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J Machac

Publications and source records attributed to J Machac.

At least 55 records · Page 3Linked to original sources
PubMed1997

Three-window transformation cross-talk correction for simultaneous dual-isotope imaging.

UNLABELLED: We developed and tested a new transformation cross-talk correction method for simultaneous dual-isotope SPECT imaging, which uses information from three energy windows in a simultaneous 18F/99mTc cardiac phantom study. METHODS: The method combines the previously reported "three-window" technique and transformation cross-talk correction methods. In the three-window technique, the images from the third energy "scatter" window are usually multiplied by a constant factor to obtain the estimates of the cross-talk. However, such an approach neglects differences in the spatial distribution between cross-talk photons in different energy windows. The transformation method is based on the assumption that the transformations, which convert the images from one energy window into the other energy windows, are known. These transformations were found by measuring the point-spread functions in different energy windows for both isotopes in water. The transformation method takes into account the different spatial distributions of the primary and scatter cross-talk photons in the different energy windows. Here, we are assuming that the imaging system and the image transformations between different energy windows are shift-invariant and linear. Thus, the new method is described by two convolution equations applied in frequency space. In addition to the cross-talk correction, the restoration filters were also applied to the resulting corrected images. The new method was performed on the simultaneous 18F/99mTc cardiac phantom study. Three separate studies were acquired in our phantom study: two single-isotope studies and one dual-isotope study. The single-isotope images were used as references. The contrast between the left ventricle cavity and the myocardium was used in transaxial slices as a parameter to evaluate results of the dual-isotope correction method with restoration. RESULTS: The contrast improvement in the dual-isotope corrected images in both energy windows, i.e., the 99mTc primary window (140 keV) and the 18F primary window (511 keV), was significant. The corrected 511-keV, dual-isotope image had a contrast of 0.74 compared to 0.60, which was the value in the noncorrected dual-isotope image. The improvement of the contrast in the corrected, dual-isotope 511-keV image was exclusively a result of the restoration correction. The restoration-corrected, 511-keV, single-isotope 18F image had the same contrast (0.74). For the dual-isotope, 140-keV transaxial slice, first, the contrast improved from 0.78 to 0.85 after cross-talk correction, and, then, it finally reached 0.92 after additional restoration correction. The contrast in the 140-keV, single-isotope 99mTc image after restoration correction improved from 0.87 to 0.95. CONCLUSION: The three-window transformation dual-isotope correction method with restoration significantly improves the contrast between the left ventricle cavity and the myocardium of the simultaneous 18F/99mTc SPECT imaging.

Fluorine Radioisotopes↗
PubMed1996

A new iterative reconstruction technique for attenuation correction in high-resolution positron emission tomography.

A new iterative reconstruction technique (NIRT) for positron emission computed tomography (PET), which uses transmission data for nonuniform attenuation correction, is described. Utilizing the general inverse problem theory, a cost functional which includes a noise term was derived. The cost functional was minimized using a weighted-least-square maximum a posteriori conjugate gradient (CG) method. The procedure involves a change in the Hessian of the cost function by adding an additional term. Two phantoms were used in a real data acquisition. The first was a cylinder phantom filled with uniformly distributed activity of 74 MBq of fluorine-18. Two different inserts were placed in the phantom. The second was a Hoffman brain phantom filled with uniformly distributed activity of 7.4 MBq of 18F. Resulting reconstructed images were used to test and compare a new iterative reconstruction technique with a standard filtered backprojection (FBP) method. The results confirmed that NIRT, based on the conjugate gradient method, converges rapidly and provides good reconstructed images. In comparison with standard results obtained by the FBP method, the images reconstructed by NIRT showed better noise properties. The noise was measured as rms% noise and was less, by a factor of 1.75, in images reconstructed by NIRT than in the same images reconstructed by FBP. The distance between the Hoffman brain slice reconstructed by FBP and the perfect PET Hoffman brain slice created from the MRI image was 0.526, while the same distance for the Hoffman brain slice reconstructed by NIRT was 0.328. The NIRT method suppressed the propagation of the noise without visible loss of resolution in the reconstructed PET images.

Algorithms↗
PubMed1996

Variable bile retention on cholescintigraphy after morphine administration.

