Functional Anatomy of Reaching and Visuomotor Learning: A Positron Emission Tomography Study

The purpose of this study was to identify the functional corticalfields involved in reaching for targets in extrapersonal space,and to identify the specific fields representing visual targetinformation in long-term memory. Ten healthy subjects were askedto learn the positions of seven circular targets that were repeatedlyprojected on a screen. The regional cerebral blood flow wasmeasured with positron emission tomography during a rest state,at an early learning stage, at a later learning stage, and finallyat 30 min after the course of learning had been completed. MeanrCBF change images for each task minus rest were calculatedand fields of significant rCBF changes were identified. In all three task states, cortical fields were consistentlyactivated in the left motor and premotor areas, the posteriorpart of the superior parietal lobule, and the right angulargyrus. When learning of the target positions had been achieved,additional fields appeared bilaterally in the posterior partof the superior parietal lobule, the right superior occipitalgyrus, the left motor and premotor areas, the medial aspectof the superior frontal gyrus, the postcentral gyrus, the superiorpart of the cuneus, the inferior part of the angular gyrus,and the anterior part of the insula. The results indicate thatthere are at least two different types of functional fieldsin the posterior part of the superior parietal lobule; one isactive during reaching for the targets when guided by internalrepresentations of target positions; the other likely representsthe storage sites of visual target information that is addressedin long-term memory.     

Area V5 of the Human Brain: Evidence from a Combined Study Using Positron Emission Tomography and Magnetic Resonance Imaging

In pursuing our work on the organization of human visual cortex,we wanted to specify more accurately the position of the visualmotion area (area V5) in relation to the sulcal and gyral patternof the cerebral cortex. We also wanted to determine the intersubjectvariation of area V5 in terms of position and extent of bloodflow change in it, in response to the same task. We thereforeused positron emission tomography (PET) to determine the fociof relative cerebral blood flow increases produced when subjectsviewed a moving checkerboard pattern, compared to viewing thesame pattern when it was stationary. We coregistered the PETimages from each subject with images of the same brain obtainedby magnetic resonance imaging, thus relating the position ofV5 in all 24 hemispheres examined to the individual gyral configurationof the same brains. This approach also enabled us to examinethe extent to which results obtained by pooling the PET datafrom a small group of individuals (e.g., six), chosen at random,would be representative of a much larger sample in determiningthe mean location of V5 after transformation into Talairachcoordinates. After stereotaxic transformation of each individual brain, wefound that the position of area V5 can vary by as much as 27mm in the left hemisphere and 18 mm in the right for the pixelwith the highest significance for blood flow change. There isalso an intersubject variability in blood flow change withinit in response to the same visual task. V5 nevertheless bearsa consistent relationship, within each brain, to the sulcalpattern of the occipital lobe. It is situated ventrolaterally,just posterior to the meeting point of the ascending limb ofthe inferior temporal sulcus and the lateral occipital sulcus.In position it corresponds almost precisely with Flechsig'sFeld 16, one of the areas that he found to be myelinated atbirth.     

Diagnosis and Staging of Pancreatic Cancer by Positron Emission Tomography

The detection of pancreatic cancer or the discrimination between pancreatic cancer and chronic pancreatitis remains an important diagnostic problem. Several imaging modalities are now used to diagnose pancreatic cancer, including transabdominal ultrasonography (US), contrast-enhanced computed tomography (CT), magnetic resonance imaging (MRI), endoscopic retrograde cholangiopancreatography (ERCP), endoscopic ultrasonography, and selective angiography. None of these six methods is perfect: Each has advantages and disadvantages, and their sensitivity and specificity are in a high range. In 1990 positron emission tomography (PET) was first applied to diagnose pancreatic cancer. This new diagnostic modality is based on functional changes in the pancreatic cancer cells caused by enhanced glucose metabolism. Increased glucose utilization is one of the characteristics of malignantly transformed cells, independent of their origin. The technical development of PET has allowed this new procedure to be used for clinical evaluation. Using 2-(¹⁸F)-fluoro-2-deoxy-d-glucose, PET can identify pancreatic cancer and differentiate pancreatic cancer from chronic pancreatitis with a sensitivity of 85% to 98% and a specificity of 53% to 93%. However, high sensitivity and high specificity are strongly dependent on the tumor stage. At present PET is still experimental and is available only in specialized centers. It may represent a new and noninvasive diagnostic procedure for the detection and the staging of pancreatic cancer. Further clinical studies, especially including patients with early tumor stages (small tumor size), are needed. This review discusses the possibilities and limits of PET and evaluates its importance in the future.     

