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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.

A woman with hydrocephalus due to aqueductal stenosis had functional imaging of cerebral perfusion and metabolism to demonstrate the effects of endoscopic third ventriculostomy--a new form of internal surgical shunting. Technetium-99m-ECD SPECT and 18F-FDG PET showed regional luxury perfusion at the left frontal region. Three months after a successful third ventriculostomy, a repeated imaging of cerebral perfusion and metabolism showed resolution of luxury perfusion and global improvement of both perfusion and metabolism. This concurred with postoperative clinical improvement. The paired imaging of cerebral perfusion and metabolism provides more information than just imaging perfusion or metabolism. Thus, the detection of perfusion and metabolism mismatch may open a new window of opportunity for surgical intervention.

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.

Purpose: The use of preoperative imaging studies in patients with persistent or recurrent hyperparathyroidism after initial operation is generally accepted to improve the success rate and minimize the morbidity from reoperative surgery. The purpose of this study was to define the performance of FDG-PET for the localization of hyperfunctioning parathyroid tissue prior to reoperation., Method: Twenty patients with biochemical evidence of recurrent or persistent hyperparathyroidism following previous neck surgery were investigated. Regional body PET imaging of the neck and upper chest (axial field of view 27.5 cm) was acquired 45 min after 5-10 mCi FDG was given intravenously., Results: Subsequent surgery revealed solitary parathyroid adenomas in 14 patients, seven hyperplastic glands in 2 patients, and parathyroid carcinoma in 1 patients. FDG-PET correctly identified 79% (11/14) of the parathyroid adenomas, 29% (2/7) of the hyperplastic glands, and the parathyroid carcinoma. FDG-PET was negative in 79% (30/38) of the surgically identified normal parathyroid glands. Eight false-positive findings led to a positive predictive value of 64%., Conclusion: These preliminary data suggest that regional body FDG-PET is a promising procedure in the evaluation of patients with persistent or recurrent postoperative hyperparathyroidism.

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.

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.

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.

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.

Background: Although reversible perfusion defects, perfusion-metabolism mismatch and match patterns are important for differentiating viable from nonviable myocardium, the frequency of these scintigraphic patterns has not been reported. The study objective was to establish the incidence of these scintigraphic patterns to estimate the clinical need for metabolic positron emission tomography for evaluating tissue viability in patients with prior myocardial infarction (MI)., Methods and Results: 82Rb perfusion images were interpreted to identify reversible or irreversible defects, followed by determination of their 18F-fluorodeoxyglucose (18F-FDG) uptake pattern. In 155 patients with prior MI, analysis of 613 abnormal segments showed reversible perfusion defects in 13%. The 87% irreversible defects, 18% showed perfusion-metabolism mismatch, whereas 69% showed the match pattern. Reversible perfusion defects and perfusion-metabolism mismatches were noted in 20% (31/155) and 29% (45/155) of patients, respectively, whereas the match pattern was noted in 51% (79/155) of patients., Conclusion: Irreversible perfusion defects were common in our patients with prior MI, and distinction between viable and nonviable tissue was not possible by perfusion imaging alone. The identification of hibernating myocardium was possible only with the additional 18F-FDG imaging in about one third of patients. This indicates a significant clinical demand for 18F-FDG imaging that identifies patients who will benefit from revascularization.

