Takeshi Nakaura

Role of diffusion-weighted imaging in the diagnosis of gynecological diseases

Recent technical advances in diffusion-weighted imaging (DWI) greatly enhanced the clinical value of magnetic resonance imaging (MRI) of the body. DWI can provide excellent tissue contrast based on molecular diffusion and may be able to demonstrate malignant tumors. Quantitative measurement of the apparent diffusion coefficient (ADC) may be valuable in distinguishing between malignant and benign lesions. We reviewed DWI and conventional MRI of the female pelvis to study the utility of DWI in patients with gynecological diseases. Although the ADC can help to differentiate between normal and cancerous tissue in the uterine cervix and endometrium, its utility may be limited by the large overlap of the uterine myometrium and ovaries. On the other hand, the ADC may be useful for monitoring the therapeutic outcome after uterine arterial embolizati (UAE), chemotherapy and/or radiation therapy. In patients with ovarian cancer, DWI demonstrates high intensity not only at the primary cancer site but also in disseminated peritoneal implants. When added to conventional MRI findings, DWI and ADC values provide additional information and DWI may play an important role in the diagnosis of patients with gynecological diseases.

Association of pericardial fat accumulation rather than abdominal obesity with coronary atherosclerotic plaque formation in patients with suspected coronary artery disease

OBJECTIVES The purpose of this study was to examine the association of pericardial fat with the presence of coronary plaques. BACKGROUND Waist circumference, reflecting abdominal obesity, is a risk factor of metabolic syndrome and coronary artery disease (CAD). Adipose tissue secretes many factors implicated in atherogenesis, however, the role of pericardial fat (ectopic visceral fat around coronary arteries) in the pathogenesis of CAD is not clear. METHODS We measured total pericardial fat volume (PFV) and determined presence and characteristics of coronary plaques using 64-slice computed tomography in 171 consecutive patients suspected of CAD (101 men; mean age, 66+/-11 years, +/-SD). RESULTS PFV correlated with age (p<0.05), body mass index (p<0.05), waist circumference (p<0.01), and high-density lipoprotein cholesterol (p<0.01) by multivariate regression analysis. PFV was significantly larger in patients with coronary plaques, even nonstenotic or noncalcified ones, than those without plaques (any plaques, n=123; 201+/-71cm(3), nonstenotic plaques, n=51; 192+/-63, noncalcified plaques, n=32; 196+/-56 vs. no plaque, n=48; 144+/-45, p<0.001, respectively). Multivariate backward logistic regression analysis demonstrated that PFV, but not waist circumference, significantly associated with the presence of any coronary plaques (odds ratio [OR]; 2.876, 95% confidence interval [95% CI]; 1.614-5.125, p<0.001), nonstenotic plaques confirmed by coronary angiography (OR; 3.423, 95% CI; 1.764-6.642, p<0.001), and noncalcified plaques (OR; 3.316, 95% CI; 1.435-7.661, p<0.01). CONCLUSIONS PFV correlated significantly with the presence of nonstenotic and noncalcified coronary plaques assessed by multislice computed tomography. Pericardial fat is more highly associated with early development of CAD than simple anthropometric measures of abdominal obesity.

Low Contrast Agent and Radiation Dose Protocol for Hepatic Dynamic CT of Thin Adults at 256–Detector Row CT: Effect of Low Tube Voltage and Hybrid Iterative Reconstruction Algorithm on Image Quality

PURPOSE To evaluate the effect on image quality of a low contrast agent dose and radiation dose protocol at abdominal dynamic computed tomography (CT) with a low tube voltage, hybrid iterative reconstruction algorithm, and a 256- detector row scanner. MATERIALS AND METHODS This prospective study received institutional review board approval, and prior informed written consent was obtained from all patients. Seventy-four patients undergoing hepatic dynamic CT were randomly assigned to one of two protocols: Thirty-nine patients underwent scanning with the conventional 120-kVp protocol and the other 35 patients underwent scanning with an 80-kVp tube voltage and a 40% reduction in contrast agent dose. The 80-kVp images were also postprocessed with a hybrid iterative reconstruction algorithm. The estimated effective radiation dose of each protocol was compared and the image noise and contrast-to-noise-ratio (CNR) of the 120-kVp, 80-kVp, and hybrid iterative reconstructed 80-kVp images were evaluated by using the Student t test. RESULTS The effective radiation dose was 51% lower during the hepatic arterial phase (HAP) and 48% lower during the portal venous phase (PVP) with the 80-kVp protocol than with the 120-kVp protocol (HAP: 5.6 mSv ± 1.0 [standard deviation] vs 11.6 mSv ± 3.3; PVP: 5.8 mSv ± 0.7 vs 11.2 mSv ± 3.2, respectively). The hybrid iterative reconstruction decreased image noise by 23% during the HAP (9.2 ± 1.9 vs 12.0 ± 2.6) and by 24% during the PVP (9.4 ± 1.8 vs 12.3 ± 2.6). There were no significant differences in the CNR of any of the regions of interest between 80-kVp with iterative reconstruction and 120-kVp protocols (P = .46-.85). CONCLUSION A low tube voltage and the hybrid iterative reconstruction algorithm can dramatically decrease radiation and contrast agent doses with adequate image quality at hepatic dynamic CT of thin adults with use of a 256-detector row scanner.