Intravenous morphine sulfate has been used in conjunction with cholescintigraphy. We studied the variations in the degree and duration of the effects of 2 mg morphine on biliary kinetics in patients with gallbladder nonvisualization and undertook a comparison with biliary kinetics in patients not given morphine. Of 24 morphine-augmented cholescintigrams that were obtained without additional injection of technetium-99m diisopropyl-iminodiacetic acid (DISIDA), 19 showed continued gallbladder nonvisualization. Time-activity curves (TACs) of the liver parenchyma and common bile/hepatic duct (CD) of the entire study (before and after morphine) were obtained. In two patients, the CD was not sufficiently visualized to define a region of interest. In 17 patients, the peak CD activity was observed between 14 and 47 min after injection of 99mTc-DISIDA. In these 17, the TAC of the CD was declining essentially in parallel with the TAC of the liver parenchyma at the end of the first hour before morphine. After morphine injection, CD activity slowly increased for a variable duration in nine patients, while it continued to decrease in eight. CD activity between 1 h and 2 h showed a continuously decreasing pattern in another group of 20 patients who did not receive morphine despite gallbladder nonvisualization at 1 h. In summary, no significant effect of 2 mg of intravenous morphine on biliary kinetics was detected scintigraphically in a considerable proportion of patients. Also, there was considerable variation in the duration of the effect of morphine, when such an effect was present. This observation may have significant clinical implications for morphine-augmented cholescintigraphy.

Bile↗
PubMed1996

Brain perfusion imaging during preoperative temporary balloon occlusion of the internal carotid artery.

UNLABELLED: The main objective of this study was to assess whether 99mTc-HMPAO brain SPECT imaging can identify patients at high risk of developing an infarct following permanent carotid occlusion in the course of brain surgery. METHODS: Test balloon occlusion of the internal carotid artery was performed in 44 patients with a variety of head and neck tumors or aneurysms. Technetium-99m-HMPAO was injected intravenously while the balloon was initiated and a SPECT study was obtained 30 min later. Follow-up CT scans were obtained routinely for all patients at 2 wk and 1 mo following surgery, or earlier when necessary. Thirty patients and five normal volunteers had semiquantitative analysis of cerebral perfusion. RESULTS: Twenty-six patients demonstrated ipsilateral perfusion abnormalities during trial occlusion. Eight patients in this group underwent bypass grafting prior to sacrifice of the artery: two resulting in infarcts. Eighteen patients had symmetric cerebral perfusion during occlusion and four of these patients underwent permanent therapeutic carotid occlusion; three patients had subsequent infarcts and the fourth patient had an impending stroke. CONCLUSION: Patients with symmetric cerebral perfusion measured by 99mTc-HMPAO SPECT may still have a high long-term complication rate following carotid sacrifice. The scan findings in these patients were not predictive of the outcome. Patients with asymmetric cerebral perfusion had alternative therapeutic approach to carotid sacrifice and most of them had good surgical outcomes.

Brain↗
PubMed1996

Rapid differential diagnosis of cerebral toxoplasmosis and primary central nervous system lymphoma by thallium-201 SPECT.

UNLABELLED: This study sought to assess whether 201Tl brain SPECT can significantly reduce the time required for the differential diagnosis of primary central nervous system (CNS) lymphoma and cerebral toxoplasmosis in patients with AIDS. METHODS: Eighteen patients who presented with focal lesions on CT or MRI, or both, underwent 201Tl brain SPECT shortly after admission and before a CT-guided stereotactic brain biopsy. Early and delayed 201Tl uptake ratios were obtained for patients with positive 201Tl study results, and the retention index of 201Tl was calculated. RESULTS: Ten patients had 11 foci of significantly increased 201Tl uptake in regions of corresponding CT/MRI lesions. Five of these patients had biopsy-proven lymphomas, one of them in two separate foci. Another patient was found to have metastatic adenocarcinoma. Three patients had a clinical course and response to radiation therapy consistent with lymphoma, and study results in another patient were considered falsely positive. Of nine patients with no 201Tl uptake in regions of CT/MRI lesions, two had biopsy findings consistent with a benign etiology, and the other seven improved clinically on antitoxoplasmosis medications alone. The overall sensitivity of 201Tl brain SPECT was 100%, and specificity was 90%. The 201Tl retention index in patients with lymphomas was significantly higher than that in patients with adenocarcinomas and nonmalignant lesions (1.35 +/- 0.16 versus 0.24 and 0.56, respectively). CONCLUSION: Thallium-201 brain SPECT is a sensitive and specific method for rapid differential diagnosis of CNS lymphoma and toxoplasmosis in patients with AIDS. The 201Tl retention index is useful in differentiating CNS lymphomas from other malignant and nonmalignant pathologies.

