Biomedical subjects

A D Elster

Publications and source records attributed to A D Elster.

At least 19 recordsLinked to original sources

PubMed2000

False cerebral activation on BOLD functional MR images: study of low-amplitude motion weakly correlated to stimulus.

BACKGROUND AND PURPOSE: Movements of the participant during blood oxygen level-dependent (BOLD) functional MR imaging cerebral activation studies are known to produce occasionally regions of false activation, especially when these movements are relatively large (>3 mm) and highly correlated with the stimulus. We investigated whether minimal (<1 mm), weakly correlated movements in a controlled functional MR imaging model could produce false activation artifacts that could potentially mimic regions of true activation in size, location, and statistical significance. METHODS: A life-size brain phantom was constructed by embedding vials of a dilute carboxylic acid solution within a gadolinium-doped gelatin mold. Imaging was performed at 1.5 T using a 2D spiral sequence (3,000/5 [TR/TE]; flip angle, 88 degrees; matrix, 64 x 64; field of view, 24 cm; section thickness, 5 mm). Controlled, in-plane, submillimeter movements of the phantom were generated using a pneumatic system and were made to correlate with a hypothetical "boxcar" stimulus over the range 0.31 < r < 0.96. Regions of false activation were sought using standard statistical methods (SPM96) that excluded phantom edges and accounted for spatial extent (regions tested at P < .05, corrected for multiple comparisons). A similar experiment was performed on a resting volunteer. RESULTS: The pneumatic system provided motion control with average in-plane displacements and rotations of 0.74 mm and 0.47 degrees, respectively, in the 18 data sets analyzed. No areas of false activation in the phantom were identified for poorly correlated motions (r < 0.52). Above this level, false activations occurred with increasing frequency, scaling in size and number with the degree of motion correlation. For motions with r > 0.67, areas of false activation were seen in every experiment. For a statistical threshold of P = .001, the median number of falsely activated regions was 3.5, with a mean size of 71.7 voxels (approximately 5 cc). Areas of possibly false activation of average size 72.5 voxels resulting from passive motion of the resting human participant were observed in two of four experiments. CONCLUSION: Participant movements of 1 mm or less that are only modestly correlated with a blocked stimulus paradigm can produce appreciable false activation artifacts on BOLD functional MR imaging studies, even when strict image realignment methods are used to prevent them.

Artifacts↗

PubMed1999

Acute cerebral infarction: quantification of spin-density and T2 shine-through phenomena on diffusion-weighted MR images.

PURPOSE: To quantify the relative contributions of spin density and T2 effects ("shine through") on diffusion-weighted (DW) magnetic resonance (MR) images of acute and subacute cerebral infarction. MATERIALS AND METHODS: In 30 patients, 1.5-T imaging was performed within the first 7 days after onset of cerebral infarction. Estimates of T2, spin density, and apparent diffusion coefficient (ADC) in the region of stroke and contralateral normal brain were computed by means of standard regression techniques after quadruple-echo conventional MR imaging and single-shot echo-planar DW imaging with a maximum b value of 1,000 sec/mm2. Expected signal intensity (S) enhancement ratios resulting from independent changes in T2, spin density, and ADC were then calculated for the DW sequence. RESULTS: The overall SI of cerebral infarction on DW images was significantly higher than that of normal brain throughout the 1st week after stroke (mean relative SI enhancement ratio, 2.29; P < .001). During the first 2 days after stroke, decreased ADC within the stroke region made the dominant contribution to increased SI on DW images. By day 3, increased T2 values in the stroke region became equally important, and, from days 3-7, the contribution to SI from T2 effects became dominant. A slight increase of spin density in the stroke region made a relatively small and constant contribution to DW SI over the 1st week. CONCLUSION: The increased SI of subacute cerebral infarction on DW images reflects not only a shortening of ADC but a prolongation of T2 and spin-density values.

Acute Disease↗

PubMed1999

A comparison of fast spin-echo, fluid-attenuated inversion-recovery, and diffusion-weighted MR imaging in the first 10 days after cerebral infarction.

