Collaboration using Internet for the development of case-based teaching files: report of the Computer and Instrumentation Council Internet Focus Group.

UNLABELLED: The Internet and particularly the World-Wide-Web is becoming a useful tool for the nuclear medicine community. METHODS: The Computer and Instrumentation Council of the Society of Nuclear Medicine convened an Internet Focus group to discuss collaboration using the Internet. The prototype application considered was development of case-based teaching files using the World-Wide-Web. Teaching file cases (clinical history, images, description of findings and discussion) on World-Wide-Web servers at different institutions are integrated using the Internet. The user can navigate from case to case using point-and-click hypertext linking. RESULTS: The initial experience with collaboration has been encouraging. An etiquette to help foster collaboration has been proposed. Development of quality control mechanisms and introduction of peer review were identified as issues needing further work. CONCLUSION: The World-Wide-Web offers great potential for new forms of collaboration. There is, however, a need to learn how to make best use of this new resource.

Photodynamic therapy for intracranial neoplasms: investigations of photosensitizer uptake and distribution using indium-111 Photofrin-II single photon emission computed tomography scans in humans with intracranial neoplasms.

Photodynamic therapy is being investigated as an adjuvant treatment for intracranial neoplasms. The efficacy of this therapy is based on the uptake of photosensitizer by neoplastic tissue, its clearance from surrounding brain tissue, and the timing and placement of photoactivating sources. Photofrin-II is the photosensitizer most actively being investigated. We labeled Photofrin-II with Indium-111 and studied the uptake and distribution of this agent in 20 patients with intracranial neoplasms, using single photon emission computed tomography (SPECT) with volume rendering in three dimensions. Of these patients, 16 had malignant glial tumors, 2 had metastatic deposits, 1 had a chordoma, and 1 had a meningioma. Anatomical-spatial data correlated well between the SPECT images and contrast-enhanced computed tomography or magnetic resonance images. Regions of focal uptake on SPECT images correlated with the surgical histopathological findings of the neoplasm. The kinetics of photosensitizer uptake varied according to the tumor's histological findings, the patient's use of steroids, and among patients with similar types of tumor histology. Peak ratios of target-to-nontarget tissue varied from 24 to 72 hours after injection. The study data show that, to be most effective, photodynamic therapy may need to be tailored for each patient by correlating SPECT images with anatomical data produced by computed tomography or magnetic resonance images. Photoactivating sources then can be placed, using computer-assisted stereotactics, to activate a prescribed volume of photosensitized tumor at the optimal time for treatment.

Errors in the determination of left ventricular functional parameters.

Gated blood-pool scans of the left ventricle are routinely employed for determination of the left ventricular ejection fraction. Recently, attempts have been made to evaluate other left ventricular functional parameters. These values include peak emptying rate (PER), time to peak emptying rate (TPER), peak filling rate (PFR), and time to peak filling rate (TPFR). In studying these parameters clinically, we identified many software errors and assumptions that impact on these values. These errors may also affect the determination of left ventricular ejection fraction (EF). We conclude that before any serious investigation of left ventricular functional parameters is undertaken, a detailed evaluation and standardization of the acquisition and edge detection algorithms must be performed.

Gamma camera radionuclide images: improved contrast with energy-weighted acquisition.

An energy-weighted acquisition (EWA) technique has been developed that utilizes all scintillation events, weighting their contributions depending on their energy, to formulate a radionuclide image. Photopeak events from primary radiation contribute positively; scatter events contribute negatively, providing for scatter subtraction and improved image contrast. EWA is employed with an on-line weighted-acquisition module (WAM) as the data are acquired, rather than as a postprocessing technique. EWA was compared with normal window imaging in patients and in phantoms. For gallium-67 and thallium-201, contrast improved by as much as 40%. A much smaller improvement in contrast was observed with technetium-99m due to its ideal monoenergetic emissions. Single photon emission computed tomographic studies also showed improved contrast and were without artifact. EWA has great promise, and with further development quantitative scatter correction may be possible.

Quality assurance in SPECT imaging.

The predominant type of single-photon emission computed tomography (SPECT) system available today is the rotating gamma camera system. These systems are complex, with many variables to control, and are prone to artifacts. To maintain optimal imaging performance, we emphasize a quality-assurance program that maintains imaging detector performance, proper mechanical alignments, periodic system calibrations, and strict adherence to imaging protocols. We urge the use of SPECT phantoms to evaluate total system performance. With SPECT phantoms, rotating camera systems with both circular and noncircular orbits can be easily evaluated. Quantitative measurements of system performance can be recorded graphically on a time chart for trend analysis, which leads to timely investigation of system failures.

The propagation of stochastic pixel noise into magnitude and phase values in the Fourier analysis of digital images.

