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Kazuo Awai

Publications and source records attributed to Kazuo Awai.

At least 37 records · Page 2Linked to original sources
PubMed2005

Added value of SPECT/CT fusion in assessing suspected bone metastasis: comparison with scintigraphy alone and nonfused scintigraphy and CT.

PURPOSE: To evaluate retrospectively if there is additional diagnostic value of fused single photon emission computed tomographic (SPECT) and computed tomographic (CT) images in assessing possible bone metastases. MATERIALS AND METHODS: Institutional review board approval was obtained, and each patient provided written informed consent. Bone scintigraphy--including planar and SPECT imaging-and CT were performed with a combined SPECT/CT system in 45 oncologic patients (24 men, 21 women; mean age, 64.7 years +/- 8.7), with a total of 42 metastatic bone foci and 40 benign foci. The reference standard was follow-up radiologic imaging. Two independent readers first analyzed only bone scintigraphic images and next analyzed two separate sets of bone scintigraphic and CT images. They then analyzed bone scintigraphic, CT, and fused images and focused on the additional value of fused images. Diagnostic confidence for each lesion was scored. The three analyses were performed 7 days apart, and the images were presented in random order at each session. The value of additional fused images was assessed by using receiver operating characteristic analysis. RESULTS: After review of fused images to classify indeterminate lesions, reviewer 1 became more confident in diagnosis of the 15 benign lesions and two metastases, and reviewer 2 became more confident in diagnosis of the seven benign lesions and one metastasis. The area under the receiver operating characteristic curve for reviewer 1 was 0.589 for scintigraphic images, 0.831 for separate data sets of scintigraphic and CT images, and 0.947 for fused images. The corresponding areas under the receiver operating characteristic curve for reviewer 2 were 0.771, 0.885, and 0.968, respectively. CONCLUSION: Results demonstrate the increased diagnostic confidence obtained with fused SPECT/CT images compared with separate sets of scintigraphic and CT images in differentiating malignant from benign bone lesions.

Adult↗
PubMed2005

A computer-simulated liver phantom (virtual liver phantom) for multidetector computed tomography evaluation.

OBJECTIVE: The purpose of study was to develop a computer-simulated liver phantom for hepatic CT studies. A computer-simulated liver phantom was mathematically constructed on a computer workstation. MATERIALS AND METHODS: The computer-simulated phantom was calibrated using real CT images acquired by an actual four-detector CT. We added an inhomogeneous texture to the simulated liver by referring to CT images of chronically damaged human livers. The mean CT number of the simulated liver was 60 HU and we added numerous 5-to 10-mm structures with 60+/-10 HU/mm. To mimic liver tumors we added nodules measuring 8, 10, and 12 mm in diameter with CT numbers of 60+/-10, 60+/-15, and 60+/-20 HU. Five radiologists visually evaluated similarity of the texture of the computer-simulated liver phantom and a real human liver to confirm the appropriateness of the virtual liver images using a five-point scale. RESULTS: The total score was 44 in two radiologists, and 42, 41, and 39 in one radiologist each. They evaluated that the textures of virtual liver were comparable to those of human liver. CONCLUSIONS: Our computer-simulated liver phantom is a promising tool for the evaluation of the image quality and diagnostic performance of hepatic CT imaging.

Computer Simulation↗
PubMed2005

Radiation dose reduction without degradation of low-contrast detectability at abdominal multisection CT with a low-tube voltage technique: phantom study.

