Functional cardiac imaging: positron emission tomography.
Explore the source record for details and available documents.
Carbon Radioisotopes↗
Biomedical subjects
N A Mullani
Publications and source records attributed to N A Mullani.
Myocardial perfusion with rubidium-82: III. Theory relating severity of coronary stenosis to perfusion deficit.
The relation between the quantitative perfusion deficit, as measured by emission computerized tomography, and the severity of coronary artery stenosis is important for the noninvasive clinical evaluation of coronary artery disease in man. Positron emission tomography allows direct noninvasive measurement of myocardial perfusion and quantification of the size of the perfusion defect. Given this important information, a mathematical model has been derived to gauge the severity of a coronary stenosis from quantitative perfusion measurements in the normal and poststenotic regions of the heart. The theoretical basis is presented for relating regional myocardial perfusion and regional perfusion resistance to total coronary blood flow and resistance at normal resting flow and during maximal coronary vasodilation. The concept of perfusion reserve is presented as a clinical measure of the severity of a stenosis.
Coronary Circulation↗
Image improvement and design optimization of the time-of-flight PET.
Positron emission tomography (PET) with the added time-of-flight information has been shown to provide a better reconstructed image over conventional positron tomography. This improvement depends on the size of the object being imaged, the intrinsic resolution of the detector, and the time-of-flight resolution. Moreover, the signal-to-noise ratio of a PET image is related not only to the total number of counts in the image but also the event-locating uncertainties, the reconstruction filter function, and the recovered resolution in the image. This study provides a physical explanation for, and description of, the improvement in signal-to-noise ratio of a reconstructed image as a function of the crucial design parameters: time-of-flight timing resolution, intrinsic detector resolution, object size, and reconstructed image resolution.
Electricity↗
First-pass measurements of regional blood flow with external detectors.
A powerful, simple model has been developed for measuring regional blood flow using first-pass tracer kinetics with external detectors such as fast positron emission tomographs (PET). Its derivation is based on the hypothesis that during the first transit of a bolus of activity through an organ there exists a period during which the tracer has not left the region of interest, so that the venous concentration of the tracer is zero. Provided that this condition is met, measurement of blood flow can be obtained in any organ with any radiotracer since there are no requirements in the derivation of the model for diffusion or extraction characteristics of the tracer. The general model has been demonstrated for a special case in the heart using intravenous bolus injections of rubidium-82 with regional positron detectors (beta probes) and validated by comparison with independently determined for by labeled microspheres over a wide range of flow values from zero to five times normal resting coronary blood flow.
Animals↗
Myocardial perfusion with rubidium-82. I. Measurement of extraction fraction and flow with external detectors.
Accurate measurement of the regional extraction of a diffusible radiopharmaceutical is essential for the quantifying of regional blood flow, and may also provide an important physiologic or diagnostic indicator of the cellular viability of an organ in man through external detection by positron emission tomography. However, extraction fraction of a diffusible tracer usually decreases as flow increases, and thus noninvasive methods for measuring flow are nonlinear unless the extraction fraction can be measured independently. This report describes the theoretical basis and documents the applicability of this theory for determining, with external detectors, the first-pass regional extraction fraction of rubidium-82 by the heart, following a single intravenous bolus injection of the tracer. Measurement of extraction fraction was found to be independent of flow, thereby making it possible to determine accurately with a single intravenous bolus injection of rubidium-82, the regional blood flow in the myocardium at up to five times normal resting flow.
Coronary Circulation↗
Myocardial perfusion with rubidium-82. II. Effects of metabolic and pharmacologic interventions.
In order to validate a new method for quantifying coronary blood flow, we injected intravenously a bolus of rubidium-82 (Rb-82) into 28 open-chested dogs under a wide range of flow and physiologic conditions, using beta probes to monitor myocardial radioactivity. Extraction fraction and perfusion were measured using a functional model that separates the data into the free and trapped myocardial rubidium. Extraction and uptake of rubidium were lower during acidosis than during alkalosis and were unchanged by glucose-insulin, digoxin, or propranolol. Myocardial flow, as indicated by rubidium, correlated linearly with simultaneous measurements of flow by microspheres in the same sample volume over a wide range of flow (r = 0.97, n = 106, range 0.02-7.76 ml/min/g). Regional myocardial blood flow can be accurately determined using generator-produced Rb-82. Studies using current state-of-the-art, fast positron-emission tomographic cameras are required to determine the utility of this approach in man.
Animals↗
PETT VI: a positron emission tomograph utilizing cesium fluoride scintillation detectors.
