Comparison of patient doses in 256-slice CT and 16-slice CT scanners

The 256-slice CT-scanner has been developed at the National Institute of Radiological Sciences. Nominal beam width was 128 mm in the longitudinal direction. When scanning continuously at the same position to obtain four-dimensional (4D) images, the effective dose is increased in proportion to the scan time. Our purpose in this work was to measure the dose for the 256-slice CT, to compare it with that of the 16-slice CT-scanner, and to make a preliminary assessment of dose for dynamic 3D imaging (volumetric cine imaging). Our group reported previously that the phantom length and integration range for dosimetry needed to be at least 300 mm to represent more than 90% of the line integral dose with the beam width between 20 mm and 138 mm. In order to obtain good estimates of the dose, we measured the line-integral dose over a 300 mm range in PMMA (polymethylmethacrylate) phantoms of 160 mm or 320 mm diameter and 300 mm length. Doses for both CT systems were compared for a clinical protocol. The results showed that the 256-slice CT generates a smaller dose than the 16-slice CT in all examinations. For volumetric cine imaging, we found an acceptable scan time would be 6 s to 11 s, depending on examinations, if dose must be limited to the same values as routine examinations with a conventional multidetector CT. Finally, we discussed the studies necessary to make full use of volumetric cine imaging.

Optimizing T2-weighted magnetic resonance sequences for surface coil microimaging of the eye with regard to lid, eyeball and head moving artifacts

PURPOSE

To acquire high-resolution magnetic resonance (MR) images, we developed a new blinking artifact reduced pulse (BARP) sequence with a surface coil specialized for microscopic imaging (47 mm in diameter).

MATERIALS AND METHODS

To reduce eye movement, we ascertained that the subjects' eyes were kept open and fixated to the target in the 1.5-T MR gantry. To reduce motion artifacts from blinking, we inserted rest periods for blinking (1.5 s within every 5 s) during MR scanning (T2-weighted fast spin echo; repetition time, 5 s; echo time, 100 ms; echo train, 11; matrix, 256 x 128; field of view, 5 cm; 1-mm thickness x 30 slices). Three scans (100 s x 3) were performed for each normal subject, and they were added together after automatic adjustment for location to reduce quality loss caused by head motion.

RESULTS

T2-weighted MR images were acquired with a high resolution and a high signal-to-noise ratio. Motion artifacts were reduced with BARP, as compared with those with random blinking. Intraocular structures such as the iris and ciliary muscles were clearly visualized. Because the whole eye can be covered with a 1-mm thickness by this method, three-dimensional maps can easily be generated from the obtained images.

CONCLUSION

The application of BARP with a surface coil of the human eye might become a useful and widely adopted procedure for MR microimaging.

Estimation of plasma IC50 of donepezil hydrochloride for brain acetylcholinesterase inhibition in monkey using N-[11C]methylpiperidin-4-yl acetate ([11C]MP4A) and PET

Donepezil hydrochloride is a potent and selective inhibitor for brain acetylcholinesterase (AChE) and is currently used worldwide for the treatment of Alzheimer's disease. Until now, there is no in vivo study on the relation between the plasma concentration and the brain AChE inhibition. The purpose of this study was to estimate in vivo plasma IC(50) of donepezil in living monkeys by measuring plasma donepezil concentration (LC/MS/MS) and brain AChE activity with positron emission tomography (PET) and N-[(11)C]methylpiperidin-4-yl acetate, which is an acetylcholine analog recently developed by us for quantifying in vivo brain AChE activity. PET scans with donepezil at two doses, 100 microg/kg (donepezil-1; N=5) or 250 microg/kg (donepezil-2; N=5), were performed using the same monkeys at 4-week intervals. Before each PET scan, baseline PET scans (N=10 in total) were performed without donepezil. The plasma donepezil concentrations 14 min after intravenous injection were proportional to the doses, 17.2+/-2.9 ng/ml (donepezil-1) and 44.0+/-5.0 ng/ml (donepezil-2), and the mean AChE inhibitions in four neocortical regions as evaluated by PET were also dose-dependent, 27% (donepezil-1) and 53% (donepezil-2). In IC(50) estimation, measured plasma donepezil concentrations were corrected for the change during PET scan. The IC(50) values (estimate+/-SE) were 42+/-9.0 (ng/ml; donepezil-1), 34+/-3.2 (donepezil-2), and 37+/-4.1 (combined data). The present method may be useful for in vivo evaluation of other AChE inhibitors and novel drugs.

