Effects of left bundle branch block on myocardial FDG PET in patients without significant coronary artery stenoses.

UNLABELLED: Cardiac PET studies in patients with left bundle branch block (LBBB) are few, and the results are conflicting. In particular, even if a reduced uptake of FDG is reported, confirmation in a large group of patients and exact understanding of the underlying cause are lacking. METHODS: We selected 29 consecutive patients who had complete LBBB and no significant stenosis on coronary angiography scheduled for FDG and 13N-NH3 PET for myocardial viability evaluation at our center. Wall motion was evaluated using 2-dimensional echocardiography. Ten volunteers without coronary stenosis or LBBB served as a control group. RESULTS: All LBBB patients had a reverse mismatch in the septum, defined as reduced uptake of FDG in comparison with 13N-NH3. The mismatch extended to the anterior and inferior walls in 17 patients. The mean (+/-SD) septal-to-lateral ratio was 0.57 +/- 0.11 for FDG (range, 0.28-0.76) and 0.99 +/- 0.12 for 13N-NH3 (range, 0.75-1.18), with P < 0.0001. In contrast, no significant differences in uptake were seen in the control group, which had a septal-to-lateral ratio of 0.95 +/- 0.13 for FDG (range, 0.78-1.15; P < 0.01 with respect to LBBB patients) and 0.94 +/- 0.11 (range, 0.85-1.20) for 13N-NH3. CONCLUSION: Our study suggests that in LBBB patients without significant coronary stenosis, FDG uptake in the septum changes without a correlating change in perfusion. To avoid possible overestimation of necrosis, especially in the LAD territory, this phenomenon must be considered in evaluations of myocardial viability using FDG images.

[Effects of spinal cord stimulation on regional myocardial blood flow in patients with refractory angina. A positron emission tomography study]. / Effetti della stimolazione spinale epidurale sul flusso miocardico regionale in pazienti con angina pectoris refrattaria. Uno studio con tomografia ad emissione di positroni.

BACKGROUND: Spinal cord stimulation (SCS) is an alternative therapy in patients with refractory angina pectoris when coronary revascularization cannot be performed. Several hypotheses have been given to explain the effects of SCS in reducing the number and the intensity of anginal crises. These hypotheses include possible variations in myocardial blood flow (MBF). The aim of our study was to assess regional MBF in a group of patients with spinal cord stimulator, using positron emission tomography (PET). METHODS: We studied 15 patients (9 male and 6 female), mean age 74 +/- 7 years, who were carriers of a spinal cord stimulator implanted 17 +/- 14 (range 1-48) months before. All patients had been affected with angina pectoris that was refractory to maximal tolerated pharmacological therapy. Eight patients had had a previous myocardial infarction and four patients had undergone a revascularization procedure. Every patient underwent two PETs with nitrogen-13-ammonia as the perfusion tracer. The first one was performed with the stimulator switched off for at least 20 hours, and the second one with the stimulator switched on for at least 4 hours. The quantitative evaluation of regional MBF (anterior, inferior, lateral, septal walls and apex) was performed with Patlak graphic analysis. The normal value of basal MBF in our laboratory is 0.6-1 ml/min/g. RESULTS: The mean value of MBF increased from 0.72 +/- 0.33 ml/min/g with the stimulator off, to 0.80 +/- 0.33 ml/min/g with it on (p = 0.004). An increase in regional myocardial perfusion, with the stimulator on as opposed to off, was observed in 47 (62%) of the 75 regions studied. With the stimulator on, in comparison with off, the value of MBF increased from 0.45 +/- 0.11 ml/min/g to 0.56 +/- 0.19 (p = 0.0001) in the 35 regions with low basal MBF (< 0.6 ml/min/g), and from 0.77 +/- 0.14 ml/min/g to 0.92 +/- 0.29 ml/min/g (p = 0.013) in the 23 regions with basal MBF between 0.6 and 1 ml/min/g. Instead, in the 17 regions with high basal MBF (> 1 ml/min/g) it decreased with the stimulator on instead of off, going from 1.22 +/- 0.20 to 1.13 +/- 0.22 ml/min/g (p = 0.112). CONCLUSIONS: Our study suggests that the beneficial effects of SCS in refractory angina may also be related to an increase in mean MBF and to a redistribution of MBF between the regions with low or normal basal flow and the regions with high basal flow.

