Biomedical subjects

G B Saha

Publications and source records attributed to G B Saha.

At least 19 recordsLinked to original sources

PubMed1999

Scintigraphic detection of post-pneumonectomy bronchopleural fistulae.

A total of 20 ventilation studies [16 with xenon-133 and four with technetium-99m diethylenetriamine pentaacetic acid (DTPA)] were performed in 11 patients with suspected post-pneumonectomy bronchopleural fistulae. The findings on the ventilation scan were correlated with bronchoscopy, taken as the gold standard for purposes of comparison. The sensitivity and specificity for 133Xe scans were 83% and 100% respectively, while the sensitivity for 99mTc-DTPA aerosol studies was poor at 0%. Special techniques for optimal visualization of the fistulae are enumerated.

Aerosols↗

PubMed1997

Myocardial viability studies using fluorine-18-FDG SPECT: a comparison with fluorine-18-FDG PET.

UNLABELLED: Multidetector SPECT systems equipped with a high-energy, or 511-keV collimator, have been proposed to offer a less expensive alternative to PET in myocardial viability studies with [18F]FDG. The objectives of this investigation included: (a) measuring the physical imaging characteristics of SPECT systems equipped with either a high-energy general-purpose collimator (HE), or the dedicated 511-keV collimator (UH), when imaging 511-keV photons, and comparing them with conventional FDG PET; and (b) directly and quantitatively comparing the diagnostic accuracy of SPECT, with either an UH or HE collimator, to that of PET in myocardial viability studies using 18F-FDG. METHODS: Physical imaging characteristics of SPECT and PET were measured and compared. Both SPECT and PET studies were performed in two groups of 18 patients each, with Group I using HE SPECT and Group II using UH SPECT. Myocardial perfusion studies were also performed using 82Rb PET at rest and during dipyridamole stress to identify areas of persistent hypoperfusion. For each myocardial region with a persistent perfusion defect, a perfusion-metabolism match or mismatch pattern was established independently, based on the results of 18F-FDG SPECT as well as PET. RESULTS: PET is superior to SPECT in all physical imaging characteristics, particularly in sensitivity and contrast resolution. PET had a sensitivity 40-80 times higher than that of SPECT, and its contrast resolution was 40-100% better than SPECT. Between FDG-SPECT using an HE collimator and that using a 511-keV collimator, the latter showed marked reduction in septal penetration (from 56% to 38%), improvement in spatial resolution (from 17 mm to 11 mm FWHM) as well as contrast resolution (from 34% to 45%), while suffering reduced system sensitivity (from 75 to 34 cpm/microCi). Patient studies demonstrated that although FDG-SPECT, using a HE or UH collimator, provided concordant viability information as FDG PET in a large majority of myocardial segments with persistent perfusion defects (88% and 90%, respectively), there is an excellent statistical agreement (kappa = 0.736) between SPECT with UH collimator and PET, while the agreement between SPECT using HE collimator and PET are moderate (kappa = 0.413). CONCLUSION: Despite its markedly inferior physical imaging characteristics compared with PET, SPECT with the dedicated 511-keV collimator offers a low-cost, practical alternative to PET in studying myocardial viability using [18F]FDG. SPECT systems with a high-energy, general-purpose collimator, on the other hand, are inadequate in such studies.

Coronary Circulation↗

PubMed1997

A rapid chromatographic method for quality control of technetium-99m-bicisate.

UNLABELLED: The purpose of this work was to develop a simple and rapid method to determine the radiochemical purity of 99mTc-bicisate. METHODS: A rapid paper chromatographic (PC) method was developed to determine the radiochemical purity of 99mTc-bicisate and compare the results with those of the manufacturer's recommended method. The present PC method included Whatman 3MM paper as the solid phase and ethyl acetate as the solvent. RESULTS: The time for chromatography by this technique was 4-5 min compared to about 23 min by the manufacturer's method. The Rf value of 99mTc-bicisate (Rf = 0.9-1.0) was widely different from those of 99mTcO4- and reduced 99mTc (Rf = 0.0 for both) so the chromatographic strip after development could be readily cut into two segments, in order to determine the labeling yield. CONCLUSION: No significant difference in labeling yields was found between the present method and the manufacturer's method. The PC method using Whatman 3MM paper and ethyl acetate is a simple and fast technique to determine the radiochemical purity of 99mTc-bicisate and may be substituted for the manufacturer's recommended method to save time.

Acetates↗

PubMed1996

Measurement of cardiac output with first-pass determination during rubidium-82 PET myocardial perfusion imaging.

In addition to providing useful clinical information, cardiac output determined during rubidium-82 positron emission tomographic (PET) myocardial perfusion studies can be used in the measurement of absolute regional myocardial blood flow using Sapirstein's method. This investigation was conducted to compare cardiac output values obtained by post-processing data acquired in a list mode PET myocardial perfusion study with those obtained using a technetium-99m-labeled red blood cell method on the same patients. Results from 14 patients showed that cardiac output can be accurately measured simultaneously in a 82Rb PET myocardial study, allowing determination of multiple perfusion and functional parameters of the heart, thus improving the cost-effectiveness of the 82Rb PET study.

