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Biomedical subjects

R T Go

Publications and source records attributed to R T Go.

At least 37 records · Page 2Linked to original sources
PubMed1994

Planar imaging with single-head large-field-of-view cameras: are they still the workhorse?

The large-field-of-view (LFOV) scintillation camera was developed in 1975 with a field of view 50% larger than the conventional camera used at that time. Not only was the new model more adaptable to large-area imaging needs, such as lungs, bone, liver, and spleen, but it could be used for small-organ imaging with a converging collimator that yielded both high resolution and high efficiency. LFOV cameras still offer the most flexibility for all of the common procedures encountered in the nuclear medicine clinic. For those installations performing up to approximately 13 procedures a day, two LFOV cameras can handle the patient load, and little advantage would be gained by the use of the multihead cameras. For the busy laboratories, however, the increased patient throughput would be the primary advantage of the multihead systems. Dual LFOV systems offer an advantage in time for whole-body imaging procedures, and three-head systems in many installations have been devoted to myocardial perfusion and brain SPECT. Although the LFOV camera is still the dominant imaging device in nuclear medicine, it is expected that in the future more procedures will gravitate to the dedicated two and three multihead system, particularly with the increasing applications of both SPECT and quantification to conventional nuclear medicine procedures.

Gamma Cameras↗
PubMed1994

Primary hyperparathyroidism: preoperative parathyroid imaging with regional body FDG PET.

PURPOSE: To explore the feasibility of use of positron emission tomography (PET) with 2-[fluorine-18]-fluoro-2-deoxy-D-glucose (FDG) to localize abnormal parathyroid tissue. MATERIALS AND METHODS: Regional body FDG PET with attenuation correction was performed in 17 adult patients with primary hyperparathyroidism (HPT) prior to surgical neck exploration. The regional body FDG PET results were correlated with surgical and histopathologic findings. RESULTS: Surgical neck exploration revealed 18 parathyroid adenomas in 16 patients and four hyperplastic parathyroid glands in one patient. Regional body FDG PET allowed correct localization of 17 of the 18 parathyroid adenomas (94% sensitivity) and two of the four hyperplastic parathyroid glands (50% sensitivity). Three false-positive FDG PET findings were encountered, including two follicular thyroid adenomas. CONCLUSION: Regional body FDG PET is a promising procedure for preoperative localization of pathologic parathyroid tissue in patients with primary HPT.

Adenoma↗
PubMed1994

Prognosis of patients with left ventricular dysfunction, with and without viable myocardium after myocardial infarction. Relative efficacy of medical therapy and revascularization.

BACKGROUND: The uptake of F-18 deoxyglucose into dysfunction segments after myocardial infarction identifies metabolically active (FDG+) or inactive (FDG-) myocardium. Although patients with FDG+ segments have been found to be at risk for adverse events, the prognostic significance of viable myocardium in relation to other influences on postinfarction prognosis, including revascularization, remain ill defined. The purpose of this study was to investigate the relative prognostic significance of FDG+ tissue and to establish whether myocardial revascularization in patients with viable tissue attenuates the risk of adverse outcome. METHODS AND RESULTS: One hundred thirty-seven patients with left ventricular dysfunction and resting perfusion defects after myocardial infarction underwent positron emission tomography with both dipyridamole stress Rb-82 perfusion imaging and FDG imaging. After the exclusion of 4 patients proceeding to transplantation, 2 with uninterpretable scans and 2 lost to follow-up, 129 patients were followed clinically for 17 +/- 9 months. Four groups were defined: patients with FDG+ dysfunctional myocardium who were revascularized (n = 49) or treated medically (n = 21) and those with FDG- segments who were revascularized (n = 19) or treated medically (n = 40). The groups of patients with FDG+ or FDG- findings, with and without revascularization, did not differ with respect to known determinants of postinfarction prognosis: age, left ventricular ejection fraction, or the prevalence of multivessel disease. Nonfatal ischemic events occurred in 48% of medically treated FDG+ patients compared with 8% of revascularized patients with FDG+ tissue (P < .001) and 5% of patients with FDG- myocardium (P < .001). Thirteen patients died from cardiac causes; 11 (85%) had a left ventricular ejection fraction of < 30%, and these patients were evenly distributed between FDG+ and FDG- groups. Using Cox's proportional hazards model, only the presence of FDG+ myocardium (odds ratio, 12.9; P < .001) and the absence of revascularization (odds ratio, 5.8; P = .002) independently predicted ischemic events, while only age (P = .02) and ejection fraction (P < .001) but not the presence of viable myocardium were predictive of death. CONCLUSIONS: Residual viable myocardium after myocardial infarction may act as an unstable substrate for further events unless it is revascularized. Despite this association, age and left ventricular dysfunction remained the strongest predictors of cardiac death after myocardial infarction in these patients with a spectrum of left ventricular dysfunction.

