Ambulatory physiological evaluation system including cardiac monitoring

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FIELD OF THE INVENTION

The present invention relates to measurement of physiological parameters through use of radionuclide detectors, in general, and to an evaluation system employing nuclear medicine to monitor and diagnosis a patient's physiological activities with the radionuclide detectors and miniature electronics being incorporated into a vestlike garment worn outside the chest of the patient.

BACKGROUND OF THE INVENTION

From statistics taken from the American Heart Association, it is known that over 40 million Americans have some form of heart and/or blood vessel disease. Over one million deaths occur annually due to cardiovascular disease, and over 600,000 deaths are the result of coronary artery disease. Accurate diagnosis and appropriate therapy are critical to the management of a patient with cardiovascular disease.

Many diagnostic tools are available to diagnose coronary artery disease or heart attack. These include blood tests, electrocardiograms (resting or during stress), angiography (conventional and digital subtraction techniques), ultrasound and nuclear cardiology techniques. The nuclear cardiology techniques, which employ nuclear imaging, are the only techniques capable of functional assessment of the heart. Nuclear cardiology techniques are capable of detecting infractions, ischemia, coronary artery disease, assessment of birth defects and predicting effectiveness of cardiac medications and/or surgical intervention.

Relative to other diagnostic imaging techniques, nuclear imaging has several important advantages which account for its current growth. Most important, nuclear imaging can provide diagnostic information related to cardiac function rather than just anatomy. By utilizing radioactive tracers, nuclear imaging of left ventricular function (LVF) can monitor physiological processes over time, whereas most other imaging methods can produce only a static picture. Therefore, the use of radionuclides in diagnosis of cardiovascular disease is continually expanding.

In addition to the diagnostic imaging procedure, an important need exists for a device which permits nuclear and ECG measurements to be made in an ambulatory mode. This need exists because, during the performance of ordinary activities associated with daily living, left ventricular function varies over a wide range in both the healthy and diseased heart. These changes in left ventricular function, brought about by such ordinary activities as walking, climbing stairs, psychological stress, exposure to severe temperature changes, etc., may equal or exceed those observed in a laboratory during the performance of a nuclear cardiac dynamic function study. In coronary artery disease, the accurate and continuous measurement of changes in cardiac physiology such as ischemia, arrhythmia, fall in ejection fraction, or a rise in relative cardiac blood volume can assist in the management of the patient's disease. In addition, measurements made before and after surgery or drug therapy may offer additional insights into the impact of these treatments on left ventricular function or dysfunction.

Likewise, in silent ischemia (also defined by many cardiologists as left ventricular dysfunction), where electrocardiographic changes may possibly be observed after several minutes of ECG recording, left ventricular function changes may be observed in a matter of seconds after the onset of the decompensation. The effective monitoring of these left ventricular changes (such as, increase in end systolic volume) result in better design and administration of a proper therapy regime.

An example of a nuclear cardiac probe designed to meet the need for noninvasive evaluation of rapidly developing flanges in global left ventricular function is discussed in "The Nuclear Cardiac Probe," by Dr. Henry N. Wagner Jr., Hospital Practice, April 1982, Volume 17, Number 4, pages 163-177. The probe discussed in the article is housed in a console which may be moved by casters from place to place. The probe, however, does not offer a system that can be easily carried by the patient.

Ambulatory monitoring of left ventricular function has been shown to be possible with the development of a miniaturized system of radionuclide detectors and electronics incorporated into a vestlike garment and worn outside the chest. See, for example, "An Ambulatory Ventricular Function Monitor: Validation and Preliminary Clinical Results," by Drs. Wilson, Sullivan, Moore, Zielonka, Alpert, Boucher, McKusick and Strauss, The American Journal of Cardiology, Sept. 1, 1983, Volume 52, pages 601-606.

A truly ambulatory cardiac evaluation system has several potential areas of application. Firstly, it may be particularly useful in evaluating the incidence of silent ischemia. There is now tremendous interest in the cardiology community in the idea that many of the episodes of myocardial ischemia in patients with coronary disease are probably pain free. There has been much talk that ST segment changes seen on Holter recordings may represent ischemia. That, however, has been extremely controversial because people are aware of other circumstances where ST segment changes are not caused by ischemia. Therefore, the issue has been to identify changes in ventricular function which could be caused by ischemia in association with the ST changes. This has been something which is very difficult to identify in ambulatory subjects. The present invention can make these measurements at the same time.

