Diffusion-weighted (DWI) magnetic resonance (MR) imaging is useful in diagnosing various pathologic conditions in the liver, such as malignant tumors or hepatic fibrosis, and is now part of routine MR imaging protocols for the liver following the development of a parallel encoding technique that has markedly improved image quality. DWI is not very sensitive for detecting hepatocellular carcinomas (HCC) and is useless for characterizing border-line hepatocellular nodules in cirrhosis, but it complements gadolinium-enhanced MR imaging in detecting regional tumor recurrence or intrahepatic metastases of HCC following treatment. DWI is more useful for detecting hepatic metastasis, because histopathologic architecture of metastases does not resemble that of liver tissue and T₂ relaxation time of hepatic metasitasis is fairly longer than that of liver parenchyma. DWI is also useful for detecting moderate and advanced hepatic fibrosis. In cirrhosis, however, decreased blood flow in fibrotic liver is thought to lower apparent diffusion coefficient of the liver.
For MR perfusion analysis, a dual-input one-compartment model is used to correlate various hepatic blood flow parameters that represent hepatic arterial/portal blood flow or fraction, mean transit time, and distribution volume with the severity of cirrhosis and portal hypertension. Conventional multisectional imaging and perfusion study can be combined using a 3-dimensional sequence with high temporal resolution, but spatial resolution is not sufficiently high to diagnose tiny hepatic lesions. The advent of liver-specific contrast agents, such as gadoxetic acid, may spur the development of a new analysis model that incorporates extracellular perfusion and hepatocyte function.

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Purpose: We evaluated the diagnostic efficacy of gadoxetic acid- and superparamagnetic iron oxide (SPIO)-enhanced magnetic resonance (MR) imaging for focal nodular hyperplasia (FNH).
Materials and Methods: We retrospectively evaluated 11 patients with 11 FNHs. Both gadoxetic acid- and SPIO-enhanced MR imaging were performed. A 3-dimensional (3D) volumetric interpolated breath-hold examination was used with the gadoxetic acid dynamic study. SPIO-enhanced MR imaging included T₂- and T₂*-weighted images. We quantitatively and qualitatively compared lesion-specific enhancement of both contrast media.
Results: The mean signal-to-noise (S/N) ratio of the FNH lesions differed significantly on pre- and postenhanced imaging of each contrast medium (P<0.05); mean contrast-to-noise (C/N) ratio did not (P>0.05). All observers described all lesions as hyperintense in the arterial phase on gadoxetic acid-enhanced MR imaging and observed the presence of central scar, fibrous septa, and rim most clearly in gadoxetic acid-enhanced hepatobiliary phase images.
Conclusion: Gadoxetic acid-enhanced MR imaging was more useful than SPIO-enhanced MR imaging in characterizing FNH.

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Purpose: We evaluated the diagnostic effectiveness of magnetic resonance (MR) imaging at 3 tesla to visualize ovarian tumors and problems associated with its use.
Materials and Methods: From the records of 423 consecutive women who underwent pelvic MR imaging using a 3T system from April 2009 to June 2010, we analyzed 50 continuous cases of ovarian tumors proved by histopathology. We evaluated visualization of these tumors for image quality and artifacts using 5-point scales. For qualitative assessment, we scored overall image quality (1, poor, to 5, excellent), degree of conviction regarding the diagnosis (1, undiagnosable, to 5, diagnosable with high certainty), and 4 representative artifacts (penetrating, chemical shift, motion, and susceptibility artifact) (1, severe, to 5, little degradation). We also retrospectively reviewed the diagnostic features of the ovarian tumors and preoperative diagnostic accuracy. For quantitative assessment, we determined tumor size and ADC value.
Results: Overall quality score was scored 4.9±0.5, and conviction regarding diagnosis was 4.9±0.3. Artifacts caused little degradation in most cases: penetrating, 4.8±0.5; chemical shift, 4.3±0.5; motion, 4.6±0.6; and susceptibility, 3.8±0.9. Preoperative diagnostic accuracy was 92% (sensitivity 94.7%, specificity 90.3%). Mean tumor diameter was 88.3±61 mm. The mean ADC value was 1.04±0.3 in malignant tumors and 1.15±0.5 (×10⁻⁶ mm²/s) in benign tumors.
Conclusion: The quality of ovarian tumor images obtained with a 3T MR imaging system is adequate for diagnosis, with only slight degradation from penetrating or susceptibility artifacts.

