The accuracy of a novel frameless stereotactic system was determined during 10 surgeries performed to resect brain tumors. An array of three charge-coupled device cameras tracked the locations of infrared light-emitting diodes on a hand-held stylus and on a reference frame attached to the patient's skull with a single bone screw. Patient-image registration was achieved retrospectively by digitizing randomly chosen scalp points with the system and fitting them to a scalp surface model derived from magnetic resonance (MR) images. The reference frame enabled continual correction for patient head movements so that registration was maintained even when the patient's head was not immobilized in a surgical clamp. The location of the stylus was displayed in real-time on cross-sectional and three-dimensional MR images of the head; this information was used to predict the locations of small intracranial lesions. The average distance (and standard deviation) between the actual position of the mass and its stereotactically predicted location was 4.8 +/- 3.5 mm. The authors conclude that frameless stereotaxy can be used for accurate localization of intracranial masses without resorting to using fiducial markers during presurgical imaging and without immobilizing the patient's head during surgery.

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ed to evaluate intrinsic urethral factors of incontinence and dysuria. Fifteen women and five men with pre-and postoperative urinary incontinence were evaluated with routine body coil or pelvic extracavitary surface coil imaging. In five women and three men, a modified rectal/vaginal coil (Medrad Corp, Pittsburgh] was used for high-resolution (300 X 300-fim pixel] imaging of the urethra. Preoperative periurethral cysts, hypoplastic urethra. muscle hypertrophy, failure of coaptation, and tumor of urethra were demonstrated. Postoperative scar tissue, overtight sutures distorting the urethra, and configuration of the bladder neck were also demonstrated. Technical factors with the intracavitary coil, including patient tolerance, rectal peristalsis, and shape distortion by overinflation, are discussed. Highresolution intracavitary surface coil images of the urethra provide a detailed map for preor reoperative planning in complex cases. The diagnostic utility of volume phased array coils in pelvic MR imaging was evaluated. With HIC approval, 30 patients undergoing clinical MR imaging of the pelvis were studied with the body coil followed by a set of four phased array coils (GE Medical Systems, Milwaukee). Ten patients were studied with identical technique with both the body coil and the phased array coils (SE TR msec/TE msec = 2.000/ 20-80, FOV = 28 cm. two NEX, 128 X 256 matrix, 5 mm section thickness, 2.5-mm gap) in the axial plane. The other 20 patients were studied with the body coil with the same technique and with the phased array coils and a small FOV (16 cm). Image analysis was conducted by two experienced radiologists with subsequent ROC analysis. Pelvic structures, uterine margins, uterine zonal anatomy (right ovary, left ovary) were individually rated on a 1 -to-5 scale, with 1 being definitely identifiable and 5 not identifiable. Pathology was rated from 1 (definitely abnormal) to 5 (definitely normal), and extent was rated from 1 (certain) to 5 (indeterminate]. Artifact was rated from 1 (none) to 5 [uninterpretable]. Contrast and overall image quality was also rated from 1 to 5. Signal-to-noise ratio was assessed with a phantom. Phantom measurements demonstrated a 2.0-fold improvement in signal-to-noise ratio in the center of the FOV and 4.4-fold improvement near the coils. With the same technique for both the body coil and the phased array coils, there was no overall difference in image quality. Artifacts were worse with the phased array coils, apparently offsetting gains in signal-to-noise ratio. The smaller FOV combined with the phased array coils resulted in definite improvement in image quality over that of the body coil, resulting in higher ratings for the phased array coil. Phased array coils enable high-resolution, small FOV images in the pelvis that cannot be obtained with the body coil. For lower-resolution. large FOV images, they offer no advantage.