The second application is to define the impact of drug therapy. This is particularly important in patients who have just been diagnosed as having coronary disease, hypertension or some other circumstances where there is a need to know whether the drug therapy has depressed the patients ventricular function. The patient can be studied before and after taking the drug. In both cases, the patient pursues his/her daily activities to see whether the drug has negatively impacted cardiac function. Currently this is done by merely monitoring the patients reaction--do they feel tired, get out of breath, etc.

The third area is to define the appropriate exercise prescription in both people who do not have known heart disease, but are just out of shape, and in people who have known heart disease. It is particularly useful on patients after they have had a myocardial infarction where the patient should begin exercising on a gradual basis so that they do not exercise to a point where their ventricular function diminishes.

Thus, there is still a need for an ambulatory evaluation system which can be worn in relative comfort by a patient for monitoring coronary artery disease, in surgical and post-operative workups, for anesthesia rehabilitation, for monitoring exercise regime, for drug and diet studies, and for monitoring the effectiveness of drug administered in the therapeutic program. The present invention is directed toward filling that need.

SUMMARY OF THE INVENTION

The present invention relates generally to an ambulatory physiological evaluation system including gamma radiation detectors, as cardiac monitors, utilized in the nuclear medicine field for the purpose of monitoring and/or diagnosing a patient's physiological activities, such as left ventricular function, during a prescribed period of time. In a preferred embodiment of the invention, a compact cardiac monitor having a main detector is placed generally over the heart of a patient and a radiation detector, mounted within the monitor, senses the ebb and flow of the blood through the heart by detection of the gamma rays emitted by Tc.sup.-99m labeled blood cells. In order to accurately measure blood volume, the radiation detector must be precisely positioned relative to the heart and this relationship must be maintained during the entire detecting period. The present invention provides an apparatus and method for determining the exact location of the left ventricle of the patient's heart, positioning the cardiac monitor relative to the left ventricle, and maintaining the position of the cardiac monitor relative to the left ventricle during an ambulatory study period.

The starting point for the inventive ambulatory physiological evaluation system is a vest made of a flexible plastic material, such as "Aquaplast", which contains a pattern of ventilation holes. The vest is adapted to be worn on the torso of a human and contains an arrangement of shoulder straps and belts to provide for a snug, yet relatively comfortable fit. The vest is worn to provide a base to which a cardiac monitor including a main detecting device is attached and held in a precise relationship between the main detecting device and an anatomical body, such as the left ventricle of the heart.

Attachment of the cardiac monitor to the vest is accomplished through the use of a detector mounting assembly which, in one embodiment is in a form of a mounting bracket which is a lightweight, formed, metallic structure with means for attaching to both the vest and to the detecting device. The mounting bracket fastens two detecting devices, a main detector and a auxiliary detector, to the vest and provides two means for adjusting the main detector relative to the left ventricle of the heart of the wearer. First, the mounting bracket has flanges so that the bracket can be adjusted relative to the vest through fasteners movably positioned within the vest. Second, for more precise adjustment, the main detector can be adjusted plus or minus one centimeter in two directions relative to the detector mounting bracket, thereby, providing for a precise adjustment of the main detector relative to the left ventricle of the heart of the wearer. A scale is provided between the main detector flange and the detector mounting bracket, reading in 5 millimeter increments. The scale precisely indicates the relative position between the mounting bracket and the main detector.

In order to properly align the detector mounting bracket relative to the left ventricle of the heart, an alignment fixture is used prior to mounting the main detector to the mounting bracket. The detector alignment fixture basically comprises a planar leveling plate to which is fastened a plate within which is embedded a centerline cursor made from lead elements. The detector alignment fixture is mounted to the face of the detector mounting bracket with four cap screws. A center guide pin on the alignment fixture enters a center hole of the detector mounting bracket and, in addition, the four posts on a floating base plate positioned behind the face of the mounting bracket, enter the four holes in the alignment fixture. The mounting bracket also has a pair of opposed flanges which aid in mounting the centerline plate. After mounting, the detector alignment fixture is centered on the detector mounting plate.

A conventional scintillation or Gamma camera is brought up to the alignment fixture and adjusted for parallelism. The picture derived from the camera on a cathode-ray tube (CRT) display shows the position of the cursor relative to the left ventricle of the heart. If the centerline of the cursor is within 10 millimeters of the desired position, any further adjustment can be made when the alignment fixture is removed and the main detector assembled to the mounting bracket. If the location of the centerline is further away from the left ventricle of the heart than 10 millimeters, the mount must be readjusted relative to the vest and the above procedure repeated.

