Faculty Bibliography

PURPOSE: Conventional noncontrast CT (NCCT) is insensitive to hyperacute cerebral infarction in the first 3 h. Our aim was to determine if CT perfusion (CTP) can improve diagnostic accuracy over NCCT for patients presenting with stroke symptoms in the 3-hour window. METHODS: Consecutive patients presenting to our emergency department with symptoms of ischemic stroke <3 h old and receiving NCCT and CTP as part of their triage evaluation were retrospectively reviewed. Patients with follow-up diffusion-weighted MRI (DWI) <7 days from ictus were included. Two readers rated the NCCT and CTP for evidence of acute infarct and its vascular territory. CTP selectively covered 24 mm of brain centered at the basal ganglia with low relative cerebral blood volume in a region of low cerebral blood flow or elevated time to peak as the operational definition for infarction. A third reader rated all follow-up DWI for acute infarct and its vascular territory as the reference standard. Sensitivity, specificity, and predictive values were calculated. An exact McNemar test and generalized estimating equations from a binary logistic regression model were used to assess the difference in detection rates between modalities. A two-sided p value <0.05 was considered significant. RESULTS: 100 patients were included. Sixty-five (65%) patients had follow-up DWI confirmation of acute infarct. NCCT revealed 17 (26.2%) acute infarcts without false positives. CTP revealed 42 (64.6%) acute infarcts with one false positive. Of the 23 infarcts missed on CTP, 10 (43.5%) were outside the volume of coverage while the remaining 13 (56.5%) were small cortical or lacunar type infarcts (<or=15 mm in size). CTP was significantly more sensitive (64.6 vs. 26.2%, p < 0.0001) and accurate (76.0 vs. 52%, p < 0.0001) and had a better negative predictive value (59.6 vs. 42.2%, p = 0.032) than NCCT. CONCLUSION: In a retrospective cohort of 100 patients with symptoms of hyperacute stroke in the 3-hour window, CTP provided improved sensitivity and accuracy over NCCT

PURPOSE: To characterize age-related MR diffusion patterns of the prefrontal brain cortex microstructure using a new method for investigating the non-Gaussian behavior of water diffusion called diffusional kurtosis imaging (DKI). MATERIALS AND METHODS: Measures of mean diffusivity (MD), fractional anisotropy (FA) and mean kurtosis (MK) were compared in the prefrontal brain cortex of 24 healthy volunteers (adolescents, young adults, and elderly) ranging from age 13 to 85 years. A Mann-Whitney test was used to compare subject groups with respect to the diffusion measures, and linear regression was used to characterize the change in each diffusion measure as a function of age. RESULTS: We found significant age-related changes in the elderly adult group, with increase of MD and decrease of FA. CONCLUSION: The current study demonstrates distinct mean kurtosis patterns for different age-ranges, with significant age-related correlation for mean kurtosis (MK) and MK peak position, showing that diffusional kurtosis is able to characterize and measure age-related diffusion changes for both grey and white matter, in the developing and aging brain

BACKGROUND AND PURPOSE: Time-resolved MR angiography (MRA) offers the combined advantage of large anatomic coverage and hemodynamic flow information. We applied parallel imaging and time-resolved imaging with stochastic trajectories (TWIST), which uses a spiral trajectory to undersample k-space, to perform time-resolved MRA of the extracranial internal carotid arteries and compare it to time-of-flight (TOF) and high-resolution contrast-enhanced (HR) MRA. MATERIALS AND METHODS: A retrospective review of 31 patients who underwent carotid MRA at 1.5T using TOF, time-resolved and HR MRA was performed. Images were evaluated for the presence and degree of ICA stenosis, reader confidence, and number of pure arterial frames attained with the TWIST technique. RESULTS: With a consensus interpretation of all sequences as the reference standard, accuracy for identifying stenosis was 90.3% for TWIST MRA, compared with 96.0% and 88.7% for HR MRA and TOF MRA, respectively. HR MRA was significantly more accurate than the other techniques (P < .05). TWIST MRA yielded datasets with high in-plane spatial resolution and distinct arterial and venous phases. It provided dynamic information not otherwise available. Mean diagnostic confidence was satisfactory or greater for TWIST in all patients. CONCLUSION: The TWIST technique consistently obtained pure arterial phase images while providing dynamic information. It is rapid, uses a low dose of contrast, and may be useful in specific circumstances, such as in the acute stroke setting. However, it does not yet have spatial resolution comparable with standard contrast-enhanced MRA