Clinical Potentials for Dynamic Contrast-Enhanced Hepatic Volumetric Cine Imaging with the Prototype 256-MDCT Scanner

OBJECTIVE

To achieve dynamic contrast-enhanced hepatic volumetric cine imaging, we developed a prototype 256-MDCT scanner. This study examined the feasibility of the technique for human hepatic imaging in three hepatocellular carcinoma patients.

CONCLUSION

Volumetric cine imaging successfully visualized dynamic contrast enhancement of the hepatocellular carcinoma. It is helpful to evaluate the phase of contrast enhancement or for functional studies of the head, renal artery, coronary artery, and liver.

Functional network in the prefrontal cortex during episodic memory retrieval

A recent consistent finding in neuroimaging studies of human memory is that the prefrontal cortex (PFC) is activated during episodic memory retrieval. To date, however, there has been no direct evidence to explain how activity in the right and left PFC and in the anterior and posterior PFC are functionally interconnected. The goal of the present study was to obtain such evidence by event-related functional magnetic resonance imaging (MRI) and the functional connectivity method. Subjects were first asked to try to remember a series of associate-word lists outside the MRI scanner in preparation for a later recognition test. In the MRI scanning phase, they were asked to make recognition judgments in regard to old words, semantically related lure words, and unrelated new words. The analysis of functional connectivity revealed that the posterior PFC in each hemisphere had strong functional interconnections with the contralateral posterior PFC, whereas the anterior PFC in each hemisphere had only weak functional interconnections with the contralateral anterior PFC. No strong functional interconnections were found between the anterior and posterior PFC in either hemisphere. These findings support the hypothesis of an associative contribution of the bilateral posterior PFC to episodic memory retrieval and a dissociative contribution of the bilateral anterior PFC.

Clinical potentials of the prototype 256-detector row CT-scanner

RATIONALE AND OBJECTIVES

To evaluate clinical potentials of the 256-detector row computed tomography (CT) in healthy volunteers.

MATERIALS AND METHODS

Eight healthy males (22-63 years) participated in the present study. They underwent a noncontrast-enhanced examination with a contiguous axial scan mode either for head, chest, abdomen, or pelvis. Dose was the same as routinely used for multislice CT examinations. Image quality was interpreted by three board-certified radiologists.

RESULTS

With the 256-detector row CT, 0.5-0.8 mm isotropic volumetric data could be acquired in one rotation. Main promising findings are as follows. Three-dimensional structures were visualized clearly in the multiple planes without secondary reconstruction, whereas the axial images had nearly the same image quality as conventional CT. Shading or streak artifacts were observed at the edge of the scan region. The latter are also known as Feldkamp artifacts. Coronal chest images showed a motion artifact from the heart beating.

CONCLUSION

The 256-detector row CT promises to be useful in clinical applications with its ability to provide three-dimensional visualization of fine structures. The Feldkamp artifacts observed did not generally affect interpretation of images. Investigations are now continuing on image correction along the craniocaudal direction to improve the overall image quality.

Physical performance evaluation of a 256-slice CT-scanner for four-dimensional imaging