BACKGROUND AND PURPOSE: Echo-planar diffusion-weighted and fluid-attenuated inversion-recovery (FLAIR) imaging have both proved valuable for detecting acute ischemic infarcts, but little is known about the value of diffusion-weighted imaging beyond the acute infarct period. Furthermore, no direct comparison of the techniques has been published. We compared the diagnostic utility of diffusion-weighted, FLAIR, and T2-weighted fast spin-echo (FSE) imaging for detecting cerebral infarctions up to 10 days old. METHODS: FSE, FLAIR, and diffusion-weighted MR sequences were obtained prospectively over a 6-month period in 212 patients with suspected cerebral infarctions. Seventy patients with nonhemorrhagic ischemic infarcts less than 10 days old whose symptoms lasted longer than 48 hours were identified. The three sequences were compared for detectability and conspicuity of abnormalities that correlated with the neurologic deficit. RESULTS: Seventy-two symptomatic infarcts were found in the 70 patients. Diffusion-weighted imaging detected 70 (97%), FLAIR, 69 (96%), and FSE, 64 (89%) of the 72 lesions. Only the difference between diffusion-weighted and FSE imaging approached statistical significance. There was no difference in the number of lesions detected in the patients imaged 48 hours or more after infarction. Lesion conspicuity on diffusion-weighted images was judged superior to that on FSE and FLAIR images in 55 (77%) and 47 (67%) of the cases, respectively. FLAIR images were judged superior to FSE in 34 (48%) of the cases. CONCLUSION: Diffusion-weighted images showed more infarcts than FLAIR and FSE images, and FLAIR images showed more than FSE images, but the differences were not statistically significant. Lesion conspicuity, however, was consistently better on diffusion-weighted images than on either FLAIR or FSE images throughout the 10-day period. Acquisition of diffusion-weighted images in the late acute and subacute periods after ischemic cerebral infarction appears to be beneficial.

Acute Disease↗

PubMed1998

Relationship between balance and abnormalities in cerebral magnetic resonance imaging in older adults.

BACKGROUND: Falling is a major cause of disability and morbidity among older adults. Because poor balance is a major reason for frequent falls, assessment of balance and its risk factors are important. In this study, we postulated that cerebral changes identified on magnetic resonance (MR) imaging are related to balance, and that older adults with balance problems would have significantly greater prevalence of such brain abnormalities than older adults without balance problems. DESIGN AND MEASUREMENTS: Several measures of balance were examined in more than 700 community-dwelling older men and women, blacks and whites. Balance measures included dynamic posturography, functional reach, Romberg and 1-foot stand tests, tandem stand, and 1-foot stand. Cerebral MR imaging assessments included ventricular size, sulcal widening, white matter disease, and ischemic infarctions. Cardiovascular disease and hypertension were determined and controlled for in the analyses. RESULTS: A summary of the balance measures was significantly related to each of the 4 MR imaging measures, with those with poorer balance having more disease. The strongest associations with balance were seen for white matter disease and ventricular size. All but the ischemic infarction variable remained significantly associated with balance after adjustments for sex, race, age, cardiovascular disease, and hypertension. CONCLUSION: Cerebral changes identified by MR imaging are associated with poorer balance among older adults.

Accidental Falls↗

PubMed1998

Cerebral infarction: time course of signal intensity changes on diffusion-weighted MR images.

