Supine breast MRI and 3D optical scanning: a novel approach to improve tumor localization for breast conserving surgery.

BACKGROUND: Wire localization for excision of nonpalpable breast cancer is an inefficient and inexact technique. METHODS: A total of 18 women with palpable invasive breast cancers underwent preoperative prone and supine magnetic resonance imaging (MRI). Intraoperatively, the edges of the tumor were palpated and marked on the skin surface. The breast was optically scanned, and the supine MRI was adjusted to match the actual breast position at the time of surgery. Image-defined tumor edges were marked on the surface of the breast. The main outcome measure was the distance between the image-defined and palpation-defined edges of the tumor. RESULTS: No significant difference was found between the mean maximal tumor diameter as measured by histopathology (29.6 ± 14.3 mm), supine MRI (25.3 ± 9.7 mm), prone MRI (27.6 ± 13 mm), or palpation (30.5 ± 9.3 mm). The distance from the tumor to the chest wall was markedly different in prone versus supine MRI (56.4 ± 38 vs 19.5 ± 20 mm, p = .002). The average distance between the palpated and supine MRI image-defined tumor edge locations was 7.2 mm (range, 0-19 mm). Accuracy improved over time; the average difference in edge locations in the last 7 patients was 4.0 mm. All 4 image-defined edge locations in the last 5 patients were ≤ 1 cm away from the palpated locations. CONCLUSIONS: We have developed a method of breast tumor localization using preoperative supine MRI and intraoperative optical scanning that defines tumor size and position as accurately as palpation.

Surface scanning through a cylindrical tank of coupling fluid for clinical microwave breast imaging exams.

PURPOSE: Microwave tomographic image quality can be improved significantly with prior knowledge of the breast surface geometry. The authors have developed a novel laser scanning system capable of accurately recovering surface renderings of breast-shaped phantoms immersed within a cylindrical tank of coupling fluid which resides completely external to the tank (and the aqueous environment) and overcomes the challenges associated with the optical distortions caused by refraction from the air, tank wall, and liquid bath interfaces. METHODS: The scanner utilizes two laser line generators and a small CCD camera mounted concentrically on a rotating gantry about the microwave imaging tank. Various calibration methods were considered for optimizing the accuracy of the scanner in the presence of the optical distortions including traditional ray tracing and image registration approaches. In this paper, the authors describe the construction and operation of the laser scanner, compare the efficacy of several calibration methods-including analytical ray tracing and piecewise linear, polynomial, locally weighted mean, and thin-plate-spline (TPS) image registrations-and report outcomes from preliminary phantom experiments. RESULTS: The results show that errors in calibrating camera angles and position prevented analytical ray tracing from achieving submillimeter accuracy in the surface renderings obtained from our scanner configuration. Conversely, calibration by image registration reliably attained mean surface errors of less than 0.5 mm depending on the geometric complexity of the object scanned. While each of the image registration approaches outperformed the ray tracing strategy, the authors found global polynomial methods produced the best compromise between average surface error and scanner robustness. CONCLUSIONS: The laser scanning system provides a fast and accurate method of three dimensional surface capture in the aqueous environment commonly found in microwave breast imaging. Optical distortions imposed by the imaging tank and coupling bath diminished the effectiveness of the ray tracing approach; however, calibration through image registration techniques reliably produced scans of submillimeter accuracy. Tests of the system with breast-shaped phantoms demonstrated the successful implementation of the scanner for the intended application.

Microwave tomographic imaging for osteoporosis screening: a pilot clinical study.

We are developing a microwave tomographic system for assessment of overall bone health. We hypothesize that as the mineralization of bone decreases due to the normal aging process and for more extreme situations such as osteoporosis, the dielectric property signature will also vary accordingly. To determine the merits of this approach, we have begun by performing initial exams of the heel to assess the level of image quality achievable. Early experience from our pilot study is encouraging and indicates that multiple planes of 2D images produce good representations of the 3D structural features within the heel.

Toward feedback controlled deep brain stimulation: dynamics of glutamate release in the subthalamic nucleus in rats.

Deep brain stimulation (DBS) is an effective symptomatic treatment in Parkinson's disease. High frequency stimulation (HFS) of the subthalamic nucleus elicits neurotransmitter release in multiple nuclei. Therefore, we tested the hypothesis that neurotransmitter release during HFS may be used to provide feedback control of the intensity and pattern of HFS. We studied the dynamic relationship between extracellular glutamate levels and HFS in and around the STN in anesthetized rats. We used a pseudorandom binary sequence (PRBS) of stimulation in the STN, the independent forcing function, while measuring extracellular glutamate in the same nucleus, the dependent variable. The PRBS consisted of 90 s periods during which stimulation (100 microA, 150Hz, 10% duty cycle) was either off or on. The stimulation and extracellular glutamate levels were fitted using an autoregressive exogenous model (ARX) to determine the transfer function between HFS and the extracellular glutamate concentration in the STN. The ARX model fit the dynamics of extracellular glutamate levels well (correlation coefficients ranged from 0.74 to 0.99; n=11). The transfer function accurately predicted extracellular glutamate levels in the STN even when the pattern of HFS was modified. We used the transfer function to develop a feedback controlled stimulation algorithm. Feedback controlled HFS maintained extracellular glutamate concentrations at any predefined level, but only intermittent HFS was required. We conclude that the transfer function between HFS and neurotransmitter levels in the brain can be used to design DBS protocols that generate specific temporal patterns of glutamate release in the STN.