Biomedical subjects

Larry A Kramer

Publications and source records attributed to Larry A Kramer.

12 recordsLinked to original sources

PubMed2007

Dynamic contrast-enhanced MRI study of male pelvic perfusion at 3T: preliminary clinical report.

PURPOSE: To detect male pelvic perfusion in patients with coronary artery disease (CAD) vs. controls by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) at 3T. MATERIALS AND METHODS: Eighteen male patients were studied with T1-weighted (T1W) DCE-MRI to measure perfusion, phase-contrast (PC) imaging to measure bulk flow, and contrast-enhanced (CE)-MRA to detect stenosis. Regions of interest (ROIs) in prostate, corpus cavernosal, and spongiosal tissues were analyzed. Two-compartment pharmacokinetic modeling was employed to fit the signal enhancement. Perfusion parameters were analyzed by curve-fitting and utilized to compare the CAD and control groups. Validated questionnaires measuring urinary and erectile function were used to evaluate pelvic symptomatology in both groups. RESULTS: Mean perfusion analysis confirmed weaker and slower enhancement in CAD patients vs. controls despite equivalent cardiac output values. The mean maximum enhancement was 26.33 +/- 0.12 (controls) vs. 22.38 +/- 0.44 (CAD) for prostate. The mean wash-in rate in units of minute(-1) was 62.10 +/- 1.74 (controls) vs. 34.44 +/- 1.08 (CAD) for prostate, 16.68 +/- 0.72 (controls) vs. 8.04 +/- 0.36 (CAD) for spongiosal, and 8.34 +/- 0.54 (controls) vs. 3.48 +/- 0.24 (CAD) for cavernosal tissues (all with P < 0.0001). CONCLUSION: This preliminary study demonstrates that perfusion parameters differ between CAD and control patients, and the findings mirror the differences in pelvic symptoms in these groups.

Aged↗

PubMed2006

Impulsivity and BOLD fMRI activation in MDMA users and healthy control subjects.

The correlation between scores on the Barratt Impulsiveness Scale (BIS) and activation measured by functional magnetic resonance imaging in a dorsolateral prefrontal cortical (DLPFC) activating task was examined in 15 MDMA-using subjects and 19 controls. A significant correlation between BIS scores and DLPFC activation was found, supporting a role for the DLPFC in BIS-measured impulsivity.

Adult↗

PubMed2006

Familial thoracic aortic aneurysms and dissections: three families with early-onset ascending and descending aortic dissections in women.

Ascending thoracic aortic aneurysms leading to type A dissections can be inherited in an autosomal dominant manner with variable age of onset and decreased penetrance, primarily in women. Three families are described with autosomal dominant inheritance of either ascending aortic aneurysms leading to type A dissections or type B dissections, and a young age of onset of aortic dissections in both men and women. Pedigree analysis suggests that a de novo mutation is responsible for the disease in one family. The discordant age of onset of aortic disease in a monozygotic twin pair in a different family indicates that environmental or stochastic factors may influence the variable expression of disease. Genetic analysis of one family excluded linkage to known loci for TAAD (TAAD1, TAAD2, FAA1, or FBN1) and sequence analysis failed to identify mutations in TGFBR2, the gene encoding transforming growth factor beta receptor type II. Thus, a novel unidentified loci may be responsible for the phenotype in these three families.

Adolescent↗

PubMed2005

Peripersonal spatial attention in children with spina bifida: associations between horizontal and vertical line bisection and congenital malformations of the corpus callosum, midbrain, and posterior cortex.