Ground-Glass Opacities on Thin-Section Helical CT: Differentiation Between Bronchioloalveolar Carcinoma and Atypical Adenomatous Hyperplasia

OBJECTIVE The purpose of our study was to investigate the differentiation between bronchioloalveolar carcinoma and atypical adenomatous hyperplasia manifesting pure ground-glass opacity (GGO) based on selected features on thin-section helical CT scans. MATERIALS AND METHODS We evaluated 35 bronchioloalveolar carcinomas and 17 atypical adenomatous hyperplasias that were histologically confirmed and that manifested pure GGO on thin-section helical CT scans. We recorded the age, sex, and smoking history (Brinkman index) of the patients. Two board-certified radiologists measured the maximum diameter and mean attenuation value of the nodules; the measured values were averaged for each nodule. Using a 3-point scale, they visually assessed the images for consensus with respect to nodular sphericity, marginal irregularity, vascular convergence, pleural retraction, and findings of an internal air bronchogram. CT findings of atypical adenomatous hyperplasia and bronchioloalveolar carcinoma were compared using univariate and multivariate logistic regression analysis; the odds ratio was computed using the atypical adenomatous hyperplasia group as the reference group. RESULTS By univariate analysis, the patient age, nodular maximum diameter, mean attenuation value, and findings of an internal air bronchogram were statistically significantly associated with bronchioloalveolar carcinoma (odds ratio [OR] = 1.10 [p = 0.012], OR = 1.27 [p < 0.01], OR = 1.01 [p = 0.023], and OR = 25.30 [p < 0.001], respectively), and sphericity was significantly associated with atypical adenomatous hyperplasia (OR = 0.059, p < 0.001). By multivariate analysis, sphericity was significantly associated with atypical adenomatous hyperplasia (OR = 0.125, p = 0.042) and findings of an internal air bronchogram were associated with bronchioloalveolar carcinoma (OR = 16.10, p = 0.007). CONCLUSION Nodular sphericity and an internal air bronchogram were useful at thin-section helical CT performed to differentiate between bronchioloalveolar carcinoma and atypical adenomatous hyperplasia. Interobserver agreement was high for each finding.

Abdominal dynamic CT in patients with renal dysfunction: Contrast agent dose reduction with low tube voltage and high tube current-time product settings at 256-detector row CT

PURPOSE To evaluate the feasibility of a low-contrast agent dose protocol at abdominal dynamic computed tomography (CT) with a low tube voltage high tube current-time product technique and a 256-detector row CT unit. MATERIALS AND METHODS This prospective study received institutional review board approval; written informed consent to participate was obtained from all patients. The study included 151 patients; 117 had an estimated glomerular filtration rate (eGFR) greater than or equal to 60 mL/min/1.73 m(2). These patients were examined with the conventional 120-kVp protocol. The other 34 patients underwent scanning with an 80-kVp tube voltage, a high tube current-time product, and a 40% reduction in contrast agent dose. Effective dose (ED), image noise, attenuation, contrast-to-noise ratio (CNR), and figure of merit of the aorta in the arterial phase and of the portal vein and hepatic parenchyma in the portal venous phase in the two groups were compared with the Student t test. RESULTS Estimated ED was about 20% lower with the 80-kVp protocol than with the 120-kVp protocol. There were no significant differences in CNR in any region of interest between the 80-kVp protocol and the 120-kVp protocol (abdominal aorta: 36.9 ± 9.7 [standard deviation] vs 36.1 ± 8.1, P = .63; portal vein: 13.4 ± 3.2 vs 13.1 ± 3.2, P = .65; hepatic parenchyma: 6.4 ± 2.6 vs 6.7 ± 2.3, P = .51). CONCLUSION Contrast dose at hepatic dynamic 256-detector row CT in patients with renal dysfunction can be decreased by 40% with this protocol by using the 80-kVp setting and a high tube current-time product.

