The value of PET scan (and MRI and Wada test) in patients with bitemporal epileptiform abnormalities.

BACKGROUND: Lateralization remains difficult in patients with bitemporal epileptiform abnormalities. OBJECTIVE: To evaluate the reliability of the interictal fluorodeoxyglucose F18-positron emission tomographic (PET) scan in this setting. METHODS: We analyzed PET scan findings in 25 patients who required bilateral depth electrodes for lateralization of temporal lobe epilepsy. The contribution of magnetic resonance imaging and the intracarotid amobarbital procedure was also analyzed. RESULTS: Positron emission tomographic scan revealed lateralized hypometabolism in 15 patients. This was in agreement with the depth evaluation in 10 cases (67%). In five cases (33%), the PET and depth findings were in disagreement, with no predominant side of seizure origin by depth electroencephalography (EEG) in four cases and PET lateralization opposite to depth findings in one case. In 10 of the 25 patients, PET scans could not lateralize hypometabolism to one temporal lobe, of which six were confirmed by depth EEG not to have a predominant side of seizure onset. The overall sensitivity of PET for concordant lateralized seizure onset was 67%. Ten of 14 patients who underwent a lobectomy had a successful outcome, including three of four patients whose temporal lobe epilepsy was lateralized by depth EEG but not by PET. One patient had PET lateralization opposite to the depth EEG and side of surgery and failed to improve. CONCLUSIONS: In this highly selected group of patients, the lateralizing value of PET and magnetic resonance imaging was somewhat diminished, and the intracarotid amobarbital procedure was not found useful for lateralization. Positron emission tomography and magnetic resonance imaging, when pointing to the side opposite depth EEG, may indicate a poor prognosis.

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.

Presurgical evaluation of temporal lobe epilepsy using interictal temporal spikes and positron emission tomography.

OBJECTIVE: Our goal was to determine the role of fludeoxyglucose F 18-positron emission tomography (18FDG-PET) and interictal temporal spikes in lateralizing the epileptogenic region in patients who (1) were diagnosed as having temporal lobe epilepsy based on clinical symptoms and exclusively temporal interictal spikes and (2) did not have a structural lesion on magnetic resonance imaging. DESIGN: This was a retrospective study of 40 consecutive patients fulfilling the above criteria who underwent 18FDG-PET scanning. A firm electrophysiologic diagnosis and 1 complete year of postsurgical follow-up, where applicable, were required. Outcome measures included surgical outcome and final electrophysiologic diagnosis. RESULTS: Unilateral, interictal temporal spikes (ITS) were present in 33 (82.5%) of 40 patients. Seven patients (17.5%) had bitemporal, independent spikes. Thirty-one (77.5%) of 40 patients had unilateral temporal hypometabolism (TH). Twenty-eight (70%) patients had concordant TH and ITS. One year after surgery, 31 of 33 patients with unilateral ITS were greatly improved; two of five who had bitemporal ITS showed similar improvement. In 28 patients, unilateral TH and unilateral ITS were concordant. The paired result always concurred with the final neurophysiologic assessment. Surgical outcome between patients with 18FDG-PET showing unilateral TH (26 of 30 greatly improved) and those not showing unilateral TH (six of eight greatly improved) was not significantly different. CONCLUSION: In temporal lobe epilepsy not associated with a mass lesion, unilateral ITS are reliable lateralizing features and suggest a good surgical outcome. Use of 18FDG-PET provides corroborative lateralizing information but 18FDG-PET that fails to show unilateral TH does not preclude a good surgical outcome.

Tracer kinetics of 15-(ortho-123/131I-phenyl)-pentadecanoic acid (oPPA) and 15-(para-123/131I-phenyl)-pentadecanoic acid (pPPA) in animals and man.

The human myocardium retains oPPA as opposed to pPPA. Therefore turnover of oPPA was compared with that of pPPA in rat hearts and in man, the latter by using substrates double-labeled with 123/131I and 14C. Moreover, substrate binding to coenzyme-A was tested in vitro. In rats, oPPA remained mainly in the pool of free fatty acids, as opposed to pPPA, which was metabolized by mitochondrial beta-oxidation. Binding to coenzyme-A at maximum was 62% for oPPA, 81% for pPPA and 90% for palmitic acid. In man, after i.v. and intracoronary injection of double-labeled oPPA, the two radionuclides reappeared together in venous blood and in coronary sinus respectively, in an unchanged ratio but at a significantly lower rate than with pPPA. It can be concluded that oPPA is bound to coenzyme-A and is retained in the cytosolic lipid pool, while pPPA is metabolized by mitochondrial beta-oxidation. A dual-tracer application of oPPA and pPPA has the potential of being a specific probe for the function of the carnitine shuttle.

Nuclear medicine studies of aging: X. Relationship of liver and spleen lengths at age 65 years and older.

For 3 groups of patients aged 65 years or greater, liver and spleen lengths were measured from calibrated radiocolloid images. Length relationships between liver (L) and spleen (S) were examined in terms of S as a function of L, as well as (S/L) and (L-S) vs S or L. Liver and spleen lengths were the least well correlated in these patients. The S/L ratio vs S produced the most significant correlation in all 3 groups. This suggests a complex but describable relationship between liver and spleen lengths in the overall aging population, and provides a baseline for comparing the effects of various diseases on S and L.