Cardiac Output↗

PubMed1996

Is image subtraction necessary in the clinical interpretation of single-day split-dose stress cerebral perfusion single-photon emission tomography using technetium-99m compounds?

The aim of this study was to validate a simplified semiquantitative method of evaluating a single-day stress cerebral perfusion test to obtain cerebrovascular reserve capacity (CVRC) for routine clinical uses. A split-dose protocol was tested in 36 pairs of technetium-99m hexamethylpropylene amino oxime baseline (low dose) and acetazolamide (high dose) stress brain single-photon emission tomographic (SPET) studies from 16 patients with cerebrovascular disease. The images were displayed on a semiquantitative color scale with (corrected) and without (uncorrected) image subtraction, dose adjustment, and decay correction. The representative CVRC was determined by placing 3x3 pixel regions of interest on midthalamic and midcerebellar slices. The corrected and uncorrected relative changes in CVRC were correlated using linear regression. The relative changes of corrected (x) and uncorrected (y) CVRC by quantitative analysis were highly correlated in a linear fashion (y=0.67x+0.002, r=0.998, P<0.0005). As predicted by theory, the slope was related to the ratio of split dose and independent of ROI sampling. Single-day split-dose stress brain SPET can be accurately performed without image subtraction and complicated dose adjustment or decay correction for clinical studies.

Acetazolamide↗

PubMed1996

Present assessment of myocardial viability by nuclear imaging.

Prospective delineation of viable from nonviable myocardium in patients with coronary artery disease in an important factor in deciding whether a patient should be revascularized or treated medically. Two common techniques--single-photon emission computed tomography (SPECT) and positron-emission computed tomography (PET)--are used in nuclear medicine using various radiopharmaceuticals for the detection of myocardial viability in patients. Thallium-201 (201Tl) and technetium-99m (99mTc)-sestamibi are the common radiopharmaceuticals used in different protocols using SPECT, whereas fluoride-18 (18F)-fluorodeoxyglucose (FDG) and rubidium-82 (82Rb) are most widely used in PET. The SPECT protocols involve stress/redistribution, stress/redistribution/reinjection, and rest/redistribution imaging techniques. Many studies have compared the results of 201Tl and (99mTc)-sestamibi SPECT with those of FDG PET; in some studies, concordant results have been found between delayed thallium and FDG results, indicating that 201Tl, although considered a perfusion agent, shows myocardial viability. Discordant results in a number of studies have been found between sestamibi and FDG, suggesting that the efficacy of sestamibi as a viability marker has yet to be established. Radiolabeled fatty acids such as iodine-123 (123I)-para-iodophenylpentadecanoic acid and carbon-11 (11C)-palmitic acid have been used for the assessment of myocardial viability with limited success. 11C-labeled acetate is a good marker of oxidative metabolism in the heart and has been used to predict the reversibility of wall motion abnormalities. (18F)-FDG is considered the marker of choice for myocardial viability, although variable results are obtained under different physiological conditions. Detection of myocardial viability can be greatly improved by developing new equipment and radiopharmaceuticals of better quality.

Artifacts↗

PubMed1996

Outcome of temporal lobe epilepsy surgery predicted by statistical parametric PET imaging.

UNLABELLED: PET is useful in the presurgical evaluation of temporal lobe epilepsy. The purpose of this retrospective study is to assess the clinical use of statistical parametric imaging in predicting surgical outcome. METHODS: Interictal 18FDG-PET scans in 17 patients with surgically-treated temporal lobe epilepsy (Group A-13 seizure-free, group B = 4 not seizure-free at 6 mo) were transformed into statistical parametric imaging, with each pixel representing a z-score value by using the mean and s.d. of count distribution in each individual patient, for both visual and quantitative analysis. RESULTS: Mean z-scores were significantly more negative in anterolateral (AL) and mesial (M) regions on the operated side than the nonoperated side in group A (AL: p < 0.00005, M: p = 0.0097), but not in group B (AL: p = 0.46, M: p = 0.08). Statistical parametric imaging correctly lateralized 16 out of 17 patients. Only the AL region, however, was significant in predicting surgical outcome (F = 29.03, p < 0.00005). Using a cut-off z-score value of -1.5, statistical parametric imaging correctly classified 92% of temporal lobes from group A and 88% of those from Group B. CONCLUSION: The preliminary results indicate that statistical parametric imaging provides both clinically useful information for lateralization in temporal lobe epilepsy and a reliable predictive indicator of clinical outcome following surgical treatment.