We designed and built a positron emission transverse tomograph (PETT VI), designed specifically for fast dynamic studies in the human brain, and for cardiac studies in experimental animals. The scintillation detectors incorporated into this device are fitted with cesium fluoride crystals. Cesium fluoride was selected for this purpose because its short fluorescence decay allows the use of a short coincidence resolving time with a concomitant reduction of unwanted random coincidences. PETT VI utilizes four rings of 72 detectors simultaneously yielding seven tomographic sections. The system can be operated in either a low or high resolution mode with intrinsic geometrical resolutions in the plane of section of 7.1 to 11.7 mm full width at half maximum (FWHM), for a slice thickness with a resolution at the center of 13.9 mm FWHM. The maximum sensitivity of the system for seven slices in the low resolution mode is 322,000 cps/microCi/cc in a 20 cm diameter phantom. The contribution of random coincidences before subtraction in PETT VI was found to be approximately 14% of the counts in the phantom image with a source of approximately 3.5 mCi of a positron emitting radionuclide dispersed in a 20 cm diameter tissue equivalent phantom with a concentration of 1 microCi/cc. The short coincidence resolving time of the system permits rapid data acquisition for attenuation corrections and clinical dynamic studies with data acquisition times of less than a minute.
Animals↗
Photon time-of-flight-assisted positron emission tomography.
In positron emission tomography (PET), the annihilation radiation is usually detected as a coincidence occurrence that localizes the position of the annihilation event to a straight line joining the detectors. The measure of the difference between the time of flight (TOF) of the annihilation photons between their inception and their detection permits the localization of the position of the annihilation event along the coincidence line. The incorporation of TOF information into the PET reconstruction process improves the signal-to-noise ratio in the image obtained. The utilization of scintillation detectors utilizing cesium fluoride scintillators, fast photomultiplier tubes, and fast timing circuits allows sub-nanosecond coincidence timing resolution needed for the effective use of TOF in PET. Mathematical considerations and pilot experiments show that with state-of-the-art electronic components and through the application of proper reconstruction algorithms, the combination of TOF and PET positional data improves severalfold the signal-to-noise ratio with respect to conventional PET image reconstruction at the cost of increasing the amount of data to be processed. The construction of a TOF-assisted PET device is within the capability of state-of-the-art technology.
Electronics, Medical↗
Tomographic imaging of the heart with thallium-201: seven-pinhole or rotating gamma camera?
Explore the source record for details and available documents.
Heart↗
Feasibility of time-of-flight reconstruction in positron emission tomography.
A feasibility study was carried out to determine whether image quality can be improved by the use of time-of-flight (TOF) information in positron emission tomography (PET). The experiment used two fast cesium fluoride detectors followed by constant-fraction discriminators for coincidence-timing resolutions of 600 to 800 psec full width at half maximum, depending on the energy discrimination level. A point source was scanned to study the spatial response of the point spread function with and without the TOF information for nonfiltered back-projected data. Back-projected images of a simplified chest phantom, 42 cm in diameter and filled with relative activity concentrations of 1.0, and 5, are presented for the unfiltered data to demonstrate the improvement in image quality obtained with the use of TOF. Filtered and reconstructed images of this phantom are also presented to show the relative differences in the images obtained with PET and TOF-PET techniques for similar filter functions.
Physical Phenomena↗
Single-slice contrasted with multiple-slice positron tomographs.
Explore the source record for details and available documents.
Costs and Cost Analysis↗
Design considerations for a positron emission transverse tomograph (PETT V) for imaging of the brain.
Imaging of the brain by positron emission tomography can be optimized for sensitivity by dedicating the design of the tomograph to this application. We have designed a multislice positron emission tomograph (PETT V) for imaging the human brain and the whole body of small experimental animals. The detector system of PETT V consists of a circular array of 48 NaI(Tl) scintillation detectors, each fitted with two photomultiplier tubes, with one dimensional positioning capability. Suitable sampling is achieved by rotation of the circular array of detectors and by a wobbling motion of the detector circle. The proposed system is capable of providing seven slices simultaneously, with a spatial resolution in the plane of the slice from 7 to 15 mm and with slice thicknesses of 7 and 14 mm. The minimum scanning time is 1 sec. The estimated overall sensitivity of PETT V is 350,000 counts/sec/mCi in a 20 cm diameter phantom for a resolution of approximately 1.5 x 1.5 cm. The system is under construction.
Animals↗
A multislice positron emission computed tomograph (PETT IV) yielding transverse and longitudinal images.
