Kazuhiro Katahira

Assessment of Coronary Artery Disease Using Magnetic Resonance Coronary Angiography: A National Multicenter Trial

OBJECTIVES This national multicenter study determined the diagnostic performance of 1.5-T whole-heart coronary magnetic resonance angiography (MRA) in patients with suspected coronary artery disease (CAD). BACKGROUND Whole-heart coronary MRA using steady-state free precession allows noninvasive detection of CAD without the administration of contrast medium. However, the accuracy of this approach has not been determined in a multicenter trial. METHODS Using a 1.5-T magnetic resonance imaging unit, free-breathing steady-state free precession whole-heart coronary MRA images were acquired for 138 patients with suspected CAD at 7 hospitals. The accuracy of MRA for detecting a ≥ 50% reduction in diameter was determined using X-ray coronary angiography as the reference method. RESULTS Acquisition of whole-heart coronary MRA images was performed in 127 (92%) of 138 patients with an average imaging time of 9.5 ± 3.5 min. The areas under the receiver-operator characteristic curve from MRA images according to vessel- and patient-based analyses were 0.91 (95% confidence interval [CI]: 0.87 to 0.95) and 0.87 (95% CI: 0.81 to 0.93), respectively. The sensitivity, specificity, positive and negative predictive values, and accuracy of MRA according to a patient-based analysis were 88% (49 of 56, 95% CI: 75% to 94%), 72% (51 of 71, 95% CI: 60% to 82%), 71% (49 of 69, 95% CI: 59% to 81%), 88% (51 of 58, 95% CI: 76% to 95%), and 79% (100 of 127, 95% CI: 72% to 86%), respectively. CONCLUSIONS Non-contrast-enhanced whole-heart coronary MRA at 1.5-T can noninvasively detect significant CAD with high sensitivity and moderate specificity. A negative predictive value of 88% indicates that whole-heart coronary MRA can rule out CAD.

Diffusion-weighted magnetic resonance imaging for diagnosing malignant pulmonary nodules/masses: Comparison with positron emission tomography

Introduction: Recent developments of diffusion-weighted magnetic resonance imaging (DWI) make it possible to image malignant tumors to provide tissue contrast based on difference in the diffusion of water molecules among tissues, which can be measured by apparent diffusion coefficient (ADC) value. The aim of this study is to examine the usefulness of DWI for benign/malignant discrimination of pulmonary nodules/masses compared with 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET). Methods: PET and DWI were carried out prospectively in 104 patients with 140 pulmonary nodules/masses before surgery. FDG uptake of each lesion was quantitatively measured by a contrast ratio of standard uptake value (SUV-CR) between the lesions and contralateral lung. Diffusion of water molecule in each lesion was quantitatively measured by a minimum ADC (ADC-min). The diagnostic results were compared between the two modalities. Results: The receiver operating characteristics curve showed cutoff values of the ADC-min and the SUV-CR for benign/malignant discrimination to be 1.1 × 10−3 mm2/s and 0.37, respectively. DWI and PET showed sensitivities of 0.70 and 0.72 and specificities of 0.97 and 0.79, respectively. Although there was no significant difference in sensitivity between the two methods, DWI showed a significantly higher specificity than PET because of fewer false-positives for active inflammatory lesions (p = 0.03). The ADC-min and SUV-CR values showed a significant reverse correlation (r = −0.504, p < 0.001). Conclusions: DWI may be able to be used in place of FDG-PET to distinguish malignant from benign pulmonary nodules/masses with fewer false-positive results compared with FDG-PET.

Monitoring therapeutic responses of primary bone tumors by diffusion-weighted image: Initial results.

The purpose of our study was to investigate whether quantitative diffusion-weighted images (DWI) were useful for monitoring the therapeutic response of primary bone tumors. We encountered 18 osteogenic and Ewing sarcomas. Magnetic resonance (MR) images were performed in all patients before and after therapy. We measured the apparent diffusion coefficient (ADC) values, contrast-to-noise ratio (CNR), and tumor volume of the bone tumors pre- and posttreatment. We determined change in ADC value, change in CNR on T2-weighted images (T2WI), change in CNR on gadopentetate dimeglumine (Gd)-T1-weighted images (Gd-T1WI), and change in tumor volume. The bone tumors were divided into two groups: group A was comprised of tumors with less than 90% necrosis after treatment and group B of tumors at least with 90%. Changes in ADC value, tumor volume, and CNR were compared between the groups. Change in the ADC value was statistically greater in group B than that in the group A (p=0.003). There was no significant difference in the changes in CNR on T2WI (p=0.683), in CNR on Gd-T1WI (p=0.763), and tumor volume (p=0.065). The ADC value on DWI is a promising tool for monitoring the therapeutic response of primary bone sarcomas.

