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George J Hunter

Publications and source records attributed to George J Hunter.

9 recordsLinked to original sources
PubMed2006

Improved preoperative planning for directed parathyroidectomy with 4-dimensional computed tomography.

BACKGROUND: Four-dimensional computed tomography (4D-CT) provides both functional and highly detailed anatomic information about parathyroid tumors. The purpose of this study was to compare 4D-CT with sestamibi imaging and ultrasonography as methods for the accurate preoperative localization of hyperfunctioning parathyroid glands before parathyroidectomy. METHODS: A study of 75 patients with primary hyperparathyroidism was performed at a tertiary-care institution. Sestamibi imaging, ultrasonography, and 4D-CT were performed on each patient preoperatively. Results of the imaging studies were compared with operative findings, pathologic data, and biochemical measurements to assess the sensitivity and specificity of each of the imaging modalities. RESULTS: 4D-CT demonstrated improved sensitivity (88%) over sestamibi imaging (65%) and ultrasonography (57%), when the imaging studies were used to localize (lateralize) hyperfunctioning parathyroid glands to 1 side of the neck. Moreover, when used to localize parathyroid tumors to the correct quadrant of the neck (ie, right inferior, right superior, left inferior, or left superior), the sensitivity of 4D-CT (70%) was significantly higher than sestamibi imaging (33%) and ultrasonography (29%). CONCLUSION: 4D-CT provides significantly greater sensitivity than sestamibi imaging and ultrasonography for precise (quadrant) localization of hyperfunctioning parathyroid glands. This allows improved preoperative planning, particularly for the case of reoperation. In addition to the data that are provided, we present a novel classification scheme for use in parathyroid localization.

Adult↗
PubMed2004

Comparison of image quality between conventional and low-dose nonenhanced head CT.

BACKGROUND AND PURPOSE: Increasing use of CT for evaluating neurologic disease may expose patients to considerable levels of ionizing radiation. We compared the image quality of low-mAs head CT scans with that of conventional nonenhanced scans. METHODS: Conventional head CT scans were obtained in 20 patients (all >65 years with history of non-CNS malignancy) by using a multidetector technique: 170 mA and 1-second scanning time (ie, 170 mAs), 140 kVp, table speed of 7.5 mm per rotation, pitch of 0.75, section thickness of 5 mm, and field of view of 25 mm. A limited volume helical data acquisition covering four 5-mm-thick images was obtained by using 90 mAs but otherwise the same parameters. Three neuroradiologists visually rated the resulting images for quality in a blinded comparison. Representative 1- to 4-mm(2) regions of interest were chosen in gray matter and white matter locations. Conspicuity and the contrast-to-noise ratio were analyzed. Statistical comparisons were done by using the Student t test. RESULTS: Mean gray matter conspicuity was not significantly different between the 170- and 90-mAs groups (0.39 +/- 0.19 vs 0.41 +/- 0.03, P =.32). Mean gray matter contrast-to-noise ratio was approximately 22% higher with 170 mAs than with 90 mAs (1.77 +/- 0.52 vs 1.39 +/- 0.38, P =.005). All 90-mAs images were rated as having slightly greater image noise than the 170-mAs scans but with sufficient perceived resolution. CONCLUSION: Although 90-mAs head CT images were moderately noisier than 170-mAs images, they were rated as having acceptable diagnostic quality.

Aged↗
PubMed2003

Whole-brain CT perfusion measurement of perfused cerebral blood volume in acute ischemic stroke: probability curve for regional infarction.

PURPOSE: To determine the probability curve for regional cerebral infarction as a function of percentage normalized perfused cerebral blood volume (pCBV) in patients with acute ischemic stroke. MATERIALS AND METHODS: The authors retrospectively analyzed whole-brain computed tomographic (CT) perfusion scans from 28 patients with acute stroke (<6 hours) due to major arterial occlusion, without intracranial hemorrhage. Each patient had a positive follow-up CT scan 1-4 days later, without interval thrombolysis. Normalized pCBV, expressed as a percentage of contralateral normal brain pCBV, was determined in the core infarction and in regions just inside and outside the boundary between infarcted and noninfarcted brain. These regions were dichotomized into infarcted (core and inner band) and noninfarcted (outer band) categories. Logistic regression analysis was then used to create a reference curve of probability of infarction as a function of percentage normalized pCBV. RESULTS: Normalized pCBV values in the core, inner band, and outer band were 24.5% +/- 2.3, 36.3% +/- 2.4, and 72.1% +/- 2.4, with corresponding probabilities of infarction of .99, .96, and .11. The normalized pCBV at which the probability of survival reached .5 was 58.0% +/- 0.5. Sensitivity, specificity, and accuracy of the reference probability curve were 90.5% (209 of 231), 89.5% (212 of 237), and 90.0% (421 of 468), respectively. Negative and positive predictive values were 90.6% (212 of 234) and 89.3% (209 of 234), respectively. R2 was 0.73, and differences in perfusion between core and inner and outer bands were highly significant (P <.0001). CONCLUSION: A probability of infarction curve can help predict the likelihood of infarction as a function of percentage normalized pCBV.