Adult↗

PubMed1995

Hibernating myocardium versus scar: severity of irreversible decreased myocardial perfusion in prediction of tissue viability.

PURPOSE: To determine whether quantitation of the relative severity of decreased perfusion in irreversible defects on myocardial perfusion images enables differentiation of viable hibernating myocardium from scar. MATERIALS AND METHODS: In 145 patients with previous myocardial infarction, 1,252 regions with irreversible defects proved by means of rubidium-82 rest-stress imaging were analyzed for relative severity (percentage decrease in perfusion). Myocardial tissue viability was determined by means of positron emission tomography with fluorine-18 fluorodeoxyglucose (FDG). RESULTS: The relative decreases in Rb-82 uptake in the 1,252 regions were categorized into nine levels of severity (30% to > or = 70%) in 381 regions of hibernating myocardium and 871 regions of scar. The values of relative decreased perfusion in the irreversible defects alone did not enable differentiation of hibernating myocardium and scar (P = .61). CONCLUSION: The results show no relationship between the relative severity of irreversible perfusion defects and the ability to distinguish between hibernating myocardium and scar.

Cell Survival↗

PubMed1994

Radiopharmaceuticals for brain imaging.

Brain imaging is performed using radiopharmaceuticals by single photon emission computed tomography (SPECT) and positron emission tomography (PET). SPECT and PET radiopharmaceuticals are classified according to blood-brain-barrier permeability, cerebral perfusion and metabolism receptor-binding, and antigen-antibody binding. The blood-brain-barrier (BBB) SPECT agents, such as 99mTcO4-, [99mTc]DTPA, 201TI and [67Ga]citrate are excluded by normal brain cells, but enter into tumor cells because of altered BBB. These agents were used in the earlier period for the detection of brain tumors. SPECT perfusion agents such as [123I]IMP, [99mTc]HMPAO, [99mTc]ECD are lipophilic agents and therefore, diffuse into the normal brain. These tracers have been successfully used to detect various cerebrovascular diseases such as stroke, Parkinson disease, Huntington's disease, epilepsy, dementia, and psychiatric disorders. Xenon-133 and radiolabeled microspheres have been used for the measurement of cerebral blood flow (CBF). Important receptor-binding SPECT radiopharmaceuticals include [123I]QNE, [123I]IBZM, and [123I]iomazenil. These tracers bind to specific receptors in the brain, thus displaying their distribution in various receptor-related cerebral diseases. Radioiodinated monoclonal antibodies were used for the detection of brain tumors. PET radiopharmaceuticals for brain imaging are commonly labeled with positron-emitters such as 11C, 13N, 15O, and 18F, although other radionuclides such as 82Rb, 62Cu and 68Ga also were used. The brain uptake of [13N]glutamate, [68Ga]EDTA and [82Rb]RbCl depends on the BBB permeability, but these are rarely used for brain imaging. Several cerebral perfusion agents have been introduced, of which [15O]water, [13N]ammonia, and [15O]butanol have been used more frequently. Regional CBF has been quantitated by using these tracers in normal and different cerebral disease states. Other perfusion agents include [15O]O2, [11C]CO, [11C]CO2, [18F]fluoromethane, [15O]O2, [11C]butanol, and [62Cu]PTSM. Among the PET cerebral metabolic agents, [18F]fluorodeoxyglucose (FDG) is most commonly used to detect metabolic abnormalities in the brain. Various brain tumors have been graded by [18F]FDG PET. This technique was used to detect epileptic foci by showing increased uptake in the foci during the ictal period and decreased uptake in the interictal period. Differentiation between recurrent tumors and radiation necrosis and the detection of Alzheimer's disease have been made successfully by [18F]FDG PET. Other PET metabolic agents such as [11C]deoxyglucose, and [11C]methylmethionine have drawn attention in the detection of brain tumors. [18F]fluorodopa is a cerebral neurotransmitter agent, which has been found very useful in the detection of Parkinson disease that shows reduced uptake of the tracer in the striatum of the brain.(ABSTRACT TRUNCATED AT 400 WORDS)

Brain↗

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

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

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↗

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↗

PubMed1990

Quantitation of abnormal 67Ga uptake in pulmonary interstitial vascular disease--a new test to detect diffuse lung disease.

Gallium 67 has been used as a modality to diagnose and follow the clinical course of diseases such as tumors, infections, inflammatory disorders, and interstitial lung disease. It has been appreciated, however, that mild to moderate changes in scan activity, when these disorders are followed over time, are less than optimal. SPECT (single-photon emission computed tomography) scanning is a new technique designed to obviate this problem. SPECT scanning utilizes computer acquisition to provide three-dimensional scanning and the additional benefit of colorization to aid in discerning differences of uptake. SPECT scanning was performed on 22 patients with interstitial lung disease of various etiologies. Additionally, 7 patients had follow-up SPECT scanning to determine their response to treatment. Two patients are presented as examples.

Female↗