We examined how the noise from magnetic resonance (MR) imaging affects the calculation of T₂ in skeletal muscle, a tissue with short T₂ values. The measured pixel intensity of the MR image (: the magnitude image) was the superimposed signal which was composed of the MR signal and the noise, and we demonstrated that noise from a magnitude image matches the DC component of the T₂ decay curve. In materials with long T₂ values, the noise has no influence on the selective echo time (TE) in calculating T₂. However, in materials with short T₂ values, noise clearly influences the selective TE. In this study, we proposed a T₂ effective signal-ratio, T₂SR, as an index for determining whether the noise of the magnitude image can be ignored in calculating T₂. When T₂SR and the signal-to-noise ratio (SNR), an index of image quality, were compared as indices to evaluate the influence of noise in the calculation of T₂, T₂SR was useful and SNR was not. The use of multiple spin echo (MSE) technique shortened imaging time, but required detailed understanding of the MSE. Our results indicated that T₂ can be calculated correctly for skeletal muscle and other tissues with short T₂ even when the receiver coil has a low SNR and few measurement points are available.

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Purpose: We evaluated radiofrequency (RF) heating of a humerus implant embedded in a gel phantom during magnetic resonance (MR) imaging for the specific absorption rate (SAR), angle between the implant and static magnetic field (B₀), and position of the implant in the irradiation coil.
Methods: We embedded a stainless steel humerus implant 2 cm deep in tissue-equivalent loop and mass phantoms, placed it parallel to the static magnetic field of a 1.5T MR scanner, and recorded the temperatures of the implant surface with RF-transparent fiberoptic sensors. We measured rises in temperature at the tips of the implant by varying the SAR from 0.2 to 4.0 W/kg and evaluated RF heating of the implant for its angle to B₀ and its displacement along B₀ from the center of the RF irradiation coil.
Results: RF heating was similar for the loop and mass phantoms because the eddy current flows through the periphery of both. As the SAR increased, the temperature at the implant tip increased, and there was a linear relationship between the SAR and temperature rise. The values were 6.4°C at 2.0 W/kg and 12.7°C at 4.0 W/kg. Rise in temperature decreased steeply as the angle between the implant and B₀ surpassed 45°. In addition, as the implant was displaced from the center of the RF coil to both ends, the rise in temperature decreased.
Conclusion: The rise in temperature in deep tissue was estimated to be higher than 1.0°C for SAR above 0.4 W/kg. RF heating was greatest when the implant was set parallel to B₀. In MR imaging of patients with implants, there is a risk of RF heating when the loop of the eddy current is formed inside the body.

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Diffusion-weighted magnetic resonance (MR) imaging (DWI) is increasingly applied to evaluate tumors in the abdomen and pelvis. However, DWI is susceptible to a variety of artifacts that arise from motion, use of strong gradient pulses, and echo-planar imaging technique. We discuss practical issues to help radiologists optimize the use of DWI to evaluate tumors in the body, including breath-hold DWI, multiple-acquisition non-breath-hold DWI, and diffusion-weighted whole-body imaging with background body signal suppression (DWIBS). Considerations of meticulous technique, sequence optimization, and quality assurance are emphasized for consistent acquisition of high quality images. We illustrate the potential use of these techniques to detect and characterize tumors and to monitor treatment effects.

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Purpose: We assessed the feasibility of utilizing three-dimensional (3D) phase sensitive inversion recovery (IR) images for preoperatively determining deep brain stimulator position.
Methods: We measured geometric distortion with a grid phantom and evaluated images of 3 volunteers to determine optimum imaging parameters for 3D phase sensitive IR.
Results: Geometric distortion measured less than 1.0%. Respective inversion and recovery times, which provided high T₁ contrast between the subthalamic nucleus and adjacent tissue, were 200 and 4000 ms. In studies of 3 volunteers and 2 patients, the subthalamic nucleus was clearly depicted in 3D phase sensitive IR images. The measured coordinates of the subthalamic nucleus agreed well with those calculated by conventional estimation from midpoint of the anterior and posterior commissure.
Conclusion: Three-dimensional phase sensitive inversion recovery was useful in visualizing the subthalamic nucleus for effective deep brain stimulation.

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In radiofrequency (RF) coil design for ultra-high-field magnetic resonance (MR) imaging, short RF wavelengths present various challenges to creating a big volume coil. When imaging a human body using an ultra-high magnetic field MR imaging system (magnetic flux density of 7 Tesla or more), short wavelength may induce artifacts from dielectric effect and other factors. To overcome these problems, we developed a patch antenna array coil (PAAC), which is a coil configured as a combination of patch antennas. We prototyped this type of coil for 7T proton MR imaging, imaged a monkey brain, and confirmed the coil's utility as an RF coil for ultra-high-field MR imaging.

