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J R Petrella

Publications and source records attributed to J R Petrella.

17 recordsLinked to original sources
PubMed2001

Cortical localization of reading in normal children: an fMRI language study.

BACKGROUND: fMRI provides a noninvasive means of identifying the location and organization of neural networks that underlie cognitive functions. OBJECTIVE: To identify, using fMRI, brain regions involved in processing written text in children. METHODS: The authors studied nine normal right-handed native English-speaking children, aged 10.2 years (range 7.9 to 13.3 years), with two paradigms: reading Aesop's Fables and "Read Response Naming" (reading a description of an object that was then silently named). Data were acquired using blood oxygen level-dependent fMRI. Group data were analyzed with statistical parametric mapping; individual data sets were analyzed with a region-of-interest approach from individual study t maps. The number of activated pixels was determined in brain regions and an asymmetry index (AI = [L - R]/[L + R]) calculated for each region. RESULTS: The authors found strong activation in the left middle temporal gyrus and left midfrontal gyrus and variable activation in left inferior frontal gyrus for both reading tasks in the group analysis (z > 5.5 to 9.1). All subjects had strong left-sided lateralization for both tasks in middle/superior temporal gyrus, inferior frontal gyrus, and middle frontal gyrus (AI = 0.76 to 1.0 for t = 4). Reading Fables activated twice as many pixels in temporal cortex as the Read Response Naming task; activation in dorsolateral prefrontal cortex was similar for both tasks. Small homologous right middle temporal region activation was seen with reading a fable. CONCLUSIONS: The neural networks that process reading appear to be lateralized and localized by middle to late childhood. Reading text paradigms may prove useful for identifying frontal and temporal language-processing areas and for determining language dominance in children experiencing epilepsy or undergoing tumor surgery.

Brain Mapping↗
PubMed2001

Cerebral abscesses: investigation using apparent diffusion coefficient maps.

The combination of high signal and reduced apparent diffusion coefficients (ADC) within abscesses on diffusion-weighted MRI (DWI) has been reported as characteristic of abscesses, and useful for distinguishing them from cystic or necrotic neoplasms. To assess whether these are consistent findings in abscesses, we used DWI-derived ADC to investigate changes in water diffusibility in cerebral abscesses. We reviewed the MRI studies and clinical records of five patients with brain abscesses, who underwent DWI. Regions of interest were drawn within the abscesses on ADC maps, to obtain the ADC. The center of all five abscesses gave signal higher than that of white matter on DWI. The three largest also appeared bright on ADC maps, i. e., showed ADC substantially lower than those of normal white matter, consistent with restricted diffusion. However, the two smaller abscesses were not visible on ADC maps because their ADC were essentially the same as that of white matter; they did not show restricted diffusion. The absence of restricted diffusion within small abscesses may be related to intrinsic differences in molecular microenvironment between small and large abscesses, or to greater influence of volume averaging with surrounding edema on the ADC in smaller abscesses.

Brain Abscess↗
PubMed2001

Use of exponential diffusion imaging to determine the age of ischemic infarcts.

