Purpose: The purpose of this study was to acquire a hyperpolarized (HP) ³He image of the mouse lung and to estimate ³He T₁ in the lung from wash-out curve analysis under spontaneous respiration.
Materials and Methods: We first tested the K-Rb hybrid method for the spin-exchange optical pumping (SEOP) of ³He using a home-built noble gas polarizer operated at atmospheric pressure and then applied it to MR imaging and spectroscopy of the mouse lung. The longitudinal relaxation time (T₁) of ³He in the mouse lung was estimated under spontaneous respiration by exploiting a novel method in which SF₆ gas at thermal equilibrium was utilized in combination with the HP ³He gas in the quantitative wash-out curve analysis. This method utilizes the difference in the profile of the wash-out curve of HP ³He and SF₆ at thermal equilibrium. That is, the slope of the ³He wash-out curve in the semi-logarithmic plots is affected by 3 factors, including RF pulse angle, respiration, and T₁, whereas the slope of the SF₆ wash-out curve is only the function of respiratory term.
Results: A ³He lung image was obtained successfully, and we were able to estimate successfully ³He T₁ in the mouse lung under spontaneous respiration using a novel method; the estimated T₁ value was 68±25 s, which was reasonable compared with the value calculated from the literature data measured during breath-hold.
Conclusion: We succeeded in acquiring the first ³He image of mouse lung in vivo in this country, and our proposed method of estimating ³He T₁ in the lung under spontaneous respiration is noninvasive and readily applied to animals and would be useful to evaluate the alveolar gas exchange function as well as oxygen partial pressure (p_O2) in lungs of animals.

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Purpose: To evaluate the hemodynamic changes of liver cirrhosis in the rat and investigate the relationship between hemodynamic changes and properties of fibrotic change in the liver.
Materials and Methods: Three rats with cirrhosis induced by thioacetamide (TAA), three with disease induced by carbon tetrachloride (CCl₄), and three with no treatment were measured on dynamic MRI using a 1.5T scanner. Compartment and moment analysis were used to quantitate hemodynamic changes.
Results: Compartment model analysis showed that increased transition speed from vessels to the liver correlated with grade of liver fibrosis. Moment analysis demonstrated that decrease of area under the curve (AUC), mean residence time (MRT), variance of residence time (VRT), half life (T_1/2) and increased total clearance (CL) correlated with grade of liver fibrosis.
Conclusions: Hemodynamic changes in injured fibrotic liver may be influenced by the grade of fibrosis. Compartment model and moment analysis may be useful for evaluating hemodynamic changes in injured liver.

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Purpose: Applying regenerated cartilage in a clinical setting requires noninvasive evaluation to detect the maturity of cartilage tissue. Magnetic resonance (MR) imaging of articular cartilage is well accepted and has been applied clinically in recent years. We attempt to establish a noninvasive method to evaluate the maturity of regenerated cartilage tissue using gadolinium-enhanced MR imaging.
Methods: To reconstruct cartilaginous tissue, we embedded articular chondrocytes harvested from bovine humeral head in agarose gel and cultured the cells in vitro up to 4 weeks. The fixed charge density (FCD) of the cartilage was determined using MRI gadolinium exclusion method. The sulfated glycosaminoglycan (sGAG) content was determined by dimethylmethylene blue dye-binding assay.
Results: The sGAG content and FCD of the regenerated cartilage increased with duration of culture. In the T₁Gd maps, the [Gd-DTPA^2-] in the specimen decreased, and the boundary between the sample disk and the bath solution of phosphate buffered saline (PBS) became clearer as time in culture increased. In the linear regression analysis, FCD and sGAG content correlated significantly.
Conclusion: Gadolinium-enhanced MR imaging measurements can be useful predictors of the degree of cartilaginous tissue formation.

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Purpose: To evaluate the effect of radiofrequency (RF) heating on a metallic implant during magnetic resonance imaging (MRI), temperatures at several positions of an implant were measured, and results are compared with electromagnetic simulations using a finite element method.
Methods: A humerus nail implant made of stainless steel was embedded at various depths of tissue-equivalent gel-phantoms with loop (loop phantom) and partially cut loop (loop-cut phantom), and the phantoms were placed parallel to the static magnetic field of a 1.5T MRI device. Scans were conducted at maximum RF for 15 min, and temperatures were recorded with 2 RF-transparent fiberoptic sensors. Finally, electromagnetic-field analysis was performed.
Results: Temperatures increased at both ends of the implants at various depths, and temperature increase was suppressed with increasing depth. The maximum temperature rise was 12.3°C at the tip of the implant and decreased for the loop-cut phantom. These tendencies resembled the results of electromagnetic simulations.
Conclusion: RF heating was verified even in a nonmagnetizing metal implant in a case of excessive RF irradiation. Particularly, rapid temperature rise was observed at both ends of the implant having large curvatures. The difference in temperature increase by depth was found to reflect the skin-depth effect of RF intensity. Electromagnetic simulation was extremely useful for visualizing the eddy currents within the loop and loop-cut phantoms and for evaluating RF heating of a metallic implant for MRI safety.