Contrast Injection Protocols for Coronary Computed Tomography Angiography Using a 64-Detector Scanner : Comparison Between Patient Weight-Adjusted-and Fixed Iodine-Dose Protocols

Objective:To compare patient-weight-adjusted and fixed iodine-dose protocols at coronary computed tomography angiography (CTA) using a 64-detector scanner and computer-assisted bolus tracking. Materials and Methods:Approval from our institutional review board and patient prior informed consent were obtained before entering 60 patients with suspected coronary disease in this study. The patients were randomly assigned to one of 2 protocols. In the fixed iodine-dose protocol, they received a fixed dose of 80 mL Iopamidol-370; the injection duration was 20 seconds. In the weight-adjusted iodine-dose protocol, the dose was tailored to the patient body weight; this group received 1.0 mL/kg and the injection duration was shorter, ie, 15 seconds. Imaging was on a 64-detector CT scanner using a computer-assisted bolus tracking technique. A radiologist blinded to the protocol used measured the Hounsfield density number of the large vessels and coronary arteries. CT attenuation in the aortic root was compared in patients whose weight was less than 58 kg (group 1) or 58 kg or more (group 2). The standard deviation (SD) of CT attenuation in the aortic root and the myocardium was compared with evaluate image noise. Using a 3-point scale, 2 radiologists independently evaluated beam-hardening artifacts and coronary enhancement. Statistical analysis was with the two-tailed Student t test and the Mann-Whitney U test. Results:There was no significant difference between the protocols with respect to CT attenuation of the ascending aorta and coronary arteries. Under the fixed-iodine-dose protocol, mean CT attenuation in the aortic root was 421.3 ± 51.5 Hounsfield unit (HU) in the lighter-, and 397.2 ± 42.3 HU in the heavier weight group, respectively; the difference was statistically significant (P = 0.03). Under the weight-adjusted iodine-dose protocol, these values were 407.6 ± 85.1 and 409.2 ± 47.9 HU, respectively and the difference was not statistically significant (P = 0.17). The SD of the ascending aorta and myocardium was significantly higher for the fixed- than the weight-adjusted iodine-dose protocol. The mean visual score for beam-hardening artifacts was significantly lower in the weight-adjusted- than the fixed-iodine-dose protocol (P < 0.01), however, there was no significant difference in the enhancement of the coronary arteries (P = 0.82). Conclusion:At 64-detector CTA of the heart, the patient weight-tailored dose protocol with the 15-second injection duration yielded significantly better image quality than the fixed-dose, 20-second injection duration protocol.

A hybrid iterative reconstruction algorithm that improves the image quality of low-tube-voltage coronary CT angiography.

OBJECTIVE We investigated whether a hybrid iterative reconstruction (HIR) algorithm improves image quality at low-tube-voltage coronary CT angiography (CTA) compared with filtered back projection (FBP). SUBJECTS AND METHODS Eighteen patients (seven men, 11 women; mean age, 67.8 years) underwent retrospectively gated coronary CTA at 80 kV with a volume CT dose index (CTDI(vol)) of 18.8 mGy on a 64-MDCT scanner. CT images were reconstructed using only FBP and only HIR. For each patient, CT images subjected to the two different reconstructions were reviewed by two observers. Quantitative image quality parameters-that is, CT attenuation (HU) of the coronary arteries, image noise, and contrast-to-noise ratio (CNR)-were calculated and compared for the two reconstruction methods and the overall image quality for each reconstruction was visually scored on a 5-point scale. RESULTS The mean estimated effective radiation dose for 80-kV coronary CTA was 4.7 ± 0.4 (SD) mSv. The two reconstruction methods did not significantly differ with respect to the CT attenuation of the coronary arteries. The image noise was significantly lower with HIR than with FBP (20.3 ± 5.3 vs 49.4 ± 12.0 HU, respectively; p < 0.01), and the CNR was significantly higher with HIR than with FBP (29.8 ± 7.4 vs 12.7 ± 2.9, p < 0.01). The visual scores for image quality were higher with HIR than with FBP (p < 0.01). CONCLUSION The HIR algorithm can reduce image noise and improve image quality at low-tube-voltage coronary CTA.

