Sodium MR Neuroimaging.

Sodium MR imaging has the potential to complement routine proton MR imaging examinations with the goal of improving diagnosis, disease characterization, and clinical monitoring in neurologic diseases. In the past, the utility and exploration of sodium MR imaging as a valuable clinical tool have been limited due to the extremely low MR signal, but with recent improvements in imaging techniques and hardware, sodium MR imaging is on the verge of becoming clinically realistic for conditions that include brain tumors, ischemic stroke, and epilepsy. In this review, we briefly describe the fundamental physics of sodium MR imaging tailored to the neuroradiologist, focusing on the basics necessary to understand factors that play into making sodium MR imaging feasible for clinical settings and describing current controversies in the field. We will also discuss the current state of the field and the potential future clinical uses of sodium MR imaging in the diagnosis, phenotyping, and therapeutic monitoring in neurologic diseases.

Providing professional mammography services: financial analysis.

PURPOSE: To perform a financial analysis of mammography services to determine whether the key underlying economic drivers of this service are aligned with the public's expectations. MATERIALS AND METHODS: The financial status of mammography services at seven university-based programs was assessed by using an extensive financial survey encompassing revenue, direct and indirect costs, and volume data for 1997 and 1998. At one of the institutions, an activity-based costing analysis was performed by procedure type: screening mammography, diagnostic mammography, breast ultrasonography, interventional procedures, and review of outside mammograms. RESULTS: All seven institutions incurred losses in the professional component of mammography services. The underlying financial problem was a negative contribution margin (total mammography revenues minus direct expenses). The driver of the financial loss was the volume of diagnostic mammograms, which generated a loss per procedure. Diagnostic mammogram volume drove the mammography full-time equivalent count (P =.039) and was highly and negatively correlated with contribution margin (P <.001). CONCLUSION: The reimbursement rate for mammography procedures, especially diagnostic mammography, needs to be increased to reflect the current reality of the resources necessary to maintain the accessibility and accuracy of this evolving mix of clinical services.

Sonography, CT, and MR imaging: a prospective comparison of neonates with suspected intracranial ischemia and hemorrhage.

BACKGROUND AND PURPOSE: Sonography, CT, and MR imaging are commonly used to screen for neonatal intracranial ischemia and hemorrhage, yet few studies have attempted to determine which imaging technique is best suited for this purpose. The goals of this study were to compare sonography with CT and MR imaging prospectively for the detection of intracranial ischemia or hemorrhage and to determine the prognostic value(s) of neuroimaging in neonates suspected of having hypoxic-ischemic injury (HII). METHODS: Forty-seven neonates underwent CT (n = 26) or MR imaging (n = 24) or both (n = 3) within the first month of life for suspected HII. Sonography was performed according to research protocol within an average of 14.4 +/- 9.6 hours of CT or MR imaging. A kappa analysis of interobserver agreement was conducted using three independent observers. Infants underwent neurodevelopmental assessment at ages 2 months (n = 47) and 2 years (n = 26). RESULTS: CT and MR imaging had significantly higher interobserver agreement (P < .001) for cortical HII and germinal matrix hemorrhage (GMH) (Grades I and II) compared with sonography. MR imaging and CT revealed 25 instances of HII compared with 13 identified by sonography. MR imaging and CT also revealed 10 instances of intraparenchymal hemorrhage (>1 cm, including Grade IV GMH) compared with sonography, which depicted five. The negative predictive values of neuroimaging, irrespective of technique used, were 53.3% and 58.8% at the 2-month and 2-year follow-up examinations, respectively. CONCLUSION: CT and MR imaging have significantly better interobserver agreement for cortical HII and GMH/intraventricular hemorrhage and can reveal more instances of intraparenchymal hemorrhage compared with sonography. The absence of neuroimaging findings on sonograms, CT scans, or MR images does not rule out later neurologic dysfunction.

Impaired cerebrovascular autoregulation after hypoxic-ischemic injury in extremely low-birth-weight neonates: detection with power and pulsed wave Doppler US.