We designed, built, and tested a positron emission tomograph (PETT IV) capable of providing seven slices of the human body simultaneously. PETT IV utilizes a moving hexagonal array of 48 scintillation detectors placed around the subject. Each detector consists of a cylindrical activated sodium iodide crystal optically coupled to two photomultiplier tubes. The multislice capability is achieved by comparing the light outputs of the two photomultiplier tubes in each detector. The images are displayed either as transverse or as longitudinal tomographic sections. This system provides high sensitivity and resolution, and permits rapid and accurate three-dimensional imaging of the head and body.
Electrons↗
Design and performance characteristics of a whole-body positron transaxial tomograph.
A whole-body positron-emission transaxial tomograph (PETT III) is described in detail and evaluated in terms of resolution, accuracy, and efficiency. The PETT III utilizes annihilation coincidence detection to provide spatial resolution; high sensitivity is achieved by using 48 Nal(tl) detectors set in a hexagonal array with a multiple-coincidence logic. The assumptions and approximations made in the reconstruction and their effect on image quality are discussed. Phantom studies shows the depth-independent resolution and response of PETT III, as well as its ability to recover activity distribution quantitatively in the cross section measured. Images obtained with patients and normal volunteers show the potential clinical utility of PETT III.
Evaluation Studies as Topic↗
A positron-emission transaxial tomograph for nuclear imaging (PETT).
An apparatus was developed for obtaining emission transaxial images of sections of organs containing positron-emitting radiopharmaceuticals. The detection system is a hexagonal array of 24 NaI(T1) detectors connected to coincidence circuits to achieve the "electronic" collimation of annihilation photons. The image is formed by a computer-applied algorithm which provides quantitative reconstruction of the distribution of activity. Computer simulations, phantom and animal studies show that this approach is capable of providing images of better contrast and resolution than are obtained with scintillation cameras. Advantages of positron vs. single photon reconstruction tomography are discussed.
Animals↗
Application of annihilation coincidence detection to transaxial reconstruction tomography.
A study was carried out to investigate the use of annihilation coincidence detection (ACD) in emmision transaxial reconstruction tomography. The ACD was evaluated in terms of spatial resolution and sensitivity with depth, detection efficiency, effect of pulse-height analysis on resolution and efficiency, correction for attenuation, and cold spot contrast. A prototype positron emission transaxial tomograph (PETT) consisting of a hexagonal array of 24 Nal (Tl) detectors employing ACD was constructed. A fast Fourier transform algorithm was employed to generate the reconstructed image. Computer simulations and phantom and animal studies were carried out to demonstrate that this approach yields tomographic radionuclide images that have high resolution and contrast (hot and cold spot) and that are independent of activity above and below the plane examined. The ACD yields a quantitative nuclear medicine imaging device with high detection efficiency. Comparisons are presented between the ACD and the scintillation camera and scanner. Discussion of the possible applications of the PETT in nuclear medicine is included.
Animals↗
Positron emission tomography instrumentation: a review and update.
Positron Emission Tomography (PET) has evolved into a powerful modality for in vivo functional imaging of the brain and the heart. Developments in PET technology and instrumentation have occurred rapidly during the last 20 years and have been driven by the requirements for improved resolution and image quality necessary for clinical and research applications. Clinical applications of PET have now been validated for the heart and the brain, and new research in the mapping of receptor density in the brain is being explored. PET cameras have developed into sophisticated imaging devices capable of both clinical and research applications. This review article updates the previous overview on PET instrumentation written by the authors with an added emphasis on performance evaluation of PET cameras. A short summary of current PET cameras available commercially is included for the purpose of comparing some important specifications between different systems.
Brain↗
Utilization statistics and diagnostic accuracy of a nonhospital-based positron emission tomography center for the detection of coronary artery disease using rubidium-82.
A retrospective analysis has been carried out to determine utilization and diagnostic accuracy of positron emission tomography of the heart with rubidium-82 at a nonhospital-based center. Utilization statistics were derived for the first 27 months of operation of the center from a total of 1,670 patients scanned. Diagnostic accuracy for detection of coronary artery disease was assessed using three readers, blinded to the clinical information, who read 225 rest and dipyridamole-stress scans of patients that had a coronary angiogram. Utilization statistics show that the center averaged 64 patients per month, 66% were males, 38% of the patients scanned had a coronary angiogram, 25% had a history of myocardial infarction, 12% had coronary artery bypass graft surgery, and 18% had percutaneous transluminal coronary angioplasty. Sensitivity was 82%, 96%, and 100% for myocardial regions perfused with greater than 67%, 84%, and 100% diameter stenosis, respectively. Specificity was 91% for all normal regions of the heart. Accuracy was 89%, 93%, and 93% for regions with greater than 67%, 84%, and 100% diameter stenosis, respectively. These results compare well with published results from major hospital based centers.
Ambulatory Care Facilities↗