In another embodiment of the invention, a modified mounting bracket structure is provided which incorporates a ball-type socket carried on a mounting plate and into which firstly an alignment fixture can be releasably clamped for use with a Gamma camera to set the positioning of the socket, after which the socket, thus set, can be used to mount a main detector. This embodiment provides somewhat greater flexibility of adjustment.

The ambulatory physiological evaluation system also contains electronic circuitry which monitors and processes information obtained from the main and auxiliary detectors. A preferred embodiment of the evaluation system basically comprises a Cadmium Telluride (CdTe) detector which is used as the auxiliary detector that is responsive to the presence of a suitable radiopharmaceutical, such as Tc.sup.-99m tagged red blood cells, injected into the circulatory system to provide an output signal representative of left lung activity. The CdTe detector may be placed at other locations on the body of the patient to evaluate other physiological parameters such as pulmonary, cereberal and muscular function. The cardiac monitor that includes the main detector is also responsive to the presence of a suitable radiopharmaceutical injected into the circulatory system to produce a signal which is proportional over the cardiac cycle. The signal produced by the main detector is representative of the left ventricular time activity of the heart. Both of these signals are fed in analog pulse form to a data logger which is housed in a bag worn by the patient. The data logger includes the circuitry necessary to accumulate and manipulate the data and transfer it to a portable cassette recording device also housed in the bag. Also, feeding information into the recording device are conventional ECG electrodes. After the information has been recorded over a desired period of time, the recorded information on cassette is presented, through an impedance matching interface and an analog-to-digital converter, to the memory of a stand alone computer located in a hospital or office. The computer calculates such items as R--R time interval, electrocardiagram and time-activity curves, and displays these items for both the main and auxiliary detectors. From the calculations made by the computer, average heart rate, number of aberrant beats, left ventricular ejection fraction and relative cardiac blood volume may be calculated for a time interval of interest.

Thus, it is the primary object of the present invention to provide a truly ambulatory physiological evaluation system including cardiac monitoring.

It is another object of the present invention to provide a mounting apparatus for mounting a radiation detector in a precise relationship to an interior organ of the body of a patient.

It is a further object of the present invention to provide an apparatus to facilitate mounting of a radiation detector to an ambulatory vest in a precise relationship with the left ventricle of the heart of the wearer of the vest.

It is still an object of the present invention to provide a device for accurately recording information detected by a radiation detector that is monitoring physiological activity of a patient.

It is yet an object of the present invention to provide an information processing system for manipulating and displaying prerecorded information detected by a detector that is monitoring physiological activity of a patient.

Other objects, advantages, and features will become apparent by reference to the following detailed description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front perspective view of a person operatively wearing an embodiment of the inventive ambulatory physiological evaluation system.

FIG. 2 is a back plan view of the person of FIG. 1 wearing the vest of the subject invention without the electronics package and shoulder strap.

FIG. 3 is a front plan view of the cardiac monitor and mounting bracket for the evaluation system of FIG. 1.

FIG. 4 is a top view partially in section of the evaluation system of FIG. 1.

FIG. 5 is a view taken along line 5--5 of FIG. 3.

FIG. 6 is a plan view of the basic elements constituting the vest of the evaluation system of FIG. 1.

FIG. 7 is a view taken along lines 7--7 of FIG. 6.

FIG. 8 is a view similar to FIG. 4 with the cardiac monitor removed and an alternative embodiment for the detector mounting bracket.

FIG. 9 is a front perspective view of the vest of FIG. 1 with the alignment fixture in place on the detector mounting bracket.

FIG. 10 is a top view of the arrangement of FIG. 9.

FIG. 11 is a plan view of the alignment fixture of FIG. 9.

FIG. 12 is a view taken along lines 12--12 of FIG. 11.

FIG. 13 is an exploded perspective view of an embodiment of the cursor-locating plate.

FIG. 14 is a perspective view of a floating base for use mounting items on the detector mounting plate of FIG. 3.

FIG. 15 is a perspective view of the auxiliary detector used in the evaluation system of FIG. 1.

FIG. 16 is a view taken along lines 16--16 of FIG. 15.

FIG. 17 is a block diagram of the electronic portion of the evaluation system of FIG. 1.

FIG. 18a is a schematic diagram of a charge coupled amplifier used in the electronic portion of FIG. 17.

FIG. 18b is a schematic diagram of a positive peak hold circuit used in the electronic portion of FIG. 17.

