Katsuya Yoshida

Effect of scattered radiation on image noise in cone beam CT

Cone beam CT has a capability for the 3-dimensional imaging of large volumes with isotropic resolution, and has a potentiality for 4-dimensional imaging (dynamic volume imaging), because cone beam CT acquires data of a large volume with one rotation of an x-ray tube-detector pair. However, one of the potential drawbacks of cone beam CT is a larger amount of scattered x-rays, which may enhance the noise in reconstructed images, and thus affect the low-contrast detectablity. Our aim in this work was to estimate the scatter fractions and effects of scatter on image noise, and to seek methods of improving image quality in cone beam CT. First we derived a relationship between the noise in a reconstructed image and in an x-ray intensity measurement. Then we estimated the scatter to primary ratios in x-ray measurements using a Monte-Carlo simulation. From these we estimated the image noise under relevant clinical conditions. The results showed that the scattered radiation made a substantial contribution to the image noise. However, focused collimators could improve it by decreasing the scattered radiation drastically while keeping the primary radiation at nearly the same level. A conventional grid also improved the image noise, though the improvement was less than that of focused collimators.

Lung as reservoir for antidepressants in pharmacokinetic drug interactions

BACKGROUND Although high-affinity imipramine binding sites have been reported in both rat and human lung, the role of the lungs in the pharmacokinetics of antidepressants has not received much attention. Substantial accumulation of selective serotonin-reuptake inhibitors (SSRIs) in the lungs has been reported. We have investigated the role of the lungs in pharmacokinetic drug interactions between tricyclic antidepressants and SSRIs. METHODS We used a carbon-11-labelled form of the imipramine derivative cyanoimipramine to measure uptake in the lungs and brain of healthy volunteers by positron emission tomography. Clomipramine (50 mg) was administered to measure the effect of antidepressants with high affinity for the serotonin transporter on lung and brain uptake. FINDINGS A large proportion of the injected 11C-cyanoimipramine (68-86% in the four volunteers) was extracted by the lungs. Clomipramine decreased the lung uptake from 68% to 35% and from 81% to 54% in the two volunteers studied. By contrast, whole-brain uptake was low in control studies (1.7-2.0% in three volunteers) and increased after clomipramine administration (to 4.5-4.9%). Plasma radioactivity was also higher after clomipramine than in control studies. INTERPRETATION The lungs may function as a reservoir for antidepressants with high affinity to the serotonin transporter. The accumulated antidepressants may be displaced by other antidepressants, and this displacement would substantially increase plasma concentrations and thus cause toxic effects.

Detection of Experimental Autoimmune Myocarditis in Rats by 111In Monoclonal Antibody Specific for Tenascin-C

Background—Although the identification of inflammatory infiltrates in endomyocardial biopsy specimens is necessary for the definite diagnosis of myocarditis, the biopsy test is invasive and is not sensitive. Therefore, a new diagnostic technique for the early and noninvasive evaluation of myocarditis has been awaited. Expression of tenascin-C (TNC), one of the oligometric extracellular glycoproteins, is induced in various pathological states, including inflammation, suggesting that TNC can be a molecular marker of myocarditis. Methods and Results—An 111In anti-TNC monoclonal antibody Fab′ fragment was injected intravenously into rats with experimental autoimmune myocarditis (EAM), and the biodistribution of this radiotracer was measured. Rapid clearance of radioactivity from the blood was observed in both EAM and control rats (<1% at 6 hours after injection). Myocardial uptake of the tracer was much higher in EAM rats than in control rats (7.54-, 4.39-, and 3.51-fold at 6, 24, and 48 hours after injection, respectively). By autoradiography, high radioactivities were clearly observed in the regions indicative of inflammation in EAM rats. Single-photon emission CT imaging demonstrated the focal myocardial uptake of 111In anti-TNC Fab′ in vivo. Conclusions—Radiolabeled anti-TNC Fab′ may be useful for the noninvasive diagnosis of myocarditis.

Increased subcutaneous fat accumulation has a protective role against subclinical atherosclerosis in asymptomatic subjects undergoing general health screening

