Faculty Bibliography

A non-localizing pulse sequence to quantify the total amount of N-acetylaspartate (NAA) in the whole brain (WBNAA) was introduced recently [Magn. Reson. Med. 40, 684-689 (1998)]. However, it is known that regional magnetic field inhomogeneities, deltaB0s, arising from susceptibility differences at tissue interfaces, shift and broaden local resonances to outside the integration window, leading to an underestimation of the true amount of NAA in the entire brain. To quantify the upper limit of this loss, the whole-head proton MR spectrum (1H-MRS) of the water was integrated over the same frequency width as the NAA. The ratio of this area/total-water-line was 75 +/- 5% in 5 volunteers. The procedure was repeated with the brain-only water peak, obtained by summing signals only from voxels within that organ from a three-dimensional chemical-shift-imaging (3D CSI) set. It indicated that <10% of the water signal loss occurred in the brain. Therefore, by analogy, WBNAA accounts for >90% of that metabolite

Image intensity standardization is a recently developed postprocessing method that is capable of correcting the signal intensity variations in MR images. We evaluated signal intensity of healthy and diseased tissues in 10 multiple sclerosis (MS) patients based on standardized dual fast spin-echo MR images using a numerical postprocessing technique. The main idea of this technique is to deform the volume image histogram of each study to match a standard histogram and to utilize the resulting transformation to map the image intensities into standard scale. Upon standardization, the coefficients of variation of signal intensities for each segmented tissue (gray matter, white matter, lesion plaques, and diffuse abnormal white matter) in all patients were significantly smaller (2.3-9.2 times) than in the original images, and the same tissues from different patients looked alike, with similar intensity characteristics. Numerical tissue characterizability of different tissues in MS achieved by standardization offers a fixed tissue-specific meaning for the numerical values and can significantly facilitate image segmentation and analysis

PURPOSE: The purpose of this work was to determine the costs of computed tomography (CT) procedures in a large academic radiology department, including both professional (PC) and technical (TC) components, by analyzing actual resource consumption using an activity-based costing (ABC) method and comparing them with Medicare payments. METHOD: Over a 12 month period from July 1, 1996, to June 30, 1997, 1,011 CT procedures, representing 16 Physicians' Current Procedural Terminology (CPT) codes and 98.3% of CT studies performed, were carefully observed by a research assistant trained in ABC methodology. Information collected during these time and motion studies included personnel/machine time and direct materials used. Actual resource units used during the different activities in each CT procedure were valued using appropriate cost drivers. Unit values for both direct and overhead costs were calculated: the cost of an individual procedure equaled the sum of component costs. Costs were compared with PC and TC payments according to the 1997 Medicare Fee Schedule. RESULTS: Total costs of CPT codes 70450 (CT Head unenhanced), 71260 (CT Chest enhanced), and 74160 (CT Abdomen enhanced), which represented 71.2% of CT studies performed, were $189.19, $273.53, and $343.20, respectively. For all 16 nonmodified CPT codes analyzed, Medicare's professional reimbursement was less than the professional cost, whereas its technical reimbursement exceeded respective cost in 14 of the 16 codes. CONCLUSION: In the setting and time period studied, Medicare underreimbursed professional costs while overreimbursing technical costs

PURPOSE: To investigate and characterize the global distribution of magnetization transfer (MT) ratio values of normal-appearing white matter (NAWM) in patients with relapsing-remitting multiple sclerosis (MS) and test the hypothesis that the MT histogram for NAWM reflects disease progression. MATERIALS AND METHODS: Conventional and MT magnetic resonance (MR) images were obtained in 23 patients and 25 healthy volunteers. Clinical tests for comparison with the MT histogram parameters included the Extended Disability Status Scale and the ambulation index. Lesion load calculated with T2-weighted MR images and whole-brain and white matter volumes were measured. RESULTS: The location of the MT histogram peak and the mean MT ratio for NAWM were significantly lower in patients with MS than in control subjects. In longitudinal studies, the histogram peak location and mean MT ratio shifted in the direction of normal values as the duration of disease increased. A mean of 26.5% of the volume of new lesions identified on the later studies were demonstrated to have originated in NAWM corresponding to 'lost' pixels on the histogram. CONCLUSION: MT histogram analysis of NAWM, including longitudinal analysis, may provide new prognostic information regarding lesion formation and increase understanding of the course of the disease

RATIONALE AND OBJECTIVES: The objective of the two pivotal phase 3 studies was to evaluate the safety and efficacy of OptiMARK (Gd-DTPA-bis(methoxyethylamide) [Gd-DTPA-BMEA]) compared with Magnevist (Gd-DTPA) in magnetic resonance imaging of the central nervous system. METHODS: Two multicenter, randomized, double-blind, parallel group studies were conducted in 395 patients with known or suspected central nervous system pathology. Subjects were randomized to receive a single 0.1 mmol/kg intravenous injection of either Gd-DTPA-BMEA or Gd-DTPA. The safety of Gd-DTPA-BMEA and Gd-DTPA was monitored for up to 72 hours after study drug administration. Precontrast and postcontrast administration magnetic resonance scans were acquired using identical imaging planes and techniques. RESULTS: No deaths or unexpected adverse events were reported in either group. A comparison of adverse events by intensity and relation demonstrated no statistically significant differences between the two groups. Gd-DTPA-BMEA and Gd-DTPA were equivalent with respect to confidence in diagnosis, conspicuity, and border delineation. CONCLUSIONS: Gd-DTPA-BMEA and Gd-DTPA demonstrated comparable efficacy profiles, and the safety profiles were considered similar