FIG. 19 is a flow chart used to explain the operation of the computer forming part of the evaluation system of FIG. 1.

FIG. 20 is a waveform used in explaining a portion of the operation of the electronic portion of FIG. 17.

FIGS. 21 and 22 are waveforms used in explaining a portion of the operation of the electronic portion of FIG. 17.

FIGS. 23a-23c are waveforms used in explaining a portion of the operation of the electronic portion of FIG. 17.

FIG. 24 is a front perspective view of a modified vest for use in the inventive system.

FIG. 25 is a rear perspective view of a modified vest.

FIG. 26 is a front perspective view of an operative portion of the modified vest with a modified mounting bracket structure and alignment fixture secured to the vest.

FIG. 27 is a sectional view on line 27--27 of FIG. 26.

FIG. 28 is a front elevational view of the modified mounting bracket structure.

FIG. 29 is a rear elevational view of the modified mounting bracket structure.

FIG. 30 is a rear elevational view of the modified alignment fixture.

FIG. 31 is an enlarged perspective view of a part of the modified alignment fixture.

FIG. 32 is a sectional view on line 32--32 of FIG. 28.

FIG. 33 is a perspective view of a spring thrust washer used in the modified mounting bracket structure.

FIG. 34 is a front perspective view of a part of the modified vest showing a tear-away feature.

FIG. 35 is a front perspective view similar to FIG. 26 but showing the manner in which a main detector is fitted into the modified mounting structure after removal of the respective alignment fixture.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Overview of Evaluation System

With reference to FIGS. 1-6, the present invention relates to an ambulatory physiological evaluation system, generally designated 10, including gamma radiation detectors 12 and 14 utilized in the nuclear medicine field for the purpose of monitoring and/or diagnosing a patient's physiological activities during a prescribed period of time. In a preferred embodiment of the invention, a compact cardiac monitor 11 including a main detector 12 is placed generally over the heart of a patient and a radiation detector, mounted within the monitor, senses the ebb and flow of the blood through the heart by detection of the gamma rays emitted by Tc.sup.-99m labeled blood cells. In order to accurately measure blood volume, the radiation detector must be precisely positioned relative to the heart and this relationship must be maintained during the entire detecting period. The present invention provides an apparatus and method for determining the exact location of the left ventricle, positioning the cardiac monitor relative to the left ventricle, and maintaining the position of the cardiac monitor relative to the left ventricle during an ambulatory study period.

With reference to FIGS. 1 through 7, the starting point for the inventive ambulatory physiological evaluation system is a vest 16 made of a flexible plastic material, such as Aquaplast, which contains a pattern of ventilation holes 18. The vest is adapted to be worn on the torso 20 of a human and contains an arrangement of shoulder straps or shoulder supports 22, 24 and belts 26, 28 to provide for a snug, yet comfortable fit.

The vest is worn to provide a base to which a detecting assembly in the form of a cardiac monitor 11 is attached and held in a precise relationship between the detecting device and an anatomical body, such as the left ventricle of the heart.

Attachment of the detecting device to the vest is accomplished through the use of a detector mounting bracket 30 which is a lightweight, formed structure with means for attaching to both the vest and to the detecting device. In a preferred embodiment, the mounting bracket is made from aluminum, but could be made from plastic or other suitable material. The mounting bracket fastens two detecting devices, the main detector 12 and the auxiliary detector 14, to the vest and provides two means for adjusting the main detector relative to the left ventricle of the heart of the wearer. First, the mounting bracket has flanges 32 and 34 so that the bracket can be adjusted relative to the vest through four fasteners 41-44 movably positioned within the vest. Second, for more precise adjustment, the main detector 12 can be adjusted plus or minus one centimeter in two directions relative to the detector mounting bracket, thereby, providing for a precise adjustment of the main detector relative to the left ventricle of the heart of the wearer. A scale 36 is provided between the main detector flange and the detector mounting bracket, reading in 5 millimeter increments. The scale precisely indicates the relative position between the mounting bracket and the main detector.

In order to properly align the detector mounting bracket relative to the left ventricle of the heart, an alignment fixture 50 is used prior to mounting the main detector to the mounting bracket. The detector alignment fixture basically comprises an elongated, planar leveling plate 52 to which is fastened a centering plate 54 within which is embedded a centerline cursor made from lead elements 58. The detector alignment fixture is mounted to the face of the detector mounting bracket with four fasteners, such as cap screws. A center guide pin 60 on the alignment fixture enters a center hole 62 of the detector mounting bracket and in addition the four posts 71-74 on a floating base plate 76 positioned behind the face of the mounting bracket, must enter the four holes in the alignment fixture 54. The mounting bracket also has a pair of opposed, upwardly extending flanges 201 and 203, which aid in aligning and mounting the centering plate. After mounting, the detector alignment fixture is centered and made parallel with the face 162 of the detector mounting plate 30.