OBJECTIVE: Diffusion-weighted magnetic resonance imaging (DWI) detects acute ischemic infarcts with high lesion conspicuity. Determination of infarct age is difficult on DWI alone because infarct signal intensity (SIinfarct) on DWI is influenced by T2 properties ("T2 shine-through"). Maps of the apparent diffusion coefficient (ADC) reflect pure diffusion characteristics without T2 effects but have low lesion conspicuity. Thus, in clinical practice, combined use of DWI and ADC maps is required. Exponential DWI (eDWI) is an innovative means of MRI-diffusion data analysis that merges the advantages of DWI and ADC maps. The authors hypothesized that SIinfarct on eDWI would correlate with infarct age. The authors studied 114 consecutive patients who had 120 ischemic strokes with clearly determined onset times and who underwent echo-planar DWI. The eDWI were generated by dividing the signal intensity on DWI by that on the corresponding T2 image on a pixel-by-pixel basis. SIinfarct on eDWI was measured in the lesion core and expressed as a percentage of contralateral control tissue. On eDWI, relative SIinfarct changed significantly with infarct age (P < .0001). When patients were sorted in infarct-age groups, no significant differences were found within the first 120 hours. However, for patients studied within 5 days, the mean relative SIinfarct was significantly higher compared with patients studied > or = 8 days after stroke (P < .05). For all infarcts up to 5 days old, the eDWI signal intensity was higher than control tissue (hyperintense appearance). All infarcts > 10 days old had an eDWI signal intensity lower than control tissue (hypointense appearance). The authors concluded that the use of eDWI, as a single set of images, reliably differentiates acute infarcts (< or = 5 days old) from infarcts > 10 days old. This feature would be expected to be helpful when the distinction between acute and nonacute infarction cannot be determined on clinical grounds.

Adolescent↗
PubMed2001

Evaluation of white matter anisotropy in Krabbe disease with diffusion tensor MR imaging: initial experience.

PURPOSE: To compare diffusion tensor magnetic resonance imaging with conventional T2-weighted imaging for evaluation of white matter changes in patients with Krabbe disease. MATERIALS AND METHODS: In eight patients with Krabbe disease and eight age-matched control subjects, anisotropy maps were generated with diffusion tensor data by using echo-planar imaging with diffusion gradient encoding in six directions. Anisotropy maps and T2-weighted images were visually inspected. Relative anisotropy (RA) and normalized T2-weighted signal intensity in white matter tracts and gray matter nuclei were quantitatively compared between patients and controls (paired Student t test). RESULTS: Loss of diffusion anisotropy appeared on anisotropy maps as areas of decreased hyperintensity in patients with Krabbe disease. Differences in RA between Krabbe disease patients and control subjects were significant in eight of nine white matter structures studied (P =.001-.01) and in basal ganglia (P =.04). T2-weighted signal intensity was also significantly different in the same white matter structures (P =.006-.049) but not in basal ganglia. In the three patients imaged after stem cell transplantation, mean RA was between the RAs of untreated patients and control subjects. CONCLUSION: Diffusion tensor-derived anisotropy maps (a) provide a quantitative measure of abnormal white matter in patients with Krabbe disease, (b) are more sensitive than T2-weighted images for detecting white matter abnormality, and (c) may be a marker of treatment response.

Anisotropy↗
PubMed2001

Quantitative assessment of diffusion abnormalities in posterior reversible encephalopathy syndrome.

BACKGROUND AND PURPOSE: Previous studies have shown that lesions in posterior reversible encephalopathy syndrome are often isointense on diffusion-weighted MR images. We hypothesized that 1) apparent diffusion coefficient (ADC) maps using various thresholds would show larger abnormalities in posterior white matter (WM) and 2) isointense appearance of lesions on isotropic diffusion-weighted images results from a balance of T2 prolongation effects and diffusibility effects. METHODS: T2-weighted MR images from 11 patients were reviewed. Hyperintense lesions were located in both anterior and posterior WM in eight patients and solely in posterior WM in three patients. The ADC maps were produced by use of ADC values > or = 3 SD and > or = 10 SD above the mean value of normal WM. Lesions on diffusion-weighted images were classified as isointense or hypointense. ADC values within lesions (ADC(L)) were compared with those of normal WM (ADC(N)), and compared for isointense lesions and hypointense lesions. RESULTS: The distribution of lesions with ADC values > or = 3 SD was essentially identical to that on T2-weighted images. Regions with ADC values > or = 10 SD were found in both anterior WM and posterior WM in two patients and solely in posterior WM in nine patients. On diffusion-weighted images, lesions appeared isointense in seven patients and hypointense in four patients. Mean ADC(L)/ADC(N) for all lesions was 1.81; for hypointense lesions, 2.30. CONCLUSION: Vasogenic edema was more severe in posterior WM. Isointense lesions result from a balance of T2 effects and increased water diffusibility. Hypointense lesions have higher ADC values, which are not balanced by T2 effects.