PURPOSE: To reduce radiation dose from abdominal computed tomography (CT) without degradation of low-contrast detectability by using a technique with low tube voltage (90 kV). MATERIALS AND METHODS: The institutional review board approved the participation of the radiologists in the observer performance test, and informed consent was obtained from all participating radiologists. A phantom for measurement of the radiation dose and a phantom containing low-contrast objects were scanned with a 16-detector row CT scanner at 120 kV and 90 kV. For determination of the radiation dose at both 90 kV and 120 kV, the tube current-time product settings were 100-560 mAs, and the doses at the center and periphery of the phantom were measured. To assess low-contrast detectability, we used a 300-mAs setting at 120 kV and 250-560-mAs settings at 90 kV. Five observers participated in the receiver operating characteristic analysis. Area under the receiver operating characteristic curve (A(z)) values were calculated in each observer. A(z) values obtained with each of the scanning techniques were recorded, and differences were examined for significance by using the Dunnet method. RESULTS: The mean A(z) value was 0.951 at 120 kV and 300 mAs. A(z) values were 0.927-0.973 at 90 kV and 450-560 mAs, and the differences between those values and values obtained at 120 kV and 300 mAs were not significant (P = .937-.952). A value of 100% was assigned to the radiation dose delivered to the center of the phantom at 120 kV and 300 mAs. The relative dose delivered at 90 kV ranged from 65% at 450 mAs to 79% at 560 mAs. CONCLUSION: A reduction from 120 kV to 90 kV led to as much as a 35% reduction in the radiation dose, without sacrifice of low-contrast detectability, at CT.

Analysis of Variance↗
PubMed2005

Abdominal CT with low tube voltage: preliminary observations about radiation dose, contrast enhancement, image quality, and noise.

PURPOSE: To prospectively investigate the effect of low tube voltage on radiation dose, contrast enhancement, image quality, and image noise at abdominal dynamic computed tomography (CT). MATERIALS AND METHODS: The institutional review board approved this study. Prior informed consent was obtained from all patients. Forty patients (24 women, 16 men; mean age, 62 years) underwent initial abdominal CT at 120 kV with 100 mL of contrast material (protocol A). Then all patients were randomly assigned to one of two protocols (protocol B, CT at 90 kV with 100 mL contrast material; protocol C, CT at 90 kV with 80 mL contrast material). The CT numbers of their abdominal organs were assessed quantitatively and qualitatively. Statistical analysis was performed by using the two-tailed paired t test, Kruskal-Wallis test, and kappa test of interobserver agreement. The radiation dose was measured with a phantom that consisted of glass-rod dosimeters. RESULTS: Quantitative analysis revealed that protocols B and C yielded significantly better enhancement of the aorta, liver, pancreas, spleen, and kidney than did protocol A (P < .05). With qualitative analysis, the difference among the three protocols in regard to image quality was not significant. At 90 kV versus 120 kV, the radiation dose reduction in the center of the phantom was 56.8% (6.3 vs 14.6 mGy); in the periphery, it was 46.2% (13.6 vs 25.3 mGy). CONCLUSION: By decreasing the tube voltage, the amount of contrast material can be reduced without image quality degradation. In scans obtained with a low tube voltage, the radiation dose can be reduced as much as 56.8%, and higher contrast material enhancement can be achieved.

Adult↗
PubMed2005

Object-specific attenuation correction at SPECT/CT in thorax: optimization of respiratory protocol for image registration.

Institutional review board approval was obtained for multiple imaging examinations in healthy volunteers and patients and for the analysis of images. The purpose of the study, and the risks associated with radiation exposure with regard to stochastic effects that might result in cancer and/or genetic mutations, were explained to all subjects, and all questions from subjects were answered. Each subject provided written informed consent. The purpose of the study was to prospectively determine the respiratory protocol at computed tomography (CT) that results in the best registration of CT images with images acquired at single photon emission computed tomography (SPECT) in the thorax. Errors of registration between myocardial SPECT images and CT images obtained with different respiratory protocols (postinhalation breath hold, postexhalation breath hold, and free breathing) in 13 healthy subjects were compared. CT scans obtained with free breathing and postexhalation breath hold better matched SPECT images than did those obtained with postinhalation breath hold (one-way analysis of variance, P < .01). Fewer SPECT/CT images showed artifacts with registration performed by using internal landmarks (four, two, and one of 13 images with postinhalation breath-hold, postexhalation breath-hold, and free-breathing protocols, respectively) than with registration performed by using external markers (nine, four, and two of 13 images). CT data acquisition with a free-breathing or postexhalation breath-hold protocol and image registration by using internal landmarks are recommended for attenuation correction.

Adult↗
PubMed2005

Initial experience with X-ray CT based attenuation correction in myocardial perfusion SPECT imaging using a combined SPECT/CT system.