Aged↗
PubMed1994

Current status of the clinical applications of cardiac positron emission tomography.

At the present time, positron emission tomography (PET) has evolved into an accurate clinical diagnostic imaging procedure for coronary artery disease that provides unique information, presently unavailable from other imaging modalities, for the management of patients with previous myocardial infarction. The superior accuracy of PET for the diagnosis of coronary artery disease has had a positive influence on the management decision process to perform revascularization. In addition to the superior accuracy of PET compared with single photon emission computed tomography, PET has the advantage of being able to identify viable hibernating myocardium.

Animals↗
PubMed1993

Parametric phase display for biventricular function from gated cardiac blood pool single-photon emission tomography.

Complete assessment of biventricular function from planar ECG-gated cardiac blood pool studies has been limited because of the overlap of adjacent activity-containing structures. Theoretically, single-photon emission tomography (SPET) can be used to comprehensively evaluate both ventricles by isolating them from surrounding anatomy. However, an enormous amount of parametric data is generated from gated SPET studies, and much of it is diagnostically irrelevant for ventricular wall motion analysis. To compress this information to a more easily interpretable format, a two-dimensional parametric display has been developed. Fourier analysis of short-axis tomograms from a gated cardiac blood pool SPET study generates three-dimensional, first-harmonic phase data. Circumferential profile data from the parametric tomograms of the right and left ventricle are mapped onto a two-dimensional polar display. This method is demonstrated in a normal patient and in three patients with abnormal ventricular contraction patterns and appears to have potential application for the analysis and characterization of biventricular wall motion.

Aged↗
PubMed1993

Pulmonary embolism: increased ventilation in areas of decreased perfusion.

An abnormal finding that is considered characteristic of large or extensive pulmonary embolism has been observed on ventilation-perfusion (V-P) lung scans. This observation is a regional area of increased ventilation radioactivity in the embolized region of the lung that is more than the normal ventilation radioactivity in the adjacent or contralateral normally perfused lung. It has been designated the "enhanced V-P mismatch sign." This sign was noted in 15 cases among approximately 700 routine V-P lung scans interpreted by a nuclear radiologist. Of these, large or extensive emboli were confirmed in only 10 cases, nine by means of angiography and one by means of autopsy studies. The remaining five cases demonstrated clinical correlation only and are not included in this report. Of the 10 confirmed cases with enhanced V-P mismatch sign, increased ventilation radioactivity involved unilateral lung distribution in five and zonal or lobar distribution in five. The Westermark sign was seen in only seven of the 10 cases. It is hoped that this observation will prove useful in the diagnosis of large or extensive pulmonary emboli.

Adult↗
PubMed1993

Clinical outcome of cardiac patients with negative thallium-201 SPECT and positive rubidium-82 PET myocardial perfusion imaging.

In a previous comparison of 202 consecutive patients who underwent myocardial perfusion imaging with both 201Tl SPECT and 82Rb PET, 27 patients were identified as having true-positive 82Rb images, but false-negative 201Tl images. The purpose of this report is to determine the effect of correct image interpretation of coronary artery disease on the final management of those patients and compare it to the previous management scheme wherein a negative image was usually accepted as the end point unless clinical symptoms dictated otherwise. A follow-up study of the clinical course and outcome of these studies showed that 63% (17/27) of the patients with a true-positive 82Rb PET image were recommended for revascularization procedures. It is doubtful that this majority of patients would have received either surgical or interventional management based on the false-negative 201Tl SPECT procedure alone.