We have developed a prototype 256-slice CT-scanner for four-dimensional (4D) imaging that employs continuous rotations of a cone-beam. Since a cone-beam scan along a circular orbit does not collect a complete set of data to make an exact reconstruction of a volume [three-dimensional (3D) image], it might cause disadvantages or artifacts. To examine effects of the cone-beam data collection on image quality, we have evaluated physical performance of the prototype 256-slice CT-scanner with 0.5 mm slices and compared it to that of a 16-slice CT-scanner with 0.75 mm slices. As a result, we found that image noise, uniformity, and high contrast detectability were independent of z coordinate. A Feldkamp artifact was observed in distortion measurements. Full width at half maximum (FWHM) of slice sensitivity profiles (SSP) increased with z coordinate though it seemed to be caused by other reasons than incompleteness of data. With regard to low contrast detectability, smaller objects were detected more clearly at the midplane (z = 0 mm) than at z = 40 mm, though circular-band like artifacts affected detection. The comparison between the 16-slice and the 256-slice scanners showed better performance for the 16-slice scanner regarding the SSP, low contrast detectability, and distortion. The inferiorities of the 256-slice scanner in other than distortion measurement (Feldkamp artifact) seemed to be partly caused by the prototype nature of the scanner and should be improved in the future scanner. The image noise, uniformity, and high contrast detectability were almost identical for both CTs. The 256-slice scanner was superior to the 16-slice scanner regarding the PSF, though it was caused by the smaller transverse beam width of the 256-slice scanner. In order to compare both scanners comprehensively in terms of exposure dose, noise, slice thickness, and transverse spatial resolution, K=Dsigma2ha3 was calculated, where D was exposure dose (CT dose index), sigma was magnitude of noise, h was slice thickness (FWHM of SSP), and a was transverse spatial resolution (FWHM of PSF). The results showed that the K value was 25% larger for the 16-slice scanner, and that the 256-slice scanner was 1.25 times more effective than the 16-slice scanner at the midplane. The superiority in K value for the 256-slice scanner might be partly caused by decrease of wasted exposure with a wide-angle cone-beam scan. In spite of the several problems of the 256-slice scanner, it took a volume data approximately 1.0 mm (transverse) x 1.3 mm (longitudinal) resolution for a wide field of view (approximately 100 mm long) along the zeta axis in a 1 s scan if resolution was defined by the FWHM of the PSF or the SSP, which should be very useful to take dynamic 3D (4D) images of moving organs.

Cardiovascular Circulation and Hepatic Perfusion of Pigs in 4-Dimensional Films Evaluated by 256-Slice Cone-Beam Computed Tomography

BACKGROUND

In both cardiac and hepatic disorders it is desirable to accurately visualize the direction and scale of blood flow in the whole organ in pulsating 3-dimensional (D) images, which are known as 4-D images.

METHODS AND RESULTS

The present study used 256-slice cone-beam computed tomography (CT) (Athena, Sony-Toshiba) at one rotation per second and a section thickness of 0.5 mm to show the dynamics of cardiovascular circulation and hepatic perfusion by contrast injection in 4-D films of pigs. Four pigs (20 kg each) were anesthetized with isoflurane. The distal tips of the catheters were positioned in the inferior vena cava (IVC) (pigs 1-3) and in the proper hepatic artery (pig 4). Volumetric scanning and injection of contrast material were started simultaneously and continued for 25 s with image reconstruction at 1-s intervals. In pigs 1-3, 4-D filming revealed the dynamics of cardiovascular circulation, first in the IVC, followed by the right ventricle and pulmonary artery, then the left ventricle, left atrium, pulmonary vein, and finally, the right heart disappeared and only the left heart and aorta remained visible. In pig 4, the hepatic arterial trees, followed by the venous trees, could be easily visualized in turn on the 4-D images.

CONCLUSIONS

This technology successfully demonstrated cardiovascular circulation and hepatic perfusion in 4-D and will have clinical applicability.

Effect of calcium trisodium DTPA in rats with puncture wound contaminated by 90Y-chloride

The efficacy of diethylenetriaminepentaacetate calcium trisodium (CaNa(3)DTPA) in a dose of 34.7 micromol kg(-1) as a function of its route of administration was investigated in rats with a puncture wound contaminated by (90)Y-chloride at a concentration of 2.55 MBq kg(-1). Approximately 60% of (90)Y-chloride at a puncture wound was absorbed into the body of rats over 72 h post-puncture and radioactivity in femoral bone increased during the timed-release of (90)Y. Intravenous administration of CaNa(3)DTPA (systemic treatment) at 15 min post-puncture reduced (90)Y at a puncture wound and in bone up to 75.6 and 84.3% of controls, respectively. Direct infiltration of CaNa(3)DTPA into a puncture wound site (local treatment) at 15 min post-puncture diminished radioactivity at the puncture wound and in bone up to 34.9 and 52.5% of controls, respectively. Thus, prompt local treatment may be effective for removing (90)Y from a puncture wound and minimising (90)Y-distribution to bone compared with systemic treatment.

