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H Jara

Publications and source records attributed to H Jara.

At least 19 recordsLinked to original sources
PubMed1999

Voxel sensitivity function description of flow-induced signal loss in MR imaging: implications for black-blood MR angiography with turbo spin-echo sequences.

The conditions in which the image intensity of vessels transporting laminar flow is attenuated in black-blood MR angiography (BB-MRA) with turbo spin-echo (TSE) and conventional spin-echo (CSE) pulse sequences are investigated experimentally with a flow phantom, studied theoretically by means of a Bloch equation-voxel sensitivity function (VSF) formalism, and computer modeled. The experiments studied the effects of: a) flow velocity, b) imaging axes orientation relative to the flow direction, and c) phase encoding order of the TSE train. The formulated Bloch equation-VSF theory describes flow effects in two-dimensional (2D)- and 3D-Fourier transform magnetic resonance imaging. In this theoretical framework, the main attenuation mechanism instrumental to BB-MRA, i.e., transverse magnetization dephasing caused by flow in the presence of the imaging gradients, is described in terms of flow-induced distortions of the individual voxel sensitivity functions. The computer simulations predict that the intraluminal homogeneity and extent of flow-induced image intensity attenuation increase as a function of decreasing vessel diameter, in support of the superior image quality achieved with TSE-based BB-MRA in the brain.

Blood Flow Velocity↗
PubMed1999

MR cholangiopancreatography techniques.

The tissue contrast principles and the technical aspects involved in the design of the imaging protocols currently used for clinical MR cholangiopancreatography are reviewed using a neutral terminology that is applicable to most of the high-field MRI equipment available from the major manufacturers. Furthermore, the technical discussions that follow are accompanied by a comprehensive set of tables listing the pulse sequence parameters used by the authors of the other articles in this issue. The tables are organized according to groups of parameters that determine the fundamental features of the protocols and of the generated images, specifically motion artifact reduction technique, scan geometry, image contrast, and recommended image post processing algorithm.

Algorithms↗
PubMed1999

Use of three-dimensional MR angiography for tracking a contrast bolus in the carotid artery.

Contrast-bolus tracking in the carotid bifurcation was accomplished using an MR angiographic technique with a 3D turbo field-echo readout (TR/TE = 6/3, flip angle = 50 degrees) modified by a keyhole scheme. Optimal visibility of the contrast bolus was achieved by digital subtraction from a reference volume. This technique reliably time-resolves the carotid arteries from the jugular veins.

Adult↗
PubMed1999

Motion artifact control in body MR imaging.

The mechanisms involved in the generation of motion artifacts in MR imaging are complex and depend both on the type and direction of motion as well as on the parameters of the imaging sequence chosen. The methods used to control or reduce motion artifacts are multiple and the appropriate method for use with any given clinical situation will depend on the particular hardware and software of the MR imaging unit, the patient's clinical status, and the specific organ or disease state to be imaged. Some general guidelines for clinical use that are applicable in most scenarios can be defined, although preferences for the different techniques vary. Appropriate T1-weighted images of the upper abdomen and liver can be obtained with breath-hold T1-weighted gradient echo. These images should be acquired with inferior-superior spatial presaturation pulses to reduce vascular pulsation artifact and ghosting. The application of GMN will depend on the individual MR imaging system. If sufficient coverage cannot be obtained with gradient-echo imaging, then conventional T1-weighted images with phase-encoding reordering is suggested. The addition of spatial presaturation pulses (inferior-superior) may be valuable. The use of fat suppression will further improve image quality by reducing ghost artifact and improving CNR, although SNR will decrease. T2-weighted imaging of the upper abdomen will depend greatly on the hardware and software of the MR imaging unit. Recent techniques of breath-hold T2-weighted imaging require faster and stronger gradients, and may not be universally available. If available, these techniques provide excellent anatomic detail, although image contrast (e.g., liver to spleen) may decrease. Respiratory-triggered FSE techniques are the preferred method of imaging in most centers, because the imaging time is considerably less than conventional T2-weighted imaging whereas the image quality is improved. Liver lesion detection capability of the various techniques is still under study. The addition of fat suppression appears to improve image quality further with an increase in lesion detection. By understanding the principles underlying motion artifacts, one can choose the appropriate method of artifact control tailored for the individual clinical situation. In addition, the recognition of the variable appearances of motion artifacts will prevent interpretive errors and misdiagnoses. Careful attention to motion artifact reduction techniques can greatly improve patient care.

Artifacts↗
PubMed1999

Black-blood MR angiography. Techniques, and clinical applications.

