Purpose: We investigated whether change in muscle microstructure associated with passive extension and contraction affects proton diffusivity.
Material and Methods: In 6 male subjects, we compared apparent diffusion coefficients (ADC) along the posterior-to-anterior (ADC-PA), right-to-left (ADC-RL) and superior-to-inferior (ADC-SI) directions of the right tibialis anterior muscle with the ankle joint in passive plantar flexion and passive dorsiflexion.
Results: Compared to the respective ADCs at plantar flexion, the ADC-PA (P=0.002) and ADC-RL (P=0.008) were significantly greater, but ADC-SI (P=0.008) significantly lower at dorsiflexion.
Conclusion: Our results indicate that change in muscle microstructure associated with passive extension and contraction would affect proton diffusivity, and this alteration of proton diffusivity could be detected by measuring ADC with a clinical magnetic resonance scanner.

View full abstract

The use of hyperpolarized (HP) ¹²⁹Xe magnetic resonance (MR) imaging to regionally evaluate gas diffusion and perfusion processes as well as ventilation in the lung has been expected. In this study, we used a continuous-flow hyperpolarizing (CF-HP) system to acquire gas- and dissolved-phase ¹²⁹Xe images from mouse lung, employing standard gradient echo sequence equipped with chemical shift selective excitation and 90° flip angle. The character of non-recoverable HP magnetization enabled the use of a phase (frequency)-selective 90° pulse for direct visualization of only a given-phase ¹²⁹Xe magnetization replenished into the slice during repetition time (TR). We combined gas- and dissolved-phase ¹²⁹Xe images to map the ratio of dissolved- to gas-phase ¹²⁹Xe replenished into the slice during TR (M_dissolved/M_gas) and found it to be approximately 0.05 to 0.08 in the peripheral regions of mouse lungs. This result suggested that replenishment of dissolved-phase ¹²⁹Xe magnetization by gas diffusion and pulmonary perfusion would be faster than that of gas-phase by ventilation. The use of a CF-HP system that allows the application of relatively long TR to HP ¹²⁹Xe imaging using a phase-selective 90° pulse would be useful in evaluating gas transport mechanisms in the lung.

View full abstract

Purpose: We evaluated the ability of the PRESTO (principles of echo shifting with a train of observations) technique to reveal small veins and microbleeds in the human brain.
Materials and Methods: In an experimental study, we calculated contrast-to-noise ratio (CNR) between a cerebral parenchymal phantom and human venous blood using 3 sequences of 3-dimensional (3D)-PRESTO, 3D-gradient recalled echo (GRE), and 3D-GRE echo-planar imaging (EPI). Then, we examined 7 healthy volunteers and 5 patients with venous angiomas or traumatic brain injuries using the 3D-PRESTO technique. In volunteer studies, MR venographies were reconstructed from 10-mm, 15-mm, and 20-mm thickness data using the minimum-intensity-projection (MinIP) technique. Three radiologists identified deep brain venous anatomy and counted the visible left medullary veins. In clinical studies, we evaluated the lesion conspicuity of small venous diseases and microbleeds.
Results: In the phantom study, 3D-PRESTO showed the highest CNR. In all volunteer studies, the deep brain venous anatomy was readily identified in the MinIP images at each thickness. The mean numbers of counted left medullary veins were 5.1 for 10 mm, 5.9 for 15 mm, and 6.7 for 20 mm in the MinIP images. The difference was significant between 10-mm and 20-mm MinIP images (P=0.02). In patient studies, abnormal small veins and microbleeds were clearly revealed.
Conclusion: High-resolution MR venography using 3D-PRESTO technique can clearly depict small veins and microbleeds in the human brain.