Carbon-11-methionine positron emission tomography imaging of chordoma

OBJECTIVE

Chordoma is a rare malignant bone tumor that arises from notochord remnants. This is the first trial to investigate the utility of (11)C-methionine (MET) positron emission tomography (PET) in the imaging of chordoma before and after carbon-ion radiotherapy (CIRT).

DESIGN AND PATIENTS

Fifteen patients with chordoma were investigated with MET-PET before and after CIRT and the findings analyzed visually and quantitatively. Tumor MET uptake was evaluated by tumor-to-nontumor ratio (T/N ratio).

RESULTS

In 12 (80%) patients chordoma was clearly visible in the baseline MET-PET study with a mean T/N ratio of 3.3+/-1.7. The MET uptake decreased significantly to 2.3+/-1.4 after CIRT ( P<0.05). A significant reduction in tumor MET uptake of 24% was observed after CIRT. Fourteen (93%) patients showed no local recurrence after CIRT with a median follow-up time of 20 months.

CONCLUSION

This study has demonstrated that MET-PET is feasible for imaging of chordoma. MET-PET could provide important tumor metabolic information for the therapeutic monitoring of chordoma after CIRT.

Changes in the pharmacokinetics of Gd-DTPA in experimental tumors after charged particle radiation: comparison with gamma-ray radiation

We performed dynamic MRI to reveal the characteristic gadopentetate dimeglumine (Gd-DTPA) uptake in carbon-ion irradiated tumor and compare it with photon irradiation. Fibrosarcomas in C3H mice legs were irradiated with either 16 Gy of carbon ions (74 keV/mm) or an equivalent dose (30 Gy) of Cs-137 gamma-rays. Dynamic MRI was performed 1 or 6 days after irradiation when the tumors showed an initial growth delay or incipient regrowth, respectively. The enhancement pattern was visualized by mapping the maximum enhanced time (Tmax), relative signal intensity maximum (SImax), and time delay of starting enhancement (Td). Significantly larger Tmax and Td values were observed in the tumors 1 day after carbon-ion irradiation than in the nonradiated tumors (No-R) and tumors 1 day after gamma-ray irradiation. Among the selected pixels in the tumors 6 days after carbon irradiation, 77% had Tmax values of less than 120 sec, significantly more than in the No-R group. The Tmax maps for the tumors irradiated with gamma-rays showed a similar tendency to the carbon-irradiated ones, and only a significant difference was obtained between tumors 1 and 6 days after irradiation. Tmax and Td in the carbon-ion irradiated tumors were different from those in the gamma-ray-irradiated tumors. These treatment-specific kinetics may be useful in predicting the therapeutic efficacy of carbon-ion treatment.

Evaluation of simplified kinetic analyses for measurement of brain acetylcholinesterase activity using N-[11C]Methylpiperidin-4-yl propionate and positron emission tomography

The applicability of two reference tissue-based analyses without arterial blood sampling for the measurement of brain regional acetylcholinesterase (AChE) activity using N-[11C]methylpiperidin-4-yl propionate ([11C]MP4P) was evaluated in 12 healthy subjects. One was a linear least squares analysis derived from Blomqvist's equation, and the other was the analysis of the ratio of target-tissue radioactivity relative to reference-tissue radioactivity proposed by Herholz and coworkers. The standard compartment analysis using arterial input function provided reliable quantification of k3 (an index of AChE activity) estimates in regions with low (neocortex and hippocampus), moderate (thalamus), and high (cerebellum) AChE activity with a coefficient of variation (COV) of 12% to 19%. However, the precise k3 value in the striatum, where AChE activity is the highest, was not obtained. The striatum was used as a reference because its time-radioactivity curve was proportional to the time integral of the arterial input function. Reliable k3 estimates were also obtained in regions with low-to-moderate AChE activity with a COV of less than 21% by striatal reference analyses, though not obtained in the cerebellum. Shape analysis, the previous method of direct k3 estimation from the shape of time-radioactivity data, gave k3 estimates in the cortex and thalamus with a somewhat larger COV. In comparison with the standard analysis, a moderate overestimation of k3 by 9% to 18% in the linear analysis and a moderate underestimation by 2% to 13% in the Herholz method were observed, which were appropriately explained by the results of computer simulation. In conclusion, simplified kinetic analyses are practical and useful for the routine analysis of clinical [11C]MP4P studies and are nearly as effective as the standard analysis for detecting regions with abnormal AChE activity.