A conventional scintillation or Gamma camera (not shown) is brought up to the alignment fixture and adjusted for parallelism. The reason the Gamma camera must be adjusted so that its focal plane is parallel to the face of the alignment fixture is because the holes of the collimator found in the main detector each have a narrow field of view. The picture derived from the Gamma camera on a cathode-ray tube (CRT) display (not shown) shows the position of the cursor 56 relative to the left ventricle of the heart. If the centerline of the cursor is within 10 millimeters of the desired position, any further adjustment can be made when the alignment fixture is removed and the main detector 12 assembled to the mounting bracket. If the location of the centerline is further away from the left ventricle of the heart than 10 millimeters, the mount must be readjusted relative to the vest and the above procedure repeated.

As shown in FIGS. 17 and 18, the ambulatory physiological evaluation system 10 also contains electronic circuitry which monitors and processes information obtained from the main and auxiliary detectors. A preferred embodiment of the evaluation system basically comprises a Cadmium Telluride (CdTe) detector 14 which is used as the auxiliary detector that is responsive to the presence of a suitable radio pharmaceutical Tc.sup.-99m tagged red blood cells, injected into the circulatory system to provide an output signal representative of left lung or background activity. A cardiac monitor 11 includes the main detector 12 which is also responsive to the presence of a suitable radiopharmaceutical injected into the circulatory system to produce a signal which is proportional over the cardiac cycle. The signal produced by the main detector is representative of the left ventricular time activity of the heart. Both of these signals are fed in analog pulse form to a data logger which is housed in a bag 80 worn by the patient by way of shoulder strap 81. The data logger includes the circuitry necessary to accumulate and manipulate the data and transfer it to a portable cassette recording device 82, also housed in the bag. Also, feeding information into the recording device are conventional ECG electrodes 84. After the information has been recorded over a desired period of time, the recorded information is presented, through a tape player 87 an impedance-matching interface 86 and an analog to digital converter 88, to the memory 90 of a stand alone computer 92 located in a hospital or office. The computer calculates and analyzes such items as R--R time interval, electrocardiagram and time-activity curves, and/or displays these items in eye readable form for both the main and auxiliary detectors. From the calculations made by the computer, such items as average heart rate, number of aberrant beats, left ventricular ejection fraction and relative cardiac blood volume may be calculated for a time interval of interest.

Ambulatory Vest

With reference to FIGS. 1-7, the detailed structure of the ambulatory vest will now be described. Basically, the vest 16 consists of a one piece, flexible, thermal plastic material which contains a plurality of ventilation holes 18 arranged in a predetermined pattern to facilitate ventilation between the atmosphere and the skin of the wearer when the vest is in its operative position on the torso as shown in FIGS. 1 and 2. In a preferred embodiment, the vest is made from a plastic material sold under the name "Aquaplast".

As shown in FIG. 6, the vest 16 basically comprises an enlarged chest area 92 that fully covers the chest of the wearer, especially in the area of the heart. With reference to its orientation on the torso of a wearer, the lower portion of the vest on either side of the chest terminates in extended strips 94 and 96. Strip 94 passes below the right underarm of the wearer and falls against the small of the back. In like manner, strip 96 passes below the left arm of the wearer and lies against the small of the back. A pair of off-set nylon straps or shoulder supports 26 and 28 are movably positioned within slits 102 and 103 defined on strips 94 and 96, respectively. Each of the straps is secured to the edge of a strip by a series of stitches 104 and terminates in an array of Velcro hooks 106 that mate with a complementary array of Velcro eyes 108 provided on the opposite side of one of the strip portions.

