The frequent diagnostic dilemma of recurrent neoplasm versus radiation necrosis is addressed in this study through a description of the varying spatial and temporal patterns of radiation necrosis at MR imaging.

Tumor necrosis, enhancement, and associated edema in patients with glioblastoma multiforme (GBM) represent biological variables that can be quantitated on preoperative MRI scans. We reviewed 48 highly selected patients, all of whom had supratentorial lesions, had undergone gross total tumor resection, and had received adjuvant treatments (radio- and chemotherapies). None of these patients had had surgery for recurrent tumor resection and none had harbored multifocal tumors. The median age was 50 years. The median Karnofsky performance score was 80. Multivariate analysis using the Cox regression model revealed that the strongest prognostic variable was the amount of tumor necrosis on preoperative scan (P < 0.001), with median survivals of 42, 24, 15, and 12 months for tumor necrosis grades of 0 (7 'pts'), I (11 'pts'), II (9 'pts'), and III (21 'pts'), respectively. The intensity of enhancement of the tumor nodule was another prognostic factor (P = 0.003), with median survivals of 35, 18, and 13.5 months for enhancement grades of 0 (2 'pts'), I (22 'pts'), and II (24 'pts'), respectively. The extent of peritumoral edema had a quadratic effect (P = 0.001), with grades I (19 'pts'), II (22 'pts'), and III (7 'pts') surviving for 24, 12, and 20 months respectively. Location and volume of tumors were not statistically significant predictors of survival (P < 0.05). In conclusion, in this highly selected group, GBM patients with little or no necrosis and with less tumor nodule enhancement on preoperative MRI survive longer than patients with greater amounts of necrosis and greater degrees of tumor enhancement. In addition, a moderate degree of peritumoral edema is associated with worse prognosis.

Neuroanatomic morphology and the developmental pattern of gray matter and white matter in subjects with neurofibromatosis type 1 differed from in control subjects. Some of these differences are related to the neuropsychological status of the neurofibromatosis type 1 group. We propose that delayed developmental apoptosis results in macrocephaly and a delay in the development of appropriate neuronal connections in children with neurofibromatosis type 1. We further propose that these morphologic delays are related to the cognitive profile of neurofibromatosis type 1.

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Restricted diffusion is a consistent imaging finding in CNS lymphoma in immunocompetent patients. Spectroscopy is helpful in initial imaging diagnosis and post-treatment surveillance. These lesions are usually paraventricular in location. MR imaging appearances differ among immunocompetent and immunosuppressed individuals in most cases.

Spinal magnetic resonance (MR) imaging was performed in 29 patients with newly diagnosed, untreated multiple myeloma. Nineteen (66%) patients were asymptomatic. Sagittal pre- and postcontrast T1-weighted spin-echo images and gradient-recalled-echo images of the thoracic and lumbosacral spine were obtained. Marrow involvement was identified in 20 (69%) patients. There were three MR patterns: focal lesions in nine patients (31%), diffuse involvement in seven (24%), and an inhomogeneous pattern of tiny lesions on a background of normal marrow in four (14%). A statistically significant correlation between MR imaging patterns of marrow involvement and serum hemoglobin values (one-way, P = .0899; Kruskal-Wallis, P = .0620) and between MR imaging patterns and percentage of marrow plasmacytosis (Kruskal-Wallis, P = .0314) was noted, with patterns of diffuse and focal marrow involvement associated with more abnormal values. Spinal MR imaging in patients with early myeloma may reveal marrow involvement in both symptomatic and asymptomatic patients. Some correlation was found between MR imaging patterns and laboratory indexes of disease.

In order to satisfy the Carr-Purcell-Meiboom-Gill (CPMG) condition, echo shift as dictated in fast-spin-echo (FSE)-based Dixon imaging was previously achieved by applying a time shift to the readout gradient and the data acquisition window. Accordingly, interecho spacing is increased, which entails increased image blurring and, in multislice imaging, a significant reduction in the slice coverage for a given imaging time. In this work, a new method is developed by which the echo shift is induced by "sandwiching" in time the readout gradient with a pair of small gradients of equal area and of opposite polarity. While data with non-zero phase shifts between water and fat signals are collected as fractional echoes, no increase in echo spacing is necessary with the modified acquisition strategy, and increased time efficiency is therefore achieved. In order to generate separate water-only and fat-only images in data processing, a set of low-resolution images are first reconstructed from the central symmetric portion (either 128 ؋ 128 or 64 ؋ 64) of the acquired multipoint Dixon data. High-resolution images using all the acquired data, including some partial Fourierreconstructed images, are then phase demodulated using the phase errors determined from the low-resolution images Since fast spin echo (FSE), or rapid acquisition with relaxation enhancement (RARE) (1), is capable of generating high-quality T 2 -weighted images in a fraction of the time required by conventional spin echo (SE), it has largely become a sequence of choice for T 2 -weighted imaging. A prominently distinguishing feature of FSE, however, is its anomalously bright fat signal (2), a phenomenon that was attributed by Henkelman et al. (3) to the demodulation of the J-coupling and desensitization of diffusion through inhomogeneities due to the rapidly refocusing RF pulse trains.Fat suppression is therefore a frequently desired imaging option in clinical T 2 -weighted imaging. Presently, the most commonly used method is chemical saturation (4), which, despite its many advantages, is known to be intrinsically susceptible to both the radiofrequency (RF) and the magnetic field inhomogeneity. An alternative technique that offers the potential of overcoming the problem is the Dixon technique (5). With this approach, the chemical shift difference between water and fat is encoded into images with different echo shifts. Field inhomogeneity effects appear as image phase errors, which in principle can be corrected for by a combination of multipoint acquisition and more elaborate image processing (6 -10). While these techniques allow for more uniform water and fat separation in the presence of the field inhomogeneity, one obvious drawback is the requirement for multiple data acquisitions and therefore longer scan times.Incorporating the Dixon approach for fat suppression into FSE presents a mutually beneficial combination. While the Dixon technique provides a potentially robust separation of the strong fat signal, FSE helps to alleviate the need for long data acq...