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Purpose: We used diffusion tensor imaging (DTI) to evaluate anisotropic changes in skeletal muscle cells under external pressure.
Materials and Methods: In 6 healthy volunteers, we compared DTI of the tibialis anterior (TA) and soleus (SOL) muscles under pressure. We performed imaging using a 1.5-tesla magnetic resonance (MR) scanner and diffusion-weighted stimulated-echo echo-planar pulse sequences optimized for skeletal muscle. We calculated diffusion tensor eigenvalues (λ), apparent diffusion coefficients, and fractional anisotropy (FA) values in a series of axially acquired DTI and compared them between the pressurized and nonpressurized lower limbs. We also measured a cross-sectional area of skeletal muscle.
Results: We observed clear differences in FA and λ₃ between pressurized muscles and the nonpressurized muscles we used as controls. The mean control FAs were 0.36±0.02 (TA) and 0.30±0.02 (SOL). The mean control λ₃s were 0.74±0.02 s/mm² (TA) and 0.85±0.03 s/mm² (SOL). FA values in the pressurized (200 mmHg) limbs increased to 0.39±0.02 (TA) and 0.35±0.04 (SOL) compared with those values in the nonpressurized controls. λ₃ values in the pressurized (200 mmHg) limbs decreased to 0.68±0.05 s/mm² (TA) and 0.77±0.06 s/mm² (SOL) compared with those in controls. Moreover, the mean value of cross-sectional area of skeletal muscle (control) was 907.3±140.1 mm² (TA) and 1522±201.0 mm² (SOL). The cross-sectional area in the pressurized (200 mmHg) limbs decreased to 590.3±68.1 mm² (TA) and 1131±112.6 mm² (SOL) compared with those in controls. One-way analysis of variance (ANOVA) and post hoc Tukey-Kramer tests showed significant differences.
Conclusion: Anisotropy changed markedly on pressurizing the lower limb based on the correlation of the cross-sectional area and λ₃ suggested marked changed in anisotropy following application of pressure to the lower limb. If compression of the cross-sectional area is assumed to represent compression of the cell, change in λ₃ reflected the change in the size of muscle cells.

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Purpose: We evaluated the effect of intravenous administration of gadoxetic acid disodium to hepatic lesions and liver parenchyma on T₂-weighted (T₂WI) and diffusion-weighted imaging (DWI).
Materials and Methods: One hundred and one consecutive patients with 259 hepatic lesions underwent T₂WI and DWI (b-values of 500 and 1000 s/mm²) before and after gadoxetic acid administration. We compared the ratio of signal intensity (SIR) of the liver parenchyma and hepatic lesions, the ratio of contrast intensity of the lesion to the liver (CIR), the apparent diffusion coefficients (ADCs) of the liver and lesions, and lesion detectability between pre- and post-contrast images.
Results: SIRs, CIRs, and ADC of focal hepatic lesions were comparable on pre- and post-contrast images, and lesion detectability did not differ significantly between pre- and post-contrast T₂WI and DWI. The SIRs of the liver parenchyma were significantly lower on post-contrast DWI (1.4±0.68 [b=500 s/mm²] and 1.71±0.67 [b=1000 s/mm²]) than pre-contrast images (1.89±0.68 [b=500 s/mm²] and 2.26±0.78 [b=1000 s/mm²]) (P<0.001). ADCs of the liver parenchyma were also significantly decreased on post-contrast DWI (0.77±0.32 mm²/s) than pre-contrast images (0.64±0.33 mm²/s) (P=0.001).
Conclusion: T₂WI and DWI after administration of gadoxetic acid are feasible and do not compromise the SIR, CIR, and ADC of focal hepatic lesions. However, the signal intensity of DWI and ADC value of the liver parenchyma were decreased on gadoxetic acid-enhanced hepatocyte phase images.

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We demonstrated that the radiofrequency (RF) reception field is proportional to B₁⁻* straightforwardly in magnetic resonance (MR) imaging experiments at 4.7T. We compared maps of the reception field and the B₁⁻ of a saline phantom in magnitude and phase. First, we measured the image using an adiabatic spin echo (ASE) sequence with homogeneous excitation. That image corresponds to a map of the reception field. Next, we rotated the RF coil with the sample 180° around the vertical axis to measure the map of the transmission field that corresponded to B₁⁻ in the original configuration. The magnitude of the distribution fields of the reception field and B₁⁻ maps was almost identical. Examining the phases of the ASE images in the original and inverted configurations, we observed almost the same distribution in both phase maps, which indicated the proportionality of the reception field to B₁⁻*.

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We report a case of spinal subdural hematoma in the lumbar spine of a 75-year-old woman. Magnetic resonance imaging showed lesions of homogeneous high intensity in the spinal canal on both T₁- and T₂-weighted images, findings closely resembling those for epidural lipomatosis. Identification of 2-layered signal intensity surrounding the cauda equina on axial images is the key for accurate diagnosis.

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We report a case of polypoid endometriosis of the ovary and correlate magnetic resonance (MR) and pathological findings. The endometriosis appeared as multiple polypoid areas along the wall of the ovarian cystic lesion with hyperintensity on T₂-weighted images and slight hyperintensity on diffusion-weighted images. However, the polypoid areas did not yield low apparent diffusion coefficient (ADC) values on ADC map images. These MR findings were similar to the signal intensity of the uterine endometrium, reflecting the presence of abundant endometrial glands.

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Susceptibility-weighted angiography (SWAN) is a state-of-the-art 3-dimensional (3D) T₂*-weighted imaging (T₂*WI) technique with multiple echo acquisitions, but its clinical utility remains to be determined. We compared the utility of susceptibility-weighting sequences among SWAN, 3D phase-sensitive magnetic resonance (MR) imaging (PSI), and conventional 2-dimensional (2D) T₂*WI in routine clinical practice. Our results indicate that SWAN can achieve susceptibility weighting more effectively than conventional 2D T₂*WI and as effectively as PSI and requires a much shorter scan time than PSI.

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For the separate visualization of endolymph, perilymph, and bone on a single image after intravenous injection of single-dose gadodiamide, we fused gray-scale inverted positive endolymph (PEI) with native positive perilymph (PPI) images, that is, we subtracted PEI from PPI. Subtraction significantly improved the contrast noise ratio between endolymph and perilymph and the subjective visibility score for endolymphatic space. The 24 patients with the suspect of Ménière's disease were included.

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