Angioplasty, Balloon, Coronary↗
PubMed1992

Identification of recurrent ischemia after coronary artery bypass surgery: a comparison of positron emission tomography and single photon emission computed tomography.

Current techniques for the detection of recurrent coronary stenoses following bypass grafting have shown disappointing diagnostic accuracy. This study used the same dipyridamole-handgrip stress to compare the accuracy of rubidium-82 positron emission tomography and thallium-201 single photon emission computed tomography, in 50 consecutive post-bypass patients undergoing coronary arteriography at a mean interval of 6.5 years after surgery. Significant stenoses in native coronary vessels (greater than 50% diameter) or grafts (greater than 70% diameter) were defined by quantitative angiography. Forty-six patients had recurrent or residual stenoses, 43 (93%) had a perfusion defect identified by positron emission tomography, and 35 (76%) were identified by single photon emission computed tomography (P = 0.04). Fourteen of the 17 patients (82%) without previous Q-wave myocardial infarction were identified by positron emission tomography; 10 of the 17 (59%) were detected by single photon emission computed tomography (P = NS). Stress-induced perfusion defects were demonstrated by positron emission tomography in 19 patients; of this group, thallium imaging identified reversible defects in 11, showed no perfusion defect in 1, and portrayed a persistent defect in 7 patients. Significant graft disease was present in 33 patients; perfusion defects were identified by positron emission tomography in 30 (91%), and by single photon emission computed tomography in 24 (73%, P = NS). Four patients were fully revascularized, without significant recurrent coronary disease; normal perfusion was present in 3 (75%) by positron emission tomography, and 4 (100%) by single photon emission computed tomography.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Radiopharmaceucticals for cardiovascular imaging.

Radionuclide cardiac imaging is a noninvasive technique routinely used to detect coronary artery disease (CAD). This imaging modality includes techniques such as planar, single photon emission computed tomography (SPECT), positron emission tomography (PET) and radionuclide ventriculography--each technique having unique features of its own. Each technique employs various radiopharmaceuticals suitable for assessing different physiological and functional parameters that may become abnormal in the presence of CAD. Various cardiac imaging techniques include myocardial perfusion or blood flow, myocardial metabolism and cardiac function and wall motion. While radionuclide ventriculography gives the global functional status of the heart, SPECT and PET techniques provide information as to the regional blood flow and metabolic status of the myocardium. The following is a review of radiopharmaceuticals that are utilized clinically and in research in different types of nuclear cardiac imaging. Radiopharmaceuticals have been grouped according to the technique employed in which they are used. Various characteristics, merits and disadvantages of each radiopharmaceutical are discussed in detail.

Animals↗
PubMed1992

Cyclotrons and positron emission tomography radiopharmaceuticals for clinical imaging.

Positron emission tomography (PET) requires positron-emitting radionuclides that emit 511-keV photons detectable by PET imagers. Positron-emitting radionuclides are commonly produced in charged particle accelerators, eg, linear accelerators or cyclotrons. The most widely available radiopharmaceuticals for PET imaging are carbon-11-, nitrogen-13-, and oxygen-15-labeled compounds, many of which, either in their normal state or incorporated in other compounds, serve as physiological tracers. Other useful PET radiopharmaceuticals include fluorine-18-, bromine-75-, gallium-68 (68Ga)-, rubidium-82 (82Rb)-, and copper-62 (62Cu)-labeled compounds. Many positron emitters have short half-lives and thus require on-site cyclotrons for application, and others (68Ga, 82Rb, and 62Cu) are available from radionuclides generators using relatively long-lived parent radionuclides. This review is divided into two sections: cyclotrons and PET radiopharmaceuticals for clinical imaging. In the cyclotron section, the principle of operation of the cyclotron, types of cyclotrons, medical cyclotrons, and production of radionuclides are discussed. In the section on PET radiopharmaceuticals, the synthesis and clinical use of PET radiopharmaceuticals are described.