As shown in FIG. 2, the straps pass across the back of the wearer to the Velcro fastener located on the opposite strip in order to securely fasten the vest to the patient. Located along a diagonal, at the front of the vest is an emergency separation or release 110 which is created by holding mating sides 112 and 114 of the vest in an abutting relationship and joining them together by a plastic tape or Velcro 116 that is arranged perpendicular to the orientation of the separation line 115. Strategically placed guides or planar tabs 113, which are secured to side 114, and guide strip 117 which spans the full length of and is secured to strip 114 facilitates placing sides 112 and 114 in abutting relationship. Should the wearer experience any distress during the use of the physiological evaluation system, the vest can be quickly released and easily removed through use of the emergency separation 110, which extends diagonally from the right side of the sternum or breastbone near the persons neck downwardly and away from the stomach area toward the right side of the wearer's body. Also defined on the front of the vest are two large apertures 34 and 36 which define open areas in the 4th and 5th intercoastal spaces for placement of ECG electrodes in conventional manner. The bottom periphery 91 of the vest terminates above the right chestwall of the wearer to permit ready placement of the ground ECG electrode.

In order to prevent the vest from moving vertically up and down, the pair of shoulder straps 22 and 24 are provided. Each of the shoulder straps has the same basic configuration with one strap being the mirror image of the other. The straps are generally shaped like an elongated triangle, with the base portion 122 having a hole 124 on one side and a slot 126 on the other side. The hole and slot are positioned relative to each other so that they mate with threaded lugs 125 and 127 defined along the upper portion of both sides of the front of the vest. The other end 128 of the strap terminates in a slot 132 which receives a belt 134 that is placed in a mating relationship with a slot 138 defined at the end of strip 96. Also defined in the strap near the forward end is an aperture 142 configured to reveal a sufficient portion of the skin of the patient in order to receive a conventional ECG electrode. Thus, straps 22 and 24 provide spaces for mounting the two clavicle ECG electrodes.

On the front of the vest, in the area covering the heart, are four vertically oriented slots 151 through 154. The placement of the slots on the front of the vest is determined in the following manner. The front of the vest may be divided in half along the sternum or breastbone of the wearer. The four slots are defined along the left side of the vest with reference to the sternum. About five inches to the left of the sternum and near the nipple area of the wearer, the vest contains a center point 156. The slots 151-154 exist along a line positioned at about a 10.degree. angle relative to the horizontal plane H through the center point 156. Each of the slots is approximately one inch in length. The slots are oriented perpendicular to the 10.degree. line that is defined through the center point 156. Alternate pairs of slots 151-153 and 152-154 are approximately 6.76 inches from each other as measured along a line parallel to the 10.degree. line. The longitudinal axes of slots 151 and 154 are essentially parallel to each other.

As will be described in greater detail hereinafter, slots 151 through 154 are used in connection with the detector mounting bracket 30 to properly position the cardiac monitor 11 and auxiliary detector 14.

The Detector Mounting Bracket

FIGS. 1, 3, and 4 show the detector mounting bracket 30 in its position of intended use and mounted on the vest 16. The bracket is made from a thin aluminum strip and basically consists of a generally square planar mounting face 162 and a pair of planar mounting flanges 32 and 34. Defined at the center of the planar face 162 is an aperture 62 which defines a locating hole used in conjunction with the locating pin 60 of a detector alignment fixture 50. Also defined at each of the corners of the planar surface are larger apertures 171 through 174. Positioned between adjacent apertures along each of the edges of the planar surface are engraved lines 176 which are typically spaced 5 millimeters apart and define scale 36. These lines are engraved on the surface 162 and are used in conjunction with complimentary marks 178 provided on side faces 251 of the main detector 12 in order to properly align the main detector relative to the heart of the wearer.

FIG. 4 shows a top view of the mounting bracket secured to the vest with the cardiac monitor assembly 11 being secured to the mounting bracket. The bracket 30 has the rear face 182 generally flush with a portion of the vest 16 so that the planar face 162 is generally perpendicular to a line L that passes through a plane P defined along the sternum of the wearer at an angle of approximately 40.degree. to 50.degree. with an angle of 45.degree. being typical. This position is also referred to as the 45.degree. left anterior oblique (LAO) position. The outward planar surface 162 of the mounting bracket terminates in an bend 192 that continues in a planar portion 184 which is at an approximately 90.degree. angle to the planar face 162. The end of planar portion 184 terminates in the flange 32 which is at an approximately 48.degree. angle with reference to the planar portion 162. The opposite bend 194 of the planar surface 162 meets with a planar portion 196 that is at an approximately 381/2.degree. angle with regard to the planar surface 162. Planar portion 196 terminates in the flange 34 which is formed at an angle of approximately 141/2.degree. with regard to the planar surface 162. Both of the flange portions 32 and 34 contain spaced slots 202 which are arranged so that when the detector mounting bracket is positioned on the vest, the longitudinal axes of slots 151 through 154 are generally perpendicular to the longitudinal axes of slots 202 defined on the mounting bracket. It is intended that the mounting bracket be secured to the vest through a series of wing nut assemblies 41 through 44. Each of the wing nut assemblies is made up of a wing nut 212 and a threaded portion 214 that terminates at its end in a flat disk 216 which is flush against the interior surface 218 of the vest when the wing nut assemblies are mounted. The arrangement of the slots 151 through 154 and 202 permit complete two dimensional freedom in positioning the detector mounting bracket relative to the vest.