As there are limitations in WB-MR angiography, so there are limitations in BB-MR angiography. Vessel morphology is visualized by means of the innermost nonattenuated layer of tissue, which, under ideal conditions, coincides with the luminal surface of the vessel wall. Vessel morphology may be depicted inaccurately whenever a portion of the vessel wall is undetectable with the MR imaging technique used. In such cases, vessel segments with exaggerated lumen diameter may result at locations where tissues with either a very short T2 or a low proton density are present. Another phenomenon that could potentially degrade the accuracy of vessel depiction with BB techniques is the effect of slowly flowing blood near the vessel walls. Residual blood signal would result in apparent vessel narrowing. Preliminary clinical experience in the brain, however, suggests that this adverse effect is less prominent with a turbo-SE-based BB technique than with a TOF WB technique. BB-MR angiography data sets may also present image postprocessing difficulties arising from the isointensity between the vessels and other dark structures such as bones and air-filled cavities. A limitation that is more specific to hybrid-SE-based BB-MR pulse sequences, particularly for very high spatial resolution applications, stems from the comparatively high RF specific absorption rates that result from the intensive use of 180 degrees refocusing pulses. GRASE-based BB-MR techniques that generate a fraction of the RF energy constitute a promising alternative for very high spatial resolution applications. In summary, to be effective, a BB technique must produce strong signal attenuation from flowing spins, ideally to the level of the baseline noise. Simultaneously it should produce good depiction of tissues with the comparatively short T2s characteristic of vessel walls and muscle, hence the need to operate with the shortest possible TE. Finally, high spatial resolution combined with fast data acquisition are requisites for imaging small vessels in the presence of motion, such as the carotid arteries. The flow properties of BB-MR angiographic sequences that meet these criteria were reviewed for different anatomic locations.

Humans↗
PubMed1998

The serotonin uptake-enhancing drug tianeptine suppresses asthmatic symptoms in children: a double-blind, crossover, placebo-controlled study.

Studies have shown that levels of free serotonin in plasma are increased in symptomatic patients with asthma. In addition, the concentration of free serotonin in symptomatic patients with asthma correlates positively with clinical status and negatively with pulmonary function. Thus, reducing the concentration of free serotonin in plasma might be useful in treating patients with asthma. We studied the effectiveness of tianeptine in treating patients with asthma. Tianeptine is the only drug known to be able to reduce levels of free serotonin in plasma and to enhance uptake by platelets. In this study, 69 children with asthma were assigned in randomized fashion to receive tianeptine and/or placebo in a double-blind crossover trial that lasted 52 weeks. Tianeptine provoked a dramatic and sudden decrease in both clinical rating and free serotonin plasma levels and an increase in pulmonary function.

Adolescent↗
PubMed1998

Effects of buspirone on plasma neurotransmitters in healthy subjects.

Buspirone is an anxiolytic drug which exerts several central effects. It antagonizes presynaptic inhibitory DA2 autoreceptors at dopaminergic neurons and acts as an agonist for 5-HT1A inhibitor autoreceptors at serotonergic cells. Thus, buspirone respectively enhances and depresses the firing rates of both type of neurons. At doses which correlate with dopaminergic stimulation, but not 5-HT inhibition, buspirone also increases the firing rates of the central noradrenergic cells. We measured levels of circulating neurotransmitters before and up to 240 minutes after the oral administration of 20 mg of buspirone in 32 healthy volunteers. Buspirone significantly increased levels of noradrenaline, dopamine, and free serotonin but did not affect levels of adrenaline, tryptophane, or platelet serotonin. Small but significant drops in systolic blood pressure and heart rate were observed after buspirone ingestion. Atropine administration before buspirone ingestion annulled the free serotonin increase as well as systolic blood pressure-heart rate decrease. We found significant positive correlations between noradrenaline and dopamine levels. The strength and significance of these correlations were increased by using the noradrenaline/adrenaline ratio instead of noradrenaline absolute values. This finding indicates that increases in both noradrenaline and dopamine arise from sympathetic nerves rather than the adrenal glands. We also found significant negative correlations between free serotonin increases and systolic blood pressure-heart rate decreases. Our results indicate that buspirone stimulates central sympathetic activity. These acute effects of buspirone are reflected in an increased peripheral neural sympathetic activity, but not adrenal sympathetic activity in healthy individuals. In addition, buspirone increases free serotonin plasma concentrations and decreases systolic blood pressure plus heart rate levels through mechanisms associated with parasympathetic activation.

Adult↗
PubMed1998

Neuropharmacologic treatment of bronchial asthma with the antidepressant tianeptine: a double-blind, crossover placebo-controlled study.