PURPOSE To evaluate the clinical role of subcutaneous fat accumulation in subclinical arteriosclerosis, using computed tomography (CT), we measured the subcutaneous fat area (SFA), the visceral fat area (VFA) and the VFA/SFA ratio and compared these with the calcium score of the whole aorta (CSWA) in asymptomatic subjects who were undergoing general health screening. METHODS 122 consecutive asymptomatic subjects (40 female, mean age 56.2+/-8.4 years) were analyzed. Whole-body low-dose CT scan (mAs=50, slice thickness=5 mm) was performed. The SFA and VFA were measured at the umbilical level. Calcification of whole aorta was defined as an area with >90 HU and 1 mm(2), and CSWA was calculated using the modified Agatston method. RESULTS Mean+/-SD of SFA, VFA and log CSWA were 158+/-67.1 cm(2), 94.0+/-44.8 cm(2), and 7.93+/-1.08, respectively. SFA was significantly and inversely correlated with log CSWA (r=-0.219, P=0.015) but VFA was not (r=0.105, P=0.250) and as a result, the VFA/SFA ratio was significantly and positively correlated with log CSWA (r=0.221, P=0.015). Subsequently, all predictor variables were used in a stepwise multiple regression model with log CSWA as dependent variable, and age, SFA and fasting plasma glucose significantly influenced log CSWA (P<0.001) by the multiple regression formula Y=0.046X1***-0.005X2**+0.015X3*+4.426, (***P<0.001, **P<0.01, and *P<0.05) where Y=log CSWA, X1=age, X2=SFA, and X3=fasting plasma glucose). CONCLUSIONS SFA was significantly and inversely associated with log CSWA, in an independent fashion. These results suggest that subcutaneous fat accumulation might have a protective role against atherosclerosis in asymptomatic subjects.

Prognostic Utility of Myocardial Blood Flow Assessed by N-13 Ammonia Positron Emission Tomography in Patients With Idiopathic Dilated Cardiomyopathy

Previous studies in patients with idiopathic dilated cardiomyopathy (IDC) have suggested that myocardial perfusion is impaired and spatially heterogeneous in such cases. Our objective was to identify any association between an abnormality in myocardial perfusion and the prognosis of patients with IDC. We collected data on N-13 ammonia positron emission tomography (PET) studies performed in 26 patients with IDC (9 nonsurvivors, 17 survivors) and in 8 normal control subjects. Regional myocardial blood flow (rMBF) was quantified using N-13 ammonia positron emission tomography and the Simple flow model. The spatial heterogeneity of myocardial perfusion was assessed by calculating the coefficient of variance of rMBF. Mean rMBF of the survivors was significantly lower (0.54 +/- 0.13 ml/min/g) than that of control subjects (0.66 +/- 0.06 ml/min/g) (p = 0.03 vs control), but did not differ significantly between nonsurvivors (0.58 +/- 0.15 ml/min/g) and control subjects. The coefficient of variance of rMBF was significantly higher in nonsurvivors than in either survivors or control subjects (0.24 +/- 0.08 vs 0.15 +/- 0.08, p = 0.007, and 0.16 +/- 0.05, p = 0.03, respectively). The probability of 3-year survival (Kaplan-Meier method) was 33.0% in subjects whose coefficient of variance of rMBF was above the median compared with 90.0% in subjects whose coefficient of variance of rMBF was below the median (p = 0.01). The probability of 3-year survival did not differ among subjects whose mean rMBF was above versus below the median (61.5% vs 62.9%, respectively). The results suggest that the prognosis of patients with IDC is associated with the spatial heterogeneity of myocardial perfusion, not with initial absolute rMBF.

Measurement of Arterial Tracer Concentrations from Cardiac Pet Images

Objective Cardiac PET imaging offers the potential capability for the noninvasive measurement of arterial input function. This capability is somewhat limited, however, because of partial volume and spillover effects. The purpose of this study was to validate arterial tracer concentration measurements using PET images by assigning a region of interest (ROI) to the left ventricle, left atrium (LA), and ascending aorta. Materials and Methods We selected [11C]CO and [13N]ammonia as tracers, because the activity of [11C]CO is primarily in the blood pool and that of [13N]amtnonia primarily in myocardial tissue. Six [11C]CO and 11 [13N]ammonia PET scans were obtained in 17 subjects. Arterial tracer concentrations determined by PET were compared with those measured by well counting of arterial blood sampling obtained at the midpoint of each image acquisition. Results Arterial tracer concentrations as determined by LA-PET imaging correlated closely with those measured by blood sampling (r = 0.996, slope = 1.00 for [11C]CO; r = 0.841, slope = 0.974 for [13N]ammonia). Partial volume and spillover effects were minimized by assigning an ROI to the LA. Conclusion Arterial tracer concentrations can be measured noninvasively with cardiac PET. Index Terms Emission computed tomography—Heart—Tracers—Emission computed tomography, techniques.

Three dimensional segmented myocardial perfusion images by selective intracoronary injection of contrast using 256 slice cone beam computed tomography

Information of the segmented left ventricular (LV) area supplied by every coronary artery is potentially useful for strategy and practice of percutaneous coronary intervention, coronary artery bypass surgery, or percutaneous transluminal septal myocardial ablation (PTSMA).1,2 Myocardial contrast echocardiography (MCE) with intracoronary contrast injection has been used to evaluate the segmented LV area supplied by a coronary artery but it is invasive and evaluation of myocardial enhancement by ultrasound contrast material may depend upon the skill of the investigator.1 With a prototype high speed cone beam computed tomography (CT) apparatus employing 256 detector rows (Athena, Sony-Toshiba), an entire heart can be imaged within a single gantry rotation.3,4 Using this technique, combined with selective intracoronary injection of contrast, we determined the segmented LV area supplied by every coronary artery selectively. Two domestic pigs (20 kg each) were anaesthetised with isoflurane, and catheters positioned in the left anterior descending branch (LAD) of the coronary artery in pig 1 and the left circumflex branch (LCx) in pig 2, via the femoral arteries. The heart rate of pigs ranged between 70–80 beats per minute. Scan conditions for the 256 slice cone beam CT were: 120 kV, 200 mA, 1.0 second exposure, 1.0 second gantry rotation time, 0.5 mm slice thickness, and 256×0.5 mm slice collimation. For comparison, those for the 16 slice multislice CT scanner routinely used at our institute (SOMATOM Sensation 16, Siemens) were: …