Brain↗
PubMed1992

Myocardial perfusion imaging in the diagnosis of coronary artery disease.

The role of myocardial perfusion imaging has been extended from diagnosis to management and prognosis in patients with coronary artery disease. Great emphasis has been placed on improving the accuracy of the test to better define perfusion, viability, and the extent of damage of the myocardium. To achieve this goal, investigators have focused on several areas including imaging technique, in which the accuracy of single-photon emission CT has been compared with that of positron emission tomography; radiopharmaceuticals, in which 201Tl has been compared with 99mTc-sestamibi and 99mTc-teboroxime; stress modalities, in which dipyridamole and adenosine stress have been compared with exercise; myocardial viability, as determined by delayed and reinjection 201Tl imaging or by measurement of cellular integrity using 82Rb compared with 18fluorodeoxyglucose metabolic PET imaging; and assessment of myocardial salvage and prognosis by exercise or dipyridamole 201Tl imaging in acute myocardial infarction.

Adenosine↗
PubMed1991

Identification of ischemic and hibernating myocardium: feasibility of post-exercise F-18 deoxyglucose positron emission tomography.

The identification of ischemic and hibernating myocardium facilitates the selection of patients most likely to benefit from revascularization. This study examined the feasibility of metabolic imaging, using post-exercise F-18 deoxyglucose positron emission tomography (FDG-PET) for the diagnosis of both ischemia and hibernation in 27 patients with known coronary anatomy. Normal post-exercise FDG uptake was defined in each patient by reference to normal resting perfusion and normal coronary supply. Abnormal elevation of FDG (ischemia or hibernation) was compared in 13 myocardial segments in each patient, with the results of dipyridamole stress perfusion imaging performed by rubidium-82 positron emission tomography (Rb-PET). Myocardial ischemia was diagnosed by either FDG-PET or Rb-PET in 34 segments subtended by significant local coronary stenoses. Increased FDG uptake was present in 32/34 (94%) and a reversible perfusion defect was identified by Rb-PET in 22/34 (65%, p less than .01). In 3 patients, ischemia was identified by metabolic imaging alone. In 16 patients with previous myocardial infarction, perfusion defects were present at rest in 89 regions, 30 of which (34%) demonstrated increased FDG uptake, consistent with the presence of hibernation. Increased post-exercise FDG uptake appears to be a sensitive indicator of ischemia and myocardial hibernation. This test may be useful in selecting post-infarction patients for revascularization.

Coronary Disease↗
PubMed1991

Myocardial perfusion imaging with positron emission tomography and single photon emission computed tomography: frequency and causes of disparate results.

The purpose of this study was to compare rubidium-82 PET with thallium-201 SPECT imaging in 150 patients. Both techniques followed a single dipyridamole-handgrip stress, and images were displayed using the same 3-dimensional format and quantitative colour scale. Coronary arteriography was employed to assign the correct diagnosis in situations of disparity. Results of PET and SPECT were at least partially concordant in 110 patients (73%), although 22 had more than one defect. A reversible perfusion defect was identified in 60 patients, but the scans were concordant in only 20 (33%). These disparities were chiefly due to false-negative SPECT imaging (22 patients, 55%), and probable delayed thallium redistribution (13 patients, 33%). No patients had ischaemia correctly identified by SPECT in the presence of normal PET imaging. Persistent defects were identified in 91 patients, some of whom also had reversible defects, and the results were consistent in 54 (59%). Other than the delayed thallium redistribution group, the major categories causing disparities were false-positive (6 patients, 16%), and false negative SPECT (8 patients, 22%), attributable to attenuation and scatter. PET appears able to identify smaller, less ischaemic areas subtended by milder coronary stenoses. The availability of a true resting scan with Rb-PET enhances the discrimination between ischaemia and infarction. Attenuation correction, and the high energy photons of positron annihilation, yield more accurate evaluation of inferior wall defects and greater specificity in the presence of soft tissue attenuation.

