Phased Array Detectors and an Automated Intensity- Correction Algorithm for High-Resolution MR Imaging of the Human Brain zyx Lawrence L. Wald, Lucas Carvajal, Susan E. Moyher, Sarah J. Nelson, P. Ellen Grant, A. James Barkovich, Daniel B. Vigneron zyxw Two- and four-coil phased array detectors were developed to increase the sensitivity and resolution of MR imaging of the human brain cortex, especially for detecting cortical dyspla- sias in pediatric epilepsy patients. An automated intensity correction algorithm based on an edge-completed, low-pass filtered image was used to correct the image intensity for the inhomogenous reception profile of the coils. Seven phased array coils were constructed and tested. The sensitivity of these coils was up to zyxwvutsrq 600% higher at the surface of the cortex than that achieved with a conventional head coil and up to zyxwvu 30% greater at the center of the head. The sensitivity obtained was comparable with that of a conventional small surface coil, but extended over the larger dimensions of the array and previously inaccessible areas such as the top of the head. The advantages of the improved sensitivity are demonstratedwith high resolution images of the brain. Key words: Magnetic resonance imaging; phased array coils; image intensity correction; brain. INTRODUCTION Although surface coils can provide a considerable im- provement in image sensitivity compared with a stan- dard quadrature head coil, their smaller region of sensi- tivity and nonuniform signal intensity greatly limit their application in brain imaging. A phased array can par- tially alleviate this problem by providing increased spa- tial coverage in the plane of the array or bilateral cover- age of a region of interest (1, 2). The zyxwvu MR phased array technique uses simultaneous data acquisition from mul- tiple, noninteracting coils to achieve a region of sensitive detection comparable with the area of the overall array (3,4).When the images from the individual receivers are combined in an optimal way, the SNR for a given pixel in the combined image is comparable with, or exceeds that, of a small individual coil alone (3, 4). Phased array coils have been beneficial in imaging the spine (3), male and female pelvis (1, 5), heart (6-8), and the temporal lobes zyxwvu MRM 34:433-439 (1995) From the Magnetic Resonance Science Center (L.L.W., L.C., S.E.M., S.J.N., D.B.V.) Graduate Group in Bioengineering (S.E.M., S.J.N., D.B.V.), Depart- ment of Radiology (PEG., A.J.B.), University of California at San Francisco, San Francisco, California Address correspondence to: Lawrence L. Wald, Ph.D., Department of Ra- diology, Magnetic Resonance Science Center, Box 1290, The University of California at San Francisco, San Francisco, CA 94143-1290. Received March 1, 1995; revised May 18, 1995; accepted May 23. 1995. This work was supported by The American Cancer Society Grant EDT-34, National Institutes of Health Grants NRSA 1F32 CA66292-01 and R01 CA57236, and The Whitaker Foundation. Copyright zyxwvutsrqpo 0 1995 by Williams & Wilkins All rights of reproduction in any form reserved. 0740-3194/95 $3.00 (2). Because the depth sensitivity and area of coverage of the array varies with the coil sizes and configurations, the array parameters must be chosen to suit the anatomy to be imaged. In this study we assess the design and performance of several different configurations of phased array detectors developed to provide high resolution im- ages of large regions the brain cortex, including bilateral coverage and the study of the cortex near the vertex. Two of the coil designs were previously assessed for proton spectroscopic imaging in the brain (9). We are currently refining our imaging protocols to best use the SNR improvements of the arrays and applying them to a clinical study of patients with suspected cor- tical dysplasia. These defects are responsible for the sei- zure disorder in a significant portion of patients with intractable epilepsy (10, 11). Some areas of dysplastic cortex can be identified by standard MR imaging tech- niques (12, 13). When the dysplasia can be identified, it is often amenable to surgical removal, which can greatly diminish the frequency of seizures and permit the pa- tients to lead much more normal lives (10, 14). In many patients, however, the dysplasia is more subtle, manifest as disordered lamination of the cortex or irregularities of the cortical-white matter junction identified only at au- topsy (15). Because dysplastic cortex can vary from grossly dysmorphic to grossly normal with microscopic abnormalities of lamination (15), the detection of subtle areas of dysplasia seems likely to benefit from increased imaging resolution. A recent study using thin partition size (1.0-1.5 mm) MR volume images acquired with a standard head coil has illustrated the diagnostic value of both improved spatial resolution and improved ability to reformat the images in a plane perpendicular to (and then parallel to) the section of gyrus being analyzed (13). Although the phased array technique provides more uniform sensitivity in the plane of the array than a single small coil, the signal decrease with depth is still charac- teristic of the size of the component coils. This can cause difficulty in visualizing pathology because multiple win- dow and level values are required to optimally view different regions of the image. Also the inhomogeneous reception profile is especially problematic for image seg- mentation or other quantitative analyses. Several meth- ods for removing the signal variation caused by the in- homogeneous reception profile of receive only surface coils have been developed. These include dividing the acquired image by a low pass filtered version of the image (16-19) by a phantom image (16, zy 20) by an ana- lytical map of the coil reception profile (3, 21, 22) or multiplying by a exponentially decreasing function (23). All of these methods improve the visual appearance of 433