Regional cerebral blood flow during gastric balloon distention in functional dyspepsia

BACKGROUND & AIMS: Hypersensitivity to proximal gastric distention as a result of abnormal central nervous system processing of visceral stimuli is a possible pathophysiologic mechanism in functional dyspepsia (FD). Increasing evidence suggests involvement of both lateral and medial pain systems in normal visceral sensitivity and aberrant brain activation patterns in visceral hypersensitivity. We hypothesized that there is involvement of aberrant brain activation in FD with hypersensitivity to gastric distention. Our aim was to investigate regional cerebral blood flow during painful proximal gastric distention in hypersensitive FD. METHODS: Brain (15)O-water positron emission tomography was performed in 13 FD patients with symptoms of gastric hypersensitivity during 3 conditions: no distention, sham distention, and isobaric distention to unpleasant or painful sensation. Pain, discomfort, nausea, and bloating during maximal distention were rated on visual analogue scales. Data were analyzed using statistical parametric mapping. RESULTS: The threshold for painful distention was 6.6 +/- 3.8 mm Hg greater than the minimal distending pressure. At the corrected P level of less than .05, subtraction analysis (painful distention - no distention) showed activations in bilateral gyrus precentralis, bilateral gyrus frontalis inferior, bilateral gyrus frontalis medialis, bilateral gyrus temporalis superior, bilateral cerebellar hemisphere, and left gyrus temporalis inferior. Sham distention minus no distention showed no activations. CONCLUSIONS: Similar to healthy volunteers, proximal stomach distention in FD activates components of the lateral pain system and bilateral frontal inferior gyri, putatively involved in regulation of hunger and satiety. In hypersensitive FD, these activations occur at significantly lower distention pressures. In contrast to findings in normosensitivity, none of the components of the medial pain system were significantly activated.     

Thoracic positron emission tomography: 18F-fluorodeoxyglucose and beyond

Ongoing technologic and therapeutic advancements in medicine are now testing the limits of conventional anatomic imaging techniques. The ability to image physiology, rather than simply anatomy, is critical in the management of multiple disease processes, especially in oncology. Nuclear medicine has assumed a leading role in detecting, diagnosing, staging and assessing treatment response of various pathologic entities, and appears well positioned to do so into the future. When combined with computed tomography (CT) or magnetic resonance imaging (MRI), positron emission tomography (PET) has become the sine quo non technique of evaluating most solid tumors especially in the thorax. PET/CT serves as a key imaging modality in the initial evaluation of pulmonary nodules, often obviating the need for more invasive testing. PET/CT is essential to staging and restaging in bronchogenic carcinoma and offers key physiologic information with regard to treatment response. A more recent development, PET/MRI, shows promise in several specific lung cancer applications as well. Additional recent advancements in the field have allowed PET to expand beyond imaging with ¹⁸F-flurodeoxyglucose (FDG) alone, now with the ability to specifically image certain types of cell surface receptors. In the thorax this predominantly includes ⁶⁸Ga-DOTATATE which targets the somatostatin receptors abundantly expressed in neuroendocrine tumors, including bronchial carcinoid. This receptor targeted imaging technique permits targeting these tumors with therapeutic analogues such as ¹⁷⁷Lu labeled DOTATATE. Overall, the proper utilization of PET in the thorax has the ability to directly impact and improve patient care.     

Imaging of transplanted islets by positron emission tomography,magnetic resonance imaging,and ultrasonography

While islet transplantation is considered a useful therapeutic option for severe diabetes mellitus (DM), the outcome of this treatment remains unsatisfactory. This is largely due to the damage and loss of islets in the early transplant stage. Thus, it is important to monitor the condition of the transplanted islets, so that a treatment can be selected to rescue the islets from damage if needed. Recently, numerous trials have been performed to investigate the efficacy of different imaging modalities for visualizing transplanted islets. Positron emission tomography (PET) and magnetic resonance imaging (MRI) are the most commonly used imaging modalities for this purpose. Some groups, including ours, have also tried to visualize transplanted islets by ultrasonography (US). In this review article, we discuss the recent progress in islet imaging.     