Developmental Changes in Brain Metabolism in Sedated Rhesus Macaques and Vervet Monkeys Revealed by Positron Emission Tomography

The present positron emission tomography study used 2-deoxy-2[¹⁸F]fluoro-D-glucoseto examine age-related changes in local cerebral metabolic ratesfor glucose (LCMRglc) in sedated rhesus macaques and vervetmonkeys. Nineteen vervet monkeys were scanned in a cross-sectionaldesign, which consisted of three age groups (birth to 59 d,60–179 d, 180 d to adult) that captured the developmentalperiod of greatest synaptic density within the second group.Two rhesus and two vervet monkeys were also examined longitudinally.Subjects were sedated throughout the procedure with a combinationof ketamine and midazolam. Longitudinal and cross-sectionalanalyses of 20 brain regions indicated lowest LCMRglc in rhesusand vervet monkeys <2 months of age (about 60% of adult levels).These metabolic rates more than doubled to approximately 155%of adult levels after the second postnatal month, coincidentwith transient synaptic overproduction and increased sociobehavioralactivity. LCMRglc remained high until 6 months postnatally,coincident with continued dendritic growth and the emergingsociobehavioral independence of the young monkey. After 6 months,LCMRglc decreased gradually to adult levels. Thus, the periodbetween 2 and 6 months is a time of peak metabolic activity,which coincides with increased histologic and behavioral activityin the developing monkey.     

18F-FDG PET显像在大肠癌诊治中的应用

目的 介绍18F-氟代脱氧葡萄糖正电子发射型断层显像(18F-FDG PET)在大肠癌诊治中使用的最新进展。方法 对近几年来国外关于18F-FDG PET显像对大肠癌诊治研究进展进行分析和总结。结果 18F-FDGPET显像对早期诊断大肠癌复发、转移及大肠癌的分期均优于CT及MRI检查。结论 18F—FDG PET显像可以作为诊断大肠癌的一种重要检查手段，并有助于治疗方案的选择。     

Real‐Time Trafficking of PEGylated Liposomes in the Rodent Focal Brain Ischemia Analyzed by Positron Emission Tomography

A liposomal drug delivery system was previously applied to ischemic brain model rats for the treatment of brain ischemia, and we observed that 100‐nm‐sized liposomes could extravasate and accumulate in the ischemic brain region even when cerebral blood flow was markedly reduced in permanent middle cerebral artery occlusion (p‐MCAO) model rats. In the present study, we investigated the real‐time cerebral distribution of polyethylene glycol (PEG)‐modified liposomes (PEG‐liposomes) labeled with 1‐[¹⁸F]fluoro‐3,6‐dioxatetracosane in p‐MCAO rats by positron emission tomography (PET). [¹⁸F]‐Labeled PEG‐liposomes were intravenously injected into p‐MCAO rats 1 h after the onset of occlusion, and then a PET scan was performed for 2 h. The PET scan showed that the signal intensity of [¹⁸F] gradually increased in the ischemic region despite the drastic reduction in cerebral perfusion, suggesting that PEG‐liposomes had accumulated in and around the ischemic region. Therefore, drug delivery to the ischemic region by use of liposomes would be possible under ischemic conditions, and a liposomal drug delivery system could be a promising strategy for protecting the ischemic brain from damage before recovery from ischemia.     

Imaging Human Cerebral Pain Modulation by Dose-dependent Opioid Analgesia: A Positron Emission Tomography Activation Study Using Remifentanil

Background: Previous imaging studies have demonstrated a number of cortical and subcortical brain structures to be activated during noxious stimulation and infusion of narcotic analgesics. This study used 15O-water and positron emission tomography to investigate dose-dependent effects of the short-acting [mu]-selective opioid agonist remifentanil on regional cerebral blood flow during experimentally induced painful heat stimulation in healthy male volunteers.

Methods: Positron emission tomography measurements were performed with injection of 7 mCi 15O-water during nonpainful heat and painful heat stimulation of the volar forearm. Three experimental conditions were used during both sensory stimuli: saline, 0.05 [mu]g [middle dot] kg-1 [middle dot] min-1 remifentanil, and 0.15 [mu]g [middle dot] kg-1 [middle dot] min-1 remifentanil. Cardiovascular and respiratory parameters were monitored noninvasively. Across the three conditions, dose-dependent effects of remifentanil on regional cerebral blood flow were analyzed on a pixel-wise basis using a statistical parametric mapping approach.

Results: During saline infusion, regional cerebral blood flow increased in response to noxious thermal stimulation in a number of brain regions as previously reported. There was a reduction in pain-related activations with increasing doses of remifentanil in the thalamus, insula, and anterior and posterior cingulate cortex. Increasing activation occurred in the cingulofrontal cortex (including the perigenual anterior cingulate cortex) and the periaqueductal gray.     