OBJECTIVE: Attenuation artifacts adversely affect the diagnostic accuracy of myocardial perfusion imaging. We assessed the clinical usefulness of X-ray CT based attenuation correction (AC) in patients undergoing myocardial perfusion imaging by comparing their myocardial AC- and non-corrected (NC) SPECT images with the coronary angiography (CAG). METHODS: We retrospectively reviewed the myocardial SPECT images of 30 patients (18 men, 12 women; mean age 68 years). Thirteen of 30 patients with coronary artery disease (CAD) and 17 without CAD were confirmed by CAG. They underwent sequential CT and myocardial SPECT imaging with thallium-201 (111 MBq) under an exercise or pharmacological stress protocol using our combined SPECT/ CT system. Two readers reviewed the myocardial SPECT images for the presence of CAD on a 4-point scale where 1 = normal, 2 = probably normal, 3 = probably abnormal, and 4 = abnormal. Two reading sessions were held. First, non-corrected (NC)-SPECT and second, AC-SPECT images using X-ray CT images were interpreted. Interobserver variability was assessed with kappa statistics. Diagnostic performance (accuracy) of coronary arterial stenosis was compared between AC- and NC-images. RESULTS: Interobserver agreement for visual assessment was substantial or almost perfect. For AC-images, the observer consensus for analysis was 0.84 for the LAD-, 0.87 for the LCX-, and 0.71 for the RCA-territory. For NC-images, it was 0.91, 0.71, and 0.78. AC resulted in statistically significant improvements in overall diagnostic accuracy (sensitivity/ specificity/accuracy = 76%/93%/89%, 67%/86%/81%, respectively, for AC- and NC-images). CONCLUSIONS: Because of an increase in the specificity, diagnostic accuracy was significantly increased on AC-images. These preliminary data suggest that X-ray CT based AC in myocardial SPECT imaging has the potential to develop into a reliable clinical technique.

Aged↗
PubMed2005

Differential diagnosis of nodular lesions in cirrhotic liver by post-vascular phase contrast-enhanced US with Levovist: comparison with superparamagnetic iron oxide magnetic resonance images.

BACKGROUND: We investigated the diagnostic utility of post-vascular phase contrast-enhanced ultrasonography (US) and superparamagnetic iron oxide (SPIO)-enhanced magnetic resonance imaging (MRI) as compared to the histological diagnosis of differential grades of hepatocellular carcinomas (HCCs). METHODS: Forty-nine patients with histologically characterized liver nodules (well-differentiated HCC, n = 20; moderately differentiated HCC, n = 19; poorly differentiated HCC, n = 1; dysplastic nodule, n = 9) received contrast-enhanced US and SPIO-MRI. Subsequently, we quantitatively evaluated the relationships between the images of the nodules and their histological diagnosis and differential grades. RESULTS: The ratio of the echogenicity of the tumorous area to that of the nontumorous area with post-vascular phase contrast-enhanced US (post-vascular phase ratio) decreased as nodules became less differentiated (P < 0.05; Kruskal-Wallis test). The ratio of the intensity of the nontumorous area to that of the tumorous area on SPIO-enhanced MR images (SPIO intensity index) also decreased as nodules became less differentiated (P < 0.01). The post-vascular phase ratio correlated with the SPIO intensity index for HCCs and dysplastic nodules (r = 0.76). The conformity of the result from the post-vascular phase contrast-enhanced US and SPIO-MRI was 96%. CONCLUSIONS: Contrast-enhanced US is a valuable method for predicting the histological grade of HCCs in cirrhotic patients, and may be a good alternative to SPIO-enhanced MRI.

Aged↗
PubMed2005

Three-dimensional cardiac image fusion using new CT angiography and SPECT methods.

OBJECTIVE: The purpose of this study was to develop a method of fused images of coronary CT angiography and myocardial perfusion SPECT. CONCLUSION: Four patients with ischemic heart disease underwent 3D volume-rendering fused images using a conversion program and volume-rendering fusion function of a computer workstation. The fusion images clearly showed the relationship of relevant coronary arteries and the abnormal perfusion territory in all patients and were useful for the evaluation of coronary artery disease.

Aged↗
PubMed2005

MDCT of hypervascular hepatocellular carcinomas: a prospective study using contrast materials with different iodine concentrations.