View full abstract

Purpose: To evaluate in healthy volunteers the usefulness of an abdominal compression belt in reducing acquisition time by stabilizing respiratory motion during whole-heart coronary magnetic resonance angiography (WHCMRA) using conventional navigator triggering.
Methods: In 10 healthy volunteers, we performed free-breathing 3-dimensional segmented true fast imaging with steady-state precession (trueFISP) WHCMRA using conventional navigator triggering without motion-adapted gating. We acquired images with the abdominal compression belt rolled tightly around the upper abdomen and without the belt. We compared image acquisition time, navigator efficiency, and visible length of coronary arteries using paired t-test and subjective image quality on a 4-point scale (1, poor; 4, excellent) using Wilcoxon signed-rank test.
Results: There were no statistically significant differences for mean acquisition time (11.5±5.0 vs. 9.3±2.4 min, P=0.150); navigator efficiency (38.7±13.6 vs. 42.8±11.0%, P=0.336); mean overall visible length of the coronary arteries (99.7±22.7 vs. 105.0±16.5 mm, P=0.530); or mean overall subjective image quality (2.5 vs. 2.7, P=0.297) between results obtained with and without the abdominal compression belt.
Conclusion: In this small group of healthy volunteers, the use of an abdominal compression belt did not reduce image acquisition time or improve image quality in trueFISP WHCMRA using conventional navigator triggering; however, the technique's feasibility requires additional consideration using other navigator-triggering methods for patients with irregular respiratory cycles.

View full abstract

Purpose: Visualization of endolymphatic hydrops by 3-dimensional fluid-attenuated inversion recovery-FLAIR using conventional turbo-spin-echo (3D-FLAIR-CONV) after intratympanic injection of Gd-DTPA has been reported in patients with Ménière's disease. Compared to 3D-FLAIR-CONV used in previous studies, the addition of a variable flip-angle technique (3D-FLAIR-VFL) enables very long echo trains and, therefore, shorter scan times. We evaluated whether 3D-FLAIR-VFL could replace 3D-FLAIR-CONV in detecting endolymphatic hydrops after intratympanic Gd-DTPA administration.
Methods: Eleven patients were included in this study. Twenty-four hours after Gd-DTPA injection, we performed 3D-FLAIR-CONV and 3D-FLAIR-VFL imaging at 3T. We compared the contrast-to-noise ratio (CNR) between cochlear fluid and the cerebellum between the 2 FLAIR sequences. We subjectively scored the size of the endolymphatic space in the cochlea and vestibule for each patient and correlated the scores with the clinical diagnoses.
Results: The CNR of 3D-FLAIR-CONV was significantly higher than that of 3D-FLAIR-VFL. Scores for the size of endolymphatic space in the vestibule were identical between the 2 sequences; however, those in the cochlea disagreed in 3 cases. 3D-FLAIR-CONV correlated better with the clinical diagnoses.
Conclusions: Currently, we may not be able to replace 3D-FLAIR-CONV with 3D-FLAIR-VFL, at least not with the scanning parameters used in the present study.

View full abstract

Purpose: To determine whether the apparent diffusion coefficient (ADC) obtained using a high b-value (2,000 s/mm²) is superior to that using a standard b-value (1,000 s/mm²) for discriminating malignant from normal peripheral tissue in the prostate.
Methods: Twenty-six patients with biopsy-proven prostate cancer underwent 1.5T magnetic resonance (MR) imaging including single-shot, echo-planar diffusion-weighted imaging (DWI) with repetition time/echo time, 3500/88 ms; 4-mm slice thickness; 1-mm interslice gap; 144×128 matrix; field of view, 250×250 mm; number of excitations, 10; and b-values, 0, 1,000, and 2,000 s/mm². For each patient, ADC values were obtained for malignant and normal tissue using b=1,000 and 2,000 in a monoexponential model. Signal-to-noise (SNR) and contrast-to-noise (CNR) ratios in DWI were also evaluated.
Results: At b=1,000, the mean ADC (×10^-3 mm²/s) for malignant tissue was 0.82±0.27 (range 0.43-1.29) and for normal tissue, 1.69±0.23 (1.31-2.18). At b=2000, the mean ADC for malignant tissue was 0.61±0.19 (0.30-0.94) and for normal tissue, 1.01±0.14 (0.73-1.35). Significant ADC overlap between the malignant and normal tissue was recognized at b=2000. As b-value increased, the mean SNR within malignant tissue decreased by 21.6%, and mean CNR decreased 17.3%.
Conclusions: Under the same imaging conditions, measuring ADC using a high b-value (2,000 s/mm²) in a monoexponential model has little diagnostic advantage over using the standard b-value (1,000 s/mm²) in discriminating malignant from normal prostate tissue.

View full abstract

We describe the case of a 63-year-old woman with a large Bartholin's duct cyst that showed high signal intensity on T₁- and T₂-weighted magnetic resonance (MR) images. Although Bartholin's duct cyst is the most frequent cystic lesion of the vulva, such a giant cyst is rare.

View full abstract