The efficacy of myocardial perfusion imaging for cardiac-risk stratification of patients undergoing vascular surgery has been disputed recently. In comparison with conventional techniques, positron emission tomography (PET) has the benefit of permitting a true resting scan, allows accurate measurement of the extent of ischemia, and is highly specific for the diagnosis of coronary disease. We therefore investigated the use of PET for risk stratification at the time of vascular surgery and subsequent follow-up in 78 patients (aged 67 +/- 11 years, 52 men), selected for testing before the performance of extensive surgery or because of one or more clinical risk factors. Perfusion images were obtained by using a standard rubidium 82 protocol before and after dipyridamole-handgrip stress. With use of a quantitative color scale in a 24-segment model of the left ventricle, scans were reported as showing normal perfusion, resting defects, or stress-induced defects (deterioration > 15% with stress). After exclusion of 6 patients referred for myocardial revascularization, 72 patients were followed up in the perioperative period and for 18 +/- 12 months for late cardiac death, myocardial infarction, or unstable angina. Perioperative events occurred in 14 patients (5 with myocardial infarction and 9 with unstable angina), 10 of whom had ischemia at PET (sensitivity, 71%; predictive value of a positive test, 45%). Isolated resting perfusion defects were not associated with events. The presence of extensive ischemia (more than five segments) had a positive predictive value of 64%, and its absence gave a negative predictive value of 89%.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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.

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)

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.

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.

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.

A patient with primary hyperparathyroidism was examined with positron emission tomography using [18F]-2-fluorodeoxyglucose. The radioactive tracer accumulated in a cervical mass that proved to be a parathyroid adenoma resulting in the correct preoperative localization of the parathyroid tumor.

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.

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.

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.

As the complexity, cost, and risks of cardiac interventions direct attention to careful selection of patients, the ability of diagnostic imaging techniques to provide quantitative documentation of the hemodynamic severity of coronary artery disease will assume greater importance. Among the various techniques currently in use, positron emission tomography yields superior spatial resolution and attenuation correction and has high sensitivity and specificity. The correlation of positron emission tomography results with coronary stenosis severity and the possibility of making quantitative flow measurements using oxygen-15 water suggest that cardiac positron emission tomography may be the best noninvasive approach for diagnostic purposes.

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.

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.

The extent of ischemic and hibernating myocardium, which may be detected by increased postexercise uptake of fluoro-18 deoxyglucose (FDG) using positron emission tomography, may determine the degree of functional benefit after revascularization. This study examined the influence of the amount of this FDG-avid myocardium on changes in left ventricular function and exercise parameters after revascularization. Echocardiography and exercise testing were performed before and after intervention in 23 patients who had undergone positron emission tomography for the evaluation of myocardial perfusion (using rubidium-82), and postexercise FDG imaging in the fasting state. Follow-up echocardiography (22 +/- 14 weeks after revascularization) was compared with preoperative FDG activity in 7 myocardial regions per patient. Systolic function improved after intervention in 19 of 26 malperfused, dysfunctional FDG-avid regions (73%), and did not improve in 35 of 47 dysfunctional regions without increased FDG uptake (74%). The influence of the amount of FDG-avid tissue on changes in functional state was examined by comparing 9 patients with multiple (greater than or equal to 2) FDG-avid regions with the remainder. Those with multiple FDG-avid regions demonstrated improvement in peak rate-pressure product (20 +/- 4 to 26 +/- 4 x 10(3), p less than 0.02), and percentage of maximal heart rate achieved at peak (84 +/- 10% to 93 +/- 6%, p = 0.04), neither of which changed significantly in the remaining patients. Exercise capacity increased from 5.6 +/- 2.7 to 7.5 +/- 1.7 METS in the group with multiple FDG-avid regions; this increase of 55 +/- 18% exceeded the increase of 13 +/- 10% in the remainder (p = 0.04).(ABSTRACT TRUNCATED AT 250 WORDS)

