The formation of senile plaques followed by deposition of amyloid β peptides (Aβ) are the earliest pathological changes of Alzheimer's disease (AD); thus, detection of the plaques remains the most important early diagnostic indicator of AD. Amyloid imaging is a noninvasive technique for visualizing senile plaques in the brains of patients with Alzheimer's using positron emission tomography (PET) or magnetic resonance (MR) imaging. Several types of probes have been developed for PET, but few ligands have been developed specifically for MR imaging detection of amyloid plaques. This review presents recent advances in amyloid imaging using MR imaging and includes our studies.

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In Japan, the medical examiner system is not widespread, the rate of autopsy is low, and many medical institutions therefore perform postmortem imaging using clinical equipment. Postmortem imaging is performed to clarify cause of death, select candidates for autopsy, make a guide map for autopsy, or provide additional information for autopsy. Findings are classified into 3 categories: cause of death and associated changes, changes induced by cardiopulmonary resuscitation, and postmortem changes. Postmortem magnetic resonance imaging shows characteristic changes in signal intensity related to low body temperature after death; they are low temperature images.

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Background: Tractography of skeletal muscle can clearly reveal the 3-dimensional course of muscle fibers, and the procedure has great potential and could open new fields for diagnostic imaging. Studying this technique for clinical application, we noticed differences in the number of visualized tracts among volunteers and among muscles in the same volunteer. To comprehend why the number of visualized tracts varied so that we could acquire consistently high quality tractography of muscle fiber, we started to examine whether differences in individual parameters affected tractography visualization.
Purpose: To determine whether there are gender- and age-specific differences that differentiate the muscles by gender and age in MR tractography of skeletal muscle fiber.
Materials and Methods: We divided 33 healthy volunteers by gender and age among 3 groups, A (13 younger men, aged 20 to 36 years), B (11 younger women, 25 to 39 years), and C (9 older men, 50 to 69), and we obtained from each volunteer tractographs of 8 fibers, including the bilateral gastrocnemius medialis (GCM), gastrocnemius lateralis (GCL), soleus (SOL), and anterior tibialis (AT) muscles. We classified the fibers into 5 grades depending on the extent of visualized tracts and used Mann-Whitney U-test to compare scores by gender (Group A versus B) and age (Group A versus C).
Results: Muscle tracts were significantly better visualized in women than men (median total visual score, 34 versus 24, P<0.05). In particular, the SOL muscles showed better visualization in the right (4.0 in women, 1.0 in men, P<0.05) and left (3.0 in women, 1.0 in men, P<0.05). Difference by age was not significant. The GCL was the highest scored muscle in all groups.
Conclusions: Our results suggest that group differences, especially by gender, affected visualization of tractography of muscle fiber of the calf.

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Purpose: q-ball imaging (QBI) reconstructs the orientation distribution function (ODF) that describes the probability for a spin to diffuse in a given direction, and it is capable of identifying intravoxel multiple fiber orientations. The local maxima of ODF are assumed to indicate fiber orientations, but there is a mismatch between the orientation of a fiber crossing and the local maxima. We propose a novel method, multi-shelled QBI (MS-QBI), that gives a new ODF based on the moment of the probability density function of diffusion displacement. We test the accuracy of the fiber orientation indicated by the new ODF and test fiber tracking using the new ODF.
Methods: We performed tests using numerical simulation. To test the accuracy of fiber orientation, we assumed that 2 fibers cross and evaluated the deviation of the measured crossing angle from the actual angle. To test the fiber tracking, we used a numerical phantom of the cerebral hemisphere containing the corpus callosum, projection fibers, and superior longitudinal fasciculus. In the tests, we compared the results between MS-QBI and conventional QBI under the condition of approximately equal total numbers of diffusion signal samplings between the 2 methods and chose the interpolation parameter such that the stabilities of the results of the angular deviation for the 2 methods were the same.
Results: The absolute value of the mean angular deviation was smaller in MS-QBI than in conventional QBI. Using the moment-based ODF improved the accuracy of fiber pathways in fiber tracking but maintained the stability of the results.
Conclusion: MS-QBI can more accurately identify intravoxel multiple fiber orientations than can QBI, without increasing sampling number. The high accuracy of MS-QBI will contribute to the improved tractography.

