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A new coregistration software package, Neuro900 Image Coregistration software (Strichman Medical Equipment), has been developed specifically for nuclear medicine. With this algorithm, the correlation coefficient is maximized between volumes generated from sets of transaxial slices. No localization markers or segmented surfaces are needed. The coregistration program was evaluated for translational and rotational registration accuracy. A Tc-49m HM-PAO split-dose study (0.53 mCi low dose, L, and 1.01 mCi high dose, H) was simulated with a Hoffman Brain Phantom with five fiducial markers. Translation error was determined by a shift in image centroid, and rotation error was determined by a simplified two-axis approach. Changes in registration accuracy were measured with respect to: 1) slice spacing, using the four different combinations LL, LH, HL,, HH, 2) translational and rotational misalignment before coregistration, 3) changes in the step size of the iterative parameters. In all the cases the algorithm converged with only small difference in translation offset, /spl theta/ and /spl phi/. At 6 mm slice spacing, translational errors ranged from 0.9 to 2.8 mm (system resolution at 200 mm, 6.8 mm). The converged parameters showed little sensitivity to count density. In addition the correlation coefficient increased with decreasing iterative step size, as expected. From these experiments, we found that this algorithm based on the maximization of the correlation coefficient between studies was an accurate way to coregister SPECT brain images. >

A three-dimensional (3D) image reconstruction method, which was originally developed for a positron emission tomography (PET) system consisting of two rotating scintillation cameras, has now been implemented for a multi-ring PET scanner with retractable septa. The method is called 'single-slice rebinning with axial deconvolution' (SSAD), and can be described as follows. The projection data are sorted into transaxial 2D sinograms. Correction for the axial blurring is made by deconvolution in the sinograms. To obtain the axial spread functions, which depend on the activity distribution, 2D reconstruction is first made using a limited axial acceptance angle. The final 3D image is obtained by 2D reconstruction of transaxial planes. The method is simple but not approximate, has a modest memory requirement, and can be combined with different 2D techniques. Evaluations by Monte Carlo simulations and phantom studies have been made.

An upwind nodal solution method is developed for the steady, two-dimensional flow of an incompressible fluid. The formulation is based on the nodal integral method, which uses transverse integrations, analytical solutions of the one-dimensional averaged equations, and node-averaged uniqueness constraints to derive the discretized nodal equations. The derivation introduces an exponential upwind bias by retaining the streamwise convection term in the homogeneous part of the transverse-integrated convection-diffusion equation. The method is adapted to the stream function-vorticity form of the Navier-Stokes equations, which are solved over a nonstaggered nodal mesh. A special nodal scheme is used for the Poisson stream function equation to properly account for the exponentially varying vorticity source. Rigorous expressions for the velocity components and the no-slip vorticity boundary condition are derived from the stream function formulation. The method is validated with several benchmark problems. An idealized purely convective flow of a scalar step function indicates that the nodal approximation errors are primarily dispersive, not dissipative, in nature. Results for idealized and actual recirculating driven-cavity flows reveal a significant reduction in false diffusion compared with conventional finite difference techniques.

Radioimmunoimaging characteristics of a new monoclonal antibody EBA-1 and its F(ab')2 fragments utilizing nu/nu mice bearing human breast carcinoma xenografts are described. 111In-DTPA conjugates of EBA-1 localized with tumor/blood ratios of 0.99 +/- 0.10 (P0.3) and 4.65 +/- 1.60 (P0.05), and localization indices of 1.25 and 2.61 at 24 and 72 h, respectively. A tumor/blood ratio as high as 28.86 +/- 6.90 (P0.025) was obtained with EBA-1 F(ab')2 radioconjugates at 48 h. These results suggest that EBA-1 and its F(ab')2 might be useful reagents in radioimmunoimaging and radioimmunotherapy.

We examined the quantitative effect of the edge artifacts caused by using a point spread function (PSF) system model for Positron Emission Tomography (PET) image reconstruction. Two phantoms were used in this study. The first phantom was a new small PET phantom that was used to measure the quantitative effects. The cylindrical phantom had 5 hot cylinder inserts with different diameters and was scanned with different hot insert-to-background ratios. Results showed that the region of interest (ROI) mean value (equal diameters for ROIs and cylinders) of PSF-OSEM was higher than that of OSEM without PSF model due to better resolution recovery, and the total activity was preserved in all images. However the ROI maximum value of PSF-OSEM could be significantly higher than the true value, and this overshoot depends on both the cylinder size and the concentration ratio. The largest effect was observed with the 8mm diameter cylinder insert at the highest concentration ratio. The second phantom was a Hoffman brain phantom, which was used to display the effect visually without quantitative measurements.

