cross sections of these vessels.

  Characteristic blood flow rates

  ticks in stenosis of varying degrees are the following

  : Degree of stenosis Average speed 0% 30 cm / s e / o 60 cm / s% 100 cm / s 80% 150 cm / s% 300 cm / s

  Since the flow velocity coro-

  nominal resting nostril is approximately 30 cm / s, the system

  teme should ideally be able to distinguish a flow speed of 60-75 cm / s from a speed of 30

  cm / s in order to detect significant lesions and dis-

  tune between them the speeds of 75, 100, 150 and 300 cm / s in order to follow the additional increases of

% in 10% of stenoses.

  According to its preferred embodiment, the -pre-

  sente invention detects a number of particles or sources emitting discrete mobile gamma rays present in the circulating blood. The system does not

  only mark the position of the sources in three di-

  but still he spots them over and over again

  at very short time intervals. The frequency born

  ceasing to locate a particular source is deter-

  undermined from the following considerations.

  As noted above, the nominal speed of

  the flow of blood through a coronary artery is from

  about 30 cm / s for a subject at rest. The flow of blood in a diseased artery segment which is stenosed at 80% has a speed equal to five times this nominal value (150 cm / s). The blood flowing in a segment of a blood vessel having a severe stenosis of 90% will have a speed of 300 cm / s. To measure a 90% stenosis which

  is a centimeter long, a particle crossing the re-

  Stenosed gion should be detected at least a few times.

  At 300 cm / s, it only takes three milliseconds to par-

  run a vessel length of one centimeter.

  As noted above, there are three main coronary arteries which branch out on average into ten secondary branches. Ai, for statistical purposes, we wish to make three speed measurements in each of the said secondary branches, a total of 3 × 10 passages of

  particle in the coronary network is then statistical-

  necessary. This will provide approximately 10 steps-

  wise men in each of the main arteries proximal in

  which most of the atheromatous lesions are so-

  killed. Since blood flow in the coronary network represents only about 5% of resting cardiac output, a given particle has only a 0.05 probability of entering the circulation

  coronary after a single pass through the heart.

  Thus, 20 circulations through the heart multiplied by 30 passages of particles in the coronary system,

  or a total of 600 particle passages in the circu-

  lation, would provide redundancy of speed measurements

  se of blood flow in the coronary system

  outlined in broad outline above.

  Since the average circulation time is one minute or less, a single particle tracked in

  traffic for 600 minutes would be suitable for

  put the redundancy mentioned if its period or half-life

  was long enough and if it continued to circulate

  1st during the ten hour period. Naturally, a

  ten hour period is a length of unsuitable length

  requested for diagnostic action. Forty particles circulating for fifteen minutes would be much more convenient to use and would provide a comparable number of

  particle passages (600 passages) in the cir-

culinary.

  The number of particles needed to reach-

  Dre 600 particle passages in the circulation is influenced by the possibility that the gamma emitting particles are eliminated from the circulation by the Kupffer cells of the liver. The tendency of the liver to extract particles is a function of their dimensions

  and their surface characteristics, the state of the system

  reticlo-endothelial teme as influenced by pretreatment

  and other causes, and other variables.

  The flow of blood in the liver represents

  approximately 25% of resting cardiac output. If the pretreatment

  moderately satisfactory results, the parties

  will be extracted from the liver with a yield of

  about 50% and the number of particles in circulation will be

  reduced by a factor of 2 every 8 minutes.

  If the period of the isotope used exceeds 15

  minutes, a reasonable administration program

  tion of particles can start with intra-

  initial venous 40 particles followed by an injection

  continuous 10 particles every 3 minutes. The name-

  bre of circulating particles will remain constant around

  about 40 during the entire 15 minute exam

  and a total of 87 particles will be administered.

  If the period of the isotope used is very

  short, for example 5 seconds, administration

  continuous trapper of 40 radioactive particles per

  minute will be required since the particles ra-

  dioactive will only be active during their first pass through the heart. (During an interval of 60 seconds between passages in the heart, activity

  of each particle will have decreased by a factor of 4,000).