Evidence for a Two-Stage Model of Spatial Working Memory Processing within the Lateral Frontal Cortex: A Positron Emission Tomography Study

Previous work in nonhuman primates and in patients with frontallobe damage has suggested that the frontal cortex plays a criticalrolein the performance of both spatial and nonspatial workingmemory tasks. The present study used positron emission tomographywith magnetic resonance imaging to demonstrate the existence,within the human brain, of two functionally distinct subdivisionsof the lateral frontal cortex, which may subserve differentaspects of spatial working memory. Five spatial memory taskswere used, which varied in terms of the extent to which theyrequired different executive processes. When the task requiredthe organization and execution of a sequence of spatial movesretained in working memory, significant changes in blood flowwere observed in ventrolateral frontal cortex (area 41) bilaterally.By contrast, when the task required active monitoring and manipulationof spatial information within working memory, additional activationfoci were observed in mid-dorsolateral frontal cortex (areas46 and 9). These findings support a two-stage model of spatialworking memory processing within the lateral frontal cortex.     

Efficacy of Direct Revascularization in Adult Moyamoya Disease: Haemodynamic Evaluation by Positron Emission Tomography

Summary  To evaluate the efficacy of direct cerebrovascular reconstruction to prevent intracranial bleeding from the point of view of haemodynamic status, we performed positron emission tomography (PET) studies in 5 adult patients with Moyamoya disease before and after superficial temporal artery to middle cerebral artery (STA-MCA) anastomosis. Regional cerebral blood flow (rCBF), regional cerebral metabolic rate of oxygen (rCMRO₂) and regional oxygen extraction fraction (rOEF) in the MCA territories and regional cerebral blood volume (rCBV) in the striatum were measured before and after STA-MCA anastomosis. Correlation between the change of these PET parameters and post-operative decreased opacification of Moyamoya vessels were analyzed. Pre-operatively, significant elevation of rCBV were observed in the basal ganglia as well as significant reduction of rCBF and elevation of rOEF with reduction of rCMRO₂ in the MCA territories, indicating “misery” perfusion in the cerebral hemisphere and blood pooling in the Moyamoya vessels under increased haemodynamic stress. Post-operative PET study showed improvement of misery perfusion and reduction of rCBV in the basal ganglia. Reduction of rCBV in the basal ganglia generally compatible with decreasing Moyamoya vessels on angiographic findings. Our results suggests that direct bypass surgery could have a potential both for decreasing haemodynamic stress on Moyamoya vessels and to improve misery perfusion in the hemisphere.     

Fusion Image of Positron Emission Tomography and Computed Tomography for the Diagnosis of Local Recurrence of Rectal Cancer

Background The aim of this study was to evaluate the clinical and therapeutic value of digital fusion image (FI) of positron emission tomography (PET) using ¹⁸F-fluorodeoxy glucose and computed tomography (CT) in patients who were suspected of having a local recurrence of rectal cancer.Methods Forty-two patients (32 men and 10 women; mean age, 61.4 years, range, 40–79 years) with a suspicion of local recurrence after curative resection of rectal cancer were prospectively recruited and underwent ¹⁸F-fluorodeoxy glucose-PET and CT. The FI was reconstructed with a commercially available digital software program, T-B Fusion. Wilcoxon signed rank test was used to compare FI with CT alone or PET alone.Results FI yielded a correct diagnosis in 39 (93%) of 42 patients, whereas CT alone and PET alone did so in 33 (79%) and 37 (88%) patients, respectively. FI had better diagnostic accuracy than CT alone (P = .0138) and PET alone (P = .0156). Overall, FI altered patient management in 11 (26.2%) patients on the basis of additional information, including differentiation of the tumor from the postoperative scar in 6 patients, exact anatomical location in 3 patients, and both in 2 patients.Conclusions FI has a potential clinical value in the treatment of suspected local recurrence of rectal cancer.Presented at the 55th Annual Cancer Symposium of the Society of Surgical Oncology, Denver, Colorado, March 2002.     

Evaluation of Shoulder Disorders by 2-[F-18]-fluoro-2-deoxy-D-glucose Positron Emission Tomography and Computed Tomography

Background

Although flourine-18-flourodeoxyglucose (FDG) positron emission tomography (PET) has a limitation for localizing anatomical structures, combining it with computed tomography (CT) has made it more efficient for overcoming such limitations. This study aims to evaluate the efficacy of PET/CT for evaluating diseases of the shoulder.

Methods

Retrospective examination was performed on 25 patients who underwent FDG-PET/CT scanning. All the patients were over 60 years of age, and they were evaluated both clinically and radiologically for shoulder pain. The study period was from May, 2006 to May, 2008. One of the patients had metastatic lesion in a shoulder and this patient was excluded from the study, so the total number of subjects in the study was finally 24 patients.