Studies have shown the levels of free serotonin in plasma are increased in symptomatic patients with asthma. In addition, the concentration of free serotonin in symptomatic children with asthma correlates positively with clinical status and negatively with pulmonary function (forced expiratory volume in 1 second [FEV1]). Thus, reducing the concentration of free serotonin in plasma may be useful in treating children with asthma. We studied the effectiveness of tianeptine in treating these patients. Tianeptine is the only drug known to be able to reduce the level of free serotonin in plasma and to enhance the uptake by platelets. Sixty-nine of the 82 children with asthma initially enrolled participated in this study. Children were randomized to receive tianeptine or placebo or both in a double-blind crossover trial. The trial lasted 52 weeks. Tianeptine provoked a dramatic and sudden decrease of both clinical rating and free serotonin plasma levels and an increase in pulmonary function.

Adolescent↗
PubMed1998

Cervical spine: three-dimensional MR imaging with magnetization transfer prepulsed turbo field echo techniques.

In 11 volunteers, magnetic resonance (MR) imaging of the cervical spine was performed with a magnetization transfer preparatory pulse (prepulsed), three-dimensional Fourier transform, turbo field echo sequence. The effects of flip angle, number of shots, phase-encoding profile order, and magnetization transfer prepulse offset frequency on cerebrospinal fluid-to-cord contrast were evaluated. The contrast was improved by lowering the flip angle, increasing the number of shots, and implementing a magnetization transfer prepulse and linear phase-encoding profile order. Maximum myelographic effect was achieved with the magnetization prepulse (500-Hz frequency offset), 3 degrees flip angle, six shots, and linear phase-encoding profile order.

Adult↗
PubMed1998

MR imaging of hemorrhagic brain lesions: a comparison of dual-echo gradient- and spin-echo and fast spin-echo techniques.

OBJECTIVE: Our objective was to assess the usefulness of the dual-echo gradient- and spin-echo (GRASE) technique in revealing acute hemorrhagic brain lesions and compare GRASE and fast spin-echo techniques for revealing acute hemorrhagic lesions and image artifacts. MATERIALS AND METHODS: Thirty-two consecutive patients with acute intracranial hemorrhage underwent dual-echo GRASE (TEeff1/TEeff2, 35/85) and fast spin-echo (25/110) imaging. The techniques were matched for TR (3032 msec), spatial resolution, and acquisition time. Two neuroradiologists reviewed the images independently, documenting the number, size (<1, >1, or 1 cm in diameter), location, and signal characteristics (hypointense versus hyperintense compared with brain) of detectable lesions. These observers also compared matched T2- and proton density-weighted GRASE and fast spin-echo images for paramagnetic lesion conspicuity, diamagnetic susceptibility artifacts, chemical shift artifacts along the phase- and frequency-encoding directions, and artifactual CSF hyperintensity in the thin curvilinear cortical sulci and the Virchow-Robin spaces on only the proton density-weighted images. RESULTS: The average number and conspicuity of dark (paramagnetic) lesions were significantly greater on GRASE than on fast spin-echo images (p < .05 and p < .001, respectively). We found no significant difference in the average number of bright lesions revealed by either technique (p > .1). Chemical shift artifacts along the phase-encoding directions were more prominent on GRASE than on fast spin-echo imaging. Chemical shift artifacts along the frequency-encoding directions and artifactual CSF hyperintensity were more prominent on fast spin-echo than on GRASE imaging. No visually apparent difference was found in the degree of diamagnetic susceptibility artifacts seen with the two techniques. CONCLUSION: Dual-echo GRASE imaging can be helpful in the examination of patients with suspected acute brain hemorrhage.

Adult↗
PubMed1997

MR imaging of soft tissues adjacent to orthopaedic hardware: techniques to minimize susceptibility artefact.

This article demonstrates and compares imaging of orthopaedic hardware (fixation plates, screws, Kischner wire and prostheses) using gradient-echo, spin-echo and fast spin-echo sequences. It describes simple techniques which minimize susceptibility artefact induced by these components at magnetic resonance (MR) imaging, allowing visualization of adjacent soft tissues. The article emphasizes the importance of selecting the appropriate imaging plane in order to avoid hardware distortion of slice select gradients, emphasizes the importance of selecting frequency encoding gradient axes in order to orientate the long axis of the artefact away from the tissue of interest and, finally, compares the marked susceptibility artefact observed adjacent to hardware using gradient-echo with the artefact reduction achieved by using fast spin-echo sequences.

Artifacts↗
PubMed1997

T2-weighted MR imaging of the liver: optimization of hybrid-RARE sequences.