OBJECTIVE: The objective of our study was to investigate the effect of different iodine concentrations in contrast materials on the depiction of hypervascular hepatocellular carcinomas (HCCs) by MDCT. SUBJECTS AND METHODS: This prospective study involved 100 consecutive patients with chronic liver disease, including 27 patients with hypervascular HCCs. The first 50 patients received 100 mL of iopamidol at a concentration of 370 mg I/mL (group A) and the subsequent 50, 100 mL at 300 mg I/mL (group B); in both groups, the contrast material was administered at a rate of 3.0 mL/sec. Unenhanced scanning and four-phase enhanced scanning at 25, 40, 60, and 180 sec after the start of contrast injection were performed. The enhancement of the aorta, liver, and portal vein was measured during each phase. In addition, tumor-to-liver contrast was calculated for the 27 patients with hypervascular HCCs. Of the 27 patients with hypervascular HCCs, 15 were in group A and 12 were in group B. RESULTS: During all phases, aortic enhancement was significantly greater in group A than group B (p < 0.01). Hepatic enhancement was significantly greater in group A than group B at 60 and 180 sec (both p < 0.01). There was no significant difference in hepatic enhancement between the two groups at 25 and 40 sec. Tumor-to-liver contrast was significantly greater in group A than group B during the late arterial phase (40 sec, p = 0.02), although there was no significant difference at 25, 60, and 180 sec. CONCLUSION: Contrast materials with higher iodine concentration are more effective for depicting hypervascular HCCs on MDCT during the late arterial phase.

Adult↗
PubMed2005

Digital cine angiography permits radiation dose reduction without reduction in image quality.

PURPOSE: To investigate how much the radiation dose in digital cine angiography (DCA) systems can be reduced while maintaining an image quality equivalent to that of conventional cine angiography (CCA). MATERIALS AND METHODS: Simulated vessel phantoms were subjected to DCA and CCA. In DCA, the input dose value to the image intensifier built in the system was 0.10, 0.12, 0.14, 0.17, 0.2, and 0.24 microGy. The detectability for simulated vessel phantoms was visually evaluated by five observers. The radiation dose was measured using radiofluorescent glass-rod dosimeters. Doses of digital cine imaging were measured as relative values with the dose of CCA considered as 1.0. RESULTS: The relative DCA/CCA values in DCA, measured by radiofluorescent glass-rod dosimeters, ranged from 0.414 to 0.901 for simulated vessel phantoms CONCLUSION: DCA allows a reduction by 59% of the radiation dose compared with CCA without reduction of image quality.

Analysis of Variance↗
PubMed2005

Reduction of radiation dose at HRCT of the temporal bone in children.

PURPOSE: The purpose of this study was to reduce the radiation exposure of the eye lens in high resolution computed tomography (HRCT) of the temporal bone using an experimental phantom. MATERIALS AND METHODS: The HRCT image that was used for analysis was obtained by changing parameters including effective-mAs (E-mAs), distance coverage, and height of object in the Y-axis. Radiation exposure was measured to calculate equivalent doses by glass rod dosimeters that were fixed above the right orbit parallel to the body axis. Deterioration in image quality was evaluated by three radiologists and the following three-point rating method was employed: grade 1 (good image quality without diagnostic limitations), grade 2 (image was deteriorated, but there were no diagnostic limitations), and grade 3 (image was deteriorated with diagnostic limitations). RESULTS: Assuming that the equivalent dose was y (mSv), and E-mAs was x, a simple regression line, y=0.506x-0.494 (decision coefficient, R2=0.999), was obtained. A standard deviation (S.D.) less than 120 (E-mAs, 220-120) was judged as grade 1, an S.D. between 120 and 150 was judged as grade 2, and an S.D. higher than 150 was judged as grade 3, indicating that deterioration of the quality of images with reduced E-mAs affected the diagnosis by imaging at S.D. higher than 150. CONCLUSION: Radiation dose at the eye lens in HRCT could be reduced up to an equivalent dose corresponding to 70 mAs without compromising diagnostic quality in the phantom experiment.

Humans↗
PubMed2004

Moderate versus high concentration of contrast material for aortic and hepatic enhancement and tumor-to-liver contrast at multi-detector row CT.