OBJECTIVE: The objective of this study was to determine the time course of signal intensity changes on diffusion-weighted MR images after cerebral infarction. MATERIALS AND METHODS: Echoplanar diffusion-weighted MR images were obtained at 1.5 T in 212 patients referred for suspected cerebral infarction over a 6-month period. Of those patients, 85 met strict criteria for inclusion in this study: final clinical diagnosis of stroke, reliable timing of clinical ictus by history, and neurologic symptoms persisting longer than 48 hr after onset. Using adjacent or contralateral normal brain for comparison, diffusion-weighted images were visually analyzed retrospectively to evaluate for abnormalities in signal intensity. Because three patients were scanned on two occasions and five patients had two anatomically separable infarctions, 93 reliably dated brain lesions were analyzed. RESULTS: Diffusion-weighted images showed abnormal findings in 13 (100%) of 13 lesions less than 1 day old, 46 (96%) of 48 lesions 1-4 days old, 16 (94%) of 17 lesions 5-9 days old, three (60%) of five lesions 10-14 days old, and zero (0%) of 10 lesions more than 14 days old. CONCLUSION: Abnormal signal intensity was present on all diffusion-weighted MR studies obtained in patients within 24 hr of acute cerebral infarction and in up to 94% of patients scanned during the first 2 weeks after ictus. The percentage of abnormal diffusion studies declined with time, and no signal intensity abnormality was seen in stroke patients scanned more than 2 weeks after symptom onset.

Aged↗

PubMed1997

How much contrast is enough?. Dependence of enhancement on field strength and MR pulse sequence.

The overwhelming majority of published studies defining the clinical utility of gadolinium administration for neuroimaging have been performed at high field using conventional spin-echo imaging. Concerning the issue of field strength, several investigations have now shown that for a given dose of contrast, enhancement is less apparent at low field than at high field. Concerning the issue of pulse sequence, there is now convincing clinical and experimental evidence that all T1-weighted sequences are not equal in demonstrating contrast enhancement. Specifically, T1-weighted spoiled gradient-echo sequences do not show the same degree of visually apparent contrast enhancement compared to conventional spin-echo sequences. The use of magnetization transfer techniques which demonstrate areas of enhancement unseen on conventional pulse sequences is also addressed.

Brain↗

PubMed1997

Sulcal, ventricular, and white matter changes at MR imaging in the aging brain: data from the cardiovascular health study.

PURPOSE: To determine the distribution of changes in sulcal size, ventricular size, and white matter signal intensity depicted on cranial magnetic resonance (MR) images, with stratification according to age, race, and sex. MATERIALS AND METHODS: Ventricular size, sulcal size, and white matter signal intensity changes were graded on cranial MR images of 3,660 community-living, elderly participants in the Cardiovascular Health Study. A healthier subgroup was also defined. Summary statistics for both groups were generated for age, race, and sex. RESULTS: Regression models of the entire imaged cohort showed higher grades of all variables with increasing age, and higher ventricular and sulcal grades in men and in nonblack individuals. White matter grade was greater in women and in black individuals. Regression models of the healthier subgroup showed similar associations, except for a lack of association of sulcal and ventricular size with race. CONCLUSION: Sulcal width, ventricular size, and white matter signal intensity change with age, sex, and race. Knowledge of these changes is important in appropriate interpretation of MR images of the elderly.

Aged↗

PubMed1997

Clinically serious abnormalities found incidentally at MR imaging of the brain: data from the Cardiovascular Health Study.

PURPOSE: To determine the prevalence of clinically serious findings unrelated to stroke on cranial magnetic resonance (MR) images in a population of community-dwelling elderly people. MATERIALS AND METHODS: Neuroradiologists reviewed MR images of 3,672 people aged 65 years and older who were enrolled in a longitudinal, population-based study of cardiovascular and cerebrovascular disease. The neuroradiologists alerted MR imaging field centers about potentially serious abnormalities. Clinical information was obtained from clinical examinations performed before MR imaging, hospital discharge summaries, and the field centers at which MR imaging was performed. RESULTS: On 3,672 image sets, 64 (1.74%) clinically serious abnormalities were found. Among the presumptive diagnoses were 19 meningiomas (0.52%), six pituitary adenomas (0.16%), five cavernous malformations (0.14%), eight vascular stenoses (0.22%), four aneurysms (0.11%), two intraventricular masses (0.05%), two subdural fluid collections (0.05%), and two other tumors (0.05%). Only nine participants with these abnormalities required surgery. All but one of the meningiomas were in women, and the prevalence of the tumor decreased with increasing age. CONCLUSION: Physicians should be alert to the possible presence of clinically serious conditions in otherwise asymptomatic elderly individuals.

