The functional anatomy of the normal human auditory system: responses to 0.5 and 4.0 kHz tones at varied intensities.
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Most functional imaging studies of the auditory system have employed complex stimuli. We used positron emission tomography to map neural responses to 0.5 and 4.0 kHz sine-wave tones presented to the right ear at 30, 50, 70 and 90 dB HL and found activation in a complex neural network of elements traditionally associated with the auditory system as well as non-traditional sites such as the posterior cingulate cortex. Cingulate activity was maximal at low stimulus intensities, suggesting that it may function as a gain control center. In the right temporal lobe, the location of the maximal response varied with the intensity, but not with the frequency of the stimuli. In the left temporal lobe, there was evidence for tonotopic organization: a site lateral to the left primary auditory cortex was activated equally by both tones while a second site in primary auditory cortex was more responsive to the higher frequency. Infratentorial activations were contralateral to the stimulated ear and included the lateral cerebellum, the lateral pontine tegmentum, the midbrain and the medial geniculate. Contrary to predictions based on cochlear membrane mechanics, at each intensity, 4.0 kHz stimuli were more potent activators of the brain than the 0.5 kHz stimuli. (+info)
Comparative efficacy of positron emission tomography with FDG and computed tomographic scanning in preoperative staging of non-small cell lung cancer.
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OBJECTIVE: To determine the sensitivity, specificity, and accuracy of positron emission tomography with 2-fluorine-18-fluorodeoxyglucose (PET-FDG) in the preoperative staging (N and M staging) of patients with lung cancer. The authors wanted to compare the efficacy of PET scanning with currently used computed tomography (CT) scanning. MATERIALS AND METHODS: Results of whole-body PET-FDG imaging and CT scans were compared with histologic findings for the presence or absence of lymph node disease or metastatic sites. Sampling of mediastinal lymph nodes was performed using mediastinoscopy or thoracotomy. RESULTS: PET-FDG imaging was significantly more sensitive, specific, and accurate for detecting N disease than CT. PET changed N staging in 35% and M staging in 11% of patients. CT scans helped in accurate anatomic localization of 6/57 PET lymph node abnormalities. CONCLUSION: PET-FDG is a reliable method for preoperative staging of patients with lung cancer and would help to optimize management of these patients. Accurate lymph node staging of lung cancer may be ideally performed by simultaneous review of PET and CT scans. (+info)
Sensitivity of [11C]phenylephrine kinetics to monoamine oxidase activity in normal human heart.
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Phenylephrine labeled with 11C was developed as a radiotracer for imaging studies of cardiac sympathetic nerves with PET. A structural analog of norepinephrine, (-)-[11C]phenylephrine (PHEN) is transported into cardiac sympathetic nerve varicosities by the neuronal norepinephrine transporter and stored in vesicles. PHEN is also a substrate for monoamine oxidase (MAO). The goal of this study was to assess the importance of neuronal MAO activity on the kinetics of PHEN in the normal human heart. MAO metabolism of PHEN was inhibited at the tracer level by substituting deuterium atoms for the two hydrogen atoms at the alpha-carbon side chain position to yield the MAO-resistant analog D2-PHEN. METHODS: Paired PET studies of PHEN and D2-PHEN were performed in six normal volunteers. Hemodynamic and electrocardiographic responses were monitored. Blood levels of intact radiotracer and radiolabeled metabolites were measured in venous samples taken during the 60 min dynamic PET study. Myocardial retention of the tracers was regionally quantified as a retention index. Tracer efflux between 6 and 50 min after tracer injection was fit to a single exponential process to obtain a washout half-time for all left ventricular regions. RESULTS: Although initial heart uptake of the two tracers was similar, D2-PHEN cleared from the heart 2.6 times more slowly than PHEN (mean half-time 155+/-52 versus 55+/-10 min, respectively; P < 0.01). Correspondingly, heart retention of D2-PHEN at 40-60 min after tracer injection was higher than PHEN (mean retention indices 0.086+/-0.018 versus 0.066+/-0.011 mL blood/ min/mL tissue, respectively; P < 0.003). CONCLUSION: Efflux of radioactivity from normal human heart after uptake of PHEN is primarily due to metabolism of the tracer by neuronal MAO. Related mechanistic studies in the isolated rat heart indicate that vesicular storage of PHEN protects the tracer from rapid metabolism by neuronal MAO, suggesting that MAO metabolism of PHEN leaking from storage vesicles leads to the gradual loss of PHEN from the neurons. Thus, although MAO metabolism influences the rate of clearance of PHEN from the neurons, MAO metabolism is not the rate-determining step in the observed efflux rate under normal conditions. Rather, the rate at which PHEN leaks from storage vesicles is likely to be the rate-limiting step in the observed efflux rate. (+info)
Enhanced myocardial glucose use in patients with a deficiency in long-chain fatty acid transport (CD36 deficiency).
