Use of the Internet for teaching in nuclear medicine.

The Internet provides several new capabilities for education in nuclear medicine, including learning at a distance, facilitation of collaboration, increased availability of training resources, and ability to develop interactive teaching materials. Dedicated case-authoring software aided development of digital teaching files at the Mallinckrodt Institute of Radiology and the Joint Program in Nuclear Medicine. Accesses to these two teaching files from sites around the world have grown rapidly. Improvements in the speed of the Internet will allow inclusion of more images at higher resolution and more extensive use of cine. Development of server-based software will allow simulation of the actual image-reading environment. A better understanding of how to use this new media will spur continued expansion in use of the Internet for nuclear medical education.

Diagnostic management of venous thromboembolism.

The accuracy of diagnostic methods for the diagnosis of deep vein thrombosis and pulmonary embolism in symptomatic patients is critically reviewed. In addition, the safety of withholding anticoagulant therapy from patients with suspected deep vein thrombosis or pulmonary embolism in whom the qualified diagnostic strategy was normal is evaluated by determining the frequency of venous thromboembolic complications during 3 months of follow-up. It is shown that the currently used available diagnostic techniques for deep vein thrombosis are all able to identify the majority of patients who indeed have venous thrombosis. However, as result of its accuracy and practical advantages, compression ultrasound is the test of choice in the evaluation of symptomatic patients. Patients with a normal test outcome should be re-tested to detect the small proportion of patients with proximally extending calf vein thrombosis. In the strategy of repeated diagnostic testing, impedance plethysmography could be used as an alternative to ultrasonography. To obtain a reduction in repeat tests various diagnostic strategies have been evaluated and it was shown that these strategies, using non-invasive tests, can be as accurate and safe as the invasive reference strategy. The safeties of the various strategies were very similar; however, important differences were observed with respect to the practical implementation of the various diagnostic strategies. Simplification of the repeated testing strategy by using a D-dimer assay and/or a clinical decision rule seems to be promising. The reference standard for the diagnosis of pulmonary embolism remains pulmonary angiography. Several strategies based on non-invasive diagnostic methods have been evaluated for their safety and complexability. Perfusion-ventilation lung scanning is the most thoroughly evaluated non-invasive technique so far. It seems safe to withhold anticoagulant therapy in patients suspected of pulmonary embolism with a normal perfusion lung scan result; however, further testing is needed in the case of a non-diagnostic perfusion-ventilation lung scan result. At this moment angiography is the method of choice in this category of patients. D-dimer assays, clinical decision rules and ultrasound examinations of the legs seem to have a high potential to limit the need for angiography. Also, spiral computerized tomography and magnetic resonance imaging are promising techniques, but their role in the diagnostic management of pulmonary embolism is still uncertain.

[Reserve concerning pulmonary angiography in pulmonary embolism is not justified]. / Terughoudendheid ten aanzien van pulmonalisangiografie bij longembolie niet terecht.

OBJECTIVE: Evaluation of the safety of pulmonary angiography in patients with clinically suspected pulmonary embolism. DESIGN: Retrospective cohort study. SETTING: Academic Hospital, Rotterdam, the Netherlands. METHOD: The data on complications of pulmonary angiography were collected from four Dutch hospitals over a period of about five years (Academic Medical Centre and Slotervaart Hospital, Amsterdam; St. Elisabeth Hospital, Tilburg and Dr. Daniel den Hoed Cancer Centre/University Hospital Rotterdam). RESULTS: Pulmonary angiography was performed in 697 patients. No fatal complications were noted (mortality: 0%; 95% confidence interval (95% CI); 0.00-0.53). Complications were seen in 3 patients; dissection of the pulmonary artery in I patient and contrast extravasation in 2 patients (morbidity: 0.4%; 95% CI: 0.09-1.25). CONCLUSION: In patients with clinically suspected pulmonary embolism, pulmonary angiography is a safe diagnostic modality. It is recommended that, in patients in whom the diagnosis of pulmonary embolism cannot be confirmed or excluded by noninvasive diagnostic methods, pulmonary angiography should be performed (according to the Dutch consensus "Diagnostic pulmonary embolism').

An optimal rotator for iterative reconstruction.