A simple method for the detection of abnormal brain regions in Alzheimer’s disease patients using [11C]MP4A: Comparison with [123I]IMP SPECT

We have developed a radiolabeled lipophilic acetylcholine analogue, N-[11C]methylpiperidin-4-yl acetate ([11C]MP4A) to measure brain acetylcholinesterase (AChE) activity by positron emission tomography (PET) in vivo. Aiming to develop a new SPECT tracer similar to MP4A, we first proposed a simple method for diagnosing Alzheimer's disease (AD) using [11C]MP4A PET. We performed [11C]MP4A PET and N-isopropyl [123I]iodoamphetamine ([123I]IMP) SPECT in 13 patients with AD and in 17 normal controls (NC). We calculated the ratio of radioactivity of the cortical region of interest (ROI) to that of the cerebellum measured with [11C]MP4A PET (MP4A ratio) and the ratio of regional cerebral blood flow (rCBF) to that of the cerebellum measured with [123I]IMP SPECT (IMP ratio). Eleven cortical ROIs were placed in the frontal, sensorimotor, temporal, parietal, and occipital cortices in both hemispheres and in the posterior cingulate cortex, and z-score was calculated in each ROI in patients with AD compared with NC. When the z-score was 2 or more in a ROI, it was defined as a positive ROI. When a patient had 3 or more positive ROIs, the patient was diagnosed as having AD. The reduction in the MP4A ratio was greater than that in the IMP ratio in all cortical ROIs except for in the right parietal cortex and cingulate cortex in patients with AD. MP4A ratio method showed 92% sensitivity and the IMP ratio method 69% sensitivity for the diagnosis of AD. These results encourage us to develop a new SPECT tracer similar to MP4A for the diagnosis of AD.

[11C]Methionine Positron Emission Tomography and Survival in Patients with Bone and Soft Tissue Sarcomas Treated by Carbon Ion Radiotherapy

PURPOSE

The development of the novel carbon ion radiotherapy (CIRT) in the treatment of refractory cancers has resulted in the need for a way to accurately evaluate patient prognosis. We evaluated whether L-[methyl-(11)C]-methionine (MET) uptake and its change after CIRT were the early survival predictors in patients with unresectable bone and soft tissue sarcomas.

EXPERIMENTAL DESIGN

MET positron emission tomography was prospectively performed in 62 patients with unresectable bone and soft tissue sarcomas before and within 1 month after CIRT. Tumor MET uptake was measured with the semiquantitative tumor:nontumor ratio (T/N ratio). The MET uptake in the tumor and relevant clinical parameters were entered into univariate and multivariate survival analysis.

RESULTS

The overall median survival time was 20 months. Patients with a baseline T/N ratio of <or=6 had a significant better survival than patients with a baseline T/N ratio >6 (2-year survival rate: 69.4% versus 32.3%; P = 0.01). Patients with a post-CIRT ratio of <or=4.4 had a better survival than that with a post-CIRT ratio >4.4 (2-year survival rate: 63.7% versus 41.3%; P = 0.01). A significant higher survival rate was observed in patients with post-therapeutic MET uptake change of >30% than patients in lower change group (2-year survival rate: 74.6% versus 41.6%; P = 0.049). The multivariate analysis showed that both baseline and post-CIRT T/N ratio were statistically significant independent predictors of patient survival. Tumors with larger T/N ratio had a significantly poorer prognosis.

CONCLUSIONS

MET uptake as measured by either baseline or post-CIRT T/N ratio was an independent predictor of survival in patients with bone and soft tissue sarcomas treated by carbon ion radiotherapy, whereas post-therapeutic MET uptake change might have potential value for the same purpose.