Results

PET/CT showed 67% sensitivity, 73% specificity, a positive predictive value of 60%, a negative predictive value of 79%, 27% false positivity and 33% false negativity concerning shoulder pain. PET/CT showed negative finding in 4 cases that were successfully treated by operative treatment (rotator cuff tear [RCT], 3 cases; impingement syndrome, 1 case). Negative findings were also noted in 6 cases in which the pain subsided after conservative treatment (RCT, 1 case; suspected RCT, 2 cases; impingement syndrome, 3 cases). All the patients with osteoarthritis and rheumatoid arthritis had positive findings on PET/CT scanning.

Conclusions

PET/CT is a useful adjunct to the existing imaging modalities to assess functional and pathophysiologic processes and at a very early stage, and so PET/CT can help physicians make better preoperative and postoperative decisions on treatment.     

Is Prostate-specific Membrane Antigen Positron Emission Tomography/Computed Tomography Imaging Cost-effective in Prostate Cancer: An Analysis Informed by the proPSMA Trial

BackgroundBefore integrating prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) into routine care, it is important to assess if the benefits justify the differences in resource use.ObjectiveTo determine the cost-effectiveness of PSMA-PET/CT when compared with conventional imaging.Design, setting, and participantsA cost-effectiveness analysis was developed using data from the proPSMA study. proPSMA included patients with high-risk prostate cancer assigned to conventional imaging or ⁶⁸Ga-PSMA-11 PET/CT with planned health economics data collected. The cost-effectiveness analysis was conducted from an Australian societal perspective.Intervention⁶⁸Ga-PSMA-11 PET/CT compared with conventional imaging (CT and bone scan).Outcome measurements and statistical analysisThe primary outcome from proPSMA was diagnostic accuracy (nodal and distant metastases). This informed a decision tree analysis of the cost per accurate diagnosis.Results and limitationsThe estimated cost per scan for PSMA PET/CT was AUD$1203, which was less than the conventional imaging cost at AUD$1412. PSMA PET/CT was thus dominant, having both better accuracy and a lower cost. This resulted in a cost of AUD$959 saved per additional accurate detection of nodal disease, and AUD$1412 saved for additional accurate detection of distant metastases. The results were most sensitive to variations in the number of men scanned for each ⁶⁸Ga-PSMA-11 production run. Subsequent research is required to assess the long-term costs and benefits of PSMA PET/CT-directed care.ConclusionsPSMA PET/CT has lower direct comparative costs and greater accuracy compared to conventional imaging for initial staging of men with high-risk prostate cancer. This provides a compelling case for adopting PSMA PET/CT into clinical practice.Patient summaryThe proPSMA study demonstrated that prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) better detects disease that has spread beyond the prostate compared with conventional imaging. Our analysis shows that PSMA PET/CT is also less costly than conventional imaging for the detection of disease spread.This research was presented at the European Association of Nuclear Medicine Scientific Meeting in October 2020.     

Prospective Analysis of Accuracy of Positron Emission Tomography,Computed Tomography,and Endoscopic Ultrasonography in Staging of Adenocarcinoma of the Esophagus and the Esophagogastric Junction

Background: Exact preoperative staging of esophageal cancer is essential for accurate prognosis and selection of appropriate treatment modalities.Methods: Forty-two patients with adenocarcinoma of the esophagus or the esophagogastric junction suitable for radical esophageal resection were staged with positron emission tomography (PET), spiral computed tomography (CT), and endoscopic ultrasonography (EUS).Results: Diagnostic sensitivity for the primary tumor was 83% for PET and 67% for CT; for local peritumoral lymph node metastasis, it was 37% for PET and 89% for EUS; and for distant metastasis, it was 47% for PET and 33% for CT. Diagnostic specificity for local lymph node metastasis was 100% with PET and 54% with EUS, and for distant metastasis, it was 89% for PET and 96% for CT. Accuracy for locoregional lymph node metastasis was 63% for PET, 66% for CT, and 75% for EUS, and for distant metastasis, it was 74% with PET and 74% with CT. Of the 10 patients who were considered inoperable during surgery, PET identified 7 and CT 4. The false-negative diagnoses of stage IV disease in PET were peritoneal carcinomatosis in two patients, abdominal para-aortic cancer growth in one, metastatic lymph nodes by the celiac artery in four, and metastases in the pancreas in one. PET showed false-positive lymph nodes at the jugulum in three patients.Conclusions: The diagnostic value of PET in the staging of adenocarcinoma of the esophagus and the esophagogastric junction is limited because of low accuracy in staging of paratumoral and distant lymph nodes. PET does, however, seem to detect organ metastases better than CT.