AIDS-Related Opportunistic Infections↗
PubMed1996

[Personal experience with laparoscopic hysterectomy].

The authors report their experience with 132 patients operated in the Boskovice hospital in the last two years. Their method-supracervical laparoscopic hysterectomy with removal of the cervical transformation zone and endocervix. All procedures were successfully completed laparoscopically. The authors analysed their cases according to the intraoperative, immediate postoperative and late postoperative complications. Average operating time is compatible with that of conventional total abdominal or vaginal hysterectomy and LAVH. The authors evaluated blood loss, hospital stay, recovery time, pain and cosmetic considerations. This method may be sufficient for cervical and endometrial cancer prophylaxis, because of thorough histologic examination and interpretation of morcellated cervical-cylinders and uterine body tissue.

Adult↗
PubMed1995

Imaging of multiple bilateral parotid gland oncocytomas.

Oncocytoma of the salivary glands is a rare tumor that usually follows a benign course and, in most cases, can be cured by surgical resection. The authors report a rare case of multiple bilateral parotid oncocytomas that presented clinically with two palpable parotid masses. Both CT and MRI scans demonstrated multiple masses in each parotid gland. The tumors exhibited intense uptake and prolonged retention of Tc-99m pertechnetate. The diagnosis was confirmed by fine needle aspiration. Sialoscintigraphy is a simple and noninvasive procedure that can usually separate benign entities like Warthin tumor and oncocytoma of the salivary glands from malignant tumors, and significantly affect the course of treatment.

Adenoma, Oxyphilic↗
PubMed1995

Avid uptake of technetium-99m-HMPAO by an intracranial plasmacytoma during carotid balloon test occlusion.

A 56-yr-old woman was evaluated for removal of a tumor at the base of the skull. A test to determine the risk of carotid artery sacrifice was performed prior to surgery using carotid balloon occlusion of the left internal carotid artery and 99mTc-HMPAO perfusion scintigraphy during the occlusion. An unusual intense focus of increased uptake was seen at the site of the primary tumor in the left cavernous sinus. The tumor, found to be plasmacytoma at surgery, demonstrated only mild washout from 30 min to 2 hr after administration of 99mTc-HMPAO, with a tumor-to-cerebellum ratio of 1.6 and 1.5, respectively, and a tumor-to-contralateral cranial ratio of 2.5 and 2.4, respectively. Intracranial plasmacytoma shows good response to radiation therapy, and the differentiation of this tumor from other neoplasms is pertinent to the mode of treatment and surgical approach. Technetium-99m-HMPAO SPECT imaging may be a useful tool in distinguishing these tumors from other neoplasms at the base of the skull.

Brain Neoplasms↗
PubMed1994

Cardiac stress testing with thallium-201 imaging reveals silent ischemia in individuals with paraplegia.

The purpose of this study was to determine through noninvasive arm ergometry and radionuclide tomographic imaging the presence of latent coronary heart disease (CHD) in subjects with paraplegia. Assessment of CHD in spinal cord injury, using these methods, has not been addressed previously. Twenty asymptomatic subjects with paraplegia performed arm ergometry exercise stress testing with thallium-201 single photon emission computerized tomography (SPECT) or planar myocardial imaging studies. All subjects had normal resting electrocardiograms (ECG). Only five subjects had ECG evidence of ischemia on exercise testing, whereas 13 subjects, including the five subjects with ECG positive stress tests, had scintigraphic evidence of ischemia. Thus, eight subjects would have been undiagnosed for CHD without thallium-201 SPECT imaging. These individuals had multiple risk factors for CHD and, except for age, were without a statistically significant difference between the groups with positive or negative thallium stress imaging studies. Arm ergometry stress thallium imaging shows a high prevalence of ischemia in subjects with paraplegia.