Neuroreceptor PET studies consisting of long dynamic data acquisitions result in data with low signal-to-noise ratio and limited spatial resolution. To address these problems we have developed a 3D wavelet-based image processing tool (wavelet filter, WF), containing both denoising and enhancement functionality. The filter is based on multi-scale thresholding and cross-scale regularization. These operations are data-driven, which may lead to non-linearity effects and hamper quantification of dynamic PET data. The aim of the present study was to investigate these effects using both phantom and human PET data. A phantom study was performed with a cylindrical phantom, filled with 18F, containing a number of spherical inserts filled with 11C. Human studies were performed on 9 healthy volunteers after injection of the serotonine transporter tracer [11C]DASB. Images from both phantom and human studies were reconstructed with filtered backprojection and post-processed by WF with a series of different denoising and enhancement parameter values. The phantom study was analyzed by computing the insert-to-background ratio as a function of time. The human study was analyzed with a 1-tissue compartment model for a series of brain regions. For the phantom study, linear relations were found between unprocessed and WF processed data for positive contrasts. However, for negative contrast, non-linearity effects were observed. For the human data, good correlation was obtained between results from unprocessed and WF processed data. Our results showed that, although non-linear effects may appear in low-contrast areas, it is possible to achieve accurate quantification with wavelet-based image processing.

The purpose of the study was to perform phantom studies to assess the impact of computed tomography (CT) system variability on quantitative measurements of contrast enhancement. A phantom containing tubes of contrast material at dilutions of 120, 1:35, 1:50, 1:100 and 1:200 arranged in air or water was imaged using 11 CT systems at 9 institutions. All systems had undergone routine calibration against air and water in accordance with the manufacturers’ recommendations. For a given tube voltage, the relationship between the iodine concentration and CT attenuation value on a single system varied by 17 to 24% over 46–48 weeks. The coefficients of variance for iodine calibration factors across different CT systems were 8.9% in air and 5.1% in water. Calibration of individual CT systems for iodine response is required to allow comparison of quantitative measurements of contrast enhancement across different institutions. Using the iodine calibration factor to express contrast enhancement as iodine concentration would facilitate the universal application of diagnostic enhancement thresholds, especially if the necessary calculations were performed by software installed on the CT console.

A multi-scale adaptive thresholding scheme is presented in this study. It was evaluated as a regularization process to filtered back-projection (FBP) for reconstructing clinical PET brain data. Adaptive selection of thresholding operators for each multi-scale sub-band enabled a unified process for noise removal and feature enhancement. A cross-scale regularization process was utilized as an effective signal recovering operator. Together with non-linear thresholding and enhancement operators, they offered remarkable postprocessing to FBP reconstructed data. In addition, such effectiveness was formulated as a regularization process to optimize FBP reconstruction. A comparison study with multiscale regularized FBP (MFBP), standard FBP with clinical settings and iterative reconstruction (OSEM) was reported. The proposed regularization process has shown competitive improvement in the image quality of PET reconstructions when compared to the current state-of-the-art method used in clinical commercial systems (OSEM).

In tomographic medical devices such as single photon emission computed tomography or positron emission tomography cameras, image reconstruction is an unstable inverse problem, due to the presence of additive noise. A new family of regularization methods for reconstruction, based on a thresholding procedure in wavelet and wavelet packet (WP) decompositions, is studied. This approach is based on the fact that the decompositions provide a near-diagonalization of the inverse Radon transform and of prior information in medical images. A WP decomposition is adaptively chosen for the specific image to be restored. Corresponding algorithms have been developed for both two-dimensional and full three-dimensional reconstruction. These procedures are fast, noniterative, and flexible. Numerical results suggest that they outperform filtered back-projection and iterative procedures such as ordered-subset-expectation-maximization.