Aged↗
PubMed2003

Multi-detector row CT: radiation dose characteristics.

PURPOSE: To determine the dose characteristics of multi-detector row computed tomography (CT) and to provide tabulated dose values and rules of thumb that assist in minimizing the radiation dose at multi-detector row CT. MATERIALS AND METHODS: Weighted CT dose index (CTDI100w) values were obtained from three multi-detector row CT scanners (LightSpeed; GE Medical Systems, Milwaukee, Wis) for both head and body CT modes by using standard CT-dose phantoms. The CTDI100w was determined as a function of x-ray tube voltage (80, 100, 120, 140 kVp), tube current (range, 50-380 mA), tube rotation time (0.5-4.0 seconds), radiation profile width (RPW) (5, 10, 15, 20 mm), and acquisition mode (helical high-quality and high-speed modes and axial one-, two-, and four-section modes). Statistical regression was performed to characterize the relationships between CTDI100w and various technique factors. RESULTS: The CTDI100w (milligray) increased linearly with tube current: in head mode, CTDI100w = (0.391 mGy/mA +/- 0.004) x tube current (milliampere) (r2 = 0.999); in body mode, CTDI100w = (0.162 mGy/mA +/- 0.002) x tube current (milliampere) (r2 = 0.999). The CTDI100w increased linearly with rotation time: in head mode, CTDI100w = (34.7 mGy/sec +/- 0.2) x rotation time (seconds) (r2 = 1.0); in body mode, CTDI100w = (13.957 mGy/sec +/- 0.005) x rotation time (seconds) (r2 = 1.0). The relationship of normalized CTDI100w (milligrays per 100 mAs) with tube voltage followed a power law: in head mode, CTDI100w = (0.00016 mGy/100 mAs. kVp +/- 0.00007) x (tube voltage)(2.5+/-0.1) (r2 = 0.997); in body mode, CTDI100w = (0.000012 mGy/100 mAs. kVp +/- 0.000007) x (tube voltage)(2.8+/-0.1) (r2 = 0.996). In all scanning modes, CTDI100w decreased when RPW increased. CTDI100w was 10% higher in head mode and 13% lower in body mode compared with the value suggested by the manufacturer, which is displayed at the scanner console. When deposited power exceeded 24 kW, CTDI100w increased by 10% as a result of use of the large focal spot. CONCLUSION: The authors provide a set of tables of radiation dose as a function of imaging protocol to facilitate implementation of radiation dose-efficient studies.

Head↗
PubMed2003

Assessing tissue viability with MR diffusion and perfusion imaging.

BACKGROUND AND PURPOSE: Diffusion- (DW) and perfusion-weighted (PW) MR imaging reflect neurophysiologic changes during stroke evolution. We sought to determine parameters that distinguish regions of brain destined for infarction from those that will survive despite hypoperfusion. METHODS: DW and PW images were obtained in 30 patients at 1-12 hours after symptom onset. Relative cerebral blood volume (rCBV), flow (rCBF), mean transit time (MTT), apparent diffusion coefficient (ADC), DW image signal intensity, and fractional anisotropy (FA) lesion-contralateral normal region ratios were obtained in the following regions: 1) infarct core with hyperintensity on DW image, abnormality on rCBF and MTT images, and follow-up abnormality; 2) infarcted penumbra with normal DW image, abnormal rCBF and MTT images, and follow-up abnormality; and 3) hypoperfused tissue that remained viable, with normal DW image, abnormal rCBF and MTT images, and normal follow-up. RESULTS: rCBF ratios for regions 1, 2, and 3 were 0.32 +/- 0.11, 0.46 +/- 0.13, and 0.58 +/- 0.12, respectively, and were significantly different. DW image intensity and ADC ratios were significantly different among all regions, but were more similar than rCBF ratios. rCBV and FA ratios were not significantly different between regions 2 and 3. No MTT ratios were significantly different. No region of interest with an rCBF ratio less than 0.36, an rCBV ratio less than 0.53, an ADC ratio less than 0.85, a DW image intensity ratio greater than 1.23, or an FA ratio greater than 1.10 remained viable. No region of interest with an rCBF ratio greater than 0.79 infarcted. CONCLUSIONS: Differences among mean ratios of three regions investigated were greatest for the rCBF ratio. The rCBF ratio may be the most useful parameter in differentiating viable tissue that is likely to infarct without intervention, from tissue that will survive despite hypoperfusion. ADC, DW intensity, FA, and rCBV ratios may provide adjunctive information.