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CD36 is a multifunctional, 88 kDa glycoprotein that is expressed on platelets and monocytes/macrophages. CD36 also has high homology with the long-chain fatty acid (LFA) transporter in the myocardium. Although platelet and monocyte CD36 levels can indicate a CD36 deficiency, they cannot predict specific clinical manifestations in the myocardium of a given person. We examined the hypothesis that a deficiency in LFA transport augments myocardial glucose uptake in patients with a type I CD36 deficiency. METHODS: Seven fasting patients with a type I CD36 deficiency and 9 controls were assessed by cardiac radionuclide imaging using beta-methyl-p-iodophenyl-pentadecanoic acid (BMIPP) as a LFA tracer and by PET with 18F-fluorodeoxyglucose (FDG). RESULTS: None of the patients with a CD36 deficiency showed myocardial uptake of BMIPP. The percentage dose uptake of BMIPP in these subjects was significantly lower than that in normal controls (1.31+/-0.24 versus 2.90+/-0.2; P < 0.005). PET studies revealed that myocardial FDG accumulation was substantially increased in patients with a CD36 deficiency. Quantitative analysis showed that the percentage dose uptake of FDG in patients with a CD36 deficiency was significantly higher than that in normal controls (1.28+/-0.35 versus 0.43+/-0.22; P< 0.01). CONCLUSION: CD36 functions as a major myocardial LFA transporter and its absence may cause a compensatory upregulation of myocardial glucose uptake. (+info)
Detection of liver metastases from pancreatic cancer using FDG PET.
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We evaluated the potential of the glucose analog [18F]fluorodeoxyglucose (FDG) as a PET tracer for the hepatic staging in 168 patients designated for resective pancreatic surgery. METHODS: Metastatic liver disease was confirmed or excluded during surgery or with CT follow-up for at least 6 mo. Proven metastases were then retrospectively identified on preoperative CT (gold standard). Hepatic PET scans of all patients were interpreted blindly. Any focal FDG uptake was considered malignant. Both proven hepatic metastases and suspicious hepatic PET lesions were then compared, lesion by lesion, with CT. Standardized uptake values (SUV) and tumor-to-liver ratios (T/L) were determined for the most intense lesion of each patient. RESULTS: Sensitivity of FDG PET was 68% (15 of 22 patients). The lesion detection rate was 97% (28 of 29 metastases) for lesions >1 cm and 43% (16 of 37 metastases) for lesions < or = 1 cm. Specificity was 95% (138 of 146 patients). Six of eight patients with false-positive results had marked intrahepatic cholestasis (versus 3 of 15 patients with true-positive lesions), one had an infrahepatic abscess and one had a right basal pulmonary metastasis. The SUV and T/L were 4.6+/-1.4 and 2.3+/-1.1, respectively, for malignant lesions and 4.1+/-1.5 and 1.9+/-0.3, respectively, for false-positive lesions and therefore are of limited value. CONCLUSION: FDG PET provides reliable hepatic staging for lesions >1 cm. False-positive results are associated with the presence of marked intrahepatic cholestasis. For lesions < or = 1 cm, FDG PET can define malignancy in 43% of suspicious CT lesions in the absence of dilated bile ducts. (+info)
L-[1-11C]-tyrosine PET to evaluate response to hyperthermic isolated limb perfusion for locally advanced soft-tissue sarcoma and skin cancer.