Neural damage due to temporal lobe epilepsy: dual-nuclei (proton and phosphorus) magnetic resonance spectroscopy study

The aim of this study was to evaluate the usefulness of proton and phosphorus (1H and 31P) magnetic resonance spectroscopy (MRS) for temporal lobe epilepsy (TLE) patients, and to evaluate neural damage and metabolite dysfunction in the TLE patient brain. We performed 1H and 31P MRS of medial temporal lobes (MTL) in the same TLE patients (n = 14) with a relatively wide range of severity from almost seizure-free to intractable, and calculated the ratio of N-acetylasparate to choline-containing compounds and creatine + phosphocreatine (NAA/Cho + Cr) in 1H MRS and inorganic phosphate to all main peaks (%Pi) in 31P MRS. There was no significant correlation between NAA/(Cho + Cr) and %Pi in each side (ipsilateral, r = -0.20; contralateral, r =-0.19). The values of NAA/(Cho + Cr) showed a significant difference between ipsilateral and contralateral MTLs to the focus of TLE patients (P < 0.01, paired t-test). Although %Pi also had a tendency to show the laterality of TLE, there was no significance. Ipsilateral (r = -0.90, P < 0.0001) and contralateral (r = -0.70, P < 0.005) NAA/(Cho + Cr) decreases and contralateral %Pi increase (r = 0.81, P < 0.001) had significant correlation with seizure frequency. 1H MRS provides more important information concerning neuronal dysfunction in MTL of TLE patients than 31P MRS.

Detection of lung cancer with positron coincidence gamma camera using fluorodeoxyglucose in comparison with dedicated PET

OBJECTIVE

Dual-head gamma cameras with sodium iodide (NaI) detectors operated in coincidence mode provide a new approach for imaging with positron-labeled tracers. The purpose of this study was to evaluate the feasibility of FDG imaging with positron coincidence detection gamma camera (PCD) in detecting lung tumor in comparison with FDG imaging with the dedicated positron emission tomography (PET).

METHODS AND MATERIAL

Twenty-six lesions of 13 patients with suspected lung cancer were studied with both FDG PET and FDG PCD on the same day. Pulmonary lesions were analyzed visually and semi-quantitatively using the ratio of target-to-background counts (T/B ratio).

RESULTS AND CONCLUSIONS

FDG PCD and FDG PET could detect visually 21 lesions (80.8%) and 23 lesions (88.0%), respectively. The mean T/B ratio and standard deviation (S.D.) of FDG PCD was 4.6 +/- 3.9, significantly lower than that of FDG PET (11.4 +/- 6.6, P<0.001). When pulmonary lesions were no more than 2.0 cm in diameter, the sensitivity of FDG PCD was 37.5%, significantly inferior to that of FDG PET (62.5%, P<0.001). There was no statistically significant difference of the sensitivity between the FDG PCD and FDG PET in lesions of more than 2.0 cm in diameter. FDG PCD with uniform attenuation correction was clinically available in detecting lung cancer. However, the sensitivity for small lesions less than 2.0 cm was limited. The application of measured attenuation correction and scatter correction may to be needed to improve the detectability of FDG PCD, especially for detecting small lung cancer.

Shielding effects of body - shields for 3D PET

We analyzed basic physics characteristics of body-shields which have been considered for screening out radioactivity outside the field of view (OFOV) in positron emission tomography (PET). Phantom experiments were performed with simple rectangular body-shields. A Monte Carlo simulation technique was used to analyze the experimental results and to simulate cases that were not examined experimentally. It was confirmed that the body-shields effectively reduced unwanted radiations from OFOV radioactivity for one of the latest commercial PET scanners, the ECAT EXACT HR(+). The geometrical conditions were the most important factor in determining the shielding effect. The shield thickness should be large enough to keep the shield-scatter component low. The body-shield should be carefully designed to minimize the gap between the body-shield and radioactive distribution as much as possible to maximize the shielding effects, and to be applicable to clinical diagnoses.

