We investigated temporal MR signal changes in the peripheral lung and proximal pulmonary vessels during the entire cardiac cycle in order to evaluate the characteristics of the diastolic-systolic subtraction method in the lung. In eight healthy volunteers free of lung diseases, changes in the MR signal during one breath-hold were investigated with the multiple ECG-triggered half-Fourier single-shot fast-spin echo (SS-FSE) technique. The signal intensity-time course curve in the lung showed that biphasic signals decreased 20% to 47% at systole and 5% to 33% at mid-diastole, measured against the maximum signals at late diastole. This signal decrease in the peripheral lung was correlated to that in the proximal pulmonary vessels during an entire cardiac cycle (r=0.667 to 1.000). The best visualization of the lung was obtained at late diastole, when the intra-vascular flow in the lung was expected to be stagnant. Compared with the late diastolic SS-FSE images, the late diastolic-systolic subtracted SS-FSE images improved the signal-to-noise ratio in the lung as well as the signal-intensity ratio of the peripheral lung to surrounding tissues. Although the flow-induced signal dephasing in the lung was completely unavoidable and its amount was unpredictable even at late diastole, the diastolic-systolic subtracted SS-FSE images showed the relative differences in flow alteration during the cardiac cycle between the images at diastole and those at systole. The main characteristic of diastolic-systolic subtracted SS-FSE was the enhancement of visibility of cardiac-dependent signal changes in the lung due to the alteration in pulsatile flow.

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Purpose: To determine the effect of the magic-angle effect on the MR signal in the posterosuperior portion of the glenoid labrum.
Methods: MR imaging of 15 arthroscopically evaluated shoulders, five with posterosuperior labrum injury and ten intact, was retrospectively reviewed. In the first part of the study, the signal intensity of the posterosuperior labrum on gradient-recalled echo (GRE) T₂^*-weighted axial images was correlated with the arthroscopy findings. The second part of the study was designed to illustrate the orientation-dependent signal that occurs in the posterosuperior labrum of three asymptomatic volunteers when imaged in the conventional supine position and in a position similar to Trendelenburg's. Another three volunteers were examined with GRE T₂^*-weighted axial images to assess the echo-time (TE)-dependent signal in the labrum.
Results: The signal increase in the posterosuperior labrum was identified not only in the injured labra but also in nine of 10 intact labra. In the volunteers' studies, the signal in the posterosuperior labrum changed according to the examinees' positions (conventional supine or similar to Trendelenburg's) and according to TE.
Conclusions: Increased signal intensity due to the magic-angle effect may be misdiagnosed as a labrum injury. Awareness of this pitfall is particularly important in MR imaging of throwing athletes whose posterosuperior labra are frequently injured by posterosuperior glenoid impingement.

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Purpose: We reviewed the MR appearance of motor denervation of the third (mandibular) division of the trigeminal nerve (V3) and of the hypoglossal nerve.
Method: Six cases of tumor of the head and neck with motor denervation were retrospectively evaluated. These comprised two patients with V3 denervation, three patients with hypoglossal nerve denervation, and one patient with both V3 and hypoglossal denervation. The observation was conducted for 6 to 44 months after onset. In denervated muscles, changes in signal intensity in T₁- and T₂-weighted images, degree of contrast enhancement, and volume of muscle were estimated during the follow-up period.
Results: In all cases of V3 denervation, the muscles showed no change in signal intensity in the T₁-weighted images up to three months after onset. In two cases of hypoglossal denervation, the tongues appeared ipsilaterally hyperintense in the T₁-weighted images within the first three months. In one case with V3 denervation and two cases with hypoglossal denervation, denervated muscles appeared hyperintense in the T₂-weighted images up to three months after onset. At three months after denervation, the signal intensities of all motor-denervated areas increased in both T₁- and T₂-weighted images. Postcontrast T₁-weighted images obtained within the first three months displayed contrast enhancement of all denervated muscles. In three cases of V3 denervation, the volumes of the affected muscles were reduced after the first three months. In three cases of hypoglossal denervation, the ipsilateral volume of the tongue decreased at three months after onset.
Conclusion: Up to three months after onset, the denervated muscles appeared hyperintense in the T₂-weighted images and contrast enhancement in postcontrast T₁-weighted images before fatty infiltration and volume loss were apparent. Familiarity with the MR appearance of denervated muscles accompanying tumors of the head and neck is important to avoid confusion with inflammatory or neoplastic processes.

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Middle cerebral artery (MCA) infarction involving the striatum can cause secondary degeneration of the substantia nigra and corticospinal tract. We present a patient with subacute hemorrhagic MCA infarction in whom diffusion-weighted MR images showed high signal intensity in the ipsilateral substantia nigra and corticospinal tract. A corresponding apparent diffusion coefficient map revealed a uniformly decreased signal in the same area. This represents secondary degeneration and should not be mistaken for other pathological conditions, such as a new infarction.

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We report a case of central neurocytoma that manifested tumor recurrence with craniospinal dissemination. Imaging studies before surgery showed a markedly enhanced tumor with small cysts and calcification, which invaded the adjacent brain parenchyma, located in the posterior horn of the right lateral ventricle. Proton MR spectroscopy showed markedly elevated choline and lactate peaks with a strongly diminished N-acetylaspartate peak. Two years after neurosurgical intervention, the tumor showed multiple craniospinal dissemination in the middle cranial fossa and the intradural extramedullary space of the spine.

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