For implementations of iterative reconstruction algorithms that rotate the image matrix, the characteristics of the rotator may affect the reconstruction quality. Desirable qualities for the rotator include: 1) preservation of global and local image counts; 2) accurate count positioning; 3) a uniform and predictable amount of blurring due to the rotation. A new rotation method for iterative reconstruction is proposed which employs. Gaussian interpolation. This method was compared to standard rotation techniques and is shown to be superior to standard techniques when measured by these qualities. The computational cost was demonstrated to be only slightly more than bilinear interpolation.

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.

An Internet-based nuclear medicine teaching file.

UNLABELLED: Teaching file cases play an important role in the training of nuclear medicine residents; however, film-based teaching files have limitations, such as difficulty in accessing cases in a department with several remote clinical sites. The goal of this project was to develop a digital teaching file with the capability for local and remote (Internet) network access, with the additional requirements that viewing existing cases and addition of new cases be easy and simple. METHODS: The teaching file software (TF-Web) utilizes applications developed for the World-Wide-Web in combination with locally developed programs for importing images, entering case information, indexing, searching, case selection and case editing. The time required to add cases to the TF-Web and to access existing cases from local and remote network sites as well as computer storage requirements were assessed. RESULTS: Cases entered in TF-Web may be viewed either with or without diagnoses and may be accessed with acceptable speed (2-14 sec) from both local and remote network sites. A relatively complex case required 1.2 megabytes of storage, with lesser storage requirements for simpler cases. CONCLUSION: A digital teaching file has been developed that allows easy access from computers located both locally and elsewhere on the Internet. Digital storage requirements are reasonable, and, because of the unique nature of TF-Web, case storage may be distributed among multiple institutions.

Use of the selective linogram in cardiac tomography quality control.

BACKGROUND: Quality control for detection of patient motion is essential in tomographic myocardial imaging. Despite significant limitations, the summation image or conventional "linogram" has long been advocated as a useful image in the detection of vertical motion. In this study a new quality control image entitled the "selective linogram" is proposed to replace the summation image in routine cardiac single-photon emission cardiac tomography (SPECT) quality control. The selective linogram is constructed in a manner somewhat analogous to the sinogram. In the sinogram, each row represents a different projection angle; in the selective linogram each column represents a different projection angle. METHODS AND RESULTS: After selection of eight motion-free studies from acquisitions at our clinical center, vertical motion of various types (bounces, shifts, and creep) were added to the projection frames. Summation image and selective linogram quality control images from these motion-containing studies and the original motion-free studies were presented in a blinded manner to two observers for scoring of patient motion. The selective linogram was significantly more accurate in allowing detection of vertical motion than was the summation image (accuracy 89% vs 47%). CONCLUSIONS: The selective linogram image is markedly superior to the summation image for the detection of vertical patient motion during cardiac SPECT. This new technique can be a valuable aid in SPECT quality control.

Increased sensitivity through use of overlapping 180 degrees orbits in clinical myocardial perfusion imaging.

Clinical cardiac imaging is hindered by noise due to limited activity and imaging time. Use of 90 degrees dual-detector systems with 90 degrees gantry rotation may provide the best sensitivity/resolution for cardiac imaging, but this option is not readily available to those using a triple-detector system with detectors at 120 degrees intervals. This study utilizes a cardiac/chest phantom to compare several triple-detector orbits, with assessment of sensitivity and resolution. A 180 degrees rotation with reconstruction of two of the three heads was evaluated, resulting in overlapping 180 degrees orbits; use of a starting angle of 165 degrees for the first head placed the overlapping portion of the orbits over the LAO myocardial region, where camera-cardiac distance is most favorable. Use of this overlapping orbit yielded resolution equivalent to a conventional (single-head) 180 degrees rotation. Sensitivity was 87%-90% of that of a 90 degrees dual-detector system, and 16%-20% better than the common practice of using a 120 degrees orbit with reconstruction of 1 1/2 heads to achieve 180 degrees of data. Use of 360 degrees acquisition with reconstruction of all three heads provided the greatest sensitivity, though at the expense of some loss in image quality. Thus, for those centers performing cardiac imaging using a triple-detector system, use of overlapping 180 degrees orbits is the preferred acquisition choice.

Attenuation correction in cardiac SPECT without a transmission measurement.

