The intent of this investigation was to quantitate the amount of misregistration between PEF emission and transmission scans of the thorax that occurs in a normal clinical environment. Methods: The data from 17 FDG myocardial studies were evaluated. Prior to injection, a transmission study was acquired for 15 min using a Ge-68/Ga-68 ring source. The location of the cross-hairs from a laser alignment system was marked on the patient who was then removed from the scanner and injected with 10 mCi of FDG. After 45 min, the patient was placed back on the table and repositioned with the previously placed marks and a 15-min emission scan was acquired. The outline of the lungs on both the transmission and emission images was manually segmented. Both attenuation-corrected and noncorrected emission images were evaluated and the one that provided clearer visualization of the outline of the lungs was chosen for segmentation. The segmented contours of the transmission and emission scans were then registered with the method described by Pelizzari et al, using the transmission image as the ''head'' and the emission image as the ''hat.'' The allowable transformations were x and y shifts and rotation in the transverse plane. Results: Shifts in the x-axis averaged 2.4 mm (range: 0.2-7.3 mm, 80% less than 3.3 mm) with shifts in the y-axis averaging 2.6 mm (range: 0.1-8.7 mm, 80% less than 2.4 mm) and rotations in the transverse plane averaging 1.6 degrees (range: 0.2 to 5.1 degrees, 80% less than 2.4 degrees). A phantom study indicated that the accuracy of this method of evaluating misregistration was 2.35 mm and 1.81 mm in the x and y directions, respectively. Conclusion: Our preliminary evaluation indicates that careful application of laser alignment is an adequate method of registration in most cases.

Harkness, B. A.; Fahey, F. H.; Gage, H. D.; Zasadny, K. R.; Wahl, R. L.; Keyes, J. W. Jr. Author Information

Harkness, B. A.; Fahey, F. H.; Martin, S.; Eades, C. G.; Watson, N.; Keyes, J. W. Jr. Author Information

This investigation sought to determine which collimation factors were most important in providing superior image quality with a three-headed SPECT device. The relationship between sensitivity, resolution and SPECT image quality was studied. Two different sets of parallel-hole collimators were used. The ultrahigh-resolution collimators have higher spatial resolution (8.9 versus 11.0 mm), but only 55% of the sensitivity of the high-resolution collimators. A phantom with hot rods was imaged with both collimator sets. Observers compared images with the ultrahigh-resolution collimators to images of varying counts with the high-resolution collimators and determined which high-resolution images matched the ultrahigh-resolution images in image quality. Eleven patient studies were acquired with both collimator sets for equal time, and observers chose which image set they preferred. Transverse images of brain and liver studies were simulated with varying resolution and counts and subjectively compared. The phantom study indicated that the improvement in resolution led to image quality comparable to increasing the number of counts by a factor of 2.5 to 3.4. The clinical studies showed that the ultrahigh-resolution collimators were preferred in a large majority of the cases. These trends were also seen in the simulation study. These results confirm that higher resolution collimators should be used with multihead SPECT devices. The improvement in resolution more than compensates for the loss in sensitivity, leading to an overall improvement in image quality.

Iodobenzamide (IBZM) is a D-2 dopamine receptor antagonist. In this paper the results of Phase I clinical studies of iodine-123-(123I)IBZM in humans are reported. Preliminary imaging studies, both planar and single-photon emission tomography (SPECT), of no-carrier added [123I]IBZM in humans show specific localization in the basal ganglia of the brain. At 2 hr after an i.v. injection, the brain uptake was 3.72% of the dose, and at 20 hr later the uptake diminished to 0.7%. Radiation dosimetry calculation indicated that the radiation dose to the brain was minimum, 0.039 rad/mCi, while the large intestine wall received the highest dose, 0.28 mrad/mCi. The radiation dosimetry and pharmacology data suggest that this agent is safe for human use.