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We investigated the amount and distribution of hydrogen peroxide (H₂O₂) generated in a solid gelatin sample irradiated by heavy ion (carbon) beam. We irradiated the gelatin sample, which contained a nitroxyl radical (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, TEMPOL), with a 290-MeV/nucleon carbon beam (~128 Gy). To verify the distribution of H₂O₂ generation in the irradiated sample, we employed both electron paramagnetic resonance (EPR) spectroscopic and magnetic resonance (MR) imaging methods based on H₂O₂-dependent paramagnetic loss of TEMPOL. We obtained a distribution profile of the H₂O₂-dependent reaction in the gelatin sample when we irradiated gelatin samples with carbon beams with several different linear energy transfer (LET) values. Because the profiles of oxygen consumption in the gelatin sample measured by L-band EPR oxymetry and of the H₂O₂-dependent reaction have almost the same shape, the profile of the H₂O₂-dependent reaction can be used as an estimation of the profile of the generation of H₂O₂. The H₂O₂ profile in one intact gelatin sample scanned by 7-tesla MR imaging showed a similar shape as a result of the EPR experiment. We obtained several hundreds of micromolars of H₂O₂ generated in a gelatin sample irradiated by carbon beam when 200 Gy was given at the surface of the sample. H₂O₂ distribution was almost flat, with only a slight peak just before the end of the beam.

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Purpose: To evaluate the utility of measuring the volumes of areas of high signal intensity on T₂-weighted magnetic resonance (MR) images immediately after irradiation for predicting the local control rate of uterine cervical cancer.
Materials and Methods: From our departmental database, we identified 109 patients with cervical cancer who underwent MR imaging before irradiation and just before or just after completion of radiation therapy from 1994 to 2007. We included 46 of the 109 patients in this study, 5 patients with local recurrence and 41 patients who were free of disease for more than 2 years. Fifteen received radiation therapy alone, and 28 patients received concurrent chemoradiation therapy. We measured the volumes of areas of high signal intensity involving the uterine cervix on T₂-weighted MR images before radiation therapy and just before or just after its completion. We measured the 3 orthogonal diameters to calculate the volume as an ellipsoid and evaluated proportional tumor volume and the rate of reduction. We analyzed statistics with Student's t-test.
Results: In patients with local recurrence, the mean volume of the areas of high signal intensity on T₂-weighted MR images just before completion of irradiation therapy or just after was 19.70 cm³, which was significantly larger than that in patients without recurrence (1.77 cm³, P<0.05). The proportional tumor volume was also significantly larger (P<0.05).
Conclusions: Although areas of high signal intensity on T₂-weighted MR images include acute radiation change, their volume and the proportional tumor volume after irradiation can be useful clues in predicting the local control rate of uterine cervical cancer.

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A woman was referred to our institution with an ultrasound (US) suggestive of right-sided heart in fetus at 34 weeks' gestation. Magnetic resonance (MR) imaging revealed right-sided heart, small right hemithorax, and completely absent right main bronchus and right pulmonary artery. From our experience with this case, we point out 5 important MR imaging findings needed for prenatal diagnosis of pulmonary agenesis. Fetal MR imaging also provided information about anomalies of other organs.

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We visualized the intraparotid facial nerve and parotid duct at 3 tesla using 3-dimensional reversed fast imaging with steady-state precession (FSIP) (3D-PSIF) with diffusion weighting. Excellent fat suppression by water-selective excitation, sufficient T₂-weighting of 3D-PSIF, vessel suppression by diffusion weighting, and high spatial resolution allowed the simultaneous visualization. We also present volumetric representation of the facial nerve and duct.

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Hybrid of opposite-contrast (HOP) magnetic resonance angiography (MRA) is a new method that combines the advantages of 3-dimensional (3D) time-of-flight (TOF) MRA and black-blood (BB) MRA without prolonging acquisition time. In phantom and clinical studies, we focused on image differences when we applied gradient moment nulling (GMN) to 2 or 3 axes in the first echo. We made an original phantom with a semicircular tube of 3- and 5-mm internal diameter, with flow rate in the tube of 0, 20, 60, 80, or 120 cm/s. In original images of the phantom obtained with TOF MRA and flow-sensitive BB MRA and in filter frequency-weighted subtraction (FWS) processed images acquired with HOP MRA, we measured the contrast-to-noise ratio (CNR) of both the inside and outside of the tubes. In FWS processed images with GMN applied to 2 axes, the CNR was high at various flow rates in both straight and bending portions of the tubes in comparison with TOF images. In a clinical study in 15 patients, we evaluated vessel visualization in images obtained using conventional TOF MRA with magnetization transfer contrast (MTC) and HOP MRA. In clinical studies, visualization scores of HOP MRA were equivalent to those of conventional TOF MRA in the bilateral internal carotid arteries (ICA) and inferior in the basilar arteries. However, visualization of the peripheral portion of the middle cerebral artery (MCA) improved significantly in HOP MRA with GMN applied to 2 and 3 axes. Visualization of the main trunk of the ICA and MCA was superior in HOP MRA with GMN applied to 2 axes. HOP MRA with 2-axis GMN may be useful for excellent visualization of both major arteries and peripheral vessels in the head.

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