Aged↗

PubMed1997

Infarctlike lesions in the brain: prevalence and anatomic characteristics at MR imaging of the elderly--data from the Cardiovascular Health Study.

PURPOSE: To determine the prevalence and anatomic characteristics of infarctlike lesions seen on cranial magnetic resonance (MR) images. MATERIALS AND METHODS: The study cohort consisted of 5,888 community-living individuals aged 65 years and older enrolled in a longitudinal, population-based study of cardiovascular disease. MR images were obtained from 3,658 participants and evaluated by trained readers. Lesion size, anatomic location, and signal intensity were recorded. Infarctlike lesion was defined as a nonmass, hyperintense region on spin-density- and T2-weighted images and, in cerebral white matter and brain stem, a hypointense region on T1-weighted images. RESULTS: Infarctlike lesions were depicted on MR images of 1,323 (36%) participants. Eighty-five percent (1,128 participants) had lesions 3 mm or larger in maximum dimension, although 70.9% (1,320 of 1,861) of these lesions were 10 mm or less. Lesion prevalence increased with age, especially with lesions 3 mm or larger, which increased from 22.1% (86 of 389) in the 65-69-year age group to 42.9% (88 of 205) in the over-85-year age group (P < .0001). Lesion prevalence was slightly greater in men (497 of 1,527 [32.5%]) than in women (631 of 2,131 [29.6%]), but did not differ between blacks and non-blacks. The deep nuclei were the most commonly affected anatomic sites, with 78.2% (1,451 of 1,856) of lesions. Lesions that involved the cerebrum and posterior fossa accounted for 11.7% (218 of 1,856) and 10.1% (187 of 1,856) of lesions, respectively. CONCLUSION: If the lesions reported in this study indicate cerebrovascular disease, subclinical disease may be more prevalent than clinical disease, and the prevalence of disease may rise with age. Also, infarctlike lesions have a distinctive anatomic profile.

Aged↗

PubMed1997

MR imaging of lumbar spondylolysis: the importance of ancillary observations.

OBJECTIVE: The purpose of this study was to determine the frequency of characteristic ancillary MR findings in patients with lumbar spondylolysis. MATERIALS AND METHODS: The radiology reports and clinical records of 64 patients (16 female, 48 male; 12-77 years old) with 66 levels of lumbar spondylolysis who had undergone MR imaging were retrospectively reviewed. Spondylolysis was established by conventional radiography in all 64 patients and by CT in 18 patients. The proportion of patients with spondylolysis in whom sagittal MR images showed ancillary findings of an increased sagittal diameter of the spinal canal, reactive marrow changes in the pedicle, or abnormal wedging of the posterior aspect of the vertebral body was retrospectively determined. This proportion was then compared with the proportion of patients in whom spondylolysis was correctly diagnosed by the initial interpreters of the MR images, who used only direct visualization of defects of the pars interarticularis to make the diagnosis. RESULTS: Twenty (30%) of 66 levels of lumbar spondylolysis were misdiagnosed when the MR images were initially interpreted using direct visualization of defects of the pars interarticularis. An increased sagittal diameter of the spinal canal was the most common ancillary observation, occurring at 60 of 66 levels of lumbar spondylolysis. This finding was present in all patients with grade II, III, or IV spondylolisthesis, in 95% of patients with grade I spondylolisthesis; and in 77% of patients with no anterolisthesis. Thirty-two (48%) of 66 lumbar levels showed wedging of the posterior aspect of the vertebral body, which correlated significantly with the grade of spondylolisthesis. Reactive marrow changes in the pedicle distinct from normal adjacent levels were seen on MR images in 24(36%) of 66 levels of lumbar spondylolysis. On MR images, 97% of all levels of lumbar spondylolysis yielded one or more ancillary observations, including all 20 of the cases originally misdiagnosed. CONCLUSION: The combined use of ancillary observations and direct visualization of pars interarticularis defects makes MR imaging effective in revealing lumbar spondylolysis.

Adolescent↗

PubMed1997