The Neuro900 Image Coregistration Software (Strichman Medical Equipment) for SPECT was evaluated for translational and rotational registration accuracy. A Tc-99m HM-PAO split-dose study (0.53 mCi low dose, L, and 1.01 mCi high dose, H) was simulated with a Hoffman Brain Phantom with five fiducial markers. Translation error was determined by a shift in image centroid, and rotation error was determined by a simplified two-axis approach. Changes in registration accuracy were measured with respect to: 1) slice spacing, using the four different combinations LL, LH, HL, HH, 2) translational misalignment before coregistration, 3) changes in the step size of the iterative parameters. In all the cases the algorithm converged with only small difference in translation offset, /spl theta/ and /spl phi/. At 6 mm slice spacing, translational errors ranged from 0.9 to 2.8 mm (system resolution at 100 mm, 6.8 mm). The converged parameters showed little sensitivity to count density. In addition the correlation coefficient increased with decreasing iterative step size, as expected. Based on the authors' results, they found that this algorithm based on the maximization of the correlation coefficient between studies was an effective and efficient way to coregister SPECT data. >

In tomographic medical devices such as SPECT or PET cameras, image reconstruction is an unstable inverse problem, due to the presence of additive noise. A new family of regularization methods for reconstruction, based on a thresholding procedure in wavelet and wavelet packet decompositions, is studied. This approach is based on the fact that the decompositions provide a near-diagonalization of the inverse Radon transform and of the prior information on medical images. An optimal wavelet packet decomposition is adaptively chosen for the specific image to be restored. Corresponding algorithms have been developed for both 2-D and full 3-D reconstruction. These procedures are fast, non-iterative, flexible, and their performance outperforms Filtered Back-Projection and iterative procedures such as OS-EM.

In tomographic reconstruction, the inversion of the Radon transform in the presence of noise is numerically unstable. Reconstruction estimators are studied where the regularization is performed by a thresholding in a wavelet or wavelet packet decomposition. These estimators are efficient and their optimality can be established when the decomposition provides a near-diagonalization of the inverse Radon transform operator and a compact representation of the object to be recovered. Several new estimators are investigated in different decomposition. First numerical results already exhibit a strong metrical and perceptual improvement over current reconstruction methods. These estimators are implemented with fast non-iterative algorithms, and are expected to outperform Filtered Back- Projection and iterative procedures for PET, SPECT and X-ray CT devices.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Background: The consistent association of impaired eye movements and schizophrenia suggests a relationship between the neurobiology of the illness and visual pursuit systems. Visual fixation (VF), an eye “movement” task at zero velocity, is the simplest such abnormality in schizophrenia patients and their relatives. Methods: We used a VF task for a functional imaging study. Six neuroleptic-free schizophrenia patients and eight gender and mean age matched comparison subjects had SPECT scans with 20 mCi of Tc99-HMPAO, during VF on a simple blue line intersection. MEDX data saved in ANALYZE format for SPM 95 was used to generate paired t-test statistical data for display in Talairach space, with rCBF changes given as Z-scores. Results: Patients, compared to controls, had increased rCBF in both the parahippocampal gyrus (bilaterally) and in the right fusiform gyrus. They had decreased rCBF in the left frontal cortex, including medial and superior frontal gyri and anterior cingulate. Overall, compared to controls, patients had medial temporal lobe hyperperfusion along with left prefrontal hypoperfusion. Conclusions: These findings are consistent with the hypothesized imbalance between the medial temporal and frontal lobes that is postulated for schizophrenia. It was of interest that the relative rCBF differences between schizophrenia patients and controls in this small sample were observable with this cognitively non-demanding visual fixation task.

PET scanner accreditation is based on reviews of images acquired from the ACR PET phantom. The phantom is relatively easy to fill and set up for a PET study and can be used to measure tomographic uniformity, spatial resolution, and the detectability of “hot” lesions. The variety of resolution and “hot” components enables the reviewers to see relatively subtle differences in system performance. The accreditation phantom images are submitted to a review panel of qualified medical physicists for scoring. The Nuclear Medicine Accreditation Committee has defined acceptable standards for uniformity, spatial resolution and lesion detection. Uniformity and noise are evaluated qualitatively by inspection of reconstructed tomographic sections. Optimal density ranges should be comparable to those used for clinical images.Spatial resolution is judged by identifying the smallest “cold” rods in the phantom and lesion detectability is determined from the “hot” cylinders. The same protocol is also used for the “cold” cylinders that demonstrate the effectiveness of the attenuation and scatter corrections. Learning Objectives: 1. Be aware of the ACR PET accreditation process and PETPhysicist Qualifications. 2. Understand the ACR PET Phantom and testing required for ACR accreditation. 3. Understand how phantom images are reviewed by the ACR. 4. Be able to activate the ACR Phantom. 5. Understand phantom image acquisition and processing. 6. Understand PET phantom imagecontrast, resolution, and uniformity.