Adult↗
PubMed1991

Whither, or wither nuclear medicine?

In summary it appears that the future of the use of radionuclide procedures will show a continual increase in demand, utilization and growth of Nuclear Medicine as a discipline. The future of nuclear medicine physicians is less clear. Can they continue as a Renaissance model, interpreting all studies on all organs with equal expertise, or will they gradually be absorbed into organ or organ imaging sections to become a specialist on all imaging techniques on that organ? Is it true that the high technological advances that have been incorporated into Nuclear Medicine may be difficult to integrate into another discipline. For example, PET imaging is very much a part of Nuclear Medicine now and its expected growth in the future, along with the accompanying cyclotron and radiochemistry complexities, may prove to be a very large bite for any other discipline to follow. This integration, if it occurs, will not be overnight. Few radiologists practicing today in non-nuclear medicine areas would feel comfortable assuming the responsibilities of radionuclide studies, based on their three to six month stint in Nuclear Medicine.(ABSTRACT TRUNCATED AT 250 WORDS)

Data Collection↗
PubMed1990

Use of the 82Sr/82Rb generator in clinical PET studies.

The use of the 82Sr/82Rb generator in clinical positron emission tomography (PET) studies of myocardial perfusion has been described. An infusion pump is used to deliver the short-lived 82Rb from the generator to the patient. Various characteristics of the generator and the infusion system are described. The 82Rb yield was 69.8 +/- 13.3% and the 82Sr breakthrough was always less than the limit of 0.02 microCi/mCi 82Rb. The yield of 82Rb increased with the flow rate and the potency of the generator. Patients with coronary artery disease were studied for myocardial perfusion abnormalities by the 82Rb PET technique and images of excellent diagnostic quality were obtained.

Coronary Circulation↗
PubMed1990

A simple and accurate grading system for orthoiodohippurate renal scans in the assessment of post-transplant renal function.

Orthoiodohippurate renal scanning has proved to be a reliable, noninvasive method for the evaluation and followup of renal allograft function. However, a standardized system for grading renal function with this test is not available. We propose a simple grading system to distinguish the different functional phases of hippurate scanning in renal transplant recipients. This grading system was studied in 138 patients who were evaluated 1 week after renal transplantation. There was a significant correlation between the isotope renographic functional grade and clinical correlates of allograft function such as the serum creatinine level (p = 0.0001), blood urea nitrogen level (p = 0.0001), urine output (p = 0.005) and need for hemodialysis (p = 0.007). We recommend this grading system as a simple and accurate method to interpret orthoiodohippurate renal scans in the evaluation and followup of renal allograft recipients.

Adult↗
PubMed1990

Left ventricular hypertrophy sensitizes the myocardium to the development of ischaemia.

To evaluate the effects of left ventricular hypertrophy in the development of myocardial ischaemia as detected by thallium-201 exercise scintigraphy, we studied 150 patients by two-dimensional echocardiography, SPECT thallium-201 scintigraphy, and coronary arteriography. Patients were divided into four groups according to the presence or absence of left ventricular hypertrophy and coronary artery disease. There were 62 patients with coronary artery disease and 28 with left ventricular hypertrophy. Left ventricular mass index ranged from a mean of 91.2 g m-2 in the no LVH no CAD group, to a mean of 150.6 g m-2 in the LVH CAD group. For the whole group, the sensitivity of thallium for the detection of coronary artery disease was 82%, specificity 75%, positive predictive value 70%, and negative predictive value 86%. The proportion of patients with abnormal thallium was highest (100%) in the group with left ventricular hypertrophy and coronary artery disease. The second largest group with abnormal perfusion by thallium imaging comprised patients with coronary artery disease and no left ventricular hypertrophy (78%). Both coronary artery disease and left ventricular mass index were demonstrated to be independent predictors of myocardial ischaemia in a multivariate regression model (P = 0.01). We conclude that left ventricular hypertrophy sensitizes the myocardium for the development of ischaemia.

Adult↗