Scar imaging using multislice computed tomography versus metabolic imaging by F-18 FDG positron emission tomography: A pilot study

Introduction

F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) FDG PET is an established metabolic imaging technique to assess myocardial viability. Delayed iodinated contrast enhancement (DE) of myocardium on computed tomography (CT) has also been shown to be an anatomical marker of nonviable myocardium. A pilot study was undertaken to determine quantitative and qualitative agreement between metabolic viability imaging and scar imaging using FDG PET and multislice CT respectively.

Methods

Fifteen patients with coronary artery disease and left ventricular dysfunction were recruited in the study. All patients underwent same day FDG PET and DECT to evaluate myocardial viability. The images were analyzed quantitatively and qualitatively using a 17 segment model.

Results

DECT diagnosed viability in 57% (146/255) whilst PET in 51% (129/255) of segments. The per-segment agreement between DECT and FDG PET on qualitative analysis was 70% (Kappa: 0.40). The agreement in quantitative measurements between the two techniques for viability showed modest correlation [Pearson ρ: 0.63; P < 0.0001] on scatter plot and the Passing–Bablok regression analysis. Higher agreement (70 vs 77%; P = 0.051; Kappa: 0.40 vs 0.53) was obtained with quantitative compared to qualitative DECT.

Conclusions

DECT may be useful in characterizing myocardial scar, and preliminary results correlate modestly with metabolic FDG PET, both qualitatively and quantitatively. Although in our study quantitative analysis offered superior agreement compared to qualitative with DECT, further studies are needed to determine its incremental value.     

Current status of positron emission tomography in oncology

Positron emission tomography (PET) has emerged as a powerful diagnostic tool in oncology patients. There is evidence of the superior utility over conventional imaging methods of the principal PET tracer 18F-fluoro-2-deoxy-glucose in the staging of a range of cancers and monitoring disease recurrence, as well as changing patient management to more appropriate therapy. The methods for evaluating the evidence for PET remain complex, particularly as the standard evidence-based approach of randomized controlled trials is not generally applicable to imaging technologies. PET has the potential to dramatically improve our ability to manage patients with cancer and is also making major contributions to the development of new therapies.     

Longitudinal change in perceptual and brain activation response to visceral stimuli in irritable bowel syndrome patients

BACKGROUND & AIMS: Symptom-related fears and associated hypervigilance toward visceral stimuli may play a role in central pain amplification and irritable bowel syndrome (IBS) pathophysiology. Repeated stimulus exposure leads to decreased salience of threat and reduction of hypervigilance. We sought to evaluate hypervigilance in IBS visceral hypersensitivity and associated brain activity. METHODS: Twenty IBS patients (14 female; moderate to severe symptoms) and 14 healthy controls participated in symptom and rectal distention assessments 6 times over 12 months. In a subset of 12 IBS patients, H2 15O-positron emission tomography images were obtained during baseline, rectal distentions, and anticipation of an aversive distention during the first and last session. Statistical parametric mapping (SPM99) was used to identify areas and networks activated during each session as well as those with differential activation across the 2 sessions. RESULTS: Perceptual ratings of the rectal inflations normalized over 12 months, whereas IBS symptom severity did not. There were no sex-related differences in these response patterns. Stable activation of the central pain matrix was observed over 12 months, and activity in limbic, paralimbic, and pontine regions decreased. During the anticipation condition, there were significant decreases in amygdala, dorsal anterior cingulate cortex, and dorsal brainstem activation at 12 months. Covariance analysis supported the hypothesis of changes in an arousal network including limbic, pontine, and cortical areas underlying the decreased perception seen over the multiple stimulations. CONCLUSIONS: In IBS patients, repeated exposure to experimental aversive visceral stimuli results in the habituation of visceral perception and central arousal, despite stable activation of networks processing visceral pain and its anticipation.     

Myocardial perfusion imaging with positron emission tomography and single photon emission computed tomography: frequency and causes of disparate results