Adult↗
PubMed1994

Clinical utility of technetium-99m-teboroxime myocardial washout imaging.

UNLABELLED: The purpose of this study was to evaluate the clinical utility of 99mTc-teboroxime myocardial washout imaging. The differential washout after a single tracer injection has been proposed as an alternative for characterization of the perfusion defects. METHODS: Fifty-six patients received 5-min adenosine infusion. The stress dose of 99mTc-teboroxime was injected at 4.5 min and stress imaging with a single-headed SPECT gamma camera was started at 6 min, washout imaging followed immediately. At 20 min, the rest tracer dose was injected at rest and imaging was started at 21.5 min. The reversibility of the perfusion defects on the washout and rest images was compared visually and quantitatively. RESULTS: There was no statistical difference in the number of stress defects that improved on the washout and rest images. The visual interpretation of the perfusion abnormalities was confirmed by quantitative analysis of relative segmental activity. CONCLUSION: Thus, 99mTc-teboroxime-adenosine washout myocardial perfusion imaging can be safely and quickly accomplished. Detected reversibility of the perfusion defects did not significantly differ from reversibility observed on the rest images.

Adenosine↗
PubMed1993

Coronary bypass with ejection fraction of 0.20 or less using centigrade cardioplegia: long-term follow-up.

Forty-two patients with an ejection fraction of 0.20 or less underwent coronary artery bypass grafting from 1986 to 1990 using a method of myocardial protection we term "centigrade cardioplegia," combining single-dose, cold, crystalloid cardioplegia, systemic hypothermia, and local hypothermia. Thirty-day mortality was 4.8% (2/42). Perioperative morbidity included two myocardial infarctions (4.8%) and one stroke (2.4%), which fully resolved. Postoperative left ventricular function improved (left ventricular ejection fraction, 0.157 +/- 0.028 to 0.226 +/- 0.085; p < 0.0002), as did New York Heart Association class (3.4 +/- 0.73 to 1.8 +/- 0.63; p < 0.0001) and Canadian class (3.3 +/- 0.81 to 0.61 +/- 0.92). Survival, 88% at 1 year, declined to 68% at 3 years and 34% at 6 years. This high-risk group had very acceptable short-term results, indicating adequate intraoperative myocardial protection. Four clinical variables were associated with long-term survival: (1) chief complaint of pain only (p = 0.05), (2) history of unstable angina (p = 0.04), (3) Canadian class less than IV (p = 0.05), and (4) New York Heart Association class less than IV (p = 0.05). Reduced survival, although not statistically significant (p = 0.07), was noted for right ventricular ejection fraction of 0.30 or less. These factors may help predict which patients with severe left ventricular dysfunction will benefit from revascularization.

Angina Pectoris↗
PubMed1993

Tomographic thallium-201 myocardial perfusion imaging after intravenous dipyridamole in asymptomatic subjects with quadriplegia.

Cardiovascular disease is the leading cause of mortality in those with a spinal cord injury (SCI). As a consequence of changes in body composition and level of activity, individuals with a SCI tend to have a high prevalence of multiple risk factors for coronary artery disease (CAD). In this report, we have demonstrated the usefulness of tomographic thallium-201 myocardial perfusion imaging after intravenous dipyridamole in six clinically asymptomatic subjects with quadriplegia. The average age of the subjects was 47 +/- 2 years, and they had a duration of injury of 15 +/- 2 years. On average, the individuals had five risk factors for CAD. After intravenous administration of dipyridamole and mild upper extremity exercise, the subjects reported no adverse symptoms and had no electrocardiographic evidence suggestive of ischemia. By contrast, three of the six subjects had reversible defects noted on thallium scintigraphy, and one additional subject had a fixed defect that was suggestive of infarction. The remaining two subjects had abnormal scans with fixed defects of the inferioposterior region, which may be ascribed to diaphragmatic attenuation, perhaps a result of partial diaphragmatic paralysis. Thus, dipyridamole thallium myocardial imaging is a safe and effective noninvasive method for the detection of myocardial ischemia or infarction in individuals with quadriplegia who are at increased risk for CAD.

Adult↗
PubMed1993

Detection of silent left ventricular dysfunction during daily activities in coronary artery disease patients by the nuclear VEST.