  In this case, a total of 600 radioactive particles will be administered. The complexity of data processing is

  significantly influenced by the number of parties

  ticles which must be simultaneously detected in the field of vision which surrounds the heart. It is for this reason that the average number of particles in circulation is kept at around 40 in the previous examples. If) it is assumed that 5% of the total volume of blood is found in the heart and that an additional 5% is found in the lungs and in the wall of the chest near the

  heart, there will be statistically an average of 4 parti-

  radioactive cules inside the field of vision which

surround the heart.

GENERAL OPERATION

  According to the present invention, the position of all radioactive sources or particles located in the vicinity of the region of the heart must be determined

  with a spatial accuracy of + 1.5 mm.

  For a number of years, the Anger scintillation camera has been used to form an image of

  distributions of isotopes emitting gamma rays internally

  of the body (see, for example, the US patent

  No. 3,011,057 issued November 28, 1961 in the name of H. 0.

  Anger). Commercially available cameras have

  spatial accuracy between + 3 mm and + 5 mm when

  that they reproduce the image of gamma rays of 141 keV.

  (The notation of + 3 mm used here means that the lateral dispersion function of the lines has half a width at the

half the maximum of 3 mm).

  The reproduction processes of classic images

  using a pinhole collimator or a multi-channel collimator which performs a simple point-by-point transposition of the distribution of the emitting isotopes

  of gamma rays on the scintillation camera. Sad-

  The process does not provide three-fold information

  dimensions and the resulting image is just a bi- projection

  dimension of the distribution in the plane of the camera

  scintillation. To be able to track sources emit-

  3-5 gamma rays in three dimensions, it was born

  require that at least two imaging systems

  ge follow the same radioactive particles from em-

different investments.

  In the embodiment shown in Figure 2a, two camera systems 5 and 7 observe

  the heart region from two different locations

  rents. These camera systems 5 and 7 can use

  Pinhole, divergent, collimators with channels in pa-

parallel or converging 9 and 11.

  In the embodiment shown in the

  figure 2b, it should be noted that when using a collima-

  pinhole camera or a multi-channel convergent (i.e. focusing) collimator 13, 15, magnification

  of the image in relation to the subject depends in a con-

  the distance from the subject to the camera. So, in posi-

  Using a collimator-camera system with variable magnification in front and another similar system behind the heart region, we can analyze a recording of the

  apparent path and speed of the radio particle

  active as created by the two camera systems

  to determine both the true velocity of the particle

  the and the path it follows, in three dimensions.

  Geometric transmission of commonly used multi-channel collimators with precision

  of + 5 mm at 141 kV is such that for each mCi of activation

  From the radioactive source, around 10,000 gamma rays per second reach the scintillator crystal. Of these rays, around 8000 are diffused in the patient's body and most of them can be rejected by selection

  by conventional pulse height made by the camera.

  It follows that for each mCi of activity of the source,

  approximately 2,000 non-scattered gamma rays are detected each

  that second and that the same number of gamma rays scattered

  cross the pulse height threshold every second

  of. So that the radioactive particle signals its position every millisecond with an accuracy of + 5 mm, in

  producing a recorded point, the activity of each

  radioactive material should be around 500 uCi. Although the accuracy of each particle detection does not meet the required accuracy of + 1.5 cm, an improvement in accuracy can be achieved when averaging the positions of a large number of points. For example, in the case of a 70% stenosis, the radioactive particle moves one centimeter during each 10 ms period and it is possible to establish the average

  10-point positions to achieve the desired accuracy

  position tracking. In the case of a 0% stenosis, 30-points are available for each centimeter of displacement.

  In another embodiment, a collima-

  Pinhole torus with a separating power of + 5 mm at 140 keV less than 5o from the transmission of the collimator to

  parallel channels and it would require the use of an ac-

  even greater activity of the source. As described below

  above, for long-lived isotopes, approximately particles are necessary to follow the path of each artery the desired number of times and this requires

  a total activity of 40 mCi. In order to maintain the do-

* is supplied to the liver within reasonable levels, it is advantageous to inject colloidal carbon particles beforehand to occupy the Kupffer cells

  of the liver and prevent absorption of radioactive particles

  tives. It is also advantageous to use isoto-

  short-lived pes, such as those produced by the

  decay of longer-lived isotopes.