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We investigated the effects of fast recovery (FR) to increase the sensitivity of fluorine-19 (¹⁹F) fast spin echo (FSE) in mapping 5-fluorouracil (5-FU) and its metabolites. We added an additional 90° pulse (which flips back longitudinal magnetization at the end of the sequence) to the chemical shift selective ¹⁹F FSE pulse sequence. In 5-FU solution, FR remarkably improved the signal-to-noise (S/N) ratio of ¹⁹F 5-FU images, having higher effects with shorter repetition time and smaller echo train numbers. In animal studies, FR produced a conspicuous increase in ¹⁹F signals in the urinary bladder. FR effects for ¹⁹F signals in the liver were smaller than those in other organs but still substantial. Utilization of FR in ¹⁹F FSE images promises more sensitive observation of ¹⁹F metabolite maps of 5-FU and other ¹⁹F-containing compounds that have relatively long relaxation times.

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Purpose: A tool to support the subject is generally used for kinematic joint imaging with an open MRI apparatus because of difficulty setting the image plane correctly. However, use of a support tool requires a complicated procedure to position the subject, and setting the image plane when the joint angle changes is time consuming. Allowing the subject to move freely enables better diagnoses when kinematic joint imaging is performed. We therefore developed an interactive scan control (ISC) to facilitate the easy, quick, and accurate setting of the image plane even when a support tool is not used.
Methods: We used a 0.4T magnetic resonance (MR) imaging system open in the horizontal direction. The ISC determines the image plane interactively on the basis of fluoroscopy images displayed on a user interface. The imaging pulse is a balanced steady-state acquisition with rewound gradient echo (SARGE) sequence with update time less than 2 s. Without using a tool to support the knee, we positioned the knee of a healthy volunteer at 4 different joint angles and set the image plane through the patella and femur at each of the angles. Lumbar imaging is also demonstrated with ISC.
Results: Setting the image plane was easy and quick at all knee angles, and images obtained clearly showed the patella and femur. Total imaging time was less than 10 min, a fourth of the time needed when a support tool is used. We also used our ISC in kinematic imaging of the lumbar.
Conclusion: The ISC shortens total time for kinematic joint imaging, and because a support tool is not needed, imaging can be done more freely in an open MR imaging apparatus.

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Developments in magnetic resonance (MR) equipment and techniques have been remarkable. Especially, respiratory-triggered three-dimensional MR cholangiopancreatography (3D-MRCP) has been developed to provide images with high spatial resolution of the biliary tract and pancreatic duct. These 3D data can be employed in MR virtual endoscopy (MRVE) with volume rendering to visualize the lumina of the gallbladder, bile duct, and pancreatic duct. To observe the changes in the lumina with threshold settings on a workstation, we made an original phantom with tubes 2, 3, and 6 mm in internal diameter. We examined the changes in luminal diameter using several threshold settings by comparing the actual internal diameters to determine an appropriate threshold setting, which we then applied in 50 clinical cases, including pancreatic tumors, hepatic tumors, and biliary tract stones. We obtained MRVE images of the gallbladder, bile duct, and pancreatic duct to assess the clinical usefulness of this method. In the phantom study, a value identical to the actual luminal diameter could be obtained with a threshold of less than 20%. In all clinical cases, we obtained MRVE images of the gallbladder, bile duct, and pancreatic duct using the threshold we had determined appropriate and scored the diagnostic usefulness in each region. The MRVE images of the biliary tract provided much supplementary information, including the presence of stones and of duct invasion by the malignancy as wells as visualization of the post-stenotic portion. MRVE images of the gall bladder did not significantly improve diagnosis (P=0.311), but those of the bile and pancreatic ducts did (P<0.05). In addition, MRVE may aid navigation during cholangioscopy. Thus, MRVE is a clinically useful technique for examining lesions of the biliary tract and pancreas.

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Biopsy is required for definitive diagnosis of lesions detected by magnetic resonance (MR) imaging that are suspicious or highly suggestive of malignancy. We performed MR-guided vacuum-assisted biopsy (VAB) using a commercially available biopsy device without a nonmagnetic needle in 5 patients with 5 lesions that were occult according to mammographic and sonographic findings. Complete removal was seen in 3 cases and partial removal in two. The VAB procedures were very well tolerated, and no important side effects were observed. MR-guided VAB can be performed safely with a nonmagnetic needle.

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