Magnetic resonance spectroscopy (MRS) was used to investigate the dynamics of hyperpolarized (HP) ¹²⁹Xe respiration in the chests of mice under spontaneous respiration. The washout curve was analyzed using Kety's exchange model of inert gases, and the 3 factors that affect the slope of the washout curve, i.e., the RF flip angle, respiratory parameters, and apparent relaxation time (which comprises terms including the relaxation time in alveoli, T_1air, and perfusion), were determined separately. Flip angle was determined precisely using the dual flip angle method, and ventilation volume was determined using SF₆ gas at thermal equilibrium. Furthermore, an attempt was made to separate out the terms of T_1air and perfusion from the apparent relaxation time after exploiting the ventilation model of lungs in steady state. Values of relaxation time T_1air=30.5 s and perfusion term λQ/V_A=0.016 s^-1 were obtained, supporting the applicability of the ventilation model proposed.

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Objective: To determine the effect of simultaneous use of respiratory triggering in hepatic diffusion-weighted imaging (DWI), we compared DWI with respiratory triggering (RT-DWI) and DWI under free breathing (FB-DWI) in terms of relative contrast between hepatic tumor and surrounding liver parenchyma, apparent diffusion coefficient (ADC) measurement, and frequency of respiratory misregistration.
Materials and Methods: Thirty patients (21 men, 9 women, aged 25 to 80 years) with liver metastasis or hepatocellular carcinoma in the right hepatic lobe were examined with RT- and FB-DWI. In patients having multiple tumors, up to 3 lesions were selected by mutual agreement of 2 diagnostic radiologists. Finally, 59 nodules were selected for evaluation. Relative contrast ratio (RCR) between the lesions and surrounding parenchyma and ADC were measured in each hepatic lesion in each sequence. The differences in RCR and ADC between RT- and FB-DWI were statistically analyzed using Wilcoxon's signed rank test. The frequency of respiratory misregistration advents in each sequence was visually evaluated by the 2 diagnostic radiologists and assessed using McNemar's test.
Results: RCRs were significantly higher in RT- than in FB-DWI (P<0.001). The difference in ADC between the 2 sequences was not significant. However, ADCs tended to be more scattered in FB- than in RT-DWI. The frequency of respiratory misregistration advents was significantly higher in FB- than in RT-DWI.
Conclusion: FB- was inferior to RT-DWI in both contrast between tumors and surrounding liver parenchyma and in accuracy of ADC measurement as far as the numbers of excitation in each sequence were the same. For preoperative examination of hepatic resection, RT- is more suitable than FB-DWI.

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Purpose: The purpose of this study was to assess the relationship between the amount of scirrhous component in invasive ductal carcinoma and its MR characteristics.
Materials and Methods: We retrospectively reviewed 71 consecutive patients with invasive ductal carcinoma smaller than 25 mm (average, 16.6 mm) in diameter. The scirrhous component was defined as invasive foci in small clusters of cancer cells showing desmoplasia. Invasive ductal carcinoma was subclassified into 3 groups in accordance with the amount of the scirrhous component (scirrhous component degree; SCD): SCD I (scirrhous component less than 20%), SCD II (intermediate), and SCD III (more than 80%). Dynamic magnetic resonance (MR) imaging was performed using volumetric interpolated sequence. Prior to dynamic study, T₂*-weighted first-pass perfusion images were obtained before, during, and after bolus injection of 0.1 mmol Gd-DTPA/kg.
Results: Twenty-eight lesions were classified as SCD I, 14 as SCD II, and 29 as SCD III. Mass margin and signal intensity loss in the perfusion study were significantly different among the 3 SCD groups (P<0.001). The kinetic patterns were significantly different among the 3 SCD groups (P=0.04), and between SCD I/II and SCD III (P=0.03). The presence of enhancing internal septations was significantly different between SCD I/II and SCD III carcinomas (P=0.05). Central enhancement was only observed in SCD I carcinoma (4%; 3/71).
Conclusion: The histological predominance of the scirrhous component in invasive ductal carcinoma may be one explanation for the differences in morphologic and kinetic patterns on MR imaging.

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Air microbubbles have been investigated recently at high magnetic field strength (2 Tesla or greater) as potential MR susceptibility contrast agents. We used a phantom to measure their susceptibility at 1.5T to clarify their usefulness for this purpose. The phantom, filled with fresh Levovist^® suspension at 4 different doses (67 to 125 mg/mL), was continuously scanned with a gradient-echo technique at a temporal resolution of 10 s. The transverse relaxation increase (R₂*) by microbubbles demonstrated a time course of exponential decay at each dose (time-constant, 39 to 57 s). The dependency of R₂* on microbubble volume fraction was linear, with a slope of 89 s^-1 per percentage microbubble volume fraction. Our study represents the first step towards applying microbubbles as susceptibility contrast agents at 1.5T.

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We speculated that meningeal pathologies might facilitate the permeability of cranial nerves at the fundus of the internal auditory canal (IAC), causing prompt enhancement after administration of Gd-DTPA. Using a 3D- fluid-attenuated inversion recovery (FLAIR) sequence, we evaluated the enhancement of the cerebrospinal fluid (CSF) space in the IAC fundus 10 min after Gd-DTPA administration in patients with meningeal diseases. Twenty patients (aged 22 to 79 years) were divided into 2 groups, a group with meningeal disease comprising 9 patients with meningeal abnormalities (6, tumor dissemination; 3, infection) and a control group of 11 patients with unilateral IAC pathology whose healthy sides were included as controls. Six of the 9 patients in the group with meningeal disease showed bilateral enhancement; one showed unilateral enhancement. None of the control group showed enhancement in the healthy side. One patient with Ramsay-Hunt syndrome showed only ipsilateral enhancement. Enhancement in the IAC fundus was frequently observed in patients with meningeal disease, even just 10 min after administration of contrast agent. This enhancement in the IAC fundus was never visible on T₁-weighted 3D-FLASH images.

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Real-time functional magnetic resonance imaging (fMRI) is an emerging technique for assessing the dynamic and robust changes in brain activation during an ongoing experiment. Real-time fMRI allows measurement of several processes within the brain as they occur. The extracted information can be used to monitor the quality of acquired data sets, serve as the basis for neurofeedback training, and manipulate scans for interactive paradigm designs. Although more work is needed, recent results have demonstrated a variety of potential applications for real-time fMRI for research and clinical use. We discuss these developments and focus on methods enabling real-time analysis of fMRI data sets, novel research applications arising from these approaches, and potential use of real-time fMRI in clinical settings.

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Focused ultrasound surgery (FUS) is a method of noninvasive focal thermal ablation. Temperature-sensitive phase-difference magnetic resonance (MR) imaging allows monitoring of the focal point and measurement of tissue temperature elevation in real time, ensuring delivery of a therapeutic dose. A newly developed respiratory monitoring system enables us to track liver tumors, which move with respiration. We report our initial experience using MR-guided FUS with respiratory gating in successfully treating a hepatocellular carcinoma 15 mm in diameter.

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