PURPOSE: To evaluate regional cerebral blood flow with power and pulsed wave Doppler ultrasound (US) in extremely low-birth-weight neonates with periventricular leukomalacia (PVL), germinal matrix hemorrhage (GMH), or both. MATERIALS AND METHODS: The lenticulostriate arteries of 17 preterm neonates (birth weight < or = 1,100 g) were assessed daily with Doppler US during the first 5-6 days of life. The mean arterial pressure and bilateral peak velocity, resistive index, coronal vascular cross-sectional area, and product of the peak velocity and vascular cross-sectional area were measured. RESULTS: Five neonates developed PVL, GMH, or both; results of follow-up examinations in 11 patients were normal. One neonate with severe intrauterine growth retardation and renal tubular acidosis was excluded. Neonates with PVL, GMH, or both showed significantly greater mean values and more variable values of vascular cross-sectional area and product of peak velocity and cross-sectional area than neonates without PVL or GMH (P < .025). Mean resistive index was significantly lower in neonates with PVL, GMH, or both than in neonates without (P < .01). There were no significant differences between mean arterial pressure in neonates with and those without PVL, GMH, or both. CONCLUSION: By enabling the detection of autoregulatory fluctuations in cerebral blood flow associated with hypoxic-ischemic injury, power and pulsed wave Doppler US may enable identification of preterm neonates who are at risk of developing PVL, GMH, or both during the 1st week of life.

Magnetization transfer magnetic resonance imaging: a clinical review.

Magnetic resonance imaging has traditionally used the T1 and T2 relaxation times and proton density (PD) of tissue water (hydrogen protons) to manipulate contrast. Magnetization transfer (MT) is a new form of tissue contrast based on the physical concept that tissues contain two or more separate populations of hydrogen protons: a highly mobile (free) hydrogen (water) pool, Hr, and an immobile (restricted) hydrogen pool, Hr, the latter being those protons bound to large macromolecular proteins and lipids, such as those found in such cellular membranes as myelin. Direct observation of the Hr magnetization pool is normally not possible because of its extremely short T2 time (< 200 microseconds). But saturation of the restricted pool will have a detectable effect on the mobile (free) proton pool. Saturation of the restricted pool decreases the signal of the free pool by transferring the restricted pool's saturation. Exchange of magnetization between the free and restricted hydrogen protons is a substantial mechanism for spin-lattice (T1) relaxation in tissues and the physical basis of MT. Through an appropriately designed pulse sequence, magnetization transfer contrast (MTC) can be produced. MT contrast is different from T1, T2, and PD, and it likely reflects the structural integrity of the tissue being imaged. A variety of clinically important uses of MT have emerged. In this clinical review of the neuroradiological applications of MT, we briefly review the physics of MT, the appearance of normal brain with MT, and the use of MT as a method of contrast enhancement/background suppression and in tissue characterization, such as evaluation of multiple sclerosis and other white-matter lesions and tumors. The role of MT in small-vessel visualization on three-dimensional time-of-flight magnetic resonance angiography and in head and neck disease and newer applications of MT are also elaborated.

Measure of magnetization transfer in multiple sclerosis demyelinating plaques, white matter ischemic lesions, and edema.

PURPOSE: To define the percentage of magnetization transfer of multiple sclerosis (MS) plaques, ischemic white matter lesions, and vasogenic edema to determine whether this measurement can help differentiate these entities. METHODS: Findings were compared in 25 patients with proved MS, 20 patients with white matter ischemic lesions, and 72 patients with white matter edema (caused by tumors, infections, or acute/subacute infarctions) in the periventricular system, centrum semiovale, and subcortical white matter. Magnetization transfer was performed using an on-resonance binomial pulse. The percentage of magnetization transfer of the normal white matter was also calculated. RESULTS: Magnetization transfer was significantly higher in white matter ischemic lesions (range, 31% to 38%; mean, 34% +/- 0.6%) than in demyelinating plaques of MS (range, 19% to 28%; mean, 22.5% +/- 1%) and in edema (range, 29% to 37%; mean, 30.2% +/- 0.4%). No statistical difference in percentage of magnetization transfer was found among lesions in the periventricular system (34% +/- 0.6%), centrum semiovale (35% +/- 0.5%), or subcortical white matter (33% +/- 0.6%), or in vasogenic edema associated with tumors, infections, or infarction. CONCLUSION: Differences in magnetization transfer suggest less change of demyelination in white matter ischemic lesions than in MS plaques and are significantly different in this respect from similar MS plaques. Magnetization transfer of edema was less than that of normal white matter or fell between ischemic abnormalities and MS plaques. Percentages of magnetization transfer below the mid-20% range is highly suggestive of demyelination. Vasogenic edema, our surrogate for increased water content of white matter, caused a decrease in the percentage of magnetization transfer.