Single photon emission computed tomography (SPECT) is the nuclear medicine jargon term for transaxial tomographic imaging of conventional radiopharmaceuticals using conventional nuclear imaging equipment. This is in contradistinction to positron emission tomography (PET), which refers to the imaging of radiopharmaceuticals labeled with positron emitting radionuclides using very specialized instrumentation. Unlike PET, SPECT is in widespread use and is well within the capability of even small nuclear medicine laboratories. Tomographic imaging is not new to nuclear medicine. Some of the first medical applications of computed tomography (CT) were in radionuclide or emission tomography in the early 1960s.' It was not, however, until the development of x-ray CT using filtered back-projection reconstruction that emission tomography began to develop as a clinical tool. Soon after development of the first whole body x-ray CT scanners, the first practical whole body emission tomographs based on the Anger gamma camera were de~c r ibed .~ .~ These machines became the basis for a subsequent generation of commercial SPECT devices in the late 1970s. Today, all commercial vendors offer SPECT systems and they are common throughout the nuclear medicine community. With few exceptions, all commercial SPECT systems use the rotating gamma camera design. The patient lies on a cantilevered table, much like an x-ray CT table, and the detector of the gamma camera rotates in a full 360" circle about the area of interest, taking a series of pictures at different angles as it rotates. These angled "projection" images are stored in a computer and from them cross-sectional images of the distribution of tracer in the body are reconstructed using mathematical algorithms analogous to those that are used for x-ray CT. Most SPECT systems use a single gamma camera detector mounted in such a way that it can be used for conventional nuclear imaging as well as for SPECT. Within the last year multidetector SPECT systems using three and even-four gamma camera detectors have appeared. These devices are designed specifically to optimize their SPECT performance at the cost of limiting their usefulness for routine imaging. Such instruments

Stress Tl-201 cardiac perfusion studies are valuable in differentiating viable (ischemic and potentially salvagable) from non-viable infarcted myocardium. The post-exercise study is typically compared to a “rest” study obtained 2–4 hours post Tl-201 Injection. We have occasionally seen patients with delayed redistribution, e.g. fixed defect at 4 hours, but redistribution at 24 hours. The purpose of this study was to evaluate the frequency and significance of delayed redistribution. Thirty (30) patients with either partial or no redistribution at 4 hours post Tl-201 injection had SPECT imaging repeated 12–48 hours later. Studies were interpreted by a consensus of at least 2 experienced observers. The quality of the delayed studies was usually quite good; 29/30 were judged interpretable. Some change in the relative perfusion pattern from 4 to 24 hours was seen in 21/29 pts. This change in perfusion was felt to be clinically important in 9/29 (31%). In 6/9 the 24 hour study demonstrated reversible ischemia when the 4 hour study showed a fixed defect, in 3/9 partial redistribution at 4 hours became complete redistribution at 24 hours. Of these 9 pts, 5 had 3, 3 had 2, and 1 had single vessel CAD. All 9 had stenoses ≥50% in the ischemic region. However, neither the percent stenosis nor the number of diseased vessels correlated well with the presence or absence of delayed redistribution. Patients with 24 hour delayed redistribution had a lower mean exercise double product (19.8) compared to patients who had complete redistribution at 4 hours (26.5) (p < .05). In conclusion, 24 hour delayed SPECT Tl-201 studies have proven quite helpful in diagnosing reversible myocardial ischemia and potentially treatable coronary artery disease.

The rotating display is a useful method for reviewing single photon emission computed tomography (SPECT) data. This study evaluated the requirements for a subjectively pleasing and useful implementation of this technique. Twelve SPECT data sets were modified and viewed by several observers who recorded the minimum framing rates for apparent smooth rotation, 3D effect, effects of image size, and other parameters. The results showed that a minimum of 16 frames was needed for a useful display. Smaller image sizes and more frames were preferred. The recommended minimal framing rate for a 64-frame study is 16-17 frames per second and for a 32-frame study, 12-13 frames per second. Other enhancements also were useful.

A correlation of new turbulent two-dimensional data and peak heating data for attaching free shear layers is presented for a 2.54-cm and 5.08-cm diam cylindrical leading-edge slab 25.4 cm long, and 7.62 and 10.16 cm wide. A 30.48 x 25.4 cm sharp leading-edge flat plate set at 15 and 20 deg is used to generate plane impinging shocks. The freestream Mach number is 6 and the freestream Reynolds number varies from 3,300,000 to 25,600,000/m. Peak heating is measured on silica-based epoxy models with a phase change coating technique. A comparison of the free shear layer data with the transition data of Birch and Keyes (1972) reveals that the shear layer data are turbulent at attachment. The trend of the data shows that peak heating is strongly affected by the state of development at attachment. As the free shear layers become more fully developed, the data approach the two-dimensional correlation. Persistence of transitional flow structures for supersonic free shear flows is pointed out.

Results of computations of two-dimensional viscous blunt-body flowfields with an impinging shock wave, with a time-dependent finite-difference method employed to solve the complete set of Navier-Stokes equations, are compared with experimental results. The experimental results were obtained in a 20-inch hypersonic tunnel with a planar shock impinging on the cylindrical leading edge of a fin, hence with the shock parallel to the centerline of the leading edge, so that type III and type IV interference patterns were generated. Close agreement is found. The overall effects of smoothing and grid size on the calculations are determined. A 31 x 51 mesh is adequate for wall pressure values (except in peaked regions).

Hypersonic flow distribution and separation types over highly swept delta wings with trailing edge flaps at Mach 6

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