  191M An example is the Ir * with a period of 4.9 s which emits only gamma rays of 129 keV and is produced

  by the disintegration of os191 within 15 days.

  The energy of gamma radiation is well suited to the camera.

  ra and lead absorption properties and the short period has the effect that the patient is subjected to a very

  low dose. In a typical exploration of the liver made

  killed using a sulfur-Tc 99m colloid at a 6 hour period, the dose to which the liver is subjected is

24931.48

  3 rads for an injection of 3 mCi. Using 600 per-

  ticles each containing 500 pCi of Ir 191m at a period of 4.9 seconds, the corresponding dose will be less than

0.05 rads.

  A more effective solution for screening

  of a small number of gamma-ray emitting particles

  my discreet is the use of coded openings

  ment to the present invention. This allows the detection of a larger fraction of the gamma rays emitted by the source and also provides position information

  three-dimensional. An embodiment of an opening

  re coded has been represented in FIG. 3 in the form of a screen 21 containing a disordered configuration of

  windows or square orifices 23 transmitting the radiation.

  It is assumed that the gamma rays 27 emitted by the radioactive particles 25 are stopped by the screen 21 unless they

pass through one of the orifices 23.

  For a unique radioactive particle station-

  the classic gamma ray image detector 29

  simply save the shape of the screen shadow 21.

  This shadow form has several useful properties.

  For a given distance between the screen 21 and the detector 29, the dimension of the shape is in a unique relationship

  with the distance between the radioactive particle 25 and the e-

  notch 21 and the position of the form is in a unique relationship with the position of the radioactive particle 25

  in a plane parallel to the screen 21. A means for determining

  undermining the position of the radioactive particle 25 in three dimensions consists in assuming a large number of test positions (for example within a regular three-dimensional volume) and in choosing the position which is most compatible with the observed shape . This is done by usefully connecting lines starting from the position

  at the detection point on the detector 29 which appears

  within a given time interval and by determining the fraction (Q) which crosses the openings 23 of the screen 21. The point of space having the factor of

  highest Q quality is the true source position

  this. (The precision of this process is limited by the flu-

  statistical kills). For the case of several parties

  radioactive cells 25, Q is maximized at each radioactive particle position. If the square holes 23 of

  screen 21 represents a fraction F of its total surface

  tale and if there is no scattering of gamma rays in

  the patient, we then have Q1 = F for the test points é-

  away from the true position of the source and QO = 1 for

  the test points located at the true position of the source.

  In the vicinity of the true position of the source, the factor

  Q varies between the two extreme values.

  Diffusion by Compton effect of gamma rays

  degrades the observed shape and reduces the QO factor. When-

  that we reproduce the image of the human heart using gamma rays having energies close to 129 keV, we

  finds that among all of the gamma rays that cross

  feels the pulse height threshold of the detector, a fraction S (approximately equal to 0.5) has diffused

  in the patient's tissues (note that for each ra-

  yon gamma accepted by the camera about 1.5 were rejected).

  Given the Compton broadcast; Qo = 1 - S (1-F) while

  Q1 = F. not being influenced by the broadcast.

  The presence of several particles or radioactive sources in the field of vision also degrades the quality factor so that Q0 = / TS (1-F) + (N-1) F7 / N at a source position and that Q1 = F in the pitches

  distant from all source positions, N being the name-

  bre particles or radioactive sources in the field of vision. For a probability of diffusion S = 0.5 and for

  N = 4 particles or radioactive sources, this equation of-

  come. = (1 + 7F) / 8 and Q1 = F. We want to choose the fac-

  screen transparency factor F (that is to say the ratio of the square orifices 23 to the total surface area of the screen) so that the minimum activity of the sources is necessary

  to accurately detect the four radio particles

  active. The values of Q0 and Q1 are subject to statistical fluctuations. A typical fluctuation of Q0 (actually its standard deviation) is (Qo / 4ND) formula in which ND is the number of gamma particles detected per radioactive particle. If it is necessary that 'Q0 and Q1 differ from five standard deviations of Qo: Qo-Q1 = 5 (Qo / 4ND). or 1-F rlT