Horizontal and vertical line bisection was studied in 129 children and adolescents between 8 and 19 years of age, one group (n=32) of typically developing controls and one group (n=97) with spina bifida (SBM), a neurodevelopmental disorder associated with dysmorphology of the corpus callosum, posterior cortex, and midbrain. For each participant, structural brain MRIs were analyzed qualitatively to identify beaking of the midbrain tectum and corpus callosum agenesis and hypoplasia and quantitatively by segmentation and volumetric analyses of regional cortical white and gray matter. Each group showed the line length effect, whereby greater estimation errors are made with longer lines. The group with SBM differed from controls in terms of both accuracy and variability of line bisection. Children with SBM showed pseudoneglect, attending more than controls to left hemispace. The extent of rightward bisection bias was unrelated to right posterior brain volumes, although an intact corpus callosum during development moderated and normalized the exaggerated leftward line bisection bias. More children with SBM than controls attended to inferior hemispace. A normal midbrain and greater posterior cortex volume during development moderated and normalized the downward bias. Children with SBM showed more intra-subject variability than controls. Line bisection in children with SBM reflects three deficits: an exaggerated attentional bias to left hemispace, an abnormal attentional bias to inferior hemispace; and a larger zone of subjective uncertainty in bisection judgments.

Adolescent↗

PubMed2005

Space-based inhibition of return in children with spina bifida.

Inhibition of return (IOR) refers to an increase in time to react to a target in a previously attended location. Children with spina bifida meningomyelocele (SBM) and hydrocephalus have congenital dysmorphology of the midbrain, a brain region associated with the control of covert orienting in general and with IOR in particular. The authors studied exogenously cued covert orienting in 8- to 19-year-old children and adolescents (84 with SBM and 37 age-matched, typically developing controls). The exogenous cue was a luminance change in a peripheral box that was 50% valid for the upcoming target location. Compared with controls, children with SBM showed attenuated IOR in the vertical plane, a deficit that was associated with midbrain dysmorphology in the form of tectal beaking but not with posterior brain volume loss. The data add to the emerging evidence for SBM deficits in attentional orienting to salient information.

Adolescent↗

PubMed2005

Reduced anterior corpus callosum white matter integrity is related to increased impulsivity and reduced discriminability in cocaine-dependent subjects: diffusion tensor imaging.

Brain imaging studies find evidence of prefrontal cortical dysfunction in cocaine-dependent subjects. Similarly, cocaine-dependent subjects have problems with behaviors related to executive function and impulsivity. Since prefrontal cortical axonal tracts cross between hemispheres in the corpus callosum, it is possible that white matter integrity in the corpus callosum could also be diminished in cocaine-dependent subjects. The purpose of this study was to compare corpus callosum white matter integrity as measured by the fractional anisotropy (FA) on diffusion tensor imaging (DTI) between 18 cocaine-dependent subjects and 18 healthy controls. The Barratt Impulsiveness Scale (BIS-11) and a continuous performance test: the Immediate and Delayed Memory Task (IMT/DMT) were also collected. Results of the DTI showed significantly reduced FA in the genu and rostral body of the anterior corpus callosum in cocaine-dependent subjects compared to controls. Cocaine-dependent subjects also had significantly higher BIS-11 scores, greater impulsive (commission) errors, and reduced ability to discriminate target from catch stimuli (discriminability) on the IMT/DMT. Within cocaine dependent subjects there was a significant negative correlation between FA in the anterior corpus callosum and behavioral laboratory measured impulsivity, and there was a positive correlation between FA and discriminability. The finding that reduced integrity of anterior corpus callosum white matter in cocaine users is related to impaired impulse control and reduced ability to discriminate between target and catch stimuli is consistent with prior theories regarding frontal cortical involvement in impaired inhibitory control in cocaine-dependent subjects.

Adult↗

PubMed2005

Spinal lesion level in spina bifida: a source of neural and cognitive heterogeneity.