Development of a dielectric equivalent gel for better impedance matching for human skin

It would be useful to develop a tissue equivalent gel to improve the uniformity of the electromagnetic field in the human body, and for making a tissue equivalent dielectric human phantom. In this study, solid type, water based gelatin-honey gels were developed which have the electrical characteristics of skin tissue. It was demonstrated that a stable and homogeneous gel, with a relative dielectric constant epsilon ' chosen from desired ranges found in skin, can be made for 200-400 MHz.

The amygdala and Alzheimer's disease: positron emission tomographic study of the cholinergic system

The primary transmitter deficit is cholinergic in Alzheimer's disease (AD), and the amygdala receives a major cholinergic projection from the nucleus basalis of Meynert (Ch4), which may play an important role in the retention of affective conditioning and/or memory consolidation. We measured brain acetylcholinesterase (AChE) activity in 54 patients with AD and in 22 normal controls by positron emission tomography and N-[(11)C]methylpiperidin-4-yl acetate to characterize the cholinergic pathology in AD. The k(3) values were calculated as an index of AChE activity in a three-compartment model analysis using the metabolite-corrected arterial input function. The k(3) values were highly significantly reduced by 20% in the cerebral neocortex (P <0.0001 in the two-tailed t test), 14% in the hippocampus (P <0.001), and 33% in the amygdala (P <0.0001) in AD patients compared with normal controls. The k(3) values were significantly correlated with the Mini-Mental State Examination scores in both the cerebral cortex (P <0.001) and the amygdala (P <0.05) in AD patients, supporting the cholinergic hypothesis of cognitive dysfuncion in AD. Further studies are required, however, to elucidate the specific role of the cholinergic deficit in the amygdala in the emotional and behavioral symptoms in AD.

11C-choline PET for the detection of bone and soft tissue tumours in comparison with FDG PET

We assessed and compared the usefulness of C-choline positron emission tomography (PET) with that of 2-[ F]fluoro-2-deoxy-D-glucose (FDG) PET for the differentiation between benign and malignant bone and soft tissue tumours. A total of 43 patients with 45 lesions were included. C-choline PET and FDG PET were performed from 5 and 40 min, respectively, after injection of 275-370 MBq tracer. PET data were evaluated by using the standardized uptake value (SUV) and were analysed according to the pathological data. C-choline uptake in malignancies was 4.9+/-2.1 (n=14), which was significantly higher than that in benign lesions (2.5+/-1.7, n=31) (P <0.0001). The sensitivity, specificity and accuracy of C-choline PET were 100%, 64.5% and 75.6%, respectively, when 2.59 of the SUV was used as the cut-off value. The FDG uptake in malignancies was 5.1+/-4.2 (n=14) and was also significantly larger than that in benign lesions 2.9+/-2.9 (n=31) (P<0.003). The sensitivity, specificity and accuracy of FDG PET were 85.7%, 41.9% and 55.6%, respectively (cut-off=1.83). The C-choline uptake in the lesions correlated with FDG uptake ( r=0.61, P<0.003). In receiver operating characteristic (ROC) analysis, the area under the ROC curve for C-choline PET (area=0.847) was higher than that for FDG PET (area=0.717). This study showed that C-choline PET was superior to FDG PET in differentiation between malignant and benign lesion in bone and soft tissue tumours. C-choline PET might be useful as a screening method for malignant bone and soft tissue tumours.

Four-dimensional computed tomography (4D CT)--concepts and preliminary development

Four-dimensional computed tomography (4D CT) is a dynamic volume imaging system of moving organs with an image quality comparable to that of conventional CT. 4D CT will be realized by several technical breakthroughs for dynamic cone-beam CT: (1) a large-area two-dimensional (2D) detector; (2) high-speed data transfer system; (3) reconstruction algorithms; (4) ultra-high-speed reconstruction computer; and (5) high-speed, continuously rotating gantry. Among these, development of the 2D detector is one of the main tasks because it should have as wide a dynamic range and as high a data acquisition speed (view rate) as present CT detectors. We are now developing a 4D CT scanner together with the key components. It will take one volume image in 0.5 sec with a 3D matrix of 512 x 512 x 512. This paper describes the concepts and designs of the 4D CT system, as well as preliminary development of the 2D detector.