Effect of the duration of fasting on myocardial fluorine-18-fluorodeoxyglucose positron emission tomography images in normal males

To evaluate the effect of the duration of fasting on myocardial fluorine-18-fluorodeoxyglucose (FDG) uptake and distribution, 16 FDG-positron emission tomography (PET) studies were performed in 7 normal volunteers under three different conditions: glucose loading, 6 h fasting and overnight fasting. In the glucose-loaded condition, all subjects had good image quality, and myocardial metabolic rates of glucose (MRGlc) were significantly higher than those in the other two conditions. In the 6 h and overnight fasting conditions, image qualities varied according to MRGlc. Although there were visually distinct regional differences with MRGlc ranging from 0.05 to 0.15 mumol/min per g, these differences were not impressive by a quantitative analysis. The ranges of MRGlc in these two fasted conditions overlapped each other. There was a significant negative linear correlation between MRGlc and serum free fatty acid levels. Thus, MRGlc and image quality in fasted normal subjects varied with the extent of the fed-to-starved transition under clinical fasting conditions (6 h to overnight), and this transition does not depend solely on the duration of fasting. These findings may explain the heterogeneity in FDG studies under fasting conditions.

[Relationship between static images of 13N ammonia positron emission tomography and left ventricular wall motion in patients with coronary artery disease]

Observed myocardial activities in static image of 13N ammonia positron emission tomography (PET) contains factors about not only myocardial blood flow but also wall motion, wall thickness and glutamine synthetase activity. Those factors may help to delineate myocardial viability in 13N ammonia static image. To assess the role of 13N ammonia static image in prediction of reversibility of regional wall motion abnormalities after revascularization, we studied 20 patients with coronary artery disease. Of these patients, 15 patients underwent successful coronary revascularization (8 PTCA, 7 CABG). Regional 13N concentration before revascularization was expressed as a percent of maximal myocardial concentration and compared with regional wall motion. Wall motion was assessed by visual analysis using left ventriculography. Regional myocardial 13N concentration in normal, hypokinetic, akinetic and dyskinetic segments was 85 +/- 9.3%, 75 +/- 11%*, 71 +/- 17%* and 58 +/- 7.7%*#+, respectively (*p < 0.05 vs. normal, #p < 0.05 vs. hypokinesis, +p < 0.05 vs. akinesis). The segments with functional improvement showed significantly higher concentration of 13N than those without functional recovery (80 +/- 9.7% vs. 67 +/- 8.3%, p < 0.05). By using an optimized threshold value for normalized 13N activities, the sensitivity and specificity reached to 67% and 100%, respectively, to predict functional recovery. Our data suggested that myocardial 13N concentration in static PET image is closely related to the left ventricular wall motion in the patients with coronary artery disease and that it has a possible value of prediction of myocardial viability.

[Quantitation of regional myocardial blood flow using continuous inhalation of C15O2 and positron emission tomography]

A C15O2 continuous inhalation and a steady-state theory using positron emission tomography (PET) have been used to quantitate regional cerebral blood flow. We extended this method for quantitative regional myocardial blood flow (RMBF) measurement. Forty-three patients, involving 4 normal volunteers, 16 patients with coronary heart disease (CHD), 20 patients with hypertrophic cardiomyopathy (HCM), and 3 patients with dilated cardiomyopathy (DCM), were studied. 6 min-scan was recorded in the steady-state condition during C15O2 continuous inhalation. A C15O inhalation scan was required to obtain the blood pool image. The subtracted image showed myocardial perfusion image. These images demonstrated homogeneous accumulation in normal volunteers. Reduced accumulation were detected in patients with myocardial infarction. Hypertrophied myocardium was demonstrated in patients with HCM. Diffuse heterogeneous accumulation was demonstrated in patients with DCM. Fourteen patients with HCM, whose left ventricular myocardial thicknesses were more than 20 mm, were selected for the RMBF measurement to minimize errors due to the partial volume effect. The arterial blood activity was measured by assigning a region of interest to the left atrial cavity on PET images. RMBF was calculated using the steady-state theory. Calculated flow values ranged from 21.2 to 152.6 ml/min/100 g. The good correlation was obtained between RMBF using 13NH3 first pass method and RMBF using gas inhalation method in six patients. These results indicate that C15O2 PET has the potential capability for the noninvasive quantitation of RMBF.