The purpose of this study was to compare rubidium-82 PET withthallium-201 SPECT imaging in 150 patients. Both techniquesfollowed a single dipyridamole-handgrip stress, and images weredisplayed using the same 3-dimensional format and quantitativecolour scale. Coronary arteriography was employed to assignthe correct diagnosis in situations of disparity. Results of PET and SPECT were at least partially concordantin 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 disparitieswere chiefly due to false-negative SPECT imaging (22 patients,55%), and probable delayed thallium redistri bution (13 patients,33%). No patients had ischaemia correctly identified by SPECTin the presence of normal PET imaging. Persistent defects wereidentified in 91 patients, some of whom also had reversibledefects, and the results were consistent in 54 (59%). Otherthan the delayed thallium redistribution group, the major categoriescausing disparities were false-positive (6 patients, 16%), andfalse negative SPECT (8 patients, 22%), attributable to attenuationand scatter. PET appears able to identify smaller, less ischaemic areas subtendedby milder coronary stenoses. The availability of a true restingscan with Rb-PET enhances the discrimination between ischaemiaand infarction. Attenuation correction, and the high energyphotons of positron annihilation, yield more accurate evaluationof inferior wall defects and greater specificity in the presenceof soft tissue attenuation.     

Diagnostic value of diffusion-weighted magnetic resonance imaging compared with fluorodeoxyglucose positron emission tomography/computed tomography for pancreatic malignancy: a meta-analysis using a hierarchical regression model

Background and Aim: To obtain diagnostic performance of diffusion‐weighted magnetic resonance imaging (DWI) and fluorine 18 fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) in the detection of pancreatic malignancy. Methods: We performed a meta‐analysis of all available studies of the diagnostic performance of DWI and PET/CT for pancreatic malignancy. MEDLINE, EMBASE, Cochrane library and some other databases were searched for initial studies. We determined sensitivities and specificities across studies, calculated positive and negative likelihood ratios (LR+ and LR?), and constructed summary receiver operating characteristic curves (SROC) using hierarchical regression models. Results: Across 16 studies with 804 patients, PET/CT sensitivity was 0.87 (95% confidence interval [CI], 0.82, 0.81) and specificity was 0.83 (95% CI, 0.71, 0.91). Overall, LR+ was 5.84 (95% CI, 4.59, 7.42) and LR? was 0.24 (95% CI, 0.17, 0.33). DWI sensitivity was 0.85 (95% CI, 0.74, 0.92) and specificity was 0.91 (95% CI, 0.71, 0.98). LR+ was 9.53 (95% CI, 2.41, 37.65) and LR? was 0.17 (95% CI, 0.09, 0.32). In subgroup analysis, the sensitivity of enhanced versus unenhanced PET/CT in the detection of pancreatic cancer was 0.91 (95% CI, 0.86, 0.96) versus 0.84 (95% CI, 0.78, 0.90) (P > 0.05), the specificity 0.88 (95% CI, 0.73, 1.00) versus 0.81 (95% CI, 0.69, 0.94) (P > 0.05). Conclusion: Positron emission tomography/computed tomography (PET/CT) was highly sensitive and DWI was a highly specific modality in diagnosing patients with pancreatic malignancy. PET/CT and DWI could play different roles in diagnosing pancreatic carcinoma. Enhanced PET/CT seems to be superior to unenhanced PET/CT. Further larger prospective studies are needed to establish its value for diagnosis in pancreatic cancer.     

Myocardial perfusion imaging with positron emission tomography and single photon emission computed tomography: frequency and causes of disparate results.

The purpose of this study was to compare rubidium-82 PET with thallium-201 SPECT imaging in 150 patients. Both techniques followed a single dipyridamole-handgrip stress, and images were displayed using the same 3-dimensional format and quantitative colour scale. Coronary arteriography was employed to assign the correct diagnosis in situations of disparity. Results of PET and SPECT were at least partially concordant in 110 patients (73%), although 22 had more than one defect. A reversible perfusion defect was identified in 60 patients, but the scans were concordant in only 20 (33%). These disparities were chiefly due to false-negative SPECT imaging (22 patients, 55%), and probable delayed thallium redistribution (13 patients, 33%). No patients had ischaemia correctly identified by SPECT in the presence of normal PET imaging. Persistent defects were identified in 91 patients, some of whom also had reversible defects, and the results were consistent in 54 (59%). Other than the delayed thallium redistribution group, the major categories causing disparities were false-positive (6 patients, 16%), and false negative SPECT (8 patients, 22%), attributable to attenuation and scatter. PET appears able to identify smaller, less ischaemic areas subtended by milder coronary stenoses. The availability of a true resting scan with Rb-PET enhances the discrimination between ischaemia and infarction. Attenuation correction, and the high energy photons of positron annihilation, yield more accurate evaluation of inferior wall defects and greater specificity in the presence of soft tissue attenuation.     