PURPOSE: To prospectively evaluate aortic and hepatic enhancement and depiction of hypervascular hepatocellular carcinoma (HCC) between two contrast materials with moderate and high iodine concentrations when administered at same iodine dose and injection duration at multi-detector row helical computed tomography (CT). MATERIALS AND METHODS: Institutional review board approval and informed patient consent were obtained. One hundred eighty-six patients were studied, and 67 patients with hypervascular HCC were identified. Ninety-four patients were assigned to receive iohexol 350 (mg iodine per milliliter) with protocol A; 92, iohexol 300 with protocol B. In both protocols, iohexol with same iodine load per weight (518 mg/kg) was administered with same injection duration (25 seconds). Multiphase CT scanning was started 10, 20, 50, and 180 seconds after the trigger (threshold level set at increase of 100 HU over baseline CT number of aorta). Enhancement of aorta and liver was measured in 186 patients. Tumor-to-liver contrast was measured in 67 patients with hypervascular HCC. Statistical analysis was performed with Mann-Whitney U test. RESULTS: Medians of aortic enhancement during four phases were 325, 185, 112, and 69 HU with protocol A. Corresponding values were 344, 266, 121, and 73 HU with protocol B. During all phases, aortic enhancement was significantly higher with protocol B (P = .046, P < .001, P < .001, and P = .002). Hepatic enhancement during four phases was 6, 21, 48, and 34 HU with protocol A. Corresponding values were 3, 17, 47, and 35 HU with protocol B. Hepatic enhancement was significantly higher with protocol A during first and second phases (P < .001 for both), although there was no significant difference between protocols during third and fourth phases (P = .778 and P = .178, respectively). Medians of tumor-to-liver contrast during four phases were 22, 34, 0.5, and -1.1 HU with protocol A. Corresponding values were 23, 45, 0, and -8.6 HU with protocol B. Tumor-to-liver contrast was significantly higher with protocol B during second phase (P = .049), although there was no difference between protocols during other phases. CONCLUSION: When total iodine dose was adjusted to body weight and injection duration was fixed, rapid administration of moderate concentration of contrast material was more effective for depiction of hypervascular HCC than was high concentration of contrast material.

Adult↗
PubMed2004

Detection of hepatocellular carcinoma using double-echo FLASH sequence during the hepatic arterial phase.

PURPOSE: The purpose of this study was to compare the performance of in-phase and opposed-phase gradient-recalled echo (GRE) pulse sequences in paramagnetic contrast-enhanced magnetic resonance (MR) imaging of hepatocellular carcinomas (HCCs) during the hepatic arterial phase. MATERIAL AND METHODS: Thirty-four patients with 84 lesions with known or suspected HCCs, nine of whom had a fatty liver, were examined with double-echo GRE techniques under 1.5T before and 30 s after injection of gadopentenate dimeglumine at a dose of 0.1 mmol/kg. Echo times were 2.4 ms (opposed phase) and 5.0 ms (in phase). Contrast enhancement of the HCC detected in both in-phase and opposed-phase images was evaluated. The liver signal-to-noise ratio (SNR), lesion-liver contrast-to-noise ratio (CNR), and enhancement ratio (ER) were calculated for the largest lesion of each patient. RESULTS: In dynamic gadolinium-enhanced images of the 84 HCCs, 81 (96.4%) were detected in both in-phase and opposed-phase images, two (2.4%) were detected in only in-phase images, and one (1.2%) was detected only in opposed-phase images. The liver SNR, CNR, and ER were 46.7+/-16.1, 15.2+/-10.3, and 0.637+/-0.268 for in-phase images, and 48.9+/-16.9, 16.3+/-11.8, and 0.647+/-0.309 for opposed-phase images, respectively. In patients with a fatty liver, the SNR, CNR, and ER were 46.0+/-18.1, 21.7+/-17.9, and 0.525+/-0.231 for in-phase images, and 44.3+/-18.7, 26.0+/-21.3, and 0.793+/-0.124 for opposed-phase images, respectively. No significant statistical differences were found between the in-phase and opposed-phase images. CONCLUSION: Opposed-phase GRE imaging is equivalent to in-phase GRE sequences in patients with or without fatty liver for detection of HCC in dynamic gadolinium-enhanced images.