PURPOSE: To evaluate the possible radiation dose reduction facilitated by using dual-energy (DE) multidetector computed tomography (CT) after endovascular repair of abdominal aortic aneurysms (AAAs). MATERIALS AND METHODS: This prospective study was HIPAA compliant and institutional review board approved. Twenty-two patients who previously had undergone endovascular repair of AAAs underwent 24 DE multidetector CT examinations, which were performed with a 64-detector scanner. Initial nonenhanced CT was followed by arterial phase and venous phase acquisitions. Virtual nonenhanced, pure 80-kVp, and weighted-average peak voltage CT data sets were generated from the venous acquisition. Two independent readers interpreted the virtual nonenhanced and DE weighted-average CT data for the presence or absence of endoleaks. These interpretations were compared with the clinical interpretations of the data performed by a different radiologist by using true nonenhanced, arterial phase, and venous phase data. Region-of-interest measurements of the abdominal aorta and of the region of the endoleaks were obtained. Effective radiation dose was calculated. RESULTS: Both independent readers' interpretations of the virtual nonenhanced and weighted-average venous CT data revealed six type II endoleaks. There were no false-positive or false-negative findings. Aortic attenuation during the arterial, 80-kVp venous, and weighted-average data acquisitions were 288, 213, and 150 HU, respectively. The attenuation of the endoleaks was higher during the 80-kVp acquisition (P < .03) than during the arterial phase and weighted-average venous phase acquisitions. The mean effective dose for DE venous phase CT was 11.1 mSv compared with 27.8 mSv for standard triple-phase CT with a single-source configuration. CONCLUSION: Preliminary observations suggest that obtaining DE multidetector CT data by using a single 60-second contrast material-enhanced acquisition may be all that is required for surveillance after endovascular repair of AAA

PURPOSE: To quantify proton magnetic resonance (MR) spectroscopy-detectable metabolite concentrations along anteroposterior axis of hippocampus in healthy young and elderly subjects. MATERIALS AND METHODS: Young (three women, three men; age range, 25-35 years) and elderly (four women, two men; age range, 68-72 years) groups underwent MR imaging and proton MR spectroscopic imaging at 3 T in this HIPAA-compliant prospective study and gave institutional review board-approved written consent. Volume of interest was centered on and tilted parallel to hippocampal anteroposterior plane. Absolute N-acetylaspartate (NAA), choline, and creatine levels were obtained in each voxel, with phantom replacement. RESULTS: Mean NAA, creatine, and choline concentrations in the young group were higher in posterior hippocampus (12.9 mmol/L +/- 2.0 [standard deviation], 7.8 mmol/L +/- 1.2, 2.3 mmol/L +/- 0.4, respectively) than anterior hippocampus (8.0 mmol/L +/- 1.1, 6.0 mmol/L +/- 1.4, 1.5 mmol/L +/- 0.2; P = .005, .02, and .0002, respectively). In the elderly group, mean concentrations were higher in posterior hippocampus (8.6 mmol/L +/- 0.9, 5.6 mmol/L +/- 0.6, 1.5 mmol/L +/- 0.2, respectively) than anterior hippocampus (7.2 mmol/L +/- 1.0, 2.4 mmol/L +/- 0.3, 1.0 mmol/L +/- 0.2; P = .006, .0001, .04, respectively). Mean concentrations were significantly higher in the young group (13.2 mmol/L +/- 1.0, 7.4 mmol/L +/- 0.8, 2.1 mmol/L +/- 0.3, respectively) than in the elderly group (9.0 mmol/L +/- 1.0, 5.8 mmol/L +/- 0.8, 1.8 mmol/L +/- 0.3; P = .0001, .01, .05, respectively). Posteroanterior metabolic gradients differed: NAA decreased faster in the young group (-1.0 mmol/L x cm(-1)) than the elderly group (-0.7 mmol/L x cm(-1)); creatine and choline concentrations decreased faster in the elderly group (-0.8 and -0.058 mmol/L x cm(-1), respectively) than the young group (-0.16 and -0.008 mmol/L x cm(-1), respectively). No left-right metabolic differences were found. CONCLUSION: Significant metabolic heterogeneity was observed between groups and along anteroposterior axis of healthy hippocampus in both groups. Age matching and consistent voxel placement are important for correct comparisons of both absolute metabolic levels and metabolite ratios in longitudinal intra- and intersubject cross-sectional studies

BACKGROUND AND PURPOSE: Concurrent temporary inflation of a nondetachable balloon in the parent artery has been reported to be useful during endovascular coiling of complex, wide-neck aneurysms, facilitating truer coil reconstruction of the native vessel. Nevertheless, there exists concern that adjunctive use of balloon assistance may lead to increased adverse events during aneurysm coiling. MATERIALS AND METHODS: A literature search of all of the unassisted and balloon-remodeling studies published between 1997 and 2006 was conducted with application of strict selection criteria based on the reporting of complication incidence and outcome. The final cohort was analyzed to determine rates and clinical outcomes of iatrogenic aneurysm rupture and thromboembolism. Additional data were collected on the degree of initial and follow-up aneurysm occlusion rates. RESULTS: A total of 83 potential studies (4973 patients) were identified, from which 23 articles reporting results for 867 traditional-unassisted and 273 balloon-assisted coiled aneurysms met inclusion criteria for the analysis of thromboembolic complications, and 21 articles with 993 routinely coiled and 170 balloon-remodeled aneurysms were eligible for iatrogenic perforation analysis. No statistically significant difference was found in the rates of thromboembolism. Iatrogenic perforation rates were also comparable, though the overall numbers were too few for meaningful statistical analysis. Both initial and follow-up aneurysm occlusion rates were higher in balloon-assisted cases. CONCLUSION: This largest-to-date literature review and meta-analysis did not demonstrate a higher incidence of thromboembolic events or iatrogenic rupture with the use of adjunctive balloon remodeling compared with unassisted coiling. Balloon remodeling appears to result in higher initial and follow-up aneurysm occlusion rates