UNLABELLED: The accuracy of SPECT cardiac perfusion imaging is impaired by artifacts induced by nonuniform gamma-ray attenuation. This study proposes a method to estimate attenuation in the chest of patients without the additional hardware and expense of transmission imaging. METHODS: After the standard 201Tl or 99mTc-sestamibi delayed images were obtained, 99mTc macroaggregated albumin (MAA) was injected and dual-energy SPECT acquisition was performed with windows centered at 140 keV and 94 keV. Lung contours were obtained by thresholding the on-peak (140 keV) reconstructions. Outer body contours were defined from images produced by reconstruction of the lower energy scatter window obtained simultaneously at the time of the lung (MAA) imaging. Following assignment of standard attenuation values to the lung and nonlung (soft tissue) regions attenuation correction was achieved by means of a modified iterative Chang algorithm. The results were quantitatively evaluated by imaging of a cardiac phantom filled with uniform activity placed in a chest phantom. Sensitivity to the choice of lung and soft tissue attenuation values, the choice of the threshold used for lung segmentation, and errors in registration of the attenuation map were assessed. RESULTS: Application of this technique in a chest phantom and in patients imaged with both 201Tl and 99mTc-sestamibi resulted in improvement in artifactually decreased inferior wall activity without adversely affecting the other walls. The results were relatively insensitive to choice of values for lung and soft-tissue attenuation, lung thresholding, and small (< or = 1.3 cm) registration errors. CONCLUSION: This simple method corrects for nonuniform attenuation in males; studies are underway to adapt the method to determine breast contour in females and to determine the value of the method in clinical practice.

Evidence for a nucleotide-dependent topoisomerase activity from yeast mitochondria.

Yeast mitochondria were found to contain a novel topoisomerase-like activity which required nucleoside di- or tri-phosphates as a cofactor. ADP supported activity as effectively as ATP and the optimal concentration for each was approximately 20 microM. None of the other standard ribo- or deoxyrib-onucleotides could fully substitute for either ADP or ATP. The non-hydrolyzable ATP analogs, adenosine-5'-0-(3-thiotriphosphate) (ATP-gamma-S), adenylyl (beta,gamma-methylene) (AMP-PCP), and andenyl-imidodiphosphate (AMP-PNP) also supported activity suggesting that the nucleotide cofactor regulated topoisomerase activity rather than serving as an energy donor in the reaction. The mitochondrial topoisomerase activity relaxed both positively and negatively supercoiled DNA. It was not inhibited by concentrations of ethidium bromide up to 2 micrograms/ml nor by either nalidixic or oxolinic acids; novobiocin, coumermycin, and berenil inhibited the activity. Genetic and biochemical analysis of the mitochondrial topoisomerase activity indicated that it was not encoded by the nuclear TOP1, TOP2, and TOP3 genes.

Immunoscintigraphy with a new indium-111-labeled monoclonal antibody (MAb 1A3) in patients with colorectal cancer.

PURPOSE: This study was designed to evaluate a new anticolorectal carcinoma monoclonal antibody (1A3), conjugated with the bifunctional chelating agent N,N'-bis(2-hydroxybenzyl)1(4-bromoacetamidobenzyl)1,2-ethylenediam ine-N,N'- diacetic acid and labeled with indium-111, in a Phase I/II study involving 38 patients with localized or advanced colorectal cancer. METHODS: Patients were injected with indium-111-N,N'-bis(2-hydroxybenzyl) 1(4-bromoacetamidobenzyl)1,2-ethylenediamine-N,N'-diacetic acid-monoclonal antibody 1A3 (1-50 mg, 1-5 mCi) and imaged at two or three sessions one to five days later. Scintigraphic findings were compared with radiologic, pathologic, surgical, and other clinical findings to assess the accuracy of radioimmunoscintigraphy. RESULTS: At least one known tumor site was clearly defined by planar scintigraphy in 29 (76 percent) patients. Increased radioactivity was seen in 40 of 63 known tumor sites (37/43 abdominal-pelvic, 3/15 hepatic, and 0/5 pulmonary sites) without any apparent dose-related effects. Nineteen previously undetected sites were considered positive by imaging, and, of these, six were biopsy-proven tumor sites, four were probable tumor sites, three were definitely false positive sites, and six were probable false positive sites. Radioimmunoscintigraphy detected proven tumor in 15 of 16 patients with negative or equivocal computed tomography results. Of of the 28 patients with rectosigmoid cancer, 25 (89 percent) had positive studies with 34 of 47 tumor sites showing definite uptake on the scintigrams. This included 3 of 9 hepatic metastases. The only adverse reaction occurred in one patient who developed transient hives. Human anti-mouse antibody responses occurred in approximately one-half of the patients injected with doses of 10 or 50 mg. CONCLUSION: This study shows that radioimmunoscintigraphy with this indium-111-labeled monoclonal antibody is safe, it can detect most nonhepatic abdominal-pelvic tumors with a positive predictive value of 83 (44/53) percent, and it should prove to be useful, particularly in the diagnosis of recurrent rectal carcinoma.