QO-Q1 = e = 5 (2 + 7) -

  This requires that ND = 50 (1 + 7F) (-F) -2. The number of photons detected ND is linked to the number NS emitted by the source.

  this, to the geometric transmission of the screen (approximately 0.15F if the screen subtends 2 steradians) and to the probability of crossing the selection by pulse height (approximately 0.4): Ns = ND (0, 0 60F) -1

NS = 883 (1 + 7F) (1-F) 2 (F) 1

  The table below shows the relationship between

tre NS et F: F NS Qo Q1

0.5 30,400 0.56 0.50

0.4 22,400 0.48 0.40

0.3 17,900 0.39 0.30

0.25 16,500 0.34- 0.25

0.20 15,800 0.30 0.20

0.175 15.600 0.28 0.175

0.15 16,000 0.26 0.15

0.10 17,600 0.21 0.10

0.05 25,400 0.17 0.05

  Within a preferred range from F'- 0.3 to F = 0.1, the choice of F = 0.175 requires that

  15,600 gamma rays are emitted by each of the 4 parties

  radioactive cells. In order to be able to track particles using time slots of 3 ms, the activity is then 15,600 per slot x 333 slots / s = 5x106 per second or 140 uCi per radioactive particle. The gamma ray detector will then detect 216,000 gamma rays per second inside its pulse height window. This is one of the possibilities of

current technology.

  A more general analysis shows that the value

  optimal of N is not very sensitive to the number of parti-

  radioactive cells N and that the number of photons emitted by the sources increases with the number N.

  N F (optimal) NS Activity required per party

  radioactive cule for 3 ms slots 1 0.218 7.700 70, uCi 2 0.214 10.400 95 pCi 3 0.193 13.000 120 pCi 4 0.176 15.600 140 pCi 5 0.164 18. 000 160 uCi 6 0.153 - 20.400 180 Ci 0.126 23.700 21 0 Ci F (optimal = 6N- 3 In figure 4 to which we will refer, we

  shows a screen 31 with coded opening provided with a unit

  that-annular opening 33. A single point source

  projects a circular shape 36 on the i-detector

  mage 37, the dimension of the circle being in a unique relationship with the distance between the point source 35

  and the screen 31 and the circle position being in a re-

  unequivocal relationship with the position of the source 35 in the plane parallel to the screen 31. If the circular opening 33

  of the screen 31 is, for example, 5 cm in diameter and if the

  0.5 cm wide, the particles that are

  in the heart region will produce 4 overlapping circles-

24931 48

  chent with very little confusion. For a radio particle

  active 10 cm above screen 31, the transmission

  geometrical sion of this opening is g = 6.3x10 3. The

  number of gamma rays NS emitted by each radio particle

  active and the number of gamma rays (ND) that cross the pulse height threshold are related to each other by the relationship: ND = N (0.4) g 2.5 x 1073 NS Since we must have ND = 60 radii

  gamma detected (half of which are diffused) we have NS -

  24,000 photons emitted by each radioactive particle. For

  track particles using time slots-

  3 ms, the activity is then 24,000 per slot x 333

  slots / s = 8.0x106 s or 220 juCi per radioactive particle.

DATA ANALYSIS

  According to the present invention, the apparatus can be used with the interposition of conventional doors synchronized with the beating of the patient's heart so as to observe the sources only during the diastolic phase of the cardiac revolution, when the movement of the heart

  is minimal and that the speed of the blood in the arteries coro-

  is the largest and most constant. The slide--

  cardiac sheet typically occupies a period of 400 to 600 milliseconds which is considerably longer than the passage time (30 to 300 milliseconds) required for a particle to flow over a length

of 10 cm of coronary artery.

  The collimation, coding and detection techniques described above are all used to provide a time list and three-dimensional coordinates of

  each particle at each of these times. The table below -

  closely shows the behavior of radioactive particles in the chambers of the heart and the contrasting behavior of radioactive particles that move through the coronary arteries and the myocardial capillary network.

