Biomedical subjects

James G Pipe

Publications and source records attributed to James G Pipe.

8 recordsLinked to original sources

PubMed2003

A correlative measure for processing multiangle diffusion-weighted images.

A simple metric for the shared diffusion anisotropy between two voxels is proposed. The metric has large values when the diffusion is highly anisotropic in both voxels and oriented in the same direction. This metric can be used in several ways, three of which are illustrated in this article. First, the metric can be used to rapidly calculate a fractional anisotropy measure using an arbitrary number of measured diffusion values. Second, a simple way to exploit the metric for filtering DWI data with neighboring voxels with similar diffusion characteristics is shown. Third, the metric can be used to create color images that reflect tract orientation.

Algorithms↗

PubMed2003

A simple measure of flow disorder and wall shear stress in phase contrast MRI.

A method for estimating the standard deviation of velocity within a voxel is proposed. This estimate is based on data collected using a phase-contrast MRI technique. Simulations are presented to characterize the estimate and in vivo data are shown. Several different uses of the estimate are proposed, including obtaining a measure of wall shear stress, aiding in data combination from different phase-contrast MRI datasets, and mitigation of flow void artifacts.

Artifacts↗

PubMed2003

Effects of zero-filled interpolation on cervical magnetic resonance angiographic measurement.

BACKGROUND AND PURPOSE: The aim of this study was to assess the effect of zero-filled interpolation (ZIP) on measurements of the cervical arteries because its benefits on the accuracy and precision of measurements in medium-sized arteries remains unknown. METHODS: Three observers measured 36 computer-simulated vessels (2-6.8 mm) and 130 normal cervical vessels (assessed with two-dimensional time-of-flight MR angiography) from 512-, 256-, and 256-ZIP matrix source images. The accuracy and precision of measurement was assessed for each matrix by using the Student t test and F test of variance, respectively. The effect of vessel size and matrix placement on measurement error was determined by means of linear regression and the Student t test, respectively. RESULTS: No significant difference was observed between simulated measurements obtained on the 512 matrix and their true value. The 256 matrix caused overestimation of vessel diameter compared with 512 matrix (mean bias, 0.3 mm for computer-simulated vessels and 0.1 mm for normal vessels). This effect was reduced with ZIP, by a mean of 0.1 mm for both groups (P <.03). Precision was not affected by the matrix size or ZIP, and vessel size and matrix placement did not alter the measurement error. CONCLUSION: Vessel diameter is overestimated on 256-matrix MR angiographic source images. ZIP reduces this overestimation; however, the effect is small and unlikely to be clinically important.

Arteries↗

PubMed2003

Brain imaging in the unsedated pediatric patient: comparison of periodically rotated overlapping parallel lines with enhanced reconstruction and single-shot fast spin-echo sequences.

BACKGROUND AND PURPOSE: Periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER or PROP) is an effective means of compensating for head motion during MR imaging in adults. The aim of this study was to assess the value of this novel technique in unsedated children. METHODS: PROP T2-weighted fast spin-echo (FSE) imaging (TR/TE/NEX, 4000/83/2; 50 seconds) and T2-weighted single-shot FSE (SS-FSE) imaging (19,929/92/0.5; imaging time, 25 seconds) were performed in 35 unsedated children (mean age, 4.7 years +/- 4.2) who were undergoing brain MR imaging. Two observers assessed unlabelled images for motion artifact, other artifacts, visibility of pathology, and the preferred image overall. Sequences were compared by using the chi(2) test and concordant data from both observers. RESULTS: Both PROP and the SS-FSE imaging offered equal degrees of motion correction. Metallic artifacts were worse on PROP imaging, likely because of a higher receiver bandwidth (P <.001, chi(2) test). Pathology was present in 28 subjects and equally well seen on PROP and SS-FSE images. Overall, PROP was preferred, largely because of its improvements in image contrast (P <.001, chi(2) test). CONCLUSION: SS-FSE imaging and PROP provide equal motion correction, although PROP enables better assessment of the brain parenchyma.

Adolescent↗

PubMed2002

Multishot diffusion-weighted FSE using PROPELLER MRI.

A method for obtaining diffusion-weighted images that are free from the artifacts associated with echo-planar acquisitions, such as signal pile-up and geometric warping, is introduced. It uses an ungated, multishot fast spin-echo (FSE) acquisition that is self-navigated. The phase of the refocusing pulses is alternated to minimize non-Carr-Purcell-Meiboom-Gill (CPMG) artifacts. Several reconstruction methods are combined to make this method robust against motion artifacts. Examples are shown of clinical diffusion-weighted imaging and high-resolution diffusion tensor imaging.

Algorithms↗

PubMed2002

Neural correlates of self-reflection.