Measurement of global and regional left ventricular function by cardiac PET.

UNLABELLED: To permit assessment by positron tomography of left ventricular mechanical function, methods were developed to measure ejection fraction and regional wall motion and produce realistic images of the beating heart from ECG-gated PET data. METHODS: Following red cell labeling with 15O-carbon monoxide, seven-slice PET data were collected in list mode and reformatted into 16 time frames. Volume-rendered cine images were created by the depth-weighted maximum-activity method. To determine the left ventricular ejection fraction, background was subtracted in voxels outside the heart and the cubic datasets were rotated to the angle with the best septal separation. Depth weighting was applied to stimulate a 99mTc study, and the beating images were rendered by summing counts along parallel projection rays. These techniques were validated in 16 patients by comparison with planar studies performed with 99mTc-red cells. RESULTS: Visual grading of regional wall motion yielded exact agreement between the PET and 99mTc methods in 62% of walls with agreement with one grade in 94%. Assessment of quantitative regional wall motion agreed closely with an independent threshold edge detection method. CONCLUSION: PET techniques have been developed to measure left-ventricular ejection fraction and regional wall motion and to produce realistic beating images of the cardiac blood pool. This information can be obtained at the same time as measurements of perfusion and metabolism and in the same spatial orientation, thereby permitting quantitative assessment by positron tomography of global and regional mechanical function in relation to flow and metabolism.

Massively parallel computers for 3D single-photon-emission computed tomography.

Since the introduction of the expectation-maximization (EM) algorithm for generating maximum-likelihood (ML) and maximum a posteriori (MAP) estimates in emission tomography, there have been many investigators applying the ML method. However, almost all of the previous work has been restricted to two-dimensional (2D) reconstructions. The major focus and contribution of this paper is to demonstrate a fully three-dimensional (3D) implementation of the MAP method for single-photon-emission computed tomography (SPECT). The 3D reconstruction exhibits an improvement in resolution when compared to the generation of the series of separate 2D slice reconstructions. As has been noted, the iterative EM algorithm for 2D reconstruction is highly computational; the 3D algorithm is far worse. To accommodate the computational complexity, we have extended our previous work in the 2D arena and demonstrate an implementation on the class of massively parallel processors of the 3D algorithm. Using a 16000 processor MasPar machine, the algorithm is demonstrated to execute at 1.24 s/EM iteration for the entire 64 x 64 x 64 cube of 64 planar measurements obtained from the Siemens Orbiter rotating camera operating in the high-resolution mode.

Rapidly converging iterative reconstruction algorithms in single-photon emission computed tomography.

Iterative reconstruction algorithms with markedly different convergence rates have been proposed in single-photon emission computed tomography (SPECT). Several new iterative reconstruction methods are described in this investigation. Differences between the methods include whether a ramp filter was used during backprojection, the type of backprojection weighting and whether camera and collimator blur were employed in the projection step. Simulated and real cylindrical phantoms with rod inserts were used to compare the properties of convergence and resolution following reconstruction by maximum likelihood (ML), iterative-Chang and the newly proposed reconstruction methods. Resolution was assessed after kernel-sieve regularization to achieve the same signal-to-noise ratio for all methods. Compared with maximum-likelihood reconstruction, methods employing a ramp converged much faster. One such method resulted in images with the same resolution and noise as ML, thus permitting termination of reconstruction at 14 iterations rather than the 1000 iterations required with ML. The major determinants of resolution were found to be use of an accurate model of the gamma camera imaging process in the projection step and inclusion of attenuation weighting and depth-dependent blur in the backprojection step. In summary, a new iterative reconstruction method was developed incorporating attenuation and blur and using a ramp filter that achieved results comparable to maximum-likelihood reconstruction in a fraction of the time.