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PET with L-[1-11C]-tyrosine (TYR) was investigated in patients undergoing hyperthermic isolated limb perfusion (HILP) with recombinant tumor necrosis factor alpha (rTNF-alpha) and melphalan for locally advanced soft-tissue sarcoma and skin cancer of the lower limb. METHODS: Seventeen patients (5 women, 12 men; age range 24-75 y; mean age 52 y) were studied. TYR PET studies were performed before HILP and 2 and 8 wk afterwards. The protein synthesis rates (PSRs) in nanomoles per milliliter per minute were calculated. After final PET studies, tumors were resected and pathologically examined. Patients with pathologically complete responses (pCR) showed no viable tumors after treatment. Those with pathologically partial responses (pPR) showed various amounts of viable tumors in the resected tumor specimens. RESULTS: Six patients (35%) showed a pCR and 11 patients (65%) showed a pPR. All tumors were depicted as hot spots on PET studies before HILP. The PSR in the pCR group at 2 and 8 wk after perfusion had decreased significantly (P < 0.05) in comparison to the PSR before HILP. A significant difference was found in PSR between the pCR and pPR groups at 2 and at 8 wk (P < 0.05). Median PSR in nonviable tumor tissue was 0.62 and ranged from 0.22 to 0.91. With a threshold PSR of 0.91, sensitivity and specificity of TYR PET were 82% and 100%, respectively. The predictive value of a PSR > 0.91 for having viable tumor after HILP was 100%, whereas the predictive value of a PSR < or = 0.91 for having nonviable tumor tissue after HILP was 75%. The 2 patients in the pPR groups with a PSR < 0.91 showed microscopic islets of tumor cells surrounded by extensive necrosis on pathological examination. CONCLUSION: Based on the calculated PSR after HILP, TYR PET gave a good indication of the pathological outcome. Inflammatory tissue after treatment did not interfere with viable tumor on the images, suggesting that it may be worthwhile to pursue TYR PET in other therapy evaluation settings. (+info)
Reproducibility studies with 11C-DTBZ, a monoamine vesicular transporter inhibitor in healthy human subjects.
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The reproducibility of (+/-)-alpha-[11C] dihydrotetrabenazine (DTBZ) measures in PET was studied in 10 healthy human subjects, aged 22-76 y. METHODS: The scan-to-scan variation of several measures used in PET data analysis was determined, including the radioactivity ratio (target-to-reference), plasma-input Logan total distribution volume (DV), plasma-input Logan Bmax/Kd and tissue-input Logan Bmax/Kd values. RESULTS: The radioactivity ratios, plasma-input Bmax/Kd and tissue-input Bmax/Kd all have higher reliability than plasma-input total DV values. In addition, measures using the occipital cortex as the reference region have higher reliability than the same measures using the cerebellum as the reference region. CONCLUSION: Our results show that DTBZ is a reliable PET tracer that provides reproducible in vivo measurement of striatal vesicular monoamine transporter density. In the selection of reference regions for DTBZ PET data analysis, caution must be exercised in circumstances when DTBZ binding in the occipital cortex or the cerebellum may be altered. (+info)
Anatomic validation of spatial normalization methods for PET.
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Spatial normalization methods, which are indispensable for intersubject analysis in current PET studies, have been improved in many aspects. These methods have not necessarily been evaluated as anatomic normalization methods because PET images are functional images. However, in view of the close relation between brain function and morphology, it is very intriguing how precisely normalized brains coincide with each other. In this report, the anatomic precision of spatial normalization is validated with three different methods. METHODS: Four PET centers in Japan participated in this study. In each center, six normal subjects were recruited for both H2(15)O-PET and high-resolution MRI studies. Variations in the location of the anterior commissure (AC) and size and contours of the brain and the courses of major sulci were measured in spatially normalized MR images for each method. Spatial normalization was performed as follows. (a) Linear: The AC-posterior commissure and midsagittal plane were identified on MRI and the size of the brain was adjusted to the Talairach space in each axis using linear parameters. (b) Human brain atlas (HBA): Atlas structures were manually adjusted to MRI to determine linear and nonlinear transformation parameters and then MRI was transformed with the inverse of these parameters. (c) Statistical parametric mapping (SPM) 95: PET images were transformed into the template PET image with linear and nonlinear parameters in a least-squares manner. Then, coregistered MR images were transformed with the same parameters used for the PET transformation. RESULTS: The AC was well registered in all methods. The size of the brain normalized with SPM95 varied to a greater extent than with other approaches. Larger variance in contours was observed with the linear method. Only SPM95 showed significant superiority to the linear method when the courses of major sulci were compared. CONCLUSION: The results of this study indicate that SPM95 is as effective a spatial normalization as HBA, although it does not use anatomic images. Large variance in structures other than the AC and size of the brain in the linear method suggests the necessity of nonlinear transformations for effective spatial normalization. Operator dependency of HBA also must be considered. (+info)