In multiple sclerosis (MS), brain stem and cerebellum are frequent sites of damage in clinically isolated syndromes at presentation and it is likely that lesions located in such structures can have an important impact on the development of disability in the definite forms of the disease. In patients presented with isolated brain stem syndromes, the symptomatic lesion was often not detected by magnetic resonance (MR) imaging. But patients with asymptomatic infratentorial lesions progressed to clinically definite MS in 65% of cases. Infratentorial lesions are included in various MR criteria designed to assist in the differential diagnosis of MS lesions from incidental lesions, to differentiate MS from subcortical encephalopathic arteriopathy. The preferred MR sequence to visualize infratentorial lesions is the fast spin echo sequence. It is preferred to conventional spin echo and fast fluid attenuated inversion recovery sequences because of its relatively short acquisition time and good sensitivity. The correlation between disability and infratentorial lesion load on T2 weighted sequences is controversial. However, it was recently shown that the correlations between clinical measures and T1 lesion load, histogram magnetization transfer ratio and peak positions, and infratentorial volume measurements are strong. These findings suggest that one of the major factors in the development of disability in patients with MS is the pathological damage in clinically eloquent sites such as the brain stem and cerebellum

In multiple sclerosis patients, magnetic resonance imaging (MRI) frequently detects lesions in the brain stem and cerebellum. However various pathologies that have a predelection to occur in posterior fossa parenchyma may share similar features with inflammatory-demyelinating lesions. In this paper, we review the contribution of MRI to the differential diagnosis of posterior fossa pathology. Vascular lesions due to chronic hypoperfusion and arteriolosclerosis or occlusion of the main supplying arteries of the posterior circulation leading to acute infarction frequently produce characteristic pontine or cerebellar lesions. Neoplastic disease, in particular pontine gliomas in younger patients may have similar MRI features and may be difficult to distinguish from inflammatory-demyelinating lesions. Central pontine myelinolysis usually occurs in severely ill patients but the pontine MRI changes have an overlapping profile with inflammatory demyelination. Diffuse axonal injury of the midbrain and brainstem after head trauma and atrophy of posterior fossa structures in degenerative diseases may appear similar on MRI to tissue changes also seen frequently in MS. Analysis of the MRI appearance and clinical information is most often useful to narrow the fairly long list of differential diagnoses of posterior fossa pathology

OBJECTIVE: To quantitate the extent of neuronal cell loss in MS via the whole brain's N-acetylaspartate (NAA) concentration (WBNAA). METHODS: Because NAA is assumed to be present only in neuronal cell bodies and their axons, we measured WBNAA as a marker for viable neurons in 12 patients (9 women and 3 men, 26 to 53 years of age) suffering from relapsing-remitting (RR) MS for at least 5 years and compared them with 13 age- and sex-matched normal controls. Total brain NAA was determined with proton MR spectroscopy, and WBNAA was obtained by dividing it by the total brain volume, calculated from high resolution MRI. RESULTS: The WBNAA of the RR MS patients was lower than their matched controls (p<0.005). This difference was greater among older than younger subjects. The linear prediction equations of WBNAA with age indicate a faster, x10, decline in the patients, approximately 0.8% per year of age (p = 0.022). CONCLUSION: The age-dependent decrease of whole brain N-acetylaspartate (WBNAA) in the patients suggests that progressive neuronal cell loss is a cardinal feature of this disease. WBNAA offers a quick, highly reproducible measure of disease progression and may be an important marker of treatment efficacy in MS as well as other neurodegenerative diseases

The authors report the findings of two patients that confirm the location of the horizontal meridian in the human visual cortex. The first patient had an inferior quadrant defect with a band of horizontal meridian sparing. Magnetic resonance imaging showed a lesion concentrated along the medial striate cortex. The second patient had a homonymous horizontal defect that resulted from removal of an arteriovenous malformation located in the lateral striate cortex. The findings of these two patients demonstrate that the horizontal meridian is represented at the calcarine fissure base in the primary visual cortex

There are presently many magnetic resonance (MR) measures that can aid the assessment of damage to the brain. The conventional measures include T2 lesion volume, T1 enhanced lesion volume, and brain atrophy. Newer methodologies include magnetization transfer measures and proton spectroscopy. These methods have the potential for improving the specificity of MR with respect to the underlying pathology. MR spectroscopy offers the ability to quantitate the component of axonal loss in multiple sclerosis. MR techniques can be implemented to assess the effectiveness of treatment algorithms