A comprehensive quality assurance (QA) program should be implemented for all teleradiology and picture archival and communications (PACS) systems. In this report we summarize our QA experience with a teleradiology system that includes a laser digitizer for x-ray film. A key component required for the evaluation of laser film scanners is an appropriate test pattern; digitizers should be evaluated with enhanced test patterns specifically designed for this purpose. The phantom pattern should measure high contrast resolution, low contrast discrimination, gray scale linearity, geometric distortion and noise. In addition, a uniformly exposed sheet of film (approx. 0.3 OD) serves as a good phantom for testing screen non- uniformities of viewing-station monitors. It is also suggested that clinical images should be included in a QA program. Finally it is recommended that any discrepancies in the interpretation of teleradiology images should be monitored and investigated.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Various quality control (QC) procedures may be used to evaluate image quality for picture archival and communications (PACS) systems. A standard PACS QC protocol, applied on a regular basis is desirable to insure optimal diagnostic performance. We describe a QC phantom designed especially to test PACS systems performance. We describe a QC phantom designed especially to test PACS systems that acquire images by digitizing x-ray films. The phantom is a sheet of x-ray film upon which a digital test pattern is printed. Multiple parameters of image quality are tested, including resolution, contrast, gray scale, geometric distortion and noise. Individual test patterns are incorporated to detect specific artifacts of laser scanner digitizers. As part of a regular QC protocol, the phantom provides an objective measurement of change in digital image quality over time, as well as an objective means for comparison with other systems.

The objectives of this workshop are to provide an overview of the different commercially available PET/CT scanners and to gain the necessary knowledge of PET/CT QC/QA procedures as well as the criteria needed for PET scanner accreditation and acceptance testing. The first objective will be met during the first day whereby three presentations will be provided covering the PET/CT scanner offerings from GE Health Care, Siemens Medical Solutions, and Philips Medical Systems respectively. The presentations will focus on PET scanner design, performance, and capabilities and will be given by respective users of the equipment rather than representatives of the manufacturers. The second objective will be met during the second day of the workshop, whereby four speakers will discuss topics on PET/CT QC/QA procedures, PET NEMA acceptance testing,PET ACR accreditation, and PET site shielding calculations and requirements.

The front collimator surface of a conventional single‐photon emission computed tomography(SPECT) detector system transcribing an elliptical orbit to approximate body contour could, under certain circumstances, penetrate the ellipse and make patient contact. The problem is associated both with the large front surface dimensions of tomographic cameras and the need to maintain the camera perpendicular to a radius through the axis of rotation. To aid in the development of an improved body contour orbit, software has been developed to simulate SPECTimagingsystems. A major feature of the algorithms is a spatially calibrated graphic representation of the pallet, patient and orbit of the camera head. Based on computer simulations performed with this software, a modified elliptical orbit has been proposed for patient contour SPECT scanning on two different types of tomographic acquisition systems: a dual camera, rotating ring system and a single camera, multimotion stand system. This peanut orbit has the advantage of minimizing collimator patient distance, as does the elliptical orbit, but also compensates for camera motion that could potentially produce patient contact. Versions of the peanut orbit algorithms have been installed and are operational on clinical systems similar to those that were simulated. The ring‐based gantry system (with cameras mounted on cantilevered arms) requires additional software to correct for translational shift in the field of view as a function of radial distance from the center of the system. This is done during uniformity correction. Standard unmodified backprojection software is used for reconstruction. The peanut orbit may represent an improved approach to body contour imaging in rotational SPECT.

A cinevideodensitometric method for measuring the dimensions of small vessels by computer analysis of digitized cineangiograms was developed and validated in radiographic phantom models. With this method, which is based on full-width-at-half-maximum analysis of videodensitometric profile curves, the diameters of contrast-filled plexiglass cylinders ranging from 1.78 mm to 4.14 mm in diameter were measured to within 2% mean error. The theoretical basis for this method of cinevideodensitometric analysis is provided.