[Usefulness of 18F-fluorodeoxyglucose positron emission tomography for evaluating myocardial viability in old myocardial infarction]

The purpose of this study is to compare the characteristics of images obtained by positron emission tomography (PET) using 18F-fluorodeoxyglucose (FDG) in the fasted state (> 6 hours) and in the glucose-loaded state (oral 50 g glucose load). In the both condition FDG-PET were performed in 18 cases with old myocardial infarction. PET images in the fasted state were divided into 2 groups (Group A; 12 cases and Group B; 6 cases). FDG uptake of normal region was visually absent (grade 0) in group A, whereas it was visually apparent (grade 1-3) in group B. Serum free fatty acid in group B was significantly lower than that in group A. In the 7 cases, the relation between myocardial FDG uptake of the infarcted regions and reversibility after coronary intervention was studied. Both in the fasted and in the glucose-loaded state, postoperative improvement was observed in the segments, in which myocardial uptake of FDG were visually apparent (glucose-loaded state, 11/13 segments; fasted state, 6/8 segments). Therefore FDG-PET images appeared to be useful for evaluating myocardial viability.

[Pulmonary kinetics of 13N-ammonia in smoking subjects--a quantitative study using dynamic PET]

To evaluate the effect of smoking on nonrespiratory function in the lung, a dynamic PET with 13NH3 in the lung was performed in 18 normal volunteers without lung disease nor congestion (9 non-smokers, 4 exsmokers, 5 smokers). After intravenous bolus injection of 13NH3, twenty serial 5.5-second scans followed by six 30-second scans were performed. Regions of interests were assigned on the ventral, lateral and dorsal part of the right lung and time-activity curves were generated through 26 images. The activity curve demonstrated a biexponential clearance from the lung with fast and slow component. The retention fraction (RF), fractional size of the slow component, was calculated, and the half-times (t 1/2) of both components were also evaluated. A significant increase of RF and prolongation of t 1/2 of slow component were observed in smokers compared to non-smokers and exsmokers. However, no significant difference of RF nor t 1/2 of both components was observed between non-smokers and exsmokers. These results suggest that long term smoking may modify the pulmonary kinetics of 13NH3, but the change is reversible after cessation of smoking for one year or longer.

[Hypertrophic cardiomyopathy associated with anomalous origin of the left coronary artery from the right sinus of valsalva]

A 47 year old Japanese male with exertional shortness of breath, cardiac murmur and ECG abnormalities was examined with invasive and non-invasive cardiology techniques that disclosed hypertrophic cardiomyopathy, and the anomalous origin of the left coronary artery from the right sinus of Valsalva. Although both situations have been known to cause sudden death especially under a state of strenuous physical stress, his exercise thallium scintigraphy performed with the symptom limited maximal test did not uncover any significant myocardial ischemia or exercise induced malignant arrhythmias. This is a very rare association of two distinctly identified clinical situations highly indicative of a likelihood of sudden cardiac death. Therefore, careful observation is needed.

[PET assessment of myocardial viability with glucose loading and fasting FDG images]

Positron emission tomography (PET) offers the potential capability of evaluating tissue viability. We have studied the changes of myocardial F-18 deoxyglucose (FDG) uptake with glucose loading. In a fasting state (for at least 5 hours) and in a glucose loading state (50 g glucose orally one hour before the study) FDG (74-148 MBq) PET studies were performed for 50-60 minutes in 3 cases. 2 were subjects with anterior myocardial infarction (MI) including one with a ventricular aneurysm (case 1), one with a recent MI (case 2). One was a subject of aortic valvular disease without coronary lesions (case 3). Arterial input function (Ca(t)) and myocardial activity (Cm(t)) were derived from the regions of interest (ROI) on the left atrium and from multiple ROI's circumferentially about the myocardium. Net extraction, FU (Fractional Uptake) = Cm(T)/integral of T0 Ca(t)dt, were calculated. Normal segment (N) showed an increase in FU with glucose loading, but the ischemic segment showed no increase (case 1) or a lower increase (case 2) relative to N. This study shows that the increase in FU with glucose loading suggests the persistence of viable myocardium. In conclusion, myocardial viability may be evaluated by comparing FDG images in a glucose loading state with those in a fasting state.