The capacity to reflect on one's sense of self is an important component of self-awareness. In this paper, we investigate some of the neurocognitive processes underlying reflection on the self using functional MRI. Eleven healthy volunteers were scanned with echoplanar imaging using the blood oxygen level-dependent contrast method. The task consisted of aurally delivered statements requiring a yes-no decision. In the experimental condition, participants responded to a variety of statements requiring knowledge of and reflection on their own abilities, traits and attitudes (e.g. 'I forget important things', 'I'm a good friend', 'I have a quick temper'). In the control condition, participants responded to statements requiring a basic level of semantic knowledge (e.g. 'Ten seconds is more than a minute', 'You need water to live'). The latter condition was intended to control for auditory comprehension, attentional demands, decision-making, the motoric response, and any common retrieval processes. Individual analyses revealed consistent anterior medial prefrontal and posterior cingulate activation for all participants. The overall activity for the group, using a random-effects model, occurred in anterior medial prefrontal cortex (t = 13.0, corrected P = 0.05; x, y, z, 0, 54, 8, respectively) and the posterior cingulate (t = 14.7, P = 0.02; x, y, z, -2, -62, 32, respectively; 967 voxel extent). These data are consistent with lesion studies of impaired awareness, and suggest that the medial prefrontal and posterior cingulate cortex are part of a neural system subserving self-reflective thought.

Adult↗

PubMed2002

Changes in brain water diffusion during the 1st year of life.

PURPOSE: To evaluate the normal water diffusion changes that occur during the 1st year of life. MATERIALS AND METHODS: Diffusion-weighted imaging was performed in 40 subjects (age range, birth to 1 year) in whom both magnetic resonance imaging and neurologic assessment results were normal at the time of imaging and, where available, at follow-up. Apparent diffusion coefficient (ADC) was calculated in four areas of white matter (anterior and posterior subcortical and internal capsule) and four of gray matter (cortex, thalamus, head of the caudate nucleus, and lentiform nucleus). Linear regression was used to examine the effect of age on ADC, and analysis of variance was used to compare ADC within different brain regions. RESULTS: ADC decreased with age in all regions (P <.01). Data best fit with a logarithmic decline (r(2) = 0.20-0.63). ADC was significantly higher in white (113 x 10(-5) mm(2)/sec) than in gray matter (102 x 10(-5) mm(2)/sec; P <.001). Significant differences were seen among three white matter regions (subcortical, 188 x 10(-5) mm(2)/sec at birth; anterior limb of internal capsule, 130 x 10(-5) mm(2)/sec; posterior limb of internal capsule, 109 x 10(-5) mm(2)/sec) and three gray matter regions (cortex, 134 x 10(-5) mm(2)/sec at birth; head of caudate nucleus, 134 x 10(-5) mm(2)/sec at birth; and thalamus and lentiform nucleus, 120 x 10(-5) mm(2)/sec; P <.01). CONCLUSION: Results suggest that in neonates and infants, water diffusion is highly dependent on both subject age and brain location.

Age Factors↗

PubMed2002

Improved image quality and detection of acute cerebral infarction with PROPELLER diffusion-weighted MR imaging.

PURPOSE: To compare periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER) multishot fast spin-echo diffusion-weighted magnetic resonance (MR) imaging with single-shot echo-planar diffusion-weighted MR imaging for image quality and visualization of acute cerebral infarction. MATERIALS AND METHODS: Seventy subjects (35 men, 35 women; mean age, 55 years +/- 24 [SD]) who were suspected of having acute cerebral infarction (symptom duration, 2.8 days +/- 2.7) underwent PROPELLER and echo-planar MR imaging (b = 1,000 sec/mm(2)). Two neuroradiologists compared unlabeled images for presence of artifacts, visualization of infarction, and their preference of images. Interobserver agreement and image comparison were assessed by using the kappa statistic and the chi(2) test, respectively. RESULTS: PROPELLER MR imaging reduced susceptibility artifacts (n = 70 subjects), which limited visualization of temporal (echo-planar, n = 64; PROPELLER, n = 0; P <.01, chi(2) test), frontal (echo-planar, n = 58; PROPELLER, n = 1; P <.01), and parietal lobes (echo-planar, n = 5; PROPELLER, n = 0; P <.05) and cerebellum (echo-planar, n = 36; PROPELLER, n = 0; P <.01) and brainstem (echo-planar, n = 23; PROPELLER, n = 0; P <.01). Acute infarction (n = 31 subjects) was better demonstrated at PROPELLER MR imaging (PROPELLER better, n = 18; echo-planar better, n = 1; PROPELLER and echo-planar equal, n = 12; P <.01, chi(2) test). PROPELLER MR imaging was preferred in all (n = 70) but one case in which the lesion lay within the intersection gap (PROPELLER preferred, n = 69; echo-planar preferred, n = 1; P <.01, chi(2) test). CONCLUSION: With a short increase in imaging time, PROPELLER MR imaging offers better image quality and detection of acute cerebral infarction than does echo-planar MR imaging.

Acute Disease↗