Diffusion-weighted magnetic resonance imaging can be used in place of positron emission tomography for N staging of non–small cell lung cancer with fewer false-positive results

OBJECTIVE One of the deficiencies of positron emission tomography for N staging in lung cancer is a false-positive result caused by concurrent lymphadenitis. Recently, diffusion-weighted magnetic resonance imaging has been reported to be able to image tumors of body organs. The aim of this study is to examine the usefulness of diffusion-weighted magnetic resonance imaging for N staging of non-small cell lung cancer compared with positron emission tomography-computed tomography. METHODS Both positron emission tomography-computed tomography and diffusion-weighted magnetic resonance imaging were prospectively used in 88 patients before surgical intervention for non-small cell lung cancer to examine 734 lymph node stations. The diagnostic results of positron emission tomography-computed tomography and diffusion-weighted magnetic resonance imaging were compared. The diameters of the metastatic foci within lymph nodes were measured on hematoxylin and eosin-stained sections to compare the detectable size of metastatic foci between positron emission tomography-computed tomography and diffusion-weighted magnetic resonance imaging. RESULTS The accuracy of N staging in the 88 patients was 0.89 with diffusion-weighted magnetic resonance imaging, which was significantly higher than the value of 0.78 obtained with positron emission tomography-computed tomography (P = .012), because of less overstaging in the former. Among the 734 lymph node stations examined pathologically, 36 had metastases, and the other 698 did not. Although there was no significant difference in the diagnosis of the 36 metastatic lymph node stations between the 2 methods, diffusion-weighted magnetic resonance imaging was more accurate for diagnosing the 698 nonmetastatic stations than positron emission tomography-computed tomography because of fewer false-positive results (P = .002). The detectable size of metastatic foci within lymph nodes was 4 mm in both positron emission tomography-computed tomography and diffusion-weighted magnetic resonance imaging. CONCLUSIONS Diffusion-weighted magnetic resonance imaging can be used in place of positron emission tomography-computed tomography for N staging of non-small cell lung cancer with fewer false-positive results compared with positron emission tomography-computed tomography.

Whole-body diffusion-weighted magnetic resonance imaging

Diffusion-weighted magnetic resonance imaging (DWI) provides information on the diffusivity of water molecules in the human body. Technological advances and the development of the concept of diffusion-weighted whole-body imaging with background body signal suppression (DWIBS) have opened the path for routine clinical whole-body DWI. Whole-body DWI allows detection and characterization of both oncological and non-oncological lesions throughout the entire body. This article reviews the basic principles of DWI and the development of whole-body DWI, illustrates its potential clinical applications, and discusses its limitations and challenges.

Is diffusion-weighted magnetic resonance imaging superior to positron emission tomography with fludeoxyglucose F 18 in imaging non–small cell lung cancer?

OBJECTIVE This retrospective analysis examined whether diffusion-weighted magnetic resonance imaging might be as useful as positron emission tomography with fludeoxyglucose F 18 for (1) discriminating between non-small cell lung cancer and benign pulmonary nodules and (2) predicting aggressiveness of non-small cell lung cancer. METHODS Diffusion-weighted magnetic resonance imaging and positron emission tomography were performed before surgery in 110 patients with 124 pulmonary nodules smaller than 3 cm, including 96 non-small cell lung cancers and 28 benign nodules. Diffusion of water molecules in magnetic resonance imaging was measured by minimum value of apparent diffusion coefficient. The criterion standard was the result of histologic diagnosis or follow-up examination. Sensitivity and specificity for differentiating between cancers and benign nodules were compared between diffusion-weighted imaging and positron emission tomography. Apparent diffusion coefficient in diffusion-weighted imaging and fludeoxyglucose F 18 uptake in positron emission tomography were examined with respect to pathologic tumor stage; lymphatic, vascular and pleural involvements; and histologic differentiation. RESULTS There were no significant differences between diffusion-weighted magnetic resonance imaging and positron emission tomography in sensitivity or specificity for non-small cell lung cancer. Whereas positron emission tomography showed significant differences in fludeoxyglucose F 18 uptake between pathologic stages IA versus IB or more advanced stages; between tumors with and without lymphatic, vascular, or pleural involvement; and between well-differentiated and moderately or poorly differentiated adenocarcinomas (P <.01-0.001), no significant differences in apparent diffusion coefficient values in were observed. CONCLUSION Diffusion-weighted magnetic resonance imaging is equivalent to positron emission tomography in distinguishing non-small cell lung cancer from benign pulmonary nodules but is not as useful for predicting aggressiveness of non-small cell lung cancer.

Evaluation of diffusion‐weighted imaging for the differential diagnosis of poorly contrast‐enhanced and T2‐prolonged bone masses: Initial experience

To determine whether quantitative diffusion‐weighted imaging (DWI) is useful for characterizing poorly contrast‐enhanced and T2‐prolonged bone masses.

