Hideaki Kawamitsu

ADC Measurement of Abdominal Organs and Lesions Using Parallel Imaging Technique

OBJECTIVE The purpose of our study was to assess the reliability and usefulness of parallel imaging for apparent diffusion coefficient (ADC) measurement of abdominal organs and lesions. MATERIALS AND METHODS Single-shot spin-echo echo-planar diffusion-weighted MRI (TE = 66, b = 0, 600 s/mm2) was performed in phantom and clinical studies. The b value was set to minimize the effects of perfusion in tissue and to maintain signal-to-noise ratio. Bottle phantoms were scanned with and without parallel imaging and with various parallel imaging factors and at various positions to evaluate the effects of parallel imaging on ADCs. In 200 consecutive clinical patients (122 men and 78 women: mean age, 61.9 years), ADCs were calculated for liver (four segments), spleen, pancreas (head, body, tail), gallbladder, renal parenchyma, and back muscle, and then compared to evaluate the reliability of clinical ADC measurements with parallel imaging. ADCs were also calculated for diffuse diseases and focal lesions (94 malignant and 93 benign) of abdominal organs to evaluate the clinical usefulness of ADC. RESULTS Location-dependent changes in water ADCs were minimal with parallel imaging factors first of 3, then of 4, and were small except for measurements at the image periphery. Acetone ADCs were saturated at 4.00 x 10(-3) mm2/s. Degraded image quality prevented ADC measurement of the left hepatic lobe and pancreas in 7-18 patients. There was no significant difference among ADCs of four liver segments (1.50 +/- 0.24 [SD] x 10(-3) mm2/s - 1.56 +/- 0.31 x 10(-3) mm2/s) and between ADCs of the right and left kidneys (2.65 +/- 0.30 x 10(-3) mm2/s, 2.59 +/- 0.33 x 10(-3) mm2/s). ADC of the pancreas tail (1.65 +/- 0.37 x 10(-3) mm2/s) was significantly lower than those of the head (1.81 +/- 0.40 x 10(-3) mm2/s) and body (1.81 +/- 0.41 x 10(-3) mm2/s) (p < 0.005). Renal ADCs were significantly lower in patients with renal failure (right: 2.15 +/- 0.30 x 10(-3) mm2/s; left: 2.11 +/- 0.25 x 10(-3) mm2/s) than in those without disease (right: 2.67 +/- 0.29 x 10(-3) mm2/s; left: 2.60 +/- 0.32 x 10(-3) mm2/s) (p < 0.005). ADC of pancreatic cancer was significantly higher than that of healthy pancreas (p < 0.05). ADC of renal angiomyolipoma was significantly lower than those of renal cell carcinoma and healthy renal parenchyma (p < 0.0005). CONCLUSION Clinical ADC measurements of abdominal organs and lesions using parallel imaging appear to be reliable and useful, and the effect of parallel imaging on calculated values is considered to be minimal.

Quantitative assessment of regional pulmonary perfusion in the entire lung using three-dimensional ultrafast dynamic contrast-enhanced magnetic resonance imaging: Preliminary experience in 40 subjects.

To assess regional differences in quantitative pulmonary perfusion parameters, i.e., pulmonary blood flow (PBF), mean transit time (MTT), and pulmonary blood volume (PBV) in the entire lung on a pixel‐by‐pixel basis in normal volunteers and pulmonary hypertension patients.

Hemorrhagic Myocardial Infarction After Coronary Reperfusion Detected In Vivo by Magnetic Resonance Imaging in Humans: Prevalence and Clinical Implications

With the advent of thrombolytic therapy, hemorrhagic myocardial infarction (HMI) has been observed in experimental and human autopsy studies. However, its clinical implications remain undetermined, because of the absence of a reliable method to detect its presence in vivo. This study was designed to evaluate the clinical implications of HMI detected by magnetic resonance (MR) imaging in vivo after coronary reperfusion. Thirty-nine patients with acute myocardial infarction (AMI) were studied. Percutaneous transluminal coronary angioplasty (PTCA) was used to reopen the occluded coronary artery. Electrocardiogram (ECG)-gated T2*-weighted gradient-echo MR imaging was performed to detect intramyocardial hemorrhage, using a 1.5-T magnet within 2 weeks after coronary reperfusion (average, 5.7 days). Thirteen patients (33%) showed intramyocardial hemorrhage as a distinct hypointense zone by gradient-echo MR imaging and 26 patients showed homogeneous intensity consistent with absence of intramyocardial hemorrhage. Coronary angiograms showed lesser development of collateral flow in the patients with HMI than in those without (81% vs. 37%). Infarct size, estimated 1 month after coronary reperfusion by thallium-201 scintigraphy, was larger among patients with HMI than in those without (37 +/- 14% vs. 21 +/- 14%, respectively, p < 0.05). Left ventricular ejection fraction at 1 month follow-up showed less recovery in patients with HMI than in those without (47 +/- 9 to 51 +/- 10%; p = 0.47, vs. 53 +/- 10 to 60 +/- 9%, respectively, p < 0.05). ECG-gated T2*-weighted gradient-echo MR imaging offers a noninvasive means of detection of intramyocardial hemorrhage in patients with reperfused AMI. HMI occurred even after primary PTCA and may be a common finding associated with severely injured myocardium.

Time-resolved contrast-enhanced pulmonary MR angiography using sensitivity encoding (SENSE)

To evaluate the relationship between gadolinium concentration and signal‐to‐noise ratio (SNR) on sensitivity encoding (SENSE) images, and determine the appropriate bolus injection protocol for visualizing pulmonary circulation.