Low-kilovoltage, high-tube-current MDCT of liver in thin adults: pilot study evaluating radiation dose, image quality, and display settings.

OBJECTIVE The purpose of our study was to evaluate the effect of a low tube voltage-high tube current-time product technique for portal phase abdominal CT of thin adults. SUBJECTS AND METHODS This study included 25 patients who had undergone portal phase abdominal CT at 120 kVp in the preceding 6 months. All were scanned using 80 kVp and high tube-current time products. We assessed the estimated effective dose (ED), image noise, attenuation, contrast-to-noise ratio (CNR), and figure of merit of the liver and portal vein. Two radiologists evaluated the quality of scans for image contrast and streak artifacts at 80 kVp, 120 kVp, and 80 kVp with wide window width display presets (W-80). RESULTS The estimated ED was 33% lower at 80 than at 120 kVp. CNR of the portal vein was 36.8% higher at 80 than 120 kVp, and for the liver it was 17.7% higher at 80 than 120 kVp. The visual score of image contrast was significantly higher for W-80 than for 120 kVp; however, there was no significant difference in the visual score of streak artifacts. CONCLUSION At portal phase abdominal CT, 80 kVp and a high tube current-time product setting significantly improved image quality and reduced the radiation dose compared with 120 kVp.

Effect of Contrast Injection Protocols with Dose Adjusted to the Estimated Lean Patient Body Weight on Aortic Enhancement at CT Angiography

OBJECTIVE The objective of our study was to investigate the effect on aortic enhancement of iodine doses adjusted for the patient estimated lean body weight (LBW) at CT angiography (CTA). SUBJECTS AND METHODS CTA for the whole aorta using a 64-MDCT scanner was performed in 97 patients (mean age, 67.4 years) with confirmed or suspected aortoiliac disease. The patients were divided into two groups: a total body weight (TBW) group (n = 49) and an estimated LBW group (n = 48). LBW was estimated from the patient weight (TBW) and height. The TBW and estimated LBW groups received 360 mg I/kg of TBW and 450 mg I/kg of estimated LBW of contrast medium, respectively. The relative dose ratio for the estimated LBW group versus the TBW group was based on the fact that the standard percentage of body fat in Japanese adults with an average TBW of 60 kg is 20% (360 = 0.8 x 450). Differences in the degree of aortic enhancement and interpatient variability in aortic enhancement between the estimated LBW and TBW group were evaluated. RESULTS Mean aortic enhancement was 308.9 HU for the estimated LBW group and 314.1 HU for the TBW group, indicating no significant difference in the degree of enhancement (Welchs t test, p = 0.61). The interquartile range was smaller for the LBW group than the TBW group (52.8 vs 79.1 HU, respectively); interpatient variability was lower in the estimated LBW group. The aortic attenuation gradient in the TBW group and estimated LBW group was 20.7 and 25.8 HU, respectively; the difference was not statistically significant. CONCLUSION The CTA protocol using an estimated LBW-tailored dose yielded more consistent aortic enhancement with reduced interpatient variability than the CTA protocol using a TBW-based dose.

Reduction of dental metallic artefacts in CT: Value of a newly developed algorithm for metal artefact reduction (O-MAR)

AIM To evaluate the image quality of O-MAR (Metal Artifact Reduction for Orthopedic Implants) for dental metal artefact reduction. MATERIALS AND METHODS This prospective study received institutional review board approval and written informed consent was obtained. Thirty patients who had dental implants or dental fillings were included in this study. Computed tomography (CT) images were obtained through the oral cavity and neck during the portal venous phase. The system reconstructed the O-MAR-processed images in addition to the uncorrected images. CT attenuation and image noise of the soft tissue of the oral cavity were compared between the O-MAR and the uncorrected images. Qualitative analysis was undertaken between the two image groups. RESULTS The image noise of the O-MAR images was significantly lower than that of the uncorrected images (p < 0.01). O-MAR offered plausible attenuations of soft tissue compared with non-O-MAR. Better qualitative scores were obtained in the streaking artefacts and the degree of depiction of the oral cavity with O-MAR compared with non-O-MAR. CONCLUSION O-MAR enables the depiction of structures in areas in which this was not previously possible due to dental metallic artefacts in qualitative image analysis. O-MAR images may have a supplementary role in addition to uncorrected images in oral diagnosis.