In an alternative embodiment of the detector mounting bracket (FIG. 8), the planar position 184 is divided up into two overlapping sections 602 and 604 which may move relative to each other to alter the distance from the face 162 to the vest 16. The overlapping sections are held together by wing nut assemblies 606. At the opposite side of the mounting bracket, flange 34 meets portion 196 through a hinge 610. In this way, the mounting bracket may be securely fastened with the face 162 at several different mounting angles without placing any bending stress on the mounting bracket.

Construction and Mounting of the Main and Background Detectors

As shown in FIGS. 3-5, the main detector 12 is mounted within a housing 330 that has a lower portion 332 generally in the shape of a cylinder and an upper portion 334 generally in the shape of an elongated rectangular solid. The housing is made up of upper and lower shells 336 and 338 which are joined together through appropriate fasteners 340 such as pan screws. Two photo multiplier tubes 344 and 346 are positioned next to each other within the upper housing. The operative ends of the photo multiplier tubes are in intimate contact with a light guiding prism 348 made of leaded glass. The lower or cylindrical part of the housing has a cover plate 350 made of black nylon which is screw mounted onto a cylindrically shaped shield 352. The planar surface of the cover plate defines a detecting plane. The part 354 of the shield which receives the cover is of narrower diameter than the remaining portion 356 of the shield. In a preferred embodiment, the shield is made of lead with 5% antimony. Positioned next to the cover is an iris 358 made up of a thin sheet 360 of spring tempered aluminum and a metal ring made from lead with 5% antimony. The iris is optionally used to restrict the field of view in the case of a child's heart or a small adult heart. Positioned next to the iris is a lead collimator 364 having an array of gamma ray guiding tubes 366. The other side of the collimator is adjacent a sodium iodide (NaI) crystal assembly 368. Between the collimator and the crystal assembly is a rubber protective gasket 370. A guide ring 372 made of lead with 5% antimony is in intimate contact with the lead shield. The guide ring receives and holds a leaded glass window 374 adjacent the NaI crystal. Between the glass window 374 and the NaI crystal 368 is a very thin layer 375 of epoxy or an RTV silicon rubber. The top of the glass window is in communication with one side of the light prism 348. A connector 380 having a built-in voltage divider and preamplifier is connected to the photo multiplier tubes. The cable 383 is connected to the other side of connector 380 and emerges from the housing 338 for connection with the circuitry in bag 80.

A generally hollow aluminum monitor base 230 completes the construction of the main detector. The base has a planar square surface 384 within the center of which is defined a large circular aperture having a diameter sized to receive the narrower portion 354 of shield 352. Also defined within the surface 384 are four mounting holes 231-234. Further details of the construction of the main detector 12 may be found in co-pending U.S. Patent Application Ser. No. 711,096 to Suzuki for High-Energy Radiation Detector and Method of Detection, which is incorporated by reference.

The way in which the main detector 12 is fastened to the detector mounting bracket 30 will now be described with reference to FIGS. 3-5. In connection with mounting the main detector to the mounting plate, use is made of a floating base plate 76 which may be movably retained to the mounting bracket 30 by a suitable means such as a spring or tape. The base plate is generally square in configuration with flattened or rounded edges 222 at the corners. At the center of the base plate is an aperture 224 which is of larger diameter than the aperture defined in the mounting plate. Located at each of the corners is a stand-off, 71 through 74, which has a vertical axis oriented perpendicular to the planar surface 226 of the base plate. Each of the stand-offs is internally threaded. The base plate, like the mounting bracket is made of aluminum and is positioned behind the planar surface 162 of the mounting bracket in the space defined between the outer surface 228 of the vest and the interior surface 182 of the bracket face so that each of the stand-offs protrude through one of the enlarged apertures 171-174. At the same time, the planar face 226 of the base plate is in intimate contact with the interior face 18 of the mounting bracket. The main detector 12 is supported on base 230 which contains apertures 231-234 in each of the corners of the base in order to receive the stand-offs 71 through 74 of the floating base plate. Knurled, threaded lugs 241, 242 are then used to secure the base plate and the main detector to the mounting bracket. With reference to FIGS. 1 and 3, it can be seen that the main detector 12 on the base 230 contains four side faces 251, each of which bears index mark 178 which is brought into registry with one of the scales 36 defined about periphery of the surface 162 of the mounting bracket. In this way, the main detector may be mounted anywhere on the surface 162 within plus or minus 10 millimeters since each of the scale gradients 176 on the surface 162 are 5 millimeters apart.