The objectives of this study were to optimize T2-weighted hybrid-RARE pulse sequences for clinical MR imaging of the liver, and to compare them to the conventional spin-echo (CSE) sequence. Specifically, the ranges of the echo train length (ETL) and the effective echo time (TEeff) were investigated to optimize image quality and liver-spleen contrast, in healthy volunteers. A total of thirteen volunteers were scanned at 1.5 Tesla with an extensive array of hybrid-RARE scans. The images were analyzed quantitatively with respect to CNR (contrast-to-noise ratio of spleen vs. liver), SNR (signal to noise ratio of the spleen), SIR (signal intensity ratio of liver and spleen) and CDR (contrast difference ratio between the spleen and liver). The images were also analyzed qualitatively with respect to image sharpness, vascular artifacts, ghosting, chemical shift, and truncations. Results of quantitative analysis indicated that CDR and SIR of hybrid-RARE at higher ETL (> 13) were consistently better than both the reference CSE and the lower ETL sequences (p < 0.05) at all TEeff. SNR was slightly inferior for all hybrid-RARE sequences than for the CSE sequence. Image quality for hybrid-RARE sequences with ETL > 13 proved to be consistently better than that for the CSE (TE = 90 ms) with respect to imaging sharpness, vascular artifacts and ghosting artifacts (p < 0.05). In conclusion, the optimized hybrid-RARE sequences with ETL greater than or equal to 13 are capable of producing sharp and relatively artifact free images with the advantage of a much greater acquisition time efficiency.

Adult↗
PubMed1997

Improved contrast of enhancing brain lesions using contrast-enhanced T1-weighted fast spin-echo MR imaging.

OBJECTIVE: The purpose of this study was to evaluate the ability of T1-weighted fast spin-echo MR sequences to provide improved contrast-to-noise ratios for contrast-enhanced lesions during acquisition times shorter than those used for conventional T1-weighted spin-echo MR sequences. SUBJECTS AND METHODS: We compared contrast-to-noise ratios of 32 enhancing brain lesions in 25 patients on T1-weighted spin-echo (546/10 [TR/TE]; two excitations; acquisition time, 4 min 12 sec) and on fast spin-echo (546/10 [TR/effective TE]; echo-train length, 4; echo spacing, 10 msec; two excitations; acquisition time, 1 min 45 sec) MR images obtained at 1.5 T after i.v. administration of 0.10 mmol/kg gadopentetate dimeglumine. RESULTS: The contrast-enhanced T1-weighted fast spin-echo MR images showed approximately a 12% reduction in the signal-to-noise ratios of the background white matter without an accompanying reduction in the signal-to-noise ratios of the enhancing lesions or CSF when compared with the contrast-enhanced T1-weighted spin-echo MR images. The contrast-enhanced T1-weighted fast spin-echo MR images provided a 23% improvement in the contrast-to-noise ratios of enhancing lesions over the contrast-enhanced T1-weighted spin-echo images (p < .001). CONCLUSION: Contrast-enhanced T1-weighted fast spin-echo MR imaging showed a statistically significant improvement in contrast-to-noise ratios at much shorter scan times than those used in conventional contrast-enhanced T1-weighted spin-echo MR imaging.

Adult↗
PubMed1997

Fluid-attenuated inversion recovery MR imaging: identification of protein concentration thresholds for CSF hyperintensity.

OBJECTIVE: Using human volunteers and phantoms emulating CSF, we analyzed the effects of varying protein concentration on the signal intensity of saline solution. Also, for different fluid-attenuated inversion recovery (FLAIR) sequences, we compared protein concentration thresholds above which the signal from these solutions becomes hyperintense to that from brain parenchyma. SUBJECTS AND METHODS: Nine albumin solutions of varying concentrations (3.9 mg/dl to 2500 mg/dl) were imaged using fast FLAIR MR sequences (TR, 6000 msec: inversion time, 1730 msec: echo train length, 20) at different effective TEs (110, 150, 200, and 250 signal-to-noise ratios from the different albumin solutions versus albumin concentration were generated and correlated with average signal-to-noise ratios from brain parenchyma and CSF. RESULTS: We saw a gradual increase in signal-to-noise ratios from the albumin solutions as a function of albumin concentration. As the effective TE increased, the point of intersection between the plots and the average signal-to-noise ratio from brain parenchyma occurred at lower albumin concentrations. CONCLUSION: FLAIR MR imaging is potentially useful to evaluate pathologic conditions that increase CSF protein concentration. Using phantoms and healthy volunteers, we defined a protein concentration threshold above which the signal from saline solutions becomes hyperintense to that from brain parenchyma. This threshold depends on the effective TE used in the FLAIR sequence and is 250 mg/dl for an effective TE of 110 msec, 125 mg/dl for 150 msec. 110 mg/dl for 200 msec, and 95 mg/dl for 250 msec.

Adult↗