Radiopharmaceuticals for studying cardiac metabolism.

(1) Metabolism is the link between myocardial blood flow and physiological performance of the heart. (2) Metabolic myocardial radiopharmaceuticals have the potential to identify metabolic alterations unique to a given intrinsic cardiac disease (e.g. cardiomyopathies), to assess acute metabolic changes or in delineating a specific chronic metabolic defect (e.g. coronary artery disease). (3) Two approaches can be employed to evaluate in vivo myocardial utilization of subtracts: (a) use of radiolabeled "physiologic" substrates e.g. positron emitting 11C-palmitic acid was successfully employed for assessing the in vivo metabolic sequelae of myocardial ischemia, infarction and cardiomyopathies, and (b) use of modified tracers which enter known metabolic pathways. However, because of their unique structure, metabolism of the tracer stops at a certain state thus leaving the radiolabel trapped in the cell, e.g. [18F]FDG for measuring glucose metabolic rate in the human brain and myocardium. (4) Among the radiopharmaceuticals for planar and single photon tomography, the para and the ortho isomers of 123I-phenyl iodoheptadecanoic acids and their beta-methyl derivatives are the most promising tracers for myocardial metabolic studies. (5) Ortho-(123I-phenyl)-pentadecanoic acid (o-IPPA) human myocardial uptake was rapidly and markedly elevated in well perfused segments; myocardial turnover was strikingly prolonged, suggesting some "trapping" phenomenon, resulting in excellent scintigrams. This is in contrast to the relatively shorter clearance of the para isomer from the myocardium. (6) 11C-Palmitic acid and [18F]FDG are the most widely used for PET scanning for following myocardial metabolism. The most important clinical application of these agents is predicting viability of ischemic myocardium. (7) A significant proportion of fixed perfusion defects seen on thallium studies can be demonstrated to be viable myocardium on PET scans using metabolic agents. If the markers of perfusion alone are relied on to assess tissue viability, the extent of salvageable myocardium may be underestimated. The demonstration of myocardial viability is crucial in the decision of the optimal treatment of the disease.

15-(ortho-123I-phenyl)-pentadecanoic acid, a new myocardial imaging agent for clinical use.

The result of previous experiments in rodents indicated different kinetics for the para- and ortho-isomers of 15-(iodophenyl)-pentadecanoic acid (p-IPPA, o-IPPA), with o-IPPA showing an enhanced rate of washout. To test the relevance of this phenomenon for clinical diagnosis, 15 fasting male patients with confirmed coronary heart disease (1-VD/7, 2-VD/4, 3-VD/4) were investigated under exercise. Serial images were recorded at a rate of 3 frames min-1 for 70 to 90 min, corrected for tracer in blood and compared with thallium-201 images obtained from these patients within less than 2 weeks. Time-activity curves were also taken from the peripheral blood. Ortho-IPPA was well taken up by healthy myocardium and, contrary to rodents, retained with elimination half times longer than 200 min. A decreased myocardial uptake was seen which was very similar to the pattern obtained with thallium. Ortho-IPPA was eliminated from the blood to less than 10% at 4 min. Almost all radioactivity was in the organic phase (greater than 95% at 5 min) and chromatography showed only one major peak (o-IPPA) indicative of minimal organic catabolism.

Causes and temporal sequence of onset of functional asplenia in adults.

To determine the causes and time course of onset of functional asplenia in adults, a four-part investigation was conducted. This consisted of a review of the world's literature, a survey of colleagues, a detailed study of 4,476 consecutive liver-spleen scans in three hospitals, and continued monitoring of 3,500 scans in five hospitals. Based on the findings, a classification was proposed of the causes of functional asplenia. The two major etiologies were circulatory disturbances and effects directly on splenic reticuloendothelial cells. The time course varied from the essentially instantaneous onset of functional asplenia in patients with acute splenic artery obstruction, to a prolonged and gradual onset in those with chronic damage to splenic reticuloendothelial cells. Functional asplenia was found in 0.14% of the adults who had liver-spleen scans for other indications.

Hormonal and metabolic studies in pheochromocytoma.

One patient with benign and another with malignant pheochromocytoma have been studied in an attempt to elucidate the effect of increased catecholamines on the response of blood sugar, unesterified fatty acids, insulin and growth hormone to a glucose load. The presence of increased catecholamines in both patients appeared to produce increased fasting plasma unesterified fatty acid levels, carbohydrate intolerance and an unusual plasma growth hormone response to glucose. There was no interference with the normal decrease in plasma unesterified fatty acids after glucose ingestion. The malignant tumour, but not the benign one, was associated with low plasma insulin levels.After removal of the benign tumour the fasting unesterified fatty acid levels became normal. In addition, following glucose ingestion there appeared to be a more normal plasma insulin and growth hormone response and improved glucose tolerance. After removal of the primary malignant tumour it is noteworthy that the distant metastases secreted abnormal amounts of both adrenaline and noradrenaline.