Reduction in radiation and contrast medium dose via optimization of low-kilovoltage CT protocols using a hybrid iterative reconstruction algorithm at 256-slice body CT: Phantom study and clinical correlation

AIM To optimize low-kilovoltage (kV) computed tomography (CT) protocols using a hybrid iterative reconstruction (HIR) algorithm at 256-detector-row body CT. MATERIALS AND METHODS Based on preliminary phantom studies, three different tube voltage protocols with an equal contrast-to-noise ratio (CNR) were developed. They were a conventional 120 kV protocol with filtered back-projection (FBP), an 80 kV protocol with HIR (a 160% increase in the tube current-time product and a 40% reduction in the contrast medium dose), and a 100 kV protocol with HIR (a 20% reduction in the tube current-time product and the contrast medium dose). The clinical study included 70 patients (34 women, 36 men; mean age 70.5 ± 9.1 years, range 44-92 years) who had undergone CT at 120 kV a mean of 148 ± 137 days before undergoing low kV contrast-enhanced body CT (80 kV with HIR, n = 35; 100 kV with HIR, n = 35). The estimated effective radiation dose (ED), image noise, and CNR were calculated and the visual image quality was scored on a four-point scale. RESULTS Mean ED was 12.3, 8.4, and 15.4 mSv for the 80, 100, and 120 kV protocol, respectively, and significantly lower using the low kV protocols. There was no significant difference in the image noise and CNR between the low kV protocols with HIR and the 120 kV protocol with FBP, or in the visual scores among the three protocols. CONCLUSION Without ensuing image-quality degradation, the radiation and contrast medium dose can be reduced with optimal contrast-enhanced CT protocols using a low kV technique and an HIR algorithm.

A Low Tube Voltage Technique Reduces the Radiation Dose at Retrospective ECG-gated Cardiac Computed Tomography for Anatomical and Functional Analyses

RATIONALE AND OBJECTIVES To investigate the effect of low-tube-voltage technique on a cardiac computed tomography (CT) for coronary arterial and cardiac functional analyses and radiation dose in slim patients. MATERIALS AND METHODS We enrolled 80 patients (52women, 28 men; mean age, 68.7 ± 8.9 years) undergoing retrospective electrocardiogram-gated 64-slice cardiac CT. Forty were subjected to the low (80-kV) and 40 to the standard (120-kV) tube-voltage protocol. Quantitative parameters of the coronary arteries (ie, CT attenuation, image noise, and the contrast-to-noise ratio [CNR]) were calculated, as were the effective radiation dose and the figure of merit (FOM). Each coronary artery segment was visually evaluated using a 5-point scale. Cardiac function calculated by using low-tube-voltage cardiac CT was compared with that on echocardiographs. RESULTS CT attenuation and image noise were significantly higher at 80- than 120-kV (P < .01). CNR of the left and right coronary artery was 18.4 ± 3.8 and 18.5 ± 3.3, respectively, at 80 kV; these values were 19.7 ± 2.7 and 19.8 ± 2.8 at 120 kV; the difference was not significant. The estimated effective radiation dose was significantly lower at 80 than 120 kV (6.3 ± 0.6 vs. 13.9 ± 1.1 mSv, P < .01) and FOM was significantly higher at 80 than 120 kV (P < .01). At visual assessment, 99% of the coronary segments were diagnostic quality; the two protocols did not differ significantly. We observed a strong correlation and good agreement between low-tube-voltage cardiac CT and echocardiography for cardiac functional analyses. CONCLUSION Low-tube-voltage cardiac CT significantly reduced the radiation dose by approximately 55% in slim patients while maintaining anatomical image quality and accuracy of cardiac functional analysis.

Usefulness of Diffusion-Weighted Imaging in the Localization of Prostate Cancer

PURPOSE Advances in high-precision radiation therapy techniques for patients with prostate cancer permit selective escalation of the radiation dose delivered to the dominant intraprostatic lesion and improve the therapeutic ratio. We evaluated the value of diffusion-weighted imaging (DWI) for dominant intraprostatic lesion assessment. METHODS AND MATERIALS The study population consisted of 23 patients with early prostate cancer. Before undergoing total prostatectomy, they were evaluated by means of magnetic resonance imaging, including DWI. T2-weighted imaging (T2WI) with and without DWI were retrospectively assessed by six independent observers. Imaging findings were compared with pathologic results from whole prostate specimens on a lesion-by-lesion basis. RESULTS Pathologic study identified 43 lesions in 23 patients. On magnetic resonance imaging, the six observers correctly identified 11-22 of 43 lesions (sensitivity, 26-51%) on T2WI alone and 20-31 (sensitivity, 47-72%) on T2WI plus DWI. Positive predictive values were 42-73% on T2WI alone and 58-80% on T2WI plus DWI. For all observers, detection was higher on combined T2WI and DWI than on T2WI alone. CONCLUSION Because the addition of DWI to T2WI improves the detectability of prostate cancer, DWI may offer a promising new approach for radiation therapy planning.