Background: The presence of persistent myocardial uptake of 18F-deoxyglucose (FDG) within hypoperfused, dysfunctional segments has been shown to predict the recovery of regional contractile function after revascularization. The spectrum of metabolic responses of such hibernating tissue to revascularization is less clear., Methods and Results: Sixteen patients with previous infarction were studied before and after revascularization by myocardial perfusion imaging using 82Rb positron emission tomography, digitized two-dimensional echocardiography, and imaging of postexercise FDG uptake. Hibernation was identified in 35 of 85 segments showing perfusion and wall motion disturbances before intervention. At follow-up (4.9 +/- 2.6 months after revascularization), hibernating segments were characterized by reduction of wall motion score (p less than 0.001), improvement of perfusion (p less than 0.001), and reduction of FDG activity (p less than 0.001). Of the 35 hibernating segments, however, 10 still had abnormal elevation of FDG uptake (greater than 2 SD above normal) without differing from other hibernating segments with respect to postoperative perfusion or wall motion score. Segments with persistently abnormal metabolism were characterized before intervention by more severe malperfusion (p less than 0.01) and greater FDG activity (p less than 0.01)., Conclusions: Although wall motion and perfusion improve with revascularization of hibernating tissue, myocardial metabolism remains abnormal in a significant proportion of segments. These segments are characterized by more extensive perfusion and metabolic changes before revascularization.

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)

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.

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)

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.

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.

The purpose of the present study is to prospectively compare myocardial perfusion imaging with rubidium-82 (82Rb) by positron emission tomography (PET) with thallium-201 (201Tl) imaging by single-photon emission tomography (SPECT) by recording both studies with a single dipyridamole handgrip stress, and reading both sets of images with the same display technique. In a series of 202 patients with previous coronary arteriography, the sensitivity, specificity, and accuracy of 82Rb PET were 93%, 78%, and 90% and for 201Tl SPECT 76%, 80%, and 77%, respectively. When 70 patients with previous therapeutic interventions were excluded, the remaining 132 patients showed a sensitivity, specificity, and accuracy of 95%, 82% and 92% for 82Rb PET and 79%, 76%, and 78% for 201Tl SPECT. The improved contrast resolution of PET resulted in markedly superior images and a more confident identification of defects.

Developments of various imaging modalities in recent years have resulted in imaging systems with greater spatial resolution, faster data acquisition, and more powerful computer processing. It is the purpose of this report to examine three of these systems, positron emission tomography (PET), magnetic resonance imaging (MRI) and ultrafast computed tomography (cine-CT) with respect to their applicability for determination of cardiac volumes and other characteristics related to hypertension. While each of these modalities has widespread applications and specific advantages, this report will be primarily concerned with two objectives: functional ability to record indicator dilution curves suitable for quantification of flow and the anatomic or geometric ability to measure chamber dimensions with high accuracy. Time concentration curves have been outlined on all modalities and used for quantification of myocardial perfusion and myocardial reserve. Only one modality, cine-CT, determined cardiac output by dilution curves although in vivo arterial recording from PET has demonstrated suitable curves for this application. Both MRI and cine-CT have demonstrated accurate determination of chamber volumes by the geometric method, the latter giving somewhat higher spatial resolution. The advantages of these machines for such purposes have yet to be determined.

For repeated determinations of cardiac output, radionuclides have provided a safe, reliable and minimally invasive approach. The techniques used are (1) the first-pass dilution method and (2) the derivation of stroke volume from end-diastolic and end-systolic ventricular volumes. Each of the two techniques offers specific advantages, thus, both may be used clinically according to the type of evaluation that is required. Their development has been helped by the availability of adequate radiopharmaceuticals as well as highly efficient precordial detection devices, computer systems, and data handling 'software'. The associated patient exposure to radioactivity has not precluded clinical application because of the small doses used and the protective measures applied.

Lymphangiomyomatosis was first reported more than forty years ago. Although its incidence is rare, its occurrence is being increasingly recognized and has been the subject of a growing number of cases reports in recent years. This study adds 2 more cases to the file. Both cases involved young women with the characteristic symptoms of dyspnea, cough, abdominal discomfort and swelling, chest pain, and hemoptysis, with abundant formation of refractory chylous, serous ascites. Although the progression of the disease differed in each case, pulmonary function was affected in a similar way by the presence of obstructive and restrictive defects and a decrease in diffusing capacity. Underlying abnormalities were dilated lymphatics, thickened lymphatic walls, and muscular proliferation of leiomyomatous origin, leading to bronchial restriction. The authors point to the subtlety required in arriving at a differentiated diagnosis of lymphangiomyomatosis lymphangioleiomyomatosis and the difference between the two conditions. They also make particular recommendations in respect to the importance of preliminary hormone receptor tests and to the wisdom to be exercised in ligating a main lymphatic duct in the chest to control the formation of ascites. Pneumothorax, a frequent manifestation of lymphangiomyomatosis, is found to be the result of chronic air trapping due to a combination of narrowing of conducting airways and disruption of normal lung parenchyma.