  In the cavi- In the ar- In the re-

  your heart teres coroseau capil-

  myocardial tract Average speed (cm / s d 30 from 30 to 300 1 Average length of stay er- 2s from 0.03 to 0.3s, -2s in specified areas

  Linear random trajectory type with essential-

occasional elbows

stationary

nary

Moves down.

from 5 to 10 cm in 4 0.3s NO YES NO

then stops for -

v 2

Average number of participants

  radioactive cells 2 0.01 0.1 present Average interval between passages in 1.5 s 30 s 30 s specified areas

Essentially station-

  nary for 2 or 3 NO NO YES successive cycles (All the given numbers are approximate) These differences form the basis on which the data are analyzed, as described with reference to Figure 5. First leu, we can set stores the data relating to the coordinates and the production times of the rays detected on tape, disk or the like (steps 41, 41) for further processing. All the radioactive particles that appeared in the capillary network of the

  myocardium since the start of the examination can thus be identi-

  tified in step 43. Each of these particles has initial-

  followed a certain route in the. coro- arterial system

  naries. As indicated in the table above, the par-

  radioactive particles in the capillary network

  re myocardium are very distinctive due to their weakness

  velocity relative to the wall of the heart.

  Of the 900 diastolic periods that occur-

  feels during the period of an exam, we choose about

  which are linked to the appearance of a radioactive particle

  active in the myocardium (step 44). So, this first

  stage rejects 97% of diastolic periods which do not pre-

then feel more interest.

  Next, we examine the data (organized in time slots of 3 milliseconds and reproduced in

  opposite of their recording) which precede the ap-

  appearance of the radioactive particle in the myocardium (6-

  step 45). The radioactive particle seems to dislodge from the wall of the heart and move quickly (from 30 to 300

  cm / s) and overall up towards a-

  toe. It is then possible to display, in step 46, a single three-dimensional image (or at least two displays, planes

  which are oriented orthogonally so as to present more

  views) representing the spatial distribution of all

  tes radioactive particle detections during 3 milliseconds of their fast motion. The shape of the coronary arterial system can be clearly observed from such a display and the frequency of detections

  inside. such time slots give an indication

  tion of the cross section of the arteries. The regions

  along any artery which indicate a more

  The frequency of detection will thus be identified as the main candidates for arterial stenosis and

  additional analysis. The lowest frequency of detection

  tion is attributable to the rapid movement of a radioactive particle in a stenosed region so that the density of detection points or frequencies along the artery is thus directly proportional to the area of the cross section of the passage opening of the artery as shown in the graphs of Figures 6a and 6b. For larger coronary arteries, data from a large number of passages can be added, which

  provides a distribution with static fluctuations

  reduced tistics. Although there are very big changes

  these so that the information available at this point is

  sufficient to establish a clinical diagnosis of the existence

  tence, extent and location of coronary heart disease

  However, the following additional analysis step can be used. Third, the distributions obtained at

  during the second stage provide tri-

  dimensions relating to the detailed shape of the coronary arterial system. This information can be stored in a computer memory in the form of a list of interconnected straight line segments. For each radioactive particle, the path is determined the

  more likely. Thus, we can determine the mo-

  yenne of a radioactive particle along any segment of Xi -X 1 line taking the average of Ifi, - formula

  where Xi is the position of the radioactive particle

  tive (projected on a line segment) at time Ti. Note that it is necessary to use

  averaging due to the limited accuracy of the coordinates

individual points data.

PARTICLE EMITTERS

  Although we have referred here to the Ir191m at a period of 4.9 s, we can also use, in accordance

  to the present invention, several other radioactive particles

  active, such as Tc99m. We indicated in the table

  below various other particular radioactive sources

res and their properties.

  - Precursor isotope Mo90 ta183 Os191 Hg195m Mo99

-Isoto period-

  eg precursor 5.7 h 5.1 d 15 D 40 h 67 D -Isotope generated (1st generation) Nb90m W183m Ir191m Au195m Tc99m

-Isoto period-

  e generated 1st generation) 24 s 5.3 s 4.9 s 31 s 6.0 h

-Issues from iso-

  tope generated 122 106; 160 129 261 144 (1st generation) (keV). stable stable 99 -Isotope generated 9 t183 1b 183j Tc hNb90183 1r918 Te (2nd generation) 15 hNb) Ir Au195 There are other decay models which involve much higher gamma radiation energies such as Ga68 with period of 68 mm (gamma rays of 68, 511 keV) from Ge68 at a period of 275 days. But of

  such radioactive particles present the fundamental problem

  damental of the realization of a coded aperture plate usable for such penetrating radiation. For this

  reason, we brought forward the discussion above

  shift over the gamma radiation energy range

between 100 and 300 keV.