Acute and chronic stroke: navigated spin-echo diffusion-weighted MR imaging.

PURPOSE: The authors evaluated a phase-navigated spin-echo (SE) motion-correction sequence for use at diffusion-weighted (DW) magnetic resonance (MR) imaging after cerebral infarction. MATERIALS AND METHODS: Twenty-nine patients underwent 32 conventional T2-weighted fast SE and SE DW imaging after stroke (n=25), transient ischemic attack (n=3), or reversible ischemic neurologic deficit (n=1). Imaging was performed in a standard head holder with standard padding. Apparent diffusion coefficient (ADC) maps were constructed. RESULTS: DW images depicted high signal intensity compatible with localization of the ischemic symptoms in all cases. Lesions were depicted more clearly on DW than on T2-weighted images. On DW images, acute infarct ADC values were uniformly low (mean, 0.401x10(-5) cm2/sec =+/- 0.143 [standard deviation]) compared with control ADC values (mean, 0.754x10(-5) cm2/sec +/- 0.201). ADC values of chronic infarcts were supranormal (mean, 1.591x10(-5) cm2/sec +/- 0.840) compared with control values (mean, 0.788x10(-5) cm2/sec +/- 0.166). DW imaging did not show a change after transient ischemic attack. with reversible ischemic neurologic deficit, however, hyperintensity on DW images and low ADC resolved after symptoms abated. CONCLUSION: Clinical phase-navigated SE DW imaging improved early diagnosis of stroke and helped differentiate acute from chronic stroke. Changes on DW images are reversed after symptoms resolve.

A model for detecting early metabolic changes in neonatal asphyxia by 1H-MRS.

In newborn rabbits, the early cerebral metabolic changes caused by hypoxic-ischemic (H-I) insult was examined by using volume localized 1H-MRS (STEAM). Partial ischemia was caused by unilateral carotid artery ligation, and hypoxia was induced by 10% oxygen inspiration for 150 minutes. Lactate immediately increased after hypoxia induction and almost disappeared 120 to 150 minutes after removal of hypoxia in both H-I and hypoxia-only experiments. Lactate production correlated well with decrease of the blood oxygen saturation. More lactate was produced on ischemic side 50 minutes post-hypoxia induction in H-I study. Ischemia alone did not cause any significant lactate production. Lactate caused by hypoxia can be dynamically monitored by localized 1H-MRS. Existence of regional ischemia can induce greater anaerobic glycolysis and may affect the pattern of brain injury under hypoxia. 1H-MRS is a sensitive tool to detect the acute metabolic change caused by H-I insult.

Neonatal intracranial ischemia and hemorrhage: diagnosis with US, CT, and MR imaging.

PURPOSE: To assess the usefulness of ultrasound (US), computed tomography (CT), and magnetic resonance (MR) imaging in the detection of intracranial hemorrhage and ischemia in newborns. MATERIALS AND METHODS: Seventy-six neonates who underwent US within 72 hours of CT or MR examination were studied. Four observers rated images for the presence of germinal matrix hemorrhage (GMH), intraventricular hemorrhage (IPH), extraaxial hemorrhage, and hypoxic-ischemic encephalopathy. RESULTS: In 39% of neonates, CT and MR imaging provided greater confidence than US for the diagnosis or exlusion of neonatal ischemia or hemorrhage. Kappa analysis revealed significantly better interobserver agreement with CT than with US for the detection of GMH, IVH, IPH, and cortical infarction or ischemia (P <.005). Interobserver agreement was significantly better with MR imaging than with US for the detection of GMH, IVH, and cortical infarction or ischemia (P < .005). CONCLUSION: Sensitivity and interobserver agreement are better with MR imaging and CT than with US for the detection of neonatal cortical ischemia or infarction.

Magnetization transfer MR of the normal adult brain.