Myocardial ischemia during routine daily activities was studied in patients with known coronary artery disease with an ambulatory radionuclide probe and recording device (VEST) and routine rest and exercise gated blood pool imaging. Seventeen patients were monitored for 60 minutes while sitting (baseline), standing in place, walking, eating (6 patients), and urinating (4 patients). Eleven of them (64%) failed to show an augmentation of at least 5% in the LVEF on an exercise gated blood pool imaging study (Group I) and 6 (36%) showed a normal response (Group II). Three patients (18%) in Group I experienced angina. Transient left ventricular dysfunction was detected by the VEST during walking, urinating or eating in 80% of the patients in Group I and 33% in Group II (p < 0.05). During walking, mean ejection fraction slightly decreased from 45 +/- 12% to 43 +/- 13% in Group I while the ejection fraction increased from 46 +/- 8% to 51 +/- 12% in Group II (p = 0.04 for the difference in responses). Standing in place and eating did not affect the mean ejection fraction. Urination in 4 patients in Group I caused a significant drop in ejection fraction in 3 patients for a mean change from 51 +/- 9% at rest to 42 +/- 15%. By contrast, none of the patients had angina or diagnostic ECG changes during the monitoring period.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Exercise-induced myocardial dysfunction in patients with coronary artery disease with and without angina.

Left ventricular dysfunction during exercise is considered a relatively sensitive marker of ischemia in patients with coronary artery disease. The purpose of this study was to determine whether exercise-induced myocardial dysfunction was more severe in patients with angina than in patients with ischemia without angina. Seventy-seven patients with angiographically documented coronary artery disease and an abnormal left ventricular response to exercise were studied by means of gated blood pool imaging. The arteriographic and functional parameters of 24 patients with angina during exercise testing imaging. The arteriographic and functional parameters of 24 patients with angina during exercise testing were compared with those of 53 patients who were pain free at the time of the test. Both groups were similar with regard to rate of multivessel disease (50% vs 51%, p = NS) and prior myocardial infarction (46% vs 51%, p = NS), as well as age, sex, and history of angina. Mean global ejection fraction remained unchanged (but abnormal) in both groups of patients during exercise. Furthermore, evidence of new regional asynergy during exercise assessed by a five-point scoring system was found to be equally abnormal in the two groups. Results of this study suggest that the severity of exercise-induced global and regional left ventricular dysfunction is independent of the presence of absence of angina during exercise testing.

Angina Pectoris↗
PubMed1991

Clinical and electrophysiologic determinants, treatment and survival of patients with sustained malignant ventricular tachyarrhythmias occurring late after myocardial infarction.

To assess the clinical and electrophysiologic determinants, treatment and survival of patients with sustained malignant ventricular tachyarrhythmias late after myocardial infarction, a total of 108 patients (mean age 61 +/- 10 years) were studied. Thirty-two patients (Group I) had sustained ventricular tachyarrhythmias 8 to 60 days (mean 13 +/- 9) after acute myocardial infarction. The remaining 76 patients (Group II), who served as a control group, had no sustained ventricular tachyarrhythmias less than or equal to 60 days after infarction. The most significant independent determinants of sustained ventricular tachyarrhythmias late after infarction were the presence of late potentials (chi square = 16.07, p = 0.0001), defined as an abnormal signal-averaged QRS complex in association with an abnormal root-mean-square voltage in the terminal 40 ms of the QRS complex, and an abnormal ejection fraction of less than 40% (chi square = 10.09, p = 0.001). Sustained ventricular tachycardia was induced in 27 (96%) of 28 Group I patients. Among the 32 patients in Group I, antitachycardia therapy included antiarrhythmic drug therapy as the sole preventive measure in 14 (44%); map-guided surgery or coronary artery bypass surgery, or both, in 14 (44%) and the automatic cardioverter-defibrillator in 4 (12%). The arrhythmias were rendered noninducible in 83% of patients after map-guided surgery and in 41% after drug therapy. During a follow-up period of 20 +/- 14 months, five Group I patients (15%) had an arrhythmic event and four (9.3%) had a cardiac-related death. All five patients who had an arrhythmic event were receiving antiarrhythmic drug therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Anti-Arrhythmia Agents↗