Pharmacokinetics and red cell utilization of iron(III) hydroxide-sucrose complex in anaemic patients: a study using positron emission tomography

The pharmacokinetics of a single intravenous injection of 100 mg iron hydroxide-sucrose complex labelled with a tracer in the form of 52Fe/59Fe was followed in six anaemic patients for a period ranging from 6 to 8 3 h using positron emission tomography (PET). Red cell utilization of the labelled iron was followed for 4 weeks. PET data showed radioactive uptake by the liver, spleen and bone marrow. The uptake by the macrophage-rich spleen demonstrated the reticuloendothelial uptake of this iron preparation, with subsequent effective release of that iron for marrow utilization. Red cell utilization, followed for 4 weeks, ranged from 59% to 97%. The bone marrow influx rate constant was independent of blood iron concentration, indicating non-saturation of the transport system in bone marrow. This implied that higher doses of the iron complex can probably be used in the same setting. A higher influx rate into the marrow compared with the liver seemed to be consistent with higher red cell utilization. This would indicate that early distribution of the injected iron complex may predict the long-term utilization.     

A pathophysiologic study of tako-tsubo cardiomyopathy with F-18 fluorodeoxyglucose positron emission tomography.

AIMS; Our study aims to investigate the pathophysiologic mechanism underlying tako-tsubo cardiomyopathy using F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET). METHODS AND RESULTS: Fifteen patients with tako-tsubo cardiomyopathy were enrolled in this study. Plasma catecholamines, cardiac troponin T (cTnT), and D-dimer were serially evaluated in all patients. Thallium-201 ((201)Tl) single-photon emission computed tomography (SPECT) and F-18 FDG PET were performed in 10 and eight patients, respectively. Emotional or physical stress occurred in 12 (80.0%) patients. ST-T segment abnormalities existed in all patients. Thirteen patients exhibited mildly elevated cTnT, although coronary angiography did not reveal significant stenosis in any patient. Endomyocardial biopsy specimens (n = 9) demonstrated contraction-band necrosis (n = 4) and mononuclear cell infiltration (n = 3). The levels of norepinephrine and epinephrine peaked on admission (744 +/- 452 and 140 +/- 166 pg/mL, respectively). There was severely reduced uptake at the apex on F-18 FDG PET image, despite slightly reduced uptake of (201)Tl. Elevation of D-dimer was observed in nine patients. CONCLUSION: The extent of metabolic defect involving apical akinetic area was more severe than perfusion abnormality. Our data suggest that sudden emotional or physical stress may cause a catecholamine-induced metabolic disorder in the myocardium, which is probably central to this syndrome.     

Value of contrast-enhanced 18F-fluorodeoxyglucose positron emission tomography/computed tomography in detection and presurgical assessment of pancreatic cancer: a prospective study

Background and Aim: Positron Emission Tomography (PET) using ¹⁸F‐fluorodeoxyglucose (FDG) associated with computed tomography (CT) is increasingly used for the detection and the staging of pancreatic cancer, but data regarding its clinical added value in pre‐surgical planning is still lacking. The aim of this study is to investigate the performance of FDG PET associated with contrast‐enhanced CT in detection of pancreatic cancer. Methods: We prospectively evaluated FDG PET/CT studies obtained in patients with suspicion of operable pancreatic cancer between May 2006 and January 2008. Staging was conducted according to a standardized protocol, and findings were confirmed in all patients by surgical resection or biopsy examination. Results: Forty‐five patients with a median age of 69 (range 22–82) were included in this study. Thirty‐six had malignant tumors and nine had benign lesions (20%). The sensitivity of enhanced versus unenhanced PET/CT in the detection of pancreatic cancer was 96% versus 72% (P = 0.076), the specificity 66.6% versus 33.3% (P = 0.52), the positive predictive value 92.3% versus 80% (P = 0.3), the negative predictive value 80% versus 25% (P = 0.2), and the accuracy 90.3% versus 64% (P = 0.085). Conclusions: Our preliminary data obtained in a limited number of patients shows that contrast‐enhanced FDG PET/CT offers good sensitivity in the detection and assessment of pancreatic cancer, but at the price of a relatively low specificity. Enhanced PET/CT seems to be superior to unenhanced PET/CT. Further larger prospective studies are needed to establish its value for pre‐surgical diagnosis and staging in pancreatic cancer.