PURPOSE: To establish a normal baseline of the percent magnetization transfer of gray (cortical and deep) and white matter structures in the brain in healthy adults and to determine whether there are adult age-related differences in these measurements. METHODS: Axial T1-weighted scans (800/20 [repetition time/echo time]) with and without magnetization transfer were prospectively performed on a 1.5-T MR imaging unit on 68 healthy patients (aged 20 to 76 years). Presaturation and postsaturation magnetization transfer images were obtained using an on-resonance binomial pulse. All patients had normal MR scans on all pulse sequences. A calculated "difference" image was used to calculate the percent magnetization transfer in multiple specific regions of the brain. In each hemisphere, 9 discrete areas of cortical and deep gray matter and 29 areas of white matter were measured in 68 patients to generate age-related changes in percent magnetization transfer in these anatomic regions. Ranges of normal percent magnetization transfer in each of the 38 measures were established. RESULTS: The percent magnetization transfer of the gray matter (28% +/- 2%) was lower than that of the white matter (36% +/- 2%). There was no statistically significant difference in the percent magnetization transfer in different areas of gray matter. Deep white matter in the different lobes (percent magnetization transfer, 31% to 38%) also showed no differences by age. Percent magnetization transfer was the highest in the genu of the corpus callosum (42%), and this was statistically significant compared with other white matter measurements. CONCLUSION: There were no statistically significant age-related variations in the percent magnetization transfer in healthy adults in gray or white matter. These percent magnetization transfer measurements provide baseline normative data, which can be used to measure the extent and severity of white matter changes in disease states.

Improved detection of enhancing and nonenhancing lesions of multiple sclerosis with magnetization transfer.

PURPOSE: To determine whether magnetization transfer imaging can improve visibility of contrast enhancement of multiple sclerosis plaques. METHODS: Fifty-nine enhancing and 63 nonenhancing lesions in 10 patients with multiple sclerosis were evaluated to calculate contrast-to-noise ratios on conventional T1-weighted and T1-weighted magnetization transfer images. The signal intensity of the lesion and the background (white matter) were measured on precontrast T1-weighted and T1-weighted magnetization transfer images (800/20/1 [repetition time/echo time/excitations]) and on postcontrast T1-weighted and T1-weighted magnetization transfer images. Mean contrast-to-noise ratios was calculated for all lesions. RESULTS: The contrast-to-noise ratio was significantly higher for enhancing and nonenhancing lesions on T1-weighted magnetization transfer images than on conventional T1-weighted images. For enhancing lesions, the contrast-to-noise ratio was significantly higher on postcontrast T1-weighted magnetization transfer images, 32 +/- 2 compared with 21 +/- 2 on conventional T1-weighted images. Fifty of the 59 enhancing lesions were seen on both the T1-weighted and the T1-weighted magnetization transfer images. Nine enhancing lesions were seen only on the postcontrast T1-weighted magnetization transfer images. In addition, of 63 nonenhancing lesions seen on proton-density, T2-weighted, and T1-weighted magnetization transfer images, 16 were not seen on the conventional T1-weighted images. Seven of the 63 nonenhancing lesions and 7 of the 59 enhancing lesions had high signal intensity on the precontrast T1-weighted magnetization transfer images suggestive of lipid signal, a finding not seen on the conventional precontrast T1-weighted images. CONCLUSION: Magnetization transfer improves the visibility of enhancing multiple sclerosis lesions, because they have a higher contrast-to-noise ratio than conventional postcontrast T1-weighted images. High signal intensity on both nonenhancing and enhancing lesions noted only on precontrast T1-weighted magnetization transfer suggests a lipid signal was unmasked. If magnetization transfer is used in multiple sclerosis patients, a precontrast magnetization transfer image is necessary.

Navigated diffusion imaging of normal and ischemic human brain.

The principal barrier to clinical application of diffusion-weighted MR imaging is the severe image degradation caused by patient motion. One way to compensate for motion effects is the use of a "navigator echo" phase correction scheme. In this work, a modification of this technique is introduced, in which the phase correction step is performed in the frequency domain (i.e., after the readout Fourier transform). This significantly improves the robustness of the navigator echo approach and, when combined with cardiac gating, allows diagnostic quality diffusion-weighted images of the brain to be routinely obtained on standard clinical scanner hardware. The technique was evaluated in phantom studies and in 23 humans (3 normal volunteers and 20 patients). Diffusion anisotropy and apparent diffusion coefficient maps were generated from the image data and showed decreased apparent diffusion in acute stroke lesions and, in several cases, increased apparent diffusion in chronic stroke lesions.