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.

The white and gray matter of the brain can be clearly differentiated by computed tomography (CT). The differentiation is enhanced by the administration of contrast material. Without contrast material, the mean attenuation number of the white matter was 29 units, of the gray matter, 35 units. The effective low contrast resolving power of CT scanners can be clinically evaluated by comparing their ability to differentiate the white and gray matter of the brain.

Using pusher-plate-type artificial hearts, changes in the degree of synchrony and stroke volume were compared to phase and amplitude calculations from the first Fourier component of individual-pixel time-activity curves generated from gated radionuclide images (RNA) of these hearts. In addition, the ability of Fourier analysis to quantify paradoxical volume shifts was tested using a ventricular aneurysm model by which the Fourier amplitude was correlated to known increments of paradoxical volume. Predetermined phase-angle differences (incremental increases in asynchrony) and the mean phase-angle difference calculated from RNAs showed an agreement of -7 degrees +/- 4.4 degrees (mean +/- SD). A strong correlation was noted between stroke volume and Fourier amplitude (r = 0.98; P less than 0.0001) as well as between the paradoxical volume accepted by the 'aneurysm' and the Fourier amplitude (r = 0.97; P less than 0.0001). The degree of asynchrony and changes in stroke volume were accurately reflected by the Fourier phase and amplitude values, respectively. In the specific case of ventricular aneurysms, the data demonstrate that using this method, the paradoxically moving areas may be localized, and the expansile volume within these regions can be quantified.

Magnetic resonance (MR) gated cardiac imaging was performed in ten subjects using a prototype 0.15-T resistive magnet imaging system. Volume and planar imaging techniques utilizing saturation recovery, proton Tl-weighted relaxation time pulse sequences produced images of the heart and great vessels with exquisite anatomic detail that showed excellent correlation with cadaver sections of the heart. The left ventricular myocardial segments also showed excellent correlation with the thallium-201 cardiac single photon emission computed tomography images. Volume acquisition allowed postprocessing selection of tomographic sections in various orientations to optimize visualization of a particular structure of interest. The excellent spatial and contrast resolution afforded by MR volume imaging, which does not involve the use of ionizing radiation and iodinated contrast material, should assure it a significant role in the diagnostic assessment of the cardiovascular system.

Postoperative improvement in left ventricular (LV) function is a common objective of LV aneurysmectomy, but is difficult to predict. The first Fourier component of time-activity curves of pre- and postoperative gated radionuclide angiographic studies was evaluated for this purpose in 20 patients who had undergone aneurysmectomy. LV aneurysms had portions that characteristically exhibited marked phase delay with varying degrees of amplitude. Total aneurysmal amplitude was obtained preoperatively by summing the amplitude component of all pixels that exhibited phase delay, suggesting paradoxical motion. LV ejection fraction (EF) before and after aneurysmectomy and the absolute postoperative increase in LVEF were calculated. Nine of 20 patients had an absolute increase of EF less than 10% despite resection of large aneurysms. A strong correlation was found between the absolute increase in EF after aneurysmectomy and the total amplitude within paradoxically moving areas (r = 0.93, p less than 0.0001). Thus, preoperative measurement of the total paradoxical amplitude predicts absolute change in EF and may be important in selecting patients for aneurysmectomy. The data also suggest that the total aneurysmal amplitude reflects the stroke volume ejected into an aneurysm in systole and that paradoxical expansion of an aneurysm contributes to LV dysfunction in some of these patients.