The use of Fourier analysis in nuclear medicine gated blood pool ventriculography provides a useful example of the application of Fourier methods to digital medical imaging. In particular, the nuclear medicine experience demonstrates that there is diagnostic significance not only in the pixel averages of temporal Fourier magnitude and phase computed in various image regions, but also in the distributions of the individual pixel values about those averages. However, a region containing pixels that are perfectly synchronous on average would still yield a finite distribution of calculated Fourier coefficients due to the propagation of stochastic pixel noise into the calculated values. We have studied this noise component of both the magnitude and phase distributions using phantom studies and computer simulation. In both approaches, several thousand one-pixel 'ventriculograms' were generated, all identical to each other except for stochastic noise. Fourier magnitudes and phases at several frequencies were calculated and histograms generated. A theoretical prediction of the distributions was developed and shown to fit the experimental results well. Our formalism can be used to estimate study count requirements or, for fixed study counts, to assess the stochastic noise contribution in the interpretation of measured phase and magnitude distributions.

Validation of 3-deoxy-3-fluoro-D-glucose as a glucose transport analogue in rat heart.

Four aspects of the behavior of 3-deoxy-3-fluoro-D-glucose (D-3FDG) were studied. The distribution of label in rat tissues after intravenous administration of [18F]D-3FDG was compared with that seen with labeled 3-deoxy-3-fluoro-L-glucose (L-3FDG). Results were consistent with a larger volume of distribution for the physiological D-isomer coupled with some degree of reabsorption by the kidneys. L-3FDG, but not its D-isomer, was excluded from the brain. D-3FDG competitively inhibited uptake of glucose by isolated perfused rat hearts. The inhibition constant was 12.8 +/- 1.6 mM compared with 6.1 +/- 1.1 mM for 3-O-methyl-D-glucose. Residue curves obtained after bolus administration of [18F]D-3FDG to isolated hearts indicated phosphorylation of the tracer at a lower rate than for 2-deoxy-2-fluoro-D-glucose but with subsequent dephosphorylation at a faster rate. Chromatographic analysis of 18F remaining in tissues after administration of [18F]D-3FDG revealed in addition to free D-3FDG three other peaks. These disappeared after treatment with alkaline phosphatase and were thus assigned as phosphates. The principal metabolite had the same retention time as D-3FDG-6-phosphate prepared with hexokinase. No phosphorylated metabolites were detected in blood. D-3FDG labeled with 18F may be a useful tracer in studies of glucose transport and metabolism.

Alternative approach to single-scan estimation of cerebral glucose metabolic rate using glucose analogs, with particular application to ischemia.

In the glucose analog method for determining local glucose utilization rates, time courses of tissue and plasma radioactivity are measured and then analyzed in terms of first-order exchange of label between tissue compartments. The rate of glucose utilization is assumed to have a fixed, linear relationship to the analog phosphorylation rate calculated from the fitted rate constants. Accurate estimation of the rate constants requires many hours of dynamic data acquisition. Therefore, techniques assuming a linear relationship between analog phosphorylation rate and total tissue concentration of label were developed to predict glucose utilization rates from a single scan. Previously reported linearizations differ in their sensitivity to differences between current and average kinetic rate constants, and thus in their accuracy. We have developed a method that is insensitive to the presumed value of the blood flow-capillary wall transport parameter k1. This new single-scan approach has been validated by comparison of the single-scan metabolic rate values with the values calculated from the dynamic measurements.

Phosphorylation of glucose analog 3-O-methyl-D-glucose by rat heart.

When isolated rat hearts were perfused with medium containing 3-O-methyl-D-glucose (3MG) a compound with the chromatographic behavior expected for 3MG-6-phosphate was formed. This assignment is supported by the action of alkaline phosphatase and by production of an identical peak on incubation of 3MG with yeast hexokinase in a buffer containing adenosine triphosphate and Mg++ ions. The clearance of labeled 3MG from isolated perfused rat hearts was biphasic and eventually total. Since sugar phosphates do not cross cellular membranes, this behavior is consistent with both formation and dephosphorylation of 3MG-6-phosphate, with dephosphorylation rate-limiting the slow phase of the clearance. Phosphatase activity was also indicated by a decrease in 3MG-6-phosphate when hearts were not chilled and homogenized immediately after perfusion. The common assumption that 3MG is not metabolized after transport into cells is shown by these experiments to be erroneous.

Estimation of absolute left ventricular volume from gated radionuclide ventriculograms. A method using phase image assisted automated edge detection and two-dimensional echocardiography.

Twenty-four patients underwent gated cardiac blood pool (GBP) imaging, two-dimensional echocardiography (2-D echo), and single-plane contrast ventriculography (within 24 hours). Variable left ventricular (LV) regions of interest on GBP images were identified by an automated threshold radial search. To avoid excluding LV counts we indexed the search threshold to the threshold identified by a phase image generated by Fourier analysis. LV depth calculated by 2-D echo was used for attenuation correction of LV counts. LV end-diastolic volume (EDV) and end-systolic volume (ESV) were calculated by dividing attenuation, background and deadtime corrected LV count rates by the background corrected count rate/ml of venous blood drawn during the study. Correlations between radionuclide and contrast volumes were good (EDV + ESV r = 0.97, EDV r = 0.94, ESV r = 0.95). Regression lines were close to the lines of identity. This method, in which GBP imaging and automated LV edge finding are complemented by 2-D echo for count attenuation correction, demonstrated reliable and reproducible noninvasive estimates of absolute LV volume.