The influence of volumetric tumor doubling time, DNA ploidy, and histologic grade on the survival of patients with intracranial astrocytomas.

PURPOSE: To improve the prediction of individual survival in patients with intracranial astrocytomas through the analysis of volumetric tumor doubling time (VDt) and DNA ploidy. METHODS: A pilot study was retrospectively conducted on a group of 25 patients with intracranial astrocytomas in whom recurrent and/or progressive disease was observed on serial contrast-enhanced CT or MR examinations. VDt was computed using two or more data points from a semilogarithmic plot of tumor volume versus time. Size-adjusted survival was calculated using a method based on VDt and initial tumor volume to decrease the lead time bias attributable to differing tumor sizes at presentation. RESULTS: Slower VDt was associated with significantly longer survival and size-adjusted survival as determined by a univariate Cox proportional hazard analysis. Aneuploidy was a significant indicator of poor survival. Aneuploid and multiclonal astrocytomas had poor size-adjusted survivals compared with diploid astrocytomas. Grade IV astrocytomas had significantly poorer survival and size-adjusted survival compared with lower grades (I to III), which individually were not significantly correlated. However, grade IV histology was not a significant independent predictor of size-adjusted survival in a multivariate Cox model, whereas VDt and DNA ploidy remained significant. VDt also had a significant direct linear correlation to survival and size-adjusted survival. CONCLUSIONS: VDt and DNA ploidy were more sensitive than histologic grading as indicators of individual survival. Initial tumor size needs to be considered when staging and assessing survival in patients with intracranial astrocytomas.

Cost effectiveness and outcome assessment of magnetic resonance imaging in diagnosing cord compression.

BACKGROUND: This study was designed to investigate the costs associated with the use of magnetic resonance imaging (MRI) in the workup of spinal cord compression caused by metastatic disease, an area in which it has proven to be diagnostically useful. METHODS: The study was divided into two parts. Part 1 consisted of a retrospective review of the hospital charts of 46 patients, half of whom were diagnosed with cord compression in the pre-MRI era and the other half diagnosed after MRI availability; costs for these two groups were compared. Part 2 consisted of a review of several major studies comparing the sensitivities and specificities of MRI with alternative imaging techniques, usually myelography. Cost effectiveness and cost/cost ratios were derived for diagnostic usefulness using prevalence, sensitivity, specificity, and cost estimates of MRI and its alternatives, including costs of false-negative and false-positive testing. RESULTS: Our hospital-based experience yielded an average cost of $ 3664 per patient without MRI and $ 2283 per patient when MRI was available (1991 dollar amounts). The cost of diagnosis was 65% more expensive without MRI. Use of the literature-based experience demonstrated that the cost of diagnosis was at least 82% more costly without MRI than when it was available. However, when key variables were altered during sensitivity analysis, this difference of increased cost of diagnosis without MRI ranged from 25% to 98%. CONCLUSION: This work suggests that MRI may result in significant economic benefits in diagnosing metastatic cord compression, but further work is needed on physician behavior and referral patterns with MRI versus myelography as is long term follow-up for potential reductions in patient debility using MRI.

Central nervous system tumor, infection, and infarction: detection with gadolinium-enhanced magnetization transfer MR imaging.

PURPOSE: To quantitatively measure the degree of contrast enhancement of central nervous system (CNS) tumor, infection, and infarction by means of magnetization transfer (MT) magnetic resonance (MR) imaging. MATERIALS AND METHODS: T1-weighted MR images obtained before and after administration of contrast material with and without MT in 14 patients with CNS tumors were evaluated by means of a contrast-to-noise ratio (C/N). Another 72 patients with a variety of lesions underwent contrast material-enhanced T1-weighted MR imaging prospectively with and without MT; C/N was also evaluated. RESULTS: All lesions had a higher C/N on T1-weighted postcontrast MT images than on conventional images. C/N was 65 +/- 5 (mean +/- standard error) for MT and 42 +/- 4 for conventional images. C/N improved by a factor of 1.6-2.1 in the three disease categories. In intracranial tumors, the MT technique itself did not contribute significantly (P < .001) to the increase in C/N in the absence of gadopentetate dimeglumine. In fact, the C/N was lower for nonenhanced T1-weighted MT images. CONCLUSION: Concurrent use of gadopentetate dimeglumine and MT results in a statistically significant (P < .001) increase in C/N in CNS tumor, infection, and infarction.