This study tested the hypothesis that the absolute dimension of a coronary stenotic lesion is a more important determinant of its hemodynamic effect on regional myocardial perfusion during exercise than is relative percent stenosis. In 31 patients with an isolated lesion of the left anterior descending coronary artery, regional myocardial perfusion was determined from thallium-201 scans recorded in the left anterior oblique projection after symptom-limited treadmill exercise. Thallium-201 uptake in the distribution of the left anterior descending coronary artery was expressed as a ratio of thallium-201 uptake in the left circumflex artery distribution. Percent area stenosis, minimal cross-sectional area and mean diameter of each stenotic lesion were measured by computer-assisted cinevideodensitometric analysis of projected coronary arteriograms digitized in a 512 × 512 pixel matrix with 256 gray levels.Thallium-201 uptake in the left anterior descending coronary artery distribution, expressed as a ratio, correlated poorly (r = 0.65) with relative percent stenosis, but correlated significantly (r = 0.83; p < 0.05) with absolute lesion area. For all 16 patients with reduced regional perfusion in the left anterior descending coronary artery distribution during exercise, lesion cross-sectional area was < 1.8 mm2(mean 0.9 ± 0.6); for 13 of the 15 patients with normal distal perfusion, the area of the stenotic lesion was > 1.S mm2(mean 2.7 ± 0.7; p < 0.001). Percent coronary stenosis failed to predict flow-limiting lesions. Thus, exercise-induced thallium-201 perfusion defects correlate better with absolute dimensions of a coronary stenotic lesion than with relative coronary stenosis expressed as a percent, which is a less precise predictor of the hemodynamic effects of a stenotic lesion.

The effect of treating a commercial skeletal imaging kit containing hydroxyethylidene diphosphonate (HEDP) with dimethyl sulfoxide (DMSO) prior to labeling with sodium pertechnetate, 99mTc[TcO4-], was investigated. Statistically, significant differences (P less than 0.05) in soft tissue retention (blood and muscle) were seen in rats after injection with the DMSO-treated HEDP compared to the nontreated HEDP. Based on i.r. and HPLC data, it appears that DMSO acts as an extractant for certain Sn2+-HEDP complexes which contribute to greater soft-tissue retention.

Advancements in three major areas of SPECT (single photon emission computed tomography) technology have resulted in improved image quality for cerebral studies. In the first area, single-crystal camera electronics, extensive use of microprocessors, custom digital circuitry, and data bus architecture have allowed precise external control of all gantry motions and improved signal processing. The new digital circuitry permits energy, uniformity, and linearity corrections to be an integral part of the processing electronics. Calibration of these corrections is controlled by algorithms stored in the camera's memory. In addition, digital signals can be routed directly to interface circuitry of auxiliary computer systems without analog-to-digital conversion. Look-up tables, downloaded to the interface from the central processing unit (CPU), permit computer-controlled real-time processing of coordinate signals, including truncation, magnification, and spatial calibration. The second area of improved SPECT technology is camera collimation and related imaging techniques. In this area, system resolution has been improved without loss of sensitivity by decreasing the air gap between patient and collimator surface. Rotating the detector in close apposition to the head has required various stratagems to avoid detectorshoulder contact: the selective reduction of camera shielding, the use of long bore collimators, and the 30° angulation of the camera head for slant hole collimation. Since cerebral studies characteristically image high-contrast regions 123 I-labled pharmaceuticals with 3% to 4% 124 I contamination. Such studies acquired with low energy or medium energy collimation and a window centered on the 159 keV 123 I photopeak contain appreciable septal breakthrough signals originating from Compton scatter of high energy photons primarily from 124 I. The third area of advacements in technology, multidetector instrumentation, offers the promise of increased sensitivity and resolution. For the dynamic computer-assisted tomograph (DCAT) system, which was especially designed for regional blood flow studies with 123 Xe or 127 Xe, a count rate of 170,000 counts per μCi/cc for three slices has been achieved. This system consists of four detector banks each with 16 rectangular Nal crystals. An alternative system at Harvard uses an array of 12 moving detectors with focused collimatiors to acquire a single slice. The single photon ring tomograph (SPRINT) system uses the novel technique of stationary Nal detectors and a rotating lead ring containing eight slits. In general, multidetector SPECT systems offer the advantage of high sensitivity and rapid data acquisition, but current systems are limited to single, or at most a few, tomographic slices. In comparison, single crystal SPECT systems, while limited in sensitivity, can acquire multiple contiguous slices as well as planar images.

The authors describe a rectilinear scanner-head assembly containing an x-ray tube and a Si(Li) detector developed to stimulate and detect fluorescence from intrinsic iodine in the thyroid. Various operational parameters were evaluated. Because of the abundant supply of photons, a scanning distance of 3 inches (7.62 cm) could be used. The full width at half maximum at this distance was 0.52 cm. Optimal exposure was obtained at 80 kVp, 0.5 mA with a copper-aluminum filter combination. The scanner with an x-ray generator appears to be a workable alternative to imaging devices using long-lived radionuclide sources.