With reference to FIGS. 3, 15, and 16, the construction and mounting of the auxiliary detector will now be described. The auxiliary detector includes a cylindrically shaped case 601, the floor of which defines a face 603 for the detector. The opposite end of the case contains a threaded portion 605 which mates with a complimentary threaded portion on a cover plate 608. Together, the case and the cover plate define a housing within which is mounted the CdTe detector. Positioned within the housing near the cover 608 is a printed circuit board 610 which contains the preamplifier circuitry associated with the detector. Mounted in the circuit board are extended pin contacts 612 and 614. Next to the underside of the circuit board is a cylindrically shaped hollow lead shield 616. Positioned within the shield is an insulator board 618 and alternate carrier boards 620 and 622. The carrier boards define a square portion 652 which houses a CdTe chip. The bottom portion of the shield receives a cover 626 which has a circular shape to receive a honeycomb collimator 624. At the underside of the cover, near the bottom of the case, are contact mounting lugs 628 and 630 which receive leads 632. The leads emerge from the cover of the housing for connection to the data logger that is contained in the bag 80. The conductive contacts 612 and 614 provide electrical contacts with the CdTe chip through the carriers 620 and 622.

Since the detector may be used on various parts of the body, it is desirable to be able to replace and easily remove the detector as desired. In a preferred embodiment, the face 603 of the detector may be coated with a double stick tape so that the auxiliary detector may be placed as shown in FIG. 3, on the detector mounting plate or in other locations on both the body and the vest.

Location of the Cardiac Monitor

In order to get the most accurate readings from the cardiac monitor, it is imperative that the optimum position of the main detector relative to the left ventricle be determined and maintained during the detecting period. Thus, as part of the present invention, a structure and method are provided for determining the exact location of the left ventricle and positioning the mounting bracket so that precise placement of the main detector may be insured.

As has already been described, the main detector 12 is secured to the vest through the use of a mounting bracket 30. In a preferred embodiment, the bracket is a light weight formed metallic structure with a series of slots 202 for attaching the bracket to the vest and a series of enlarged apertures 171-174 for mounting the cardiac monitor. Thus, it can be seen that the bracket may be adjustably mounted to the vest and the main detector may be adjustably mounted to the bracket thus providing adjustment of the main detector relative to the left ventricle of the heart within two degrees of freedom.

An alignment fixture 50 is employed in order to properly align the detector mounting bracket relative to the vest. The alignment fixture is generally illustrated in FIGS. 9-14. The purpose of the fixture is to transfer a location of an anatomical body, such as the left ventricle of the heart, utilizing a conventional scintillation camera.

With reference to FIGS. 9-11, the alignment fixture may be described as follows. The fixture basically comprises an elongated planar leveling plate 52 on which is mounted a generally square planar cursor-locating plate 54. Both the leveling plate and the cursor plate are preferably made of a transparent plastic material. Defined on one side 281 of the mid-portion of the planar leveling plate are a series of four holes 291-294 aligned to receive the stand-offs 71-74 from the floating backing plate 76. Positioned on one surface 296 of the leveling plate is the cursor or centering plate 54 which also contains four apertures that are brought into alignment with the apertures 291 through 294 defined in the leveling plate.

The cursor plate actually consists of two planar portions 302 and 304. Sandwiched between these surfaces are an array of lead cursors 58 which aid in aligning the detector mounting bracket relative to the left ventricle of the heart. As shown in FIG. 13 the lead cursors generally consist of lead slugs which are one millimeter thick and 10 millimeters on a side. The slugs are arranged within evacuated areas defined on a middle layer 306 in a cross with one cursor 308 being at the center of the cross and two cursors 310 and 312 being on either side of the center cursor on the legs of the cross. Together, the cursors define a centerline. All of the lead cursors are the same size with the exception of the cursor located on the left as shown in FIG. 11. This cursor 314 is 10 millimeters by 20 millimeters and acts as a direction alignment cursor to identify left and right on any image that includ