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Purpose: To investigate the proton relaxation mechanisms and the optimal MR imaging parameters in superparamagnetic iron oxide (SPIO)-enhanced MR imaging of liver injury.
Methods: A liver injury model was created in the rat using carbon tetrachloride. The T₁ and T₂ relaxation effects of SPIO in normal and injured liver were estimated by ex vivo relaxometry. In vivo laser confocal microscopy of the liver was performed to simulate the distribution and clustering of SPIO particles in the hepatic macrophages. SPIO-enhanced MR imaging (1.5T) of normal and diseased rats was performed with variable parameters. The liver specimens were prepared for histopathological examination.
Results: Histopathological and laser confocal microscopic findings showed diffuse macrophage distribution but decreased intracellular clustering of SPIO in injured liver. Ex vivo relaxometry showed sustained T₁ and T₂ relaxation effects of SPIO in liver injury. On MR images obtained with moderate echo time (spin echo [SE] 2000/40 and gradient echo [GRE] 130/9.0/60°), injured liver showed significantly lower decrease in signal-to-noise ratio (SNR) than the normal liver, whereas little difference in SNR was found between the normal and injured liver on heavily T₂-(SE 2000/80) and T₁-weighted (SE 300/11 and GRE 130/2.0/90°) MR images.
Conclusion: Pulse sequences with a moderately long echo time (TE) may be more appropriate than heavily T₁- or T₂-weighted images for distinguishing normal and injured liver in SPIO-enhanced MR imaging because of the maintained T₁ and T₂ relaxation effect but decreased T₂* relaxation effect of SPIO in injured liver.

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Magnetic resonance (MR) imaging features of white matter lesions, often seen in the elderly, are correlated with histologic findings. Dilatation of perivascular spaces is seen, especially in the frontal and/or parietal subcortical white matter; the spaces are less than 3 mm in diameter and have sharp margins with no perifocal abnormality. Old lacunar infarcts are larger than 3 mm in diameter and are irregularly shaped and accompanied by perifocal myelin pallor and gliosis. Periventricular hyperintensity, including cap and rim, histologically shows myelin pallor, dilatation of perivascular spaces, discontinuity of the ependymal lining, and subependymal gliosis. Deep and subcortical white matter hyperintensity reflects myelin pallor and dilatation of perivascular spaces. Diffuse white matter lesion, seen in Binswanger's disease, shows myelin pallor and tissue rarefaction associated with loss of myelin and axons. U-fibers are usually well preserved. Severe arteriosclerosis and arteriolosclerosis are usually seen in the white matter. Knowledge of the pathologic features of incidental changes in white matter helps in understanding MR imaging findings.

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Because nipple discharge is caused by carcinoma as well as benign disease, identification of intraductal abnormalities with ductography is important. Ductography is an invasive mammographic examination in which contrast material is injected directly into the duct. Failure to cannulate or extravasation may occur. Ductography shows evidence of lesions, such as filling defects, duct obstruction, or wall irregularity, but it does not reveal the lesion itself. Furthermore, ductography produces a two-dimensional image, so it does not show the shape of the dilated duct or the precise location of the intraductal lesion in the breast.
We applied three-dimensional (3D) heavily T₂-weighted imaging with fat suppression of the breast to produce MR ductography. The dilated ducts are seen in 3D as tubular structures with high signal, and intraductal abnormalities are seen as signal defects. Furthermore, MR ductography can show an obstructed duct that cannot be seen on ductography. We also performed 3D breast MRI with the intravenous infusion of contrast material to show the lesion itself. Finally, we fused these 2 volume images into a single 3D fused image that not only shows the existence of intraductal abnormality, but reveals the shape, size, and extent of lesion, allowing us to understand easily the relationship between the ducts with dilation and any intraductal lesions in the breast.
We herein introduce and describe this noninvasive method and discuss various factors related to its diagnostic use.

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Angioleiomyomas are smooth muscle tumors that occur most often in the extremities and are usually less than 2 cm in diameter. We present 2 case reports of giant angioleiomyoma. Case 1 was a 51-year-old woman with a 5-year history of a slowly growing mass 12×10 cm in diameter in the right posterior thigh. The tumor was larger than any previously reported. Case 2 was a 72-year-old man with an 8-year history of a slowly growing mass 6×6 cm in diameter in the left palm. The tumor was unique in that it grew to a giant size in the hand of the elderly patient. Magnetic resonance imaging of both cases confirmed the tumors' presence in the subcutis. T₁-weighted images showed homogenous signal isointense to muscle. On T₂-weighted images, areas of hyperintensity and hypointensity intermingled. Three-dimensional gadolinium-enhanced magnetic resonance angiography showed rapid initial enhancement followed by a gradual increase in enhancement, suggesting that the tumors were rich in vessels. Microscopic examination revealed numerous vascular channels embedded within a huge smooth muscle component.

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