Allan M. Haggar

Eigenimage filtering in MR imaging.

This article presents the technical aspects of a linear filter, referred to as eigenimage filtering, and its applications in magnetic resonance (MR) imaging. The technique is used to obtain a single composite image depicting a particular feature of interest while suppressing one or more interfering features. The appropriate weighting components to be used in the linear filter are determined on the criterion that the desired feature is enhanced while the interfering features are suppressed. The criterion is expressed mathematically as a ratio. By applying Rayleighs principle, the ratio is maximized by finding the eigenvector associated with the maximum eigenvalue of the corresponding generalized eigenvalue problem. The appropriate weighting factors for the linear filter are the elements of the eigenvector which maximize the ratio. The utilization of the technique is demonstrated in its application to a simulated MR image sequence as well as to acquired MR image sequences of a normal and an abnormal brain. Index Terms: Magnetic resonance imaging, physics and instrumentation—Magnetic resonance imaging, techniques—Eigenimage filtering.

VASCULAR AND SOFT TISSUE CALCIFICATION IN SYSTEMIC OXALOSIS: CT DIAGNOSIS

Hyperoxaluria may result in diffuse deposition of calcium oxalate crystals in multiple organs. A patient with primary hyperoxaluria presented with peripheral ischemia on this basis. Computed tomography clarified the diagnosis and helped to direct the appropriate management.

Spontaneous Gastroesophageal Reflux During Double-Contrast Upper Gastrointestinal Radiography with Glucagon

A prospective double-blind study of 240 patients found the incidence of spontaneous gastroesophageal reflux (SGER) during glucagon-assisted double-contrast upper gastrointestinal examination to be 37.5%, compared to a control group with an incidence of 22.5% (P<0.05). Furthermore, SGER in individuals who receive glucagon is not a consistently reproducible phenomenon. We feel the observation of SGER in individuals who receive glucagon is of questionable value. When SGER may be of clinical importance, the patient should be re-examined after at least 30 minutes when plasma clearance of the drug has occurred.

Case report 538

This 27-year-old black man presented to the Henry Ford Hospital (Orthopedic clinic) reporting a painful, slowly growing mass of the left foot which had become more noticeable in the past two weeks. Occasional pain had been present in the region of the mass for several months. No fever, chills, weight loss, or other constitutional symptoms were present. Bunion surgery of the first toe had been performed uneventfully nine years earlier. Physical examination revealed a firm, mildly tender mass over the dorsum of the left foot in the metatarsal region. Neurovascular status of the extremity was intact and a normal range of motion of the foot and toes was present. Laboratory data were unremarkable. Radiographs revealed a lesion of the second metatarsal shaft with mild sclerosis and marked periosteal reaction that was spiculated in one area of cortical saucerization (Fig. 1). A radionuclide bone scan showed increased uptake at the site of the lesion, nonspecific in nature. Further evaluation included computed tomography (Fig. 2) and magnetic resonance imaging (Figs. 3, 4). Definitive surgery was performed with resection of the second metatarsal and placement of iliac crest bone graft.

Juxta-articular large cell lymphoma

Three patients with juxta-articular large cell lymphoma presented as suffering from monarthropathies. A spectrum of radiographic changes was observed that included subchondral sclerosis, regional osteopenia, effusion, and mottled lytic changes in the juxta-articular region of the affected joint. MRI was performed in two patients. In one, it revealed a high signal mass on T2-weighted sequences. In the second, a mass bridging the joint was demonstrated which was difficult to appreciate on CT and was not visible radiographically. In all cases, biopsies revealed large cell non-Hodgkins lymphoma of bone. We present these studies to emphasize this unusual pattern of non-Hodgkins lymphoma as well as to demonstrate the contribution of MRI to the diagnosis.

Magnetic Resonance Imaging for Meniscal Tears of the Knee.

In brief: Magnetic resonance imaging (MRI). has become a standard diagnostic technique in many medical facilities for evaluating the menisci of the knee. MRI provides superior soft-tissue contrast with high resolution and takes little time (typically less than 30 minutes). It does not require intra-articular contrast media and is not limited to surface abnormalities, as are arthrography and arthroscopy. Unlike MRI, both arthrography and arthroscopy cause disturbances to the external capsule of the knee, with associated patient discomfort and limited physical activity for some time following the procedure. The author discusses the advantages of MRI and presents a case report in which it was used to make the diagnosis and determine the appropriate treatment modality.