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Biomedical subjects

R T Go

Publications and source records attributed to R T Go.

18 recordsLinked to original sources
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↗
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↗
PubMed1979

The role of radionuclide brain imaging and computerized tomography in the early diagnosis of herpes simplex encephalitis.

We have reviewed the medical records and radiographic examinations of 12 patients with herpes simplex encephalitis to assess the role of RN and CT in the early diagnosis of this disease. The initial RN study was positive in 83% (10/12) of cases while the initial CT study was positive in 75% (9/12) of cases. The earliest positive RN was seen on the second day after the onset of neurologic signs or symptoms while the earliest positive CT was seen on the third day. We describe various abnormal patterns encountered in HSE and discuss their diagnostic reliability. We make recommendations for the diagnosis of HSE based on our findings and on the information available in the literature

Adult↗
PubMed1977

Computed tomography in cerebral hemiatrophy.

The clinical and radiographic findings in four cases of cerebral hemiatrophy are presented. CT findings reflect the underlying gross pathologic changes and are in agreement with those seen on plain skull radiography and pneumoencephalography. The most impressive finding was unilateral loss of cerebral volume with ipsilateral displacement of the midline structures. The differential diagnosis primarily includes Sturge-Weber syndrome and linear sebaceous nevus syndrome. The recognition of compensatory calvarial changes should indicate that the cerebral abnormalities are the result of an atrophic or hypoplastic process that began in early life.

Adolescent↗
PubMed1976

Computed tomography and radionuclide studies in the diagnosis of intracranial disease.

The accuracy of CT and radionuclide studiies in the diagnosis of intracranial disease is analyzed based on experience in 641 patients. Results indicate that both modalities give reasonably similar precision and that a modest improvement in diagnosis can be expected if both techniques are employed. It is emphasized that the radionuclide studies used routinely included what are rightfully considered adjunctive scanning procedures, so that results must be considered in this light.

Brain Diseases↗
PubMed1975

Sequential brain scanning as an adjunctive scanning procedure.

Sequential brain scans were performed at various time intervals of up to four hours after injection of 99mTc pertechnetate in 108 patients who had previously undergone "routine" one-hour brain scans which were considered normal or equivocal. Forty-six patients were proved to have a discrete morphologic brain lesion. Pathologic processes were demonstrated by the sequential scanning technique in all but 6 cases. In nearly a third of these 46 patients (28%), careful observation of the progressive and subtle changes in radioactivity in the whole sequential scan series was necessary for detection of the lesions: they could not be appreciated on any single static scan when viewed independently.

Adenoma, Chromophobe↗
PubMed1975

The manifestations of diaphragmatic and juxtadiaphragmatic diseases in the liver-spleen scintigraph.

Diaphragmatic and juxtadiaphragmatic abnormalities can be recognized on liver-spleen scintigraphs by alteration of the normal disparity in height between the liver and the spleen and by flattening of the superior margins of the liver and spleen. A unilateral abnormality is manifested by exaggeration or reversal of the normal disparity in height between the superior margins of the liver and spleen by cephalad or caudad displacement of one of these organs. Bilateral peridiaphragmatic abnormalities are manifested by flattening of the superior margins of the liver and spleen by caudad displacement of both organs.

Diaphragm↗
PubMed1975

A new method of diagnosing myocardial contusion in man by radionuclide imaging.

A new method of diagnosing myocardial contusion was studied in 8 patients in whom the injured mycardium was visualized as an abnormal area of increased activity in the region of the heart one hour after intravenous injection of 10 mCi of 99m-Tc-Sn-polyphosphate or pyrophosphate. Serum enzymes in these patients were elevated, but electrocardiograms were nonspecific for myocardial injury. It is hoped that this new technique of imaging the injured myocardium will provide specific and confirmatory diagnosis of myocardial contusion associated with closed chest injuries.

Animals↗
PubMed1975

Coronary angiographic and scintigraphic findings in experimental cardiac contusion.

Clinical, angiographic, scintigraphic and pathologic observations in myocardial contusion were correlated. Radionuclide imaging of the injured heart with 99mTc-Sn-polyphosphate provides an accurate diagnosis in acute, even mild, myocardial contusion. The study can be carried out without danger to the critically ill patient. The coronary angiographic findings in this study explain what is occurring pathologically in the heart. Since arteriography is a more invasive technique than radionuclide imaging, its use is recommended only when the image is negative if it is neccessary to establish the clinical diagnosis for treatment or when more than one week has elapsed since the injury.

Acute Disease↗
PubMed1975

The diagnostic value of serial brain scanning.

A survey of the literature pertaining to several serial brain scanning procedures has been presented. These procedures include rapid brain imaging, sequential brain imaging, delayed from imaging, and follow-up brain imaging. Applications of these techniques to specific clinical problems have been stressed and the reported results reviewed. Thus, it has been indicated that rapid brain imaging is most useful in detecting lesions secondary to cerebrovascular disease but may also provide some helpful information pertaining to the differential diagnosis of other C.N.S. lesions demonstrated on subsequent static brain scans. Sequential brain imaging is a time-consuming adjunctive procedure which, however, can be extraordinarily helpful in a highly selected group of problem cases which present with relatively small lesions adjacent to normal anatomic structures which themselves have considerable radioactivity. Delayed brain imaging has the distinction of detecting the greatest number of intracranial lesions but is attended by tactical problems in maintaining an optimal patient flow through the department and also has the undesirable consequence of reduced information density and diminished image quality, unless greater radiation doses are injected. Follow-up brain imaging is useful in the differential diagnosis of cerebrovascular and neoplastic disease and in the assessment of effectiveness of radiation therapy.

Adenoma, Chromophobe↗
PubMedDate not supplied

Atrial natriuretic factor and catecholamine levels during exercise in patients with and without coronary artery disease.

To investigate the effects of exercise-induced ischemia on the release of atrial natriuretic factor (ANF), we measured peripheral plasma ANF, epinephrine and norepinephrine in 18 male patients with and without coronary artery disease. The patients underwent tomographic thallium treadmill stress tests. After exercise, patients with coronary artery disease showed higher increments of plasma ANF than patients without coronary disease, but the increase of ANF was not related to exercise-induced ischemia, nor to changes in catecholamines, heart rate, or blood pressure. This suggests that ANF release is not associated with myocardial ischemia per se, but to other factors which are more pronounced in the presence of coronary disease, such as changes in intracardiac pressures associated with exercise. Further studies are needed to clarify the role of myocardial ischemia on ANF release.

Adult↗