Contrast on T2-weighted images of the lumbar spine using fast spin-echo and gated conventional spin-echo sequences.

A prospective study in 31 patients was designed to compare contrast quantitatively using axial conventional, gated spin-echo T2-weighted (T2W) (SE) (asymmetrical echo TE 30 and 80 ms) and axial dual-echo fast spin-echo (FSE) sequences (TEeff 20 and 120 ms) to image lumbar discs, nerve roots, and cerebrospinal fluid CSF. We used two quantitative measures, percent (%) contrast and contrast-to-noise ratio (CNR), to compare the sequences. The FSE sequence had greater % contrast and CNR on the first and second echo images for both disc and nerve root detection using these scan parameters. An axial FSE sequence, therefore, provided contrast characteristics similar to those of gated axial T2W SE sequence in the lumbar spine, with a 60% saving in acquisition time. The FSE sequence is now our standard axial T2W study for the lumbar spine.

Progressive multifocal leukoencephalopathy: unusual MR findings.

A case of progressive multifocal leukoencephalopathy (PML) with a classic clinical presentation but with unusual pathological and radiographic findings is reported. The pathology revealed evidence of prior hemorrhage, and imaging studies revealed focal cerebral atrophy as well as contrast enhancement on MR scans. The contrast enhancement was visible only by utilizing magnetization transfer pulses on T1-weighted scans. The case report indicates that image criteria for PML may need to be redefined in the future.

MR evaluation of vertebral metastases: T1-weighted, short-inversion-time inversion recovery, fast spin-echo, and inversion-recovery fast spin-echo sequences.

PURPOSE: To compare the detectability of vertebral metastatic disease on T1-weighted, short-inversion-time inversion recovery (STIR), fast spin-echo (FSE), fat-saturated FSE, and inversion recovery FSE (IRFSE) MR sequences using percent contrast and contrast-to-noise ratios. METHODS: Patients with proved metastatic disease underwent imaging on a 1.5-T MR system with sagittal T1-weighted (800/20/2 [repetition time/echo time/excitations]) (91 patients), STIR (1400/43/2; inversion time, 140) (91 patients), FSE (4000/180/2) (46 patients), fat-saturated FSE (4000/180/2) (16 patients), and IRFSE (29 patients) sequences. Percent contrast and contrast-to-noise ratio were calculated for the lesions. The number of metastatic lesions detected with each of the pulse sequences was also calculated. RESULTS: Mean percent contrast was, for T1-weighted sequence, -42.2 +/- 1%; STIR, 262 +/- 34%; FSE, 121 +/- 21%; fat-saturated FSE, 182 +/- 6%; and IRFSE, 272 +/- 47%. The mean contrast-to-noise ratio for T1-weighted was -4.63 +/- 1.7; STIR, 10.8 +/- .98; FSE, 4.16 +/- .76; fat-saturated FSE, 4.87 +/- .19; and IRFSE, 5.2 +/- .87. STIR and IRFSE showed the highest number of lesions, followed by T1-weighted, fat-saturated FSE, and FSE sequences. T1-weighted sequences showed 94%, FSE 55%, and fat-saturated FSE 78% of the lesions detected. Epidural metastatic lesions were better depicted on T1-weighted, FSE, and fat-saturated FSE sequences. CONCLUSION: STIR was superior to both T1-weighted and FSE (with and without fat saturation) for detection of metastatic lesions, in terms of both percent contrast and contrast-to-noise ratio and visibility. IRFSE was equal to STIR for the detection of metastasis by both subjective and objective criteria. T1-weighted, FSE, and fat-saturated FSE sequences were superior to STIR and IRFSE in the detection of epidural metastatic disease. IRFSE provided faster scanning time, which could be translated into greater resolution.