Myocardial perfusion, glucose utilization and oxidative metabolism in a patient with left bundle branch block, prior myocardial infarction and diabetes.

A diabetic patient affected by insulin-dependent diabetes, significant stenosis of left anterior descending (LAD) coronary, thrombolyzed myocardial infarction and complete left bundle branch block (LBBB) was examined by PET. Myocardial perfusion, glucose utilization and oxidative metabolism were evaluated by 13N-ammonia, 18F-fluorodeoxyglucose (FDG) and 11C-acetate, respectively. Despite severe damage in 18F-FDG uptake in the septum, with a septum-to-lateral ratio (S/L R) equal to 0.38, the oxidative metabolism in this area, evaluated quantitatively by dynamic acquisition, was relatively preserved (S/L R = 0.82), with a distribution similar to perfusion (S/L R = 0.87). These data reveal selective damage in glucose utilization in the septum in LBBB, unrelated to perfusion reduction and with preserved oxidative metabolism. Moreover, our experience could suggest an overestimation of the necrotic area by 18F-FDG in LBBB patients.

The role of fluorine-18-deoxyglucose (FDG) positron emission tomography (PET) whole body scan (WBS) in the staging and follow-up of cancer patients: our first experience.

We report the results of FDG PET whole body scan in 75 cancer patients in whom tumor extent was defined by surgical, histological or cytological findings and clinical follow-up. Twenty-five had malignant lymphomas, 24 lung carcinomas, and 26 other types of solid tumors. Twenty-three patients were evaluated at disease onset, before therapy, and 37 at the moment of tumor recurrence; the remaining 15 patients were in complete remission after treatment and were taken as controls. Visual and quantitative PET results were compared with conventional imaging (US, CT scan and/or MRI, and Tc99m MDP bone scan). In the 60 patients with active disease, PET as well as conventional imaging were able to locate the primary tumor in all 23 patients studied at disease onset. However, with regard to lymph node and distant metastases, PET provided the same information as conventional imaging in 31 cases (51.6%), but revealed further neoplastic foci in 29 cases (48.4%), 21 in lymph nodes and 8 at distant sites. The sensitivity of PET, in comparison with conventional imaging, was 100% versus 100% for the detection of the primary tumor, 97.6% versus 55.8% for the localization of node metastases, and 100% versus 55.5% for the visualization of distant metastases. The specificity, calculated in the group of 15 disease-free patients, was 100% for PET and 86.6% for conventional imaging. The therapeutic approach was modified in 12 patients (20%) on the basis of the PET results. Furthermore, in 14 cases (23.3%) with advanced disease, PET provided complete information on tumor spread, otherwise obtainable only by taking together the results of all other diagnostic procedures. Our data indicate a higher accuracy of FDG PET whole body scan compared to conventional imaging techniques in the evaluation of metastatic spread both at initial diagnosis and during follow-up, with an important impact on therapeutic decision-making. Moreover, by providing complete information on tumor spread in some cases, PET can become a profitable tool in terms of cost reduction.

A hybrid method of attenuation correction for positron emission tomography brain studies.

A hybrid method for attenuation correction (HAC) in positron emission tomography (PET) brain studies is proposed. The technique requires the acquisition of two short (1 min) transmission scans immediately before or after the emission study, with the patient and the head fixation system in place and after removing the patient from the scanner with the head fixation system alone. The method combines a uniform map of attenuation coefficients for the patient's head with measured attenuation coefficients for the head fixation system to generate a hybrid attenuation map. The HAC method was calibrated on 30 PET cerebral studies for comparison with the conventional measured attenuation correction method by ROI analysis. Average differences of less than 3% were found for cortical and subcortical regions. The HAC technique is particularly suitable in a PET clinical environment, allowing a reduction of the total study time, greater comfort for patients and an increase in patient throughput.