Sukehiko Koga

A Multicenter Validation of Regional Cerebral Blood Flow Quantitation Using [123I]Iodoamphetamine and Single Photon Emission Computed Tomography

Recently, two methods have been proposed for regional cerebral blood flow (rCBF) quantitation using [123I]iodoamphetamine (IMP) and single-photon emission computed tomography (SPECT). The table look-up (TLU) method has been shown to provide both rCBF and volume of distribution, Vd, images from two SPECT scans, while a single-scan autoradiographic (ARG) technique provided rCBF using a fixed and assumed Vd. In both methods, a single blood sample was referred to calibrate the previously determined standard input function The present multicenter project was designed to evaluate the accuracy of both methods for use as clinical investigative tools. Ten independent institutions performed [123I]IMP-SPECT studies according to both methods in 76 subjects (10 normal volunteers, 32 patients with cerebrovascular disease, and 34 patients with other diseases). Calculated rCBF values were compared with those obtained by the following reference methods available in the participating institutions; [15O] H2O positron emission tomography (PET) (five institutions), [133Xe]SPECT (four institutions), and the [123I]IMP microsphere method (three institutions). Both ARG and TLU methods provided rCBF values that were significantly correlated with those measured by the [15O] H2O PET technique (p < 0.001 for all subjects; overall regression equation, y = 15.14 + 0.54×) and those measured by the [123I]IMP-microsphere method (p < 0.001 for all subjects; y = 2.0 + 0.80×). Significant correlation (p < 0.05) was observed in 18 of 24 subjects studied with the [133Xe] SPECT reference technique (overall regression equation, y = 15.0 + 0.55×). Mean cortical gray matter rCBF in a group of normal subject was 43.9 ± 3.3 and 43.4 ± 2.0 ml/min/100 g for the ARG and TLU methods, respectively. Regional Vd of [123I]IMP estimated by the TLU method was 45 ml/ml ± 20% in the normal cortical region. Close agreement between ARG and TLU rCBF values was observed (y = −3.21 + 1.07×, r = 0.97), confirming the validity of assuming a fixed Vd in the ARG method. Results of this study demonstrate that both the ARG and TLU methods accurately and reliably estimate rCBF in a variety of clinical settings.

Integrated life-sized solid model of bone and soft tissue: application for cleft lip and palate infants.

The recent development of three-dimensional computed tomography (3D-CT) and laser stereolithography has allowed the creation of life-sized skeletal models. The development of helical CT has enabled us to apply this method to very young children. However, skeletal models alone do not reveal the spatial relationship between soft tissue and bone in complicated craniofacial deformities. We have therefore developed a model that shows both soft and bony tissue by first using CT values that result in a model in which soft tissue is solid and bone is replaced by empty space. The space is then filled with plaster to represent the skeleton. This model also can provide baseline data for evaluating facial growth after surgical repair of clefts. Two infants with cleft lip and palate are presented to illustrate this method of creating an integrated solid model and its applications.

Early and delayed Tc-99m ECD brain SPECT in SLE patients with CNS involvement.

We compared early and delayed Tc-99m ECD SPECT scans in 32 SLE patients (Group 1, definite neuropsychiatric disorders; Group 2, minor neurologic symptoms or normal) with those of normal controls by visual inspection and semi-quantitative evaluation. With visual interpretation, 13 out of 14 patients in Group 1 (93%) and 7 out of 18 patients in Group 2 (39%) had diffuse uneven decrease in early scans. Seven patients in Group 2 (39%) who had normal early scans demonstrated focal decrease in the medial frontal lobe in delayed scans. With cerebral region to cerebellar ratios, in early scans, the medial frontal lobe in Group 1 and Group 2 was significantly lower than in normal controls, and lateral frontal lobe and occipital lobes in Group 1 were significantly lower than in normal controls. Nevertheless, in delayed scans, every cortical region except for the parietal lobe in Groups 1 and 2 was significantly lower than in normal controls. The retention rates in all regions in SLE patients were significantly lower than in normal controls. No case showed SPECT improvement on follow-up studies in either group in spite of clinical improvement. Delayed Tc-99m ECD brain SPECT of high sensitivity might be useful in detecting CNS involvement. Although the SPECT findings did not correlate with the neuropsychiatric symptoms, early and delayed Tc-99m ECD SPECT seems to provide useful objective diagnostic information in SLE patients.

Characterization of neuronal damage by iomazenil binding and cerebral blood flow in an ischemic rat model

I-123-iomazenil is a SPECT probe for central benzodiazepine receptors (BZR) which may reflect intact cortical neuron density after ischemic insults. We evaluated whether neuronal damage in rats could be characterized by iomazenil as compared with cerebral blood flow (CBF). Serial changes in I-125-iomazenil for BZR and I-123-IMP for CBF were analyzed after the unilateral middle cerebral artery occlusion in rats by using anin vivo dualtracer technique. Uptake ratios of affected to contralateral regions were calculated. The iomazenil as well as IMP were decreased in all regions except for the cerebellum (remote area). Both iomazenil and IMP increased over time except in the temporal region (ischemic core). The iomazenil uptake was higher than IMP except in the ischemic core between 1 and 3–4 wk when iomazenil was lower than IMP. Iomazenil showed a moderate decrease in the proximal and middle parietal regions (peri-infarct areas) at 3–4 wk. The triphenyl-tetrazolium-chloride (TTC) stain at 1 wk demonstrated unstained tissue in the temporal region indicating tissue necrosis. With hematoxylin-eosin (HE) stain at 1 wk, widespread neuronal necrosis with occasional intact neurons were found in the proximal parietal region, and isolated necrotic neurons were represented in the distal parietal region. Iomazenil correlated well with the neuron distribution and the finding of a discrepancy between iomazenil and IMP might be useful in evaluating the neuronal damage.