A rapid microprocessor technique for measuring the cross-sectional area, diameter, and relative percentage stenosis of coronary atherosclerotic lesions by cinevideodensitometric analysis was developed and validated. Video images of projected 35-mm coronary arteriographic cine frames were analyzed from cinevideodensitometric profile curves recorded for the catheter shaft, normal artery, and stenotic segment. In radiographic phantom studies of calibrated, contrast-filled, plexiglass cylinders, cinevideodensitometric measurements correlated linearly with percentage relative stenosis (r = 0.98; SEE = 4.1%), diameter (r = 0.99; SEE = 0.12 mm), and cross-sectional area (r = 0.99; SEE = 0.32 mm2). In postmortem studies of two patients dying after coronary arteriography, cross-sectional areas of arterial segments measured by cinevideodensitometry correlated well (r = 0.99; SEE = 0.71 mm) with areas of acrylic resin casts of the coronary arteries. Intraobserver variability (r = 0.99; SEE = 2.6%) and interobserver variability (r = 0.96; SEE = 5.3%) of cinevideodensitometric measurements of coronary arteriograms were low. Additionally, percentage relative stenosis measured in the right anterior oblique projection correlated well with measurements in the left anterior oblique projection (r = 0.98; SEE = 0.11 mm2) of patients with eccentric stenotic lesions. Lastly, cinevideodensitometric measurements were significantly (p less than 0.05) more reproducible than caliper measurements. This inexpensive dedicated microprocessor system provides rapid cinevideodensitometric measurements of coronary arterial dimensions, without requiring manual tracing of arterial segments or the major expense of a main-frame computer system.

Progression of coronary artery stenosis was measured using a quantitative, computer-assisted cinevideodensitometric method in 144 arterial segments in 44 subjects undergoing coronary arteriography on two separate occasions at least 6 months apart. Projected coronary arteriograms were digitized into 512 X 512 pixel mode and percent stenosis was calculated by comparing background-corrected videodensitometric values over stenotic and normal segments. Subjects underwent repeat coronary arteriography because of worsening symptoms of angina or heart failure; subjects with renal failure, coronary artery bypass grafts or cardiac transplant were excluded. Clinical variables determined at the time of the first arteriogram included age, sex, serum cholesterol, systolic blood pressure and presence or absence of cigarette smoking, diabetes mellitus and left ventricular hypertrophy. The mean interval between arteriograms was 29.3 months. Overall progression of coronary stenosis was observed in 40 of the 44 subjects; the mean progression at 24 months was 39% (90% confidence interval, 33 to 45%) and at 36 months was 48% (40 to 56%). The degree of overall progression was related to the length of time between arteriograms (F = 5.81, p less than 0.05) and to serum cholesterol level (F = 4.37, p less than 0.05). These data indicate that using an accurate, quantitative method, it is possible to measure progression of coronary artery atherosclerosis within 2 to 3 years of the initial arteriogram. Serum cholesterol appears to be an important determinant of disease progression.

Accurate scintigraphic determination of organ dimensions is often difficult because of the wide variety of camera-collimator combinations and display formats used for imaging. An algorithm (SPACE-CAL) was developed for digital spatial calibration of up to six large- or small-field gamma cameras using various collimators and magnification factors. The algorithm employs a master calibration file that can be used at multiple terminals. An interactive subroutine permits the operator to measure distances and areas directly from the images. Evaluation of three operators' measurements of a pine-tree phantom acquired at various magnifications showed that distances could be measured with a high degree of accuracy. Calculation of ejection fraction from end-diastolic and end-systolic areas determined by SPACE-CAL showed a high correlation with automatic count determinations (r = 0.96) and angiographic calculations (r = 0.93) of ejection fraction in 12 patients. SPACE-CAL provides an easily implemented, reproducible, and rapid method for accurate analysis of organ dimensions in digital images.

Total hip arthroplasty was performed in 13 hips with acetabular bone grafts for secure component fixation. The incorporation and healing of acetabular bone grafts were investigated with the aid of roentgenograms, planar bone scans, and a newer scintigraphic technique, three-dimensional single photon emission computed tomography (SPECT). Conventional roentgenograms proved unreliable in evaluating bone graft reconstitution because of overlapping trabecular bone patterns of the graft and iliac wing. There was no evidence of graft failure or acetabular loosening. Bone grafts in the late follow-up group (four to seven years postoperation) exhibited normal radionuclide activity, whereas grafts less than one year postsurgery demonstrated patterns of increased activity. SPECT was helpful in producing an anatomic reconstruction of the acetabulum. The observation that bone grafts exhibited normal biological viability is crucial for ensuring secure acetabular component fixation on a long-term basis.