OBJECT: The aim of this study was to evaluate whether the level of a spinal lesion is associated with variations in anomalous brain development and neurobehavioral outcomes in children suffering from the meningomyelocele form of spina bifida and hydrocephalus (SBM-H). METHODS: Two hundred sixty-eight children with SBM-H were divided into upper (T-12 and above; 82 patients) and lower (L-1 and below; 186 patients) lesion-level groups. Magnetic resonance images were qualitatively coded by radiologists and quantitatively segmented for cerebrum and cerebellum volumes. Psychometric assessments of handedness, intelligence, academic skills, and adaptive behavior were compared between lesion-level groups and also used to determine the number of children who met research-based criteria for mental retardation, attention deficit hyperactivity disorder, and learning disabilities. The magnetic resonance images obtained in children with upper-level spinal lesions demonstrated more qualitative abnormalities in the midbrain and tectum, pons, and splenium, although not in the cerebellum, compared with images obtained in children with lower-level spinal lesions. Upper-level lesions were also associated with reductions in cerebrum and cerebellum volumes, lower scores on measures of intelligence, academic skills, and adaptive behavior, and with a higher frequency of individuals meeting the criteria for mental retardation. Hispanic children (who were also more economically disadvantaged) were more likely to have upper-level lesions and poorer neurobehavioral outcomes, but lesion-level effects were generally independent of ethnicity. CONCLUSIONS: A higher level of spinal lesion in SBM-H is a marker for more severe anomalous brain development, which is in turn associated with poorer neurobehavioral outcomes in a wide variety of domains that determine levels of independent functioning for these children at home and school.

Adolescent↗

PubMed2004

Covert orienting to exogenous and endogenous cues in children with spina bifida.

Children with spina bifida meningomyelocele and hydrocephalus (SBM) have congenital dysmorphology of the midbrain and thinning of the posterior cortex, brain regions associated with the control of covert orienting. We studied cued covert orienting in 92 children with SBM, and 40 age-matched typically developing controls. Cues were of three types: exogenous (luminance change in a peripheral box either valid or invalid for upcoming target location), endogenous arrow (a central arrow either valid or invalid for upcoming target location), or endogenous word (a central word either valid or invalid for upcoming target location). Compared to controls, children with SBM showed slowed covert orienting to both exogenous and endogenous cues and a higher cost of attentional disengagement (e.g., a greater cue-validity effect) for exogenous although not for endogenous cues. Covert orienting deficits were associated with midbrain dysmorphology in the form of beaking of the tectum, and with right posterior brain volume loss.

Adolescent↗

PubMed2004

Functional MRI study of working memory in MDMA users.

RATIONALE: Methylene-dioxymethamphetamine (MDMA) is known to cause degeneration of serotonin nerve terminals after acute doses in animals. Similarly, behavioral studies in human MDMA users regularly find abnormalities in memory, mood, and impulse control. However, studies of brain function using brain imaging in MDMA users have been less consistent. OBJECTIVES: The purpose of this study was to determine, using functional magnetic resonance imaging (fMRI), whether individuals with a self-reported history of MDMA use would differ from non-MDMA using controls on activation while performing a working memory task. METHODS: Fifteen MDMA using subjects and 19 non-MDMA using controls underwent fMRI scanning while performing the immediate and delayed memory task (IMT/DMT). The study was based on a block design in which the delayed memory task (DMT) alternated with the immediate memory task (IMT), which served as a control condition. FMRI scans were acquired on a 1.5 T scanner, using a gradient echo echoplanar pulse sequence. RESULTS: Random effects SPM99 analysis showed significantly greater activation (whole volume corrected cluster P<0.05) during the DMT relative to the IMT in the MDMA subjects compared with the control subjects in the medial superior frontal gyrus, in the thalamus extending into putamen, and in the hippocampus. CONCLUSIONS: Although these effects could be due to other drugs used by MDMA users, these results are consistent with behavioral problems that are associated with MDMA use, and with animal studies on the effects of MDMA on brain function.

Adult↗

PubMed2004

Neurobiology of perceptual and motor timing in children with spina bifida in relation to cerebellar volume.