Development of a Japanese Adult Female Voxel Phantom

A Japanese adult female voxel (volume pixel) phantom (JF) was developed using CT images of a healthy female volunteer. The height (152 cm) and weight (44 kg) of JF are smaller than the averages of Japanese adult female. The voxel size of JF is 0:98 × 0:98 × 1mm3. Therefore, the shapes of small or complicated organs, such as thyroid and stomach, are distinctly reproduced. The shapes of female-specific organs, such as ovary and uterus, in JF are also realistically represented compared with those of a previously developed phantom. These results suggest that JF enables the accurate evaluation of organ doses due to diverse exposures to Japanese adult females. Photon-specific absorbed fractions (SAFs) for liver or stomach as target organs and for kidney as a source organ were calculated using JF and compared with those of other phantoms. It was concluded that the SAFs calculated using JF and other phantoms depend on the organ distances from source to target.

Evaluation of asialoglycoprotein receptor imaging agent as a marker of hepatic ischemia-reperfusion injury and recovery.

Protection of hepatocytes from ischemia-reperfusion injury is a clinically important issue. The purpose of this study was to evaluate changes in acute liver damage and recovery after ischemiareperfusion in rats with asialoglycoprotein receptor (ASGP-R) ligand. Ischemia was induced by clamping the hepatoduodenal ligament for 90 min. At 1, 3,24, 48 hr, 1 and 2 wk after reperfusion, I-125-GSA was injected. Five min after injection, blood samples were obtained and the liver was removed. Several regions from each lobe were dissected, weighed and counted. Mean uptakes (% dose/g) in the liver and blood samples were calculated. Histologic sections stained with hematoxylin-eosin (H-E) stain showed ischemic damage at 1 and 3 hr, and focal hepatocyte necrosis at 24 hr. Predominant massive necrosis was not seen. The mitotic index with H-E stain and proliferating cell nuclear antigen (PCNA) labeling index were highest at 1 wk, indicating liver regeneration. At 1 and 3 hr, liver uptake was significantly decreased, and blood uptake was significantly increased, indicating decreased tissue blood flow and ischemic damage. Liver uptake showed significant increases at 48 hr and 1 wk, and was the highest at 1 wk, indicating liver regeneration during the convalescence stage. ASGP-R binding may provide valuable information on ischemia-reperfusion injury and recovery.

Development and early trials of real-time CT fluoroscopy

A CT fluoroscopy system that permits real-time monitoring of CT images was developed. In phantom studies the images were displayed at a rate of 6 per s, with a delay time of 0.67 s. Early clinical trials in aspiration of intracranial haematoma and brain tumour biopsy indicated that CT fluoroscopy is useful for CT-guided intervention on the central nervous system.

CALCIFICATION OF THE VERTEBRAL ARTERY

A series of 3,648 computed tomographic (CT) scans was reviewed to determine the incidence of intracranial vertebral artery calcification. Calcification was identified in one or both vertebral arteries in 3.4% and was more frequent in the higher age groups. Skull radiographs demonstrated vertebral artery calcification in only one of 48 patients in whom CT studies showed it. A high correlation was observed between vertebral artery calcification on CT and vertebral artery stenosis on cerebral angiography.

The detectability of intracranial aneurysms using helical CT compared with conventional cerebral angiography

Helical CT (HCT) was applied to the diagnosis of cerebral aneurysms. The diagnostic accuracy of HCT, including the detectability of aneurysms, was compared with that of conventional cerebral angiography in 62 aneurysms of 43 patients. The scanning parameters were 135 kV, 260 mA and 1 mm slice thickness. The couch top was moved at 1 to 1.2 mm/s during the scanning of 30 s. In a prospective study, the detection rates using HCT and angiography were 91.9% and 93.5%. Retrospectively, the detection rates with HCT and with angiography were 95.4% and 98.4%. HCT was also effective in illustrating the detailed contours of aneurysms and calcifications and thrombosed parts of aneurysms. Three-dimensional CT (3D-CT) images were helpful in diagnosing complicated vascular anomalies. Our results indicate that HCT was an effective diagnostic modality to supplement cerebral angiography.

Role of Real-Time CT (CT Fluoroscopy) in Multislice Helical Scanning

Real-time computed tomography (CT) is a relatively new application that permits real-time reconstruction and display of CT images using a high-speed pipeline processor and an image reconstruction algorithm with improved temporal resolution (Katada et al. 1993). Since its introduction in 1993, real-time CT has been used for optimization of scan timing in contrast studies (Anno et al. 1997), as well as for guidance in biopsy or drainage procedures as CT fluoroscopy (Dary et al. 1998; Katada et al. 1996; Kato et al. 1996; Meyer et al. 1998). The clinical application of real-time CT has been further promoted by the introduction of multislice CT (Katada 1999). As one example, real-time CT can be used to precisely determine the optimal scan timing and to trigger scanning in contrast-enhanced studies with a short scanning time. Another useful application of real-time CT is multislice CT fluoroscopy. This report discusses the clinical usefulness of these new applications of real-time CT.