Adult↗
PubMed2000

Assessment of vasogenic edema in eclampsia using diffusion imaging.

We qualitatively assessed the regional distribution of vasogenic edema in a case of postpartum eclampsia. Although diffusion-weighted imaging showed no abnormalities, bilateral high signal was seen on T2-weighted images and apparent diffusion coefficient (ADC) maps. ADC of 1.45 +/- 0.10 mm2/s x 10(-3) for the posterior cerebral artery (PCA) territory and 1.22 +/- 0.12 mm2/s x 10(-3) for the watershed areas were significantly higher than those in the territories of the anterior (0.85 +/- 0.07 mm2/s x 10(-3) and middle cerebral (0.79 +/- 0.06 mm2/s x 10(-3)) arteries (P < 0.05). The predilection of ADC changes within the PCA territory and in a previously undescribed watershed distribution supports the hypothesis that vasogenic edema in eclampsia is due to hypertension-induced failure of vascular autoregulation.

Adult↗
PubMed2000

Rapid three-dimensional MR imaging method for tracking a bolus of contrast agent through the brain.

A gradient-echo three-dimensional magnetic resonance imaging technique (principles of echo shifting with a train of observations, or PRESTO) is presented for use in tracking a bolus of paramagnetic contrast agent through the brain. The approach combines a segmented echo-planar type of acquisition with echo shifting, which leads to echo times that are longer than the repetition time. Unlike echo-planar imaging, the method maintains image resolution despite drastic T2* changes and frequency shifts.

Adult↗
PubMed2000

The effect of aging on the apparent diffusion coefficient of normal-appearing white matter.

OBJECTIVE: The purpose of our study was to test the hypothesis that the apparent diffusion coefficient (ADC) of normal-appearing white matter increases with advancing age. SUBJECTS AND METHODS: We selected 38 patients with normal MR imaging findings from 332 patients undergoing clinical MR imaging. Diffusion-weighted MR imaging was performed with diffusion gradients applied in three orthogonal directions. For each patient, the average ADC on trace-weighted diffusion images of white matter at prespecified regions of interest and at the thalamus were compared with the patient's age. RESULTS: For the white matter, ADC sorted by patient age in decades increased with advancing age. Patients at least 60 years old had significantly higher ADC (0.769 +/- 0.019 mm(2)/sec x 10(-3)) than patients less than 60 years old (0.740 +/- 0.013 mm(2)/sec x 10(-3)) (p < 0.001). Comparison of individual white matter ADC and age showed a significant increase with advancing age (p < 0.0001). For the thalamus, the average ADC among patients at least 60 years old (0.766 +/- 0.015 mm(2)/sec x 10(-3)) exceeded the average ADC for patients less than 60 years old (0.745 +/- 0.022 mm(2)/sec x 10(-3)) (p < 0.05). However, comparison of individual thalamic ADC and patient ages, although showing a trend to higher ADC with increasing age, did not reach statistical significance (p = 0.06). CONCLUSION: Advancing age is associated with a small but statistically significant increase of water diffusibility in human white matter. A similar trend was present in the thalamus. These increases may reflect mild structural changes associated with normal aging.

Adult↗
PubMed1998

Age-related vasodilatory response to acetazolamide challenge in healthy adults: a dynamic contrast-enhanced MR study.