Aged↗
PubMed2004

Effect of contrast material injection duration and rate on aortic peak time and peak enhancement at dynamic CT involving injection protocol with dose tailored to patient weight.

PURPOSE: To investigate the effect of duration and rate of contrast material injection on aortic peak time and peak enhancement in an injection protocol in which the contrast material dose is adjusted according to patient weight. MATERIALS AND METHODS: One hundred ninety-nine patients were randomly divided into three groups in which the fixed duration of contrast material injection was 25 seconds (group A) or 35 seconds (group B) or the fixed injection rate was 4.0 mL/sec (group C). Computed tomography (CT) at the L3 vertebral level was performed before and after contrast material injection. Aortic peak time, aortic peak enhancement, and period when aortic enhancement is 200 HU or greater (T200) were calculated. The Pearson product-moment correlation coefficient (r) was used to investigate relationships between patient weight and aortic peak time, aortic peak enhancement, and T200 in each group. RESULTS: A significant correlation between aortic peak time and patient weight (r = 0.91, P <.001) was observed in group C. No significant correlations between patient weight and aortic peak time were observed in group A (r = 0.16, P =.21) or B (r = -0.05, P =.69). A significant inverse correlation between aortic peak enhancement and patient weight (r = -0.70, P <.001) was observed in group C. No significant correlations between patient weight and aortic peak enhancement were observed in group A (r = 0.09, P =.48) or B (r = 0.10, P =.41). A significant correlation between T200 and patient weight (r = 0.72, P <.001) was observed in group C. No significant correlations between patient weight and T200 were observed in group A (r = 0.12, P =.34) or B (r = 0.001, P =.99). CONCLUSION: Aortic peak time, aortic peak enhancement, and T200 were closely related to injection duration in the protocol with contrast material dose determined according to patient weight.

Adult↗
PubMed2004

Pulmonary nodules at chest CT: effect of computer-aided diagnosis on radiologists' detection performance.

PURPOSE: To evaluate the effect of computer-aided diagnosis (CAD) on radiologists' detection of pulmonary nodules. MATERIALS AND METHODS: Fifty chest computed tomographic (CT) examination cases were used. The mean nodule size was 0.81 cm +/- 0.60 (SD) (range, 0.3-2.9 cm). Alternative free-response receiver operating characteristic (ROC) analysis with a continuous rating scale was used to compare the observers' performance in detecting nodules with and without use of CAD. Five board-certified radiologists and five radiology residents participated in an observer performance study. First they were asked to rate the probability of nodule presence without using CAD; then they were asked to rate the probability of nodule presence by using CAD. RESULTS: For all radiologists, the mean areas under the best-fit alternative free-response ROC curves (Az) without and with CAD were 0.64 +/- 0.08 and 0.67 +/- 0.09, respectively, indicating a significant difference (P <.01). For the five board-certified radiologists, the mean Az values without and with CAD were 0.63 +/- 0.08 and 0.66 +/- 0.09, respectively, indicating a significant difference (P <.01). For the five resident radiologists, the mean Az values without and with CAD were 0.66 +/- 0.04 and 0.68 +/- 0.04, respectively, indicating a significant difference (P =.02). At observer performance analyses, there were no significant differences in Az values obtained either without (P =.61) or with (P =.88) CAD between the board-certified radiologists and the residents. For all radiologists, in the detection of pulmonary nodules 1.0 cm in diameter or smaller, the mean Az values without and with CAD were 0.60 +/- 0.11 and 0.64 +/- 0.11, respectively, indicating a significant difference (P <.01). CONCLUSION: Use of the CAD system improved the board-certified radiologists' and residents' detection of pulmonary nodules at chest CT.

Adult↗
PubMed2004

Imaging of the liver by helical CT and MR imaging.

With modern imaging technologies, including helical CT and MR imaging, the evaluation of liver morphology, blood flow and detection and characterization of liver neoplasms is possible in a noninvasive manner. Experiences in numerous institutions have established that both imaging methods are highly accurate in diagnosing hepatic pathology. Three-dimensional evaluation is feasible with fast imaging techniques such as multislice CT. With tissue-specific MR contrast agents such as SPIO, our capability is enhanced not only with respect to lesion detection but also lesion characterization.

Carcinoma, Hepatocellular↗