Adult↗
PubMedDate not supplied

Functional CT perfusion imaging in predicting the extent of cerebral infarction from a 3-hour middle cerebral arterial occlusion in a primate stroke model.

BACKGROUND AND PURPOSE: Our purpose was to determine whether cerebral perfusion functional CT (fCT), performed after endovascular middle cerebral artery (MCA) occlusion, can be used to predict final cerebral infarction extent in a primate model. METHODS: fCT with bolus tracking was performed before and 30 and 150 minutes after 3-hour digital subtraction angiography (DSA)-guided endovascular MCA occlusion in five baboons. Parametric cerebral blood flow (CBF), cerebral blood volume (CBV) and mean transit time (MTT) maps were constructed by voxel-by-voxel gamma variate fitting and used to determine lesion sizes. Animals were sacrificed 48 hours after the occlusion, and ex vivo MR imaging was performed. Lesion sizes on fCT and MR images were compared. RESULTS: Hypoperfusion was clearly identified on all images obtained after MCA occlusion. Thirty and 150 minutes after occlusion onset, respectively, mean lesion sizes were 737 mm(2) +/- 33 and 737 mm(2) +/- 44 for CBF, 722 mm(2) +/- 32 and 730 mm(2) +/- 43 for CBV, and 819 mm(2) +/- 14 and 847 mm(2) +/- 11 for MTT. Mean outcome infarct size on MR images was 733 mm(2) +/- 30. Measurements based on CBV and CBF (R(2) = 0.97 and 0.96, P <.001), but not MTT (R(2) = 0.40, P >.5), were highly correlated with final lesion size. CONCLUSION: An endovascular approach to MCA occlusion provides a minimally invasive, reproducible animal model for controlled studies of cerebral ischemia and infarction. Derived cerebral perfusion maps closely predict the 48-hour infarct size after 3-hour MCA occlusion.

Angiography, Digital Subtraction↗
PubMedDate not supplied

Predicting cerebral ischemic infarct volume with diffusion and perfusion MR imaging.

BACKGROUND AND PURPOSE: Diffusion and perfusion MR imaging have proved useful in the assessment of acute stroke. We evaluated the utility of these techniques in detecting acute ischemic infarction and in predicting final infarct size. METHODS: Diffusion and hemodynamic images were obtained in 134 patients within a mean of 12.3 hours of onset of acute ischemic stroke symptoms. We retrospectively reviewed patient radiology reports to determine the presence or absence of lesion identification on initial diffusion- (DW) and perfusion-weighted (PW) images. Radiologists were not blinded to the initial clinical assessment. For determination of sensitivity and specificity, the final discharge diagnosis was used as the criterion standard. Neurologists were not blinded to the DW or PW imaging findings. In 81 patients, acute lesions were compared with final infarct volumes. RESULTS: Sensitivities of DW imaging and cerebral blood volume (CBV), cerebral blood flow (CBF), and mean transit time (MTT) perfusion parameters were 94%, 74%, 84%, and 84%, respectively. Specificities of DW imaging, CBV, CBF, and MTT were 96%, 100%, 96%, and 96%, respectively. Results were similar in 93 patients imaged within 12 hours. In 81 patients with follow-up, regression analysis yielded r(2) = 0.9, slope = 1.24 for DW imaging; r(2) = 0.84, slope = 1.22 for CBV; r(2) = 0.35, slope = 0.44 for CBF; and r(2) = 0.22, slope = 0.32 for MTT, versus follow-up volume. A DW-CBV mismatch predicted additional lesion growth, whereas DW-CBF and DW-MTT mismatches did not. Results were similar in 60 patients imaged within 12 hours. CONCLUSION: Diffusion and hemodynamic images are sensitive and specific for detecting acute infarction. DW imaging and CBV best predict final infarct volume. DW-CBV mismatch predicts lesion growth into the CBV abnormality. CBF and MTT help identify additional tissue with altered perfusion but have lower correlation with final volume.

Adult↗