Three-vessel study of cerebral blood flow using phase-contrast magnetic resonance imaging: Effect of physical characteristics

The development of phase-contrast magnetic resonance imaging (P-C MRI) provides a noninvasive method for measurement of volumetric blood flow (VFR). We performed P-C MRI to study the effects of physical characteristics on cerebral blood flow. VFR of the left and right internal carotid arteries and basilar artery were measured using P-C MRI and total cerebral blood flow (tCBF) was calculated by summing up the VFR values in the three vessels. Moreover, we investigated the changes in these blood flows as influenced by age, head size, height, weight, body surface area, and handedness. The blood flows were 142 +/- 58 ml/min (mean +/- standard deviation) in the basilar artery; and 229 +/- 86 ml/min in the left, and 223 +/- 58 ml/min in the right internal carotid artery; and tCBF was 617 +/- 128 ml/min. Significant increases were observed in head size-related change of VFR in the basilar artery (p = .028) and height-related change of tCBF (p = .045). The other characteristics did not significantly influence any VFR. The results suggest that head size and height may reflect CBF, and that these effects should be considered when changes of CBF are diagnosed. Phase-contrast MRI is useful for a noninvasive and rapid analysis of cerebral VFR and has potential for clinical use.

Myocardial Fibrosis in Fabry Disease Demonstrated by Multislice Computed Tomography Comparison With Biopsy Findings

A54-year-old man presented with dyspnea on effort. Echocardiogram revealed reduced apical wall motion of the left ventricle (LV) with extreme hypertrophy of the interventricular septum (IVS). Conventional coronary angiogram showed normal coronary arteries. Endomyocardialbiopsy specimens obtained from the IVS revealed extensive vacuolization of cardiac myocytes and mild fibrosis on light microscopy, and typical lysosomal inclusions with a concentric lamellar configuration were seen with electron microscopy (Figure 1). With these findings and low plasma -galactosidase activity, he was diagnosed as having Fabry disease. To evaluate the characteristics of the LV, ECG-gated enhanced multislice computed tomography (CT) (Light Speed Ultra, General Electric) was performed with a 1.25-mm slice thickness, helical pitch 3.25. After intravenous injection of 100 mL of iodinated contrast material (350 mgI/mL), CT scanning was performed with retrospective ECG-gated reconstruction at 30 seconds and 8 minutes after injection. In the axial source images, extreme hypertrophy of the IVS and the posterior wall of the LV compared with the apical and lateral walls of the LV could be observed (Figure 2). The apical and lateral portions of the LV revealed lower CT intensity than the IVS in the early phase (arrows), and in the late phase they were abnormally enhanced compared with the IVS, suggesting fibrotic changes in the apical and lateral myocardium. Therefore, we concluded that despite the IVS biopsy results, more fibrotic changes occurred in the apical and lateral portions of the LV rather than in the IVS.A 54-year-old man presented with dyspnea on effort. Echocardiogram revealed reduced apical wall motion of the left ventricle (LV) with extreme hypertrophy of the interventricular septum (IVS). Conventional coronary angiogram showed normal coronary arteries. Endomyocardial-biopsy specimens obtained from the IVS revealed extensive vacuolization of cardiac myocytes and mild fibrosis on light microscopy, and typical lysosomal inclusions with a concentric lamellar configuration were seen with electron micros-copy (Figure 1). With these findings and low plasma α-galactosidase activity, he was diagnosed as having Fabry disease. To evaluate the characteristics of the LV, ECG-gated …

Noninvasive quantification of regional myocardial blood flow and ammonia extraction fraction using nitrogen-13 ammonia and positron emission tomography

This report describes the theoretical basis and a method to quantitate regional myocardial blood flow (RMBF) and ammonia extraction fraction (E) in man, noninvasively, with N-13 ammonia and positron emission tomography (PET). Two patients with hypertrophic cardiomyopathy, whose left ventricular (LV) walls were markedly thick, were employed in this study to avoid partial volume effects and cross contamination between LV walls and blood pool. RMBF and E were calculated from time-activity curves of myocardial tissue and left atrium derived from serial 6-second PET images of the heart. The time-activity curve of left atrium was used as an arterial input function. The results were RMBF=67 ±4 m//rm’n/ 100 g, E=80±13% and 65±10ml/min/100 g, 81±16% for each patient. The validity of the present method was discussed.