Paul H. Murphy

Single Photon Emission Computed Tomography Using Multi-Slice Fan Beam Collimators

Scintillation camera systems using parallel collimation have been used for single-photon emission computed tomography (SP/ECT). A major problem is the limited resolution of present parallel-hole collimators. We have built and evaluated collimators for a SP/ECT system, consisting of two opposing LFOV scintillation cameras and a gantry, which have parallel collimation along the cranial-caudal axis of the patient and converging collimation in a direction perpendicular to this axis. The collimator converges to a line of focus located 58 cm from the collimator face and parallel to the cranial-caudal axis of the patient. Two converging collimators combined with opposing LFOV cameras are capable of simultaneously imaging 11 contiguous, 2.6 (or 1.3) cm thick, transverse sections from data collected during a single revolution of the cameras about the patient. A fan beam convolution algorithm reconstructs the transverse slices and provides partial compensation for ?-ray attenuation. It is concluded that the fan-beam collimator system, when compared with conventional parallel-hole collimator systems, produces simultaneous improvements in SP/ECT system sensitivity and resolution. This results in improved visualization of small centrally located organs.

ECG-gated emission computed tomography of the cardiac blood pool.

ECG-gated cross-sectional images of the cardiac blood pool were produced using a specially constructed emission computed tomographic scanner. A pair of large-field-of-view cameras were mounted in opposition in a gantry that rotates 360 degrees about the patient. The coordinates of each detected event, the output of a physiological synchronizer, and the position of the camera heads were input to a dedicated minicomputer which was used to produce the images. Display as a movie permitted evaluation of regional and global wall motion in cross section without the disadvantages of superimposed blood pools as obtained in nontomographic views.

Experimentally determining a parametric model for the point source response of a gamma camera (SPECT)

The authors experimentally investigate the response of a gamma camera to a source as a function of depth of the source in water and of distance from the gamma camera. They compute a least-squares estimate of the FWHM (full width at half maximum) of the camera line spread function as an affine function of these two parameters. They demonstrate a method for experimentally estimating the parameters of a camera response model and use this approach to estimate the parameters of a 2-D Gaussian model for the camera point source response in a true 3-D formulation. The 2-D Gaussian model was shown to yield good agreement with experimental data.<<ETX>>

Sensitivity Analysis and Improved Identification of a Systemic Arterial Model

An identification scheme for the determination of several parameters associated with a third-order lumped-parameter model of the systemic arterial system has been developed previously [1]. In the present study a parameter sensitivity analysis of this model is conducted in conjunction with the identification scheme. This analysis indicates that the state variables of this system are indeed sensitive to changes in the model parameters and initial conditions, but not unduly so. It also indicates the relative sensitivities of individual model parameters and provides valuable insight into the behavior of the arterial model. This insight has resulted in a significant simplification and modification of our identification scheme [1] that makes it more likely to be employed in practice.

A fully automated optimization algorithm for determining the 3-D patient contour from photo-peak projection data in SPECT

The class of noninverse problems versus inverse problems is discussed. A general optimization approach to solving certain constrained noninverse problems is presented. This approach is applied in the area of single photon emission computed tomography to estimate the patient outer contour directly from the photo-peak projection data. The resulting algorithm is fully automated, fast, and the determined 3-D patient contour satisfies smoothness constraints. The accuracy and reliability of the algorithm is evaluated through Monte Carlo simulations, patient studies, and an experimental validation study.

Imaging Characteristics of a New Low-Energy Diverging∕Converging Collimator

A new, commercially available diverging∕converging collimator is evaluated. In the diverging mode, the collimator is approximately twice as efficient as the older medium-energy diverging collimator and offers equivalent resolution. Increased resolution in the converging mode indicates that the unit may be useful in imaging small superficial organs.

Validation of a knowledge-based boundary detection algorithm: a multicenter study

A completely operator-independent boundary detection algorithm for multigated blood pool (MGBP) studies has been evaluated at four medical centers. The knowledge-based boundary detector (KBBD) algorithm is nondeterministic, utilizing a priori domain knowledge in the form of rule sets for the localization of cardiac chambers and image features, providing a case-by-case method for the identification and boundary definition of the left ventricle (LV). The nondeterministic algorithm employs multiple processing pathways, where KBBD rules have been designed for conventional (CONV) imaging geometries (nominal 45° LAO, nonzoom) as well as for highly zoomed and/or caudally tilted (ZOOM) studies. The resultant ejection fractions (LVEF) from the KBBD program have been compared with the standard LVEF calculations in 253 total cases in four institutions, 157 utilizing CONV geometry and 96 utilizing ZOOM geometries. The criteria for success was a KBBD boundary adequately defined over the LV as judged by an experienced observer, and the correlation of KBBD LVEFs to the standard calculation of LVEFs for the institution. The overall success rate for all institutions combined was 99.2%, with an overall correlation coefficient ofr=0.95 (P<0.001). The individual success rates and EF correlations (r), for CONY and ZOOM geometers were: 98%,r=0.93 (CONV) and 100%,r=0.95 (ZOOM). The KBBD algorithm can be adapted to varying clinical situations, employing automatic processing using artificial intelligence, with performance close to that of a human operator.

Large-field-of-view (LFOV) scintillation cameras

Large-field-of-view scintillation cameras are general purpose, cost effective, imaging devices if one maximizes the use of the crystal with respect to the size of the object under study. This means using parallel-hole collimation for large-organ systems to reduce the number of views necessary to complete a study or to obtain a better appreciation of continuity of structure. A further increase in photon utization is gained for small-organ imaging with converging collimators, which produce images with superior resolution and sensitivity to that obtained with equivalent parallel-hole collimators. The disadvantages of converging collimators, including decreasing field of view and distortion with depth, have been insignificant in light of the advantages gained. Larger detectors with converging collimation result in much higher photon input rates to the scintillation crystal in routine clinical studies than has occurred in the past. This requirement places added burdens on electronic circuitry of the cameras. Count rate processing capabilities of 200,000 counts per second are currently available and are necessary for present generation first-pass cardiovascular studies.

Clinical Applications of Nuclear Medicine in Gastroenterology

Nuclear medicine (NM) has traditionally been a non-nursing field. This specialty has grown rapidly and continues to expand. Most nurses have had very limited exposure to nuclear medicine, except in the area of patient preparation for the nuclear medicine department. Because this specialty has had significant advances that require patient monitoring in many diagnostic and therapeutic procedures, nurses will benefit by learning more about this field and by equipping themselves to care for pre- and postprocedural patients. This article is an overview of the nuclear medicine process and its most common clinical applications in the GI field as they relate to nursing practice.

Determination of the patient outer surface from photo-peak window projection data in SPECT

An iterative algorithm for extracting patient contours solely from photo-peak window projection images is presented. No operator input is required, and the solutions satisfy a number of global criteria. Results from a 99m-Tc bone study are presented.<<ETX>>