Recruitment of effector T cells to inflamed peripheral tissues is regulated by chemokines and their receptors, but the factors regulating recruitment to tumors remain largely undefined. Ionizing radiation (IR) therapy is a common treatment modality for breast and other cancers. Used as a cytocidal agent for proliferating cancer cells, IR in combination with immunotherapy has been shown to promote immune-mediated tumor destruction in preclinical studies. In this study we demonstrate that IR markedly enhanced the secretion by mouse and human breast cancer cells of CXCL16, a chemokine that binds to CXCR6 on Th1 and activated CD8 effector T cells, and plays an important role in their recruitment to sites of inflammation. Using a poorly immunogenic mouse model of breast cancer, we found that irradiation increased the migration of CD8(+)CXCR6(+) activated T cells to tumors in vitro and in vivo. CXCR6-deficient mice showed reduced infiltration of tumors by activated CD8 T cells and impaired tumor regression following treatment with local IR to the tumor and Abs blocking the negative regulator of T cell activation, CTLA-4. These results provide the first evidence that IR can induce the secretion by cancer cells of proinflammatory chemotactic factors that recruit antitumor effector T cells. The ability of IR to convert tumors into 'inflamed' peripheral tissues could be exploited to overcome obstacles at the effector phase of the antitumor immune response and improve the therapeutic efficacy of immunotherapy

BACKGROUND AND PURPOSE: Despite the prominent peak of N-acetylaspartate (NAA) in proton MR spectroscopy ((1)H-MR spectroscopy) of the adult brain and its almost exclusive presence in neuronal cells, the total amount of NAA, regarded as their marker, is difficult to obtain due to signal contamination from the skull lipids. This article compares the performance of 2 methods that overcome this difficulty to yield the whole-brain NAA signal, important for the assessment of the total disease load in diffuse neurologic disorders. MATERIALS AND METHODS: The heads of 12 healthy volunteers, 3 women and 9 men, 31.0 +/- 7.1 years of age, were scanned at 3T by using 2 nonlocalizing (1)H-MR spectroscopy sequences: One nulls the NAA (TI = 940 ms) every second acquisition by inversion-recovery to cancel the signals of the lipids (T1 << TI) in an add-subtract scheme. The other nulls the signal of the lipids (TI = 155 ms) directly after each acquisition, requiring half as many averages for the same signal-to-noise ratio. Each sequence was repeated 3 times back-to-back on 3 occasions, and the comparison criteria were intrasubject precision (reproducibility) and total measurement duration. RESULTS: NAA nulling is nearly twice as precise in its intrinsic back-to-back (5.8% versus 8.6%) as well as longitudinal (10.6% versus 19.7%) coefficients of variation compared with lipid nulling, but at the cost of double the acquisition time. CONCLUSION: When speed is a more stringent requirement than precision, the new lipid-nulling sequence is a viable alternative. For precision in cross-sectional or longitudinal global NAA quantification, however, NAA nulling is still the approach of choice despite its x2 ( approximately 5 minutes) time penalty compared with the lipid-nulling approach

OBJECTIVE: Conventional MR sequences are sometimes nonspecific in differentiating benign from pathologic fractures. To address this difficulty, diffusion-weighted images were conjectured to aid in this discrimination with variable results. As each of these studies contained somewhat small numbers of patients, we performed a meta-analysis to determine if this sequence may be used for this important diagnostic problem. MATERIALS AND METHODS: We reviewed and statistically analyzed the results of eight studies, performed between 1998 and 2003, comparing diffusion-weighted magnetic resonance signal intensity characteristics of benign and pathologic vertebral body fractures. Diffusion-weighted imaging (DWI) signal characteristics and apparent diffusion coefficient (ADC) values of 104 benign fractures and 161 combined malignant vertebral body lesions and pathologic fractures were statistically evaluated in terms of mean ADC, as well as percentage classified as either hypointense or isointense. The meta-analysis to compare benign fractures with the combined pathologic fractures and metastatic lesions in terms of mean ADC used Hedge's g statistic with a small sample bias adjustment; the comparison of the percentage hypo- or isointense used the Mantel-Haenszel method to calculate a weighted summary odds ratio. All summary effect sizes were computed under a random effects model to account for study heterogeneity. RESULTS: The mean ADC was significantly higher (p < 0.01) among benign fractures, with a standardized mean difference (SMD) of 2.8 and a 95% confidence interval (CI) for the SMD of 2.1 to 3.5. Lesions classified as hypointense were significantly more likely to be benign (p < 0.01), based on a summary odds ratio (OR) of 24.5 and 95% confidence that the OR exceeds 1.7. Lesions classified as isointense were not significantly more likely to be benign or malignant (p > 0.1), based on a summary OR of 3.6 and a 95% CI for the OR of 0.35 to 36.6. CONCLUSION: Even though the literature has been inconsistent, ADC maps appear to be a reliable method to differentiate benign from malignant fractures