PURPOSE: We examined age-related changes in baseline regional cerebral blood volume (rCBV) and response to acetazolamide stimulation by using dynamic contrast-enhanced MR imaging. METHODS: Thirty healthy volunteers ranging widely in age (23 to 82 years) were examined before and after intravenous injection of acetazolamide with dynamic susceptibility contrast-enhanced MR imaging. rCBV values were normalized for intersubject and intrasubject comparison by estimating an arterial input function directly from the imaging data. Preacetazolamide baseline rCBV and the percentage volume change index (PVCI) of the postacetazolamide to preacetazolamide state were calculated and examined as a function of age. RESULTS: Older adults (>50 years) had lower baseline rCBV per unit tissue than did younger adults (<50 years), but higher rCBV after acetazolamide stimulation. Baseline rCBV tended to decrease with age in the medial frontal and frontoparietal gray matter regions. Response to acetazolamide stimulation, measured by PVCI, showed a significant age-related increase in gray matter, approximately 0.5% per year. CONCLUSION: rCBV can be significantly increased after acetazolamide stimulation in the healthy aged. These results support the notion that age-related decreases in rCBV measured at rest reflect reduced regional metabolic requirements rather than reduced capacity for regional substrate delivery. These data serve as a normative baseline for comparison studies of rCBV vascular reserve in aging persons with various cerebrovascular disorders.

Acetazolamide↗
PubMedDate not supplied

Multiple sclerosis lesions: relationship between MR enhancement pattern and magnetization transfer effect.

PURPOSE: To investigate the relationship between the enhancement pattern of a multiple sclerosis lesion and its magnetization transfer effect. METHODS: Fifty-four lesions were chosen from 29 patients with multiple sclerosis on the basis of enhancement pattern on contrast-enhanced T1-weighted MR images. They included 14 homogeneously enhancing lesions, 26 nonenhancing lesions, and 14 ring-enhancing lesions. Magnetization transfer ratios of the homogeneously enhancing lesions, nonenhancing lesions, and central portion of the ring-enhancing lesions were measured. Means were calculated and compared. RESULTS: The magnetization transfer ratios for homogeneously enhancing lesions were higher (mean, 32.2%; SD, 3.4%) than those for nonenhancing lesions (mean 29.4%; SD, 4.3%) and for the central portion of ring-enhancing lesions (mean, 24.5%; SD, 4.0%). Significant differences were found between the ring-enhancing lesions and the homogeneously enhancing lesions and between the ring-enhancing lesions and the nonenhancing lesions. CONCLUSION: We found a relationship between decreased magnetization transfer ratios and those enhancement patterns in which myelin is known to be decreased histopathologically. Thus, use of the magnetization transfer technique may increase the specificity of MR imaging in assessing the extent of residual myelination in multiple sclerosis lesions.

Blood-Brain Barrier↗
PubMedDate not supplied

Assessment of whole-brain vasodilatory capacity with acetazolamide challenge at 1.5 T using dynamic contrast imaging with frequency-shifted burst.

PURPOSE: To determine whether whole-brain acetazolamide-induced changes in regional cerebral blood volume (rCBV) can be assessed on a conventional gradient 1.5-T MR system using 3-D dynamic susceptibility contrast-enhanced MR imaging. METHODS: A 3-D frequency-shifted (FS) burst technique was used to assess the intravascular first pass of contrast agent. Changes in rCBV were calculated in 40 volunteers before and after acetazolamide (n = 30) or saline (n = 10) injection using customized analysis software on an independent workstation. A single-section gradient-echo technique with better spatial resolution was used in one additional volunteer to examine the effect of partial volume averaging on calculation of absolute rCBV. RESULTS: A statistically significant increase in rCBV (gray matter = 23%, white master = 32.5%) was noted after acetazolamide compared with saline. Baseline fractional CBVs were 22% +/- 3% for gray matter and 12% +/- 2% for white matter. Partial volume averaging was probably responsible for a systematic but linear overestimation of absolute rCBV. CONCLUSION: Acetazolamide-induced changes in rCBV can be assessed using 3-D dynamic susceptibility contrast-enhanced MR imaging with FS-burst on a conventional gradient 1.5-T MR system. Values obtained with this technique overestimate absolute rCBV but are systematically biased and can be used for intersubject and intrasubject ratio comparisons.

Acetazolamide↗