Utility of phase contrast MR imaging for assessment of pulmonary flow and pressure estimation in patients with pulmonary hypertension: Comparison with right heart catheterization and echocardiography

To compare the utility of phase contrast MR imaging (PC‐MRI) for assessment of pulmonary flow and pressure estimation with that of right heart catheterization and echocardiography (cardiac US) in patients with pulmonary arterial hypertension (PAH).

Hepatic CT perfusion measurements: a feasibility study for radiation dose reduction using new image reconstruction method.

OBJECTIVES To assess the effects of image reconstruction method on hepatic CT perfusion (CTP) values using two CT protocols with different radiation doses. MATERIALS AND METHODS Sixty patients underwent hepatic CTP and were randomly divided into two groups. Tube currents of 210 or 250 mA were used for the standard dose group and 120 or 140 mA for the low dose group. The higher currents were selected for large patients. Demographic features of the groups were compared. CT images were reconstructed by using filtered back projection (FBP), image filter (quantum de-noising, QDS), and adaptive iterative dose reduction (AIDR). Hepatic arterial and portal perfusion (HAP and HPP, ml/min/100ml) and arterial perfusion fraction (APF, %) were calculated using the dual-input maximum slope method. ROIs were placed on each hepatic segment. Perfusion and Hounsfield unit (HU) values, and image noises (standard deviations of HU value, SD) were measured and compared between the groups and among the methods. RESULTS There were no significant differences in the demographic features of the groups, nor were there any significant differences in mean perfusion and HU values for either the groups or the image reconstruction methods. Mean SDs of each of the image reconstruction methods were significantly lower (p<0.0001) for the standard dose group than the low dose group, while mean SDs for AIDR were significantly lower than those for FBP for both groups (p=0.0006 and 0.013). Radiation dose reductions were approximately 45%. CONCLUSIONS Image reconstruction method did not affect hepatic perfusion values calculated by dual-input maximum slope method with or without radiation dose reductions. AIDR significantly reduced images noises.

Functional MRI of regional brain responses to ‘pleasant’ and ‘unpleasant’ odors

Conclusions: Our findings demonstrate that functional MRI (fMRI) combined with a questionnaire is a useful method for studying the neuroanatomy of olfaction. Further studies with various odorants and questionnaires would provide an even better understanding of the mechanism of olfactory perception. Objectives: To better understand the mechanism of odorant perception in the central nervous system. Subjects and methods: fMRI was used to identify the activated regions during stimulation by two odorants, beta-phenyl ethyl alcohol and gamma-undecalactone. Participants were asked to describe the quality of the odor and to rate odor intensity and odor hedonic valence. Activation at each region was statistically analyzed according to the answers. Results: The bilateral middle orbitofrontal cortex (OFC), left lateral OFC, right insula, and bilateral anterior/middle cingulate gyri were most frequently activated by odor stimulation. Left middle OFC was significantly more often activated in the participants who could not identify the odor correctly (p=0.016). The left middle OFC and right lateral OFC were significantly more often activated in the participants who perceived the odor stimulation as unpleasant (p=0.03), while the right anterior cingulate gyrus was more often activated in those who perceived the odor as pleasant (p=0.03).

Apparent diffusion coefficient and fractional anisotropy in the vertebral bone marrow

To assess the state of cancellous tissue we analyzed the apparent diffusion coefficient (ADC) and fractional anisotropy (FA) in vertebral bone marrow.

Abdominal apparent diffusion coefficient measurements: effect of diffusion-weighted image quality and usefulness of anisotropic images

This study aimed to assess the effect of diffusion-weighted image (DWI) quality on abdominal apparent diffusion coefficient (ADC) measurements and the usefulness of anisotropic images. Twenty-six patients (10 men and 16 women; mean, 58.1 years) who underwent DW imaging and were diagnosed not to have any abdominal diseases were analyzed. Single-shot spin-echo echo-planar DW imaging was performed, and one isotropic and three orthogonal anisotropic images were created. ADCs were calculated for liver (four segments), spleen, pancreas (head, body, tail) and renal parenchyma. Image quality for each organ part was scored visually. We estimated the correlation between ADC and image quality and evaluated the feasibility of using anisotropic images. ADCs and image quality were affected by motion probing gradient directions in the liver and pancreas. A significant inverse correlation was found between ADC and image quality. The r values for isotropic images were -.46, -.48, -.70 and -.28 for the liver, spleen, pancreas and renal parenchyma, respectively. Anisotropic images had the best quality and lowest ADC in at least one organ part in 17 patients. DWIs with the best quality among isotropic and anisotropic images should be used in the liver and pancreas.

Esophageal magnetic resonance fluoroscopy: Optimization of the sequence

Objective The purpose of this study was to try to delineate the esophageal passage under dynamic conditions and to determine optimum settings for esophageal magnetic resonance (MR) imaging. Methods Ten healthy volunteers underwent MR fluoroscopy with two T1-weighted sequences: turbo field echo (TFE) and T1-weighted fast field echo (T1-FFE). These sequences were compared for signal-to-noise ratios (SNRs) and image quality. To determine the optimum slice thickness, an additional 10 healthy volunteers underwent MR fluoroscopy. Results obtained for slice thicknesses of 25, 35, 45, and 55 mm were compared for delineated length of the esophagus and image quality. Results The T1-FFE sequences provided higher SNRs and better image quality than the TFE sequences (T1-FFE: 89.4 ± 28.0, TFE: 52.4 ± 16.7; P < 0.001). Artifacts were less prominent and delineation of the esophageal wall was better on the T1-FFE images. The delineation of the esophageal wall was best with a 35-mm slice thickness, although delineated length was the longest with a 55-mm slice thickness. Conclusion This study showed T1-FFE to be a more suitable sequence than TFE and that the 35-mm slice thickness was the optimum slice thickness for esophageal MR fluoroscopy.