  The particles in circulation must not â-

  be of a size greater than 6-8 pm so that they

  freely pass through the capillary networks and each

  ticule must have a specific activity between and 200 pCi. The particles can be made up

  by small crystals of an insoluble salt containing the iso-

  top emitter gamma rays desired or by small par-

  very absorbent material (such as a sieve)

  molecular) on which the gamot-emitting isotope

my was fixed.

  Small insoluble salt crystals have the advantage of very high specific activity, but such radioactive particles must be sorted by sieving before being injected. An absorbent support has the advantage that all radioactive particles have uniform dimensions and uniform activity but the specific activity is less. For short-lived isotopes, this is not a significant problem. For short-lived isotopes, this is not a significant problem. Typically, only one atom of an isotope is needed with a period of 5 seconds per 100,000

  stable atoms to give a 61um sphere an activity

vity of 100 UCi.

THE DETECTOR -

  The detector system according to the present invention comprises one or more conventional gamma radiation detectors capable of determining the coordinates of incident gamma rays on the plane of the detector and one or more aperture-coded plates which may be constituted by a pinhole collimator, a collimator with multiple channels

  (parallel, converging or divergent channels) or a plate

  that, as shown in Figures 3 and 4, having one or

  several areas that are practically opaque to rayon-

  gamma which is of interest and one or more zones which are practically transparent to these gamma rays, or the like. A coded opening plate, 21, 31

  is placed between the volume of interest in the-

  which radioactive particles are located and a detector

  29, 37 and it is used to represent the position of the

  radioactive particles on the detector, in a con-

  naked. The detector can be a commercially available conventional Anger scintillation camera which includes a single scintillator crystal which is in the optical field of a series of photomultipliers provided with circuits to determine the center of the light intensity where it can be a single scintillator crystal located in the optical field of a series of photomultipliers of the type which can be obtained from the company Baird Atomic, Inc. The present invention can also use other detectors with increased spatial precision, such as the germanium camera which has a mosaic of germanium crystals which are read by charge amplifiers or wire chambers filled with pressurized gas or liquid in which gamma rays

  interact in pressurized gas or liquid

  of and in which the resulting electronic signal

  present on the wires is amplified and transmitted at output.

  Therefore, the apparatus and method of the present invention detect stenotic regions in the coronary arteries by detecting gamma-emitting radioactive particles from outside the patient's body. Coded opening plates used

  in combination with gamma ray detectors allows

  attempt to provide the coordinates of detected gamma rays in a convenient form suitable for data reduction and analysis. By choosing coordinate data of a radioactive particle within successive time periods as being indicative of the

  path followed by a radioactive particle in an artery

  re coronary of a patient, it is possible to determine the cross sections of the artery at different points

  of its length. In regions the length of the ar-

  in which the frequency of detection of the parties

  radioactive cells per time interval is low, the

  speed of blood and radioactive particles flowing

  slow in the artery is high and the flow of blood at higher speed is indicative of stenosis in such a region.

Claims (2)

  1. Particles capable of being introduced into the body of a patient, characterized in that they are applied to the implementation of a process consisting in introducing into the body of the patient a certain   number of particulate radiation sources which can   wind produce, from inside a pre-   sensing interest, radiation which can pass through the walls of the patient's body, to selectively filter radiation from the patient's body through spaced regions in a predetermined configuration having radiation transmission coefficients   relatively different, to detect selected radiation   filtered through the patient's body to determine   mine the successive locations of the ray source-   as a function of time and to determine, from these detections, the path of the vessel of interest inside the patient's body, and in that these particles produce gamma radiation at -a   energy level which does not exceed 300 keV.   2. Particles according to claim 1, charac-   terized in that their composition contains Ir 1