The cerebellum is important for perceptual and motor timing in the mature brain, but the timing function of the cerebellum in the immature brain is less well understood. We investigated timing in children with spina bifida meningomyelocele (SB), a neural tube defect that involves cerebellar dysgenesis, and in age-matched controls. Specifically, we studied perceptual timing (judgements of 400 ms duration) and motor timing (isochronous motor tapping); measured cerebellar volumes; and related perceptual and motor timing to each other and to cerebellar volume measurements. Children with SB had impairments in the perception of duration (around 400 ms) but not frequency (around 3000 Hz), showing that their perceptual timing deficit was not a generalized auditory impairment. Children with SB had motor timing deficits on unpaced but not paced isochronous tapping, and their unpaced timing performance was associated with clock variance rather than with motor implementation. Perceptual and motor timing were correlated, suggesting that children with SB have impairments in a central timing mechanism. Children with SB, especially those with upper spinal cord lesions, had significant cerebellar volume reductions in grey and white matter, as well as different regional patterns of grey matter, white matter and CSF. Duration perception was correlated with cerebellar volumes, and the number of valid tapping trials was correlated with cerebellar volumes in the SB group, which data demonstrate structure-function relations between timing and cerebellar volumes.

Acoustic Stimulation↗

PubMed2003

Increased pelvic vein thrombi in cryptogenic stroke: results of the Paradoxical Emboli from Large Veins in Ischemic Stroke (PELVIS) study.

BACKGROUND AND PURPOSE: Cryptogenic stroke is associated with an increased prevalence of patent foramen ovale. The Paradoxical Emboli From Large Veins in Ischemic Stroke (PELVIS) study hypothesized that patients with cryptogenic stroke have an increased prevalence of pelvic deep venous thrombosis (DVT). METHODS: At 5 sites, patients 18 to 60 years of age received an MRI venogram (MRV) of the pelvis within 72 hours of new symptom onset. Clinical data were then determined. Radiologists blinded to clinical data later read the scans. RESULTS: The 95 patients who met entry criteria were scanned. Their mean+/-SD age was 46+/-10 years, and time from stroke onset to pelvic MRV scan was 49+/-16 hours. Compared with those with stroke of determined origin (n=49), patients with cryptogenic stroke (n=46) were significantly younger, had a higher prevalence of patent foramen ovale (61% versus 19%), and had less atherosclerosis risk factors. Cryptogenic patients had more MRV scans with a high probability for pelvic DVT (20%) than patients with stroke of determined origin (4%, P<0.03), with most having an appearance of a chronic DVT. CONCLUSIONS: In this study of young stroke patients evaluated early after stroke, patients with cryptogenic stroke showed differences in several clinical features compared with patients with stroke of determined origin, including increased prevalence of pelvic DVT. The results require confirmation but suggest that paradoxical embolus from the pelvic veins may be the cause of stroke in a subset of patients classified as having cryptogenic stroke.

Adolescent↗

PubMed2003

Paradoxical emboli from calf and pelvic veins in cryptogenic stroke.

PURPOSE: The increased prevalence of patent foramen ovale in patients with cryptogenic strokes suggests the occurrence of paradoxical embolism. The identification of deep venous thromboses (DVTs) in this population would strengthen this hypothesis. The purpose of this study was to image the subdiaphragmatic venous system in a cohort of patients with cryptogenic strokes. MATERIALS AND METHODS: In 37 patients with cryptogenic brain ischemia and interatrial communication, duplex studies of calf, popliteal, and femoral veins, and magnetic resonance imaging venograms of the pelvis veins were performed. RESULTS: In 10 patients, DVTs were diagnosed that were considered to be the cause of cryptogenic brain ischemia on probable (n = 6) or possible (n = 4) bases. In these patients, the median time from stroke to DVT was 3.25 days. In 5 of these 10 patients, DVTs did not involve popliteal and femoral veins, areas thought most important to pulmonary embolism, but instead were isolated to calf or pelvic veins. Although none of these 10 patients had abnormal blood hypercoagulation tests, 8 of the 10 did have clinical conditions suggesting predisposition to developing DVTs, such as concomitant neoplasms or pulmonary embolism. CONCLUSIONS: Increased evidence for paradoxical embolism may emerge when diagnostic strategies use multiple imaging methods and evaluate a broad extent of the subdiaphragmatic veins.

Adult↗