Biomedical subjects

Jeffry R Alger

Publications and source records attributed to Jeffry R Alger.

22 records · Page 2Linked to original sources

PubMed2002

Late secondary ischemic injury in patients receiving intraarterial thrombolysis.

Although animal models have demonstrated that late secondary cerebral injury after arterial occlusion and subsequent recanalization may limit the benefit of reperfusion therapy, this phenomenon has not been well characterized in humans. Diffusion-perfusion magnetic resonance imaging studies were performed before treatment, early after treatment, and at day 7 in patients undergoing vessel recanalization with intraarterial thrombolytics. Among 18 patients studied, mean age was 71 (range, 27-94), and median entry National Institutes of Health Stroke Scale score was 13 (range, 6-25). Early after recanalization, partial or complete normalization of diffusion imaging abnormalities occurred in 8 of 18 (44%) patients. Among the eight patients with early diffusion imaging reversal, late secondary injury by day 7 occurred in 5 (63%), and sustained normalization of all reversed tissue occurred in 3 (38%). Pretreatment apparent diffusion coefficient values were lowest in regions experiencing no reversal (mean apparent diffusion coefficient, 608 microm(2)/sec), intermediate in regions with reversal and secondary decline (617 microm(2)/sec), and highest in regions with sustained reversal (663 microm(2)/sec). There was a trend toward less improvement in neurological deficit in patients with secondary injury versus patients with sustained reversal. In the future, late secondary tissue injury may become an important therapeutic target for postreperfusion neuroprotective therapies, with treatment efficacy monitored by serial diffusion magnetic resonance imaging.

Adult↗

PubMed2002

Novel methodology for the archiving and interactive reading of clinical magnetic resonance spectroscopic imaging.

Archiving clinical magnetic resonance spectroscopic imaging (MRSI) data and presenting the data to specialists (e.g., neuroradiologists, neurosurgeons, neurologists, neuro-oncologists, and MR scientists) who work in different physical locations is a practical problem of significance. This communication describes a novel solution. The study hypothesis was that it is possible to use widely available distributed computing techniques to create a clinical MRSI user interface addressable from any personal computer with a suitable network connection. A worldwide web MRSI archive and interface system was created that permits the user to interactively view individual MRSI voxel spectra with correlation to MR images and to parametric spectroscopic images. Web browser software (i.e., Netscape and Internet Explorer) permits users in various physical locations to access centrally archived MRSI data using a variety of operating systems and client workstations. The system was used for archiving and displaying more than 1000 clinical MRSI studies performed at the authors' institution. The system also permits MRSI data to be viewed via the Internet from distant locations worldwide. The study illustrates that widely available software operating within highly distributed electronic networks can be used for archiving and interactive reading of large amounts of clinical MRSI data.

Humans↗

PubMed2002

Brain responses associated with the Valsalva maneuver revealed by functional magnetic resonance imaging.

The Valsalva maneuver, a test frequently used to evaluate autonomic function, recruits discrete neural sites. The time courses of neural recruitment relative to accompanying cardiovascular and breathing patterns are unknown. We examined functional magnetic resonance imaging signal changes within the brain to repeated Valsalva maneuvers and correlated these changes with physiological trends. In 12 healthy subjects (age, 30-58 yr), a series of 25 volumes (20 gradient echo echo-planar image slices per volume) was collected using a 1.5-Tesla scanner during a 60-s baseline and 90-s challenge period consisting of three Valsalva maneuvers. Regions of interest were examined for signal intensity changes over baseline and challenge conditions in cardiorespiratory-related regions. In addition, whole brain correlations between signal intensity and heart rate and airway load pressure were performed on a voxel-by-voxel basis. Significant signal changes, correlated with the time course of load pressure and heart rate, emerged within multiple areas, including the amygdala and hippocampus, insular and lateral frontal cortices, dorsal pons, dorsal medulla, lentiform nucleus, and fastigial and dentate nuclei of the cerebellum. Signal intensities peaked early in the Valsalva maneuver within the hippocampus and amygdala, later within the dorsal medulla, pons and midbrain, and deep cerebellar nuclei, and last within the lentiform nuclei and the lateral prefrontal cortex. The ventral pontine signals increased during the challenge, but not in a fashion correlated to load pressure or heart rate. Sites showing little or no correlation included the vermis and medial prefrontal cortex. These data suggest an initiating component arising in rostral brain areas, a later contribution from cerebellar nuclei, basal ganglia, and lateral prefrontal cortex, and a role for the ventral pons in mediating longer term processes.

Adult↗

PubMed2002

Magnetic resonance imaging detection of microbleeds before thrombolysis: an emerging application.

BACKGROUND: Hemorrhagic transformation (HT) is a major complication of thrombolytic treatment for acute ischemic stroke. Although a history of prior intracerebral hemorrhage diagnosed by head CT is a contraindication to thrombolysis, there are no guidelines or data regarding evidence of prior asymptomatic microbleeds visualized with T2*-weighted magnetic resonance imaging (MRI). METHODS: Pretreatment T2*-weighted MRI sequences were retrospectively analyzed in all patients receiving intra-arterial thrombolytic therapy and undergoing a pretreatment MRI at our institution. The frequency and location of prior microbleeds was determined and compared with the frequency and location of secondary HT after therapy. RESULTS: Five of 41 patients undergoing MRI before receiving intra-arterial thrombolytic therapy demonstrated evidence of prior microbleeds on the pretreatment MRI studies. Major symptomatic hemorrhage occurred in 1 of 5 patients with microbleeds compared with 4 of 36 patients without. Only 1 patient in the entire 41-patient cohort experienced any HT outside the acute ischemic field. In this patient, the symptomatic hemorrhage occurred directly at the site of a prior microbleed, contralateral to the acute ischemic event. CONCLUSIONS: Old silent microbleeds, visualized with T2*-weighted MRI sequences, may be a marker of increased risk of HT in patients receiving thrombolytic therapy for acute ischemic stroke. Pretreatment screening of thrombolytic candidates with these MRI sequences may be useful in the future to identify these patients.

Acute Disease↗