Biomedical subjects

R R Rizi

Publications and source records attributed to R R Rizi.

10 recordsLinked to original sources

PubMed2005

Quantitative assessment of emphysema using hyperpolarized 3He magnetic resonance imaging.

In this experiment, Sprague-Dawley rats with elastase-induced emphysema were imaged using hyperpolarized (3)He MRI. Regional fractional ventilation r, the fraction of gas replaced with a single tidal breath, was calculated from a series of images in a wash-in study of hyperpolarized gas. We compared the regional fractional ventilation in these emphysematous rats to the regional fractional ventilations we calculated from a previous baseline study in healthy Sprague-Dawley rats. We found that there were differences in the maps of fractional ventilation and its associated frequency distribution between the healthy and emphysematous rat lungs. Fractional ventilation tended to be much lower in emphysematous rats than in normal rats. With this information, we can use data on fractional ventilation to regionally distinguish between healthy and emphysematous portions of the lung. The successful implementation of such a technique on a rat model could lead to work toward the future implementation of this technique in human patients.

Animals↗

PubMed2004

A small animal model of regional alveolar ventilation using HP 3He MRI1.

RATIONALE AND OBJECTIVES: The aim of this study was to establish a standardized procedure for the measurement of regional fractional ventilation in a healthy rat model as a baseline for further studies of pulmonary disorder models. MATERIALS AND METHODS: The lungs of five healthy male Sprague-Dawley rats were imaged using hyperpolarized helium-3 magnetic resonance imaging. From these images, regional fractional ventilation was calculated and maps generated detailing the distribution of fractional ventilation in the lung. The 1.56 mm x 1.56 mm x 4 mm regions of interest were assigned on 5 cm x 5 cm field of view lung maps. Histograms were also generated showing the frequency distribution of fractional ventilation values. To compare fractional ventilation values between animals, the ventilation procedure was standardized to results from individual pulmonary function tests. Each animal's spontaneous tidal volume, respiratory rate, and inspiration percentage (percent of total respiratory cycle in inspiration) were used in their mechanical ventilation settings. RESULTS: Results were similar among all five healthy rats based on examination of ventilation distribution maps and frequency distribution histograms. Mean (0.13) and standard deviation (0.07) were calculated for fractional ventilation in each animal. However, these values were determined to be influenced by slice selection, and therefore the maps and histograms were favored in analysis of results. CONCLUSION: This study shows consistent results in healthy rat lungs and will serve as a baseline study for future measurements in emphysematous rat lungs.

Animals↗

PubMed2001

Dynamic observation of pulmonary perfusion using continuous arterial spin-labeling in a pig model.

The continuous arterial spin-labeling (CASL) method of perfusion MRI is used to observe pulmonary perfusion dynamically in an animal model. Specifically, a respiratory-triggered implementation of the CASL method is used with approximate spatial resolution of 0.9 x 1.8 x 5.0 mm (0.008 cc) and 2-minute temporal resolution. Perfusion MRI is performed dynamically during repeated balloon occlusion of a segmental pulmonary artery, as well as during pharmacological stimulation. A total of three Yorkshire pigs were studied. The results demonstrate the ability of the endogenous spin-labeling method to characterize the dynamic changes in pulmonary perfusion that occur during important physiological alterations.

Animals↗

PubMed2000

Demonstration of a compact compressor for application of metastability-exchange optical pumping of 3He to human lung imaging.

Hyperpolarized gas magnetic resonance imaging has recently emerged as a method to image lungs, sinuses, and the brain. The best lung images to date have been produced using hyperpolarized 3He, which is produced by either spin-exchange or metastability-exchange optical pumping. For hyperpolarized gas MRI, the metastable method has demonstrated higher polarization levels and higher polarizing rates, but it requires compression of the hyperpolarized gas. Prior to this work, compression of hyperpolarized gas had only been accomplished using a large, complex and expensive apparatus. Here, human lung ventilation images are presented that were obtained using a compact compressor that is relatively simple and inexpensive. For this test, 1.1 bar-L of 15% hyperpolarized 3He gas was produced at the National Institute of Standards and Technology using a modified commercial diaphragm pump. The hyperpolarized gas was transported to the University of Pennsylvania in a holding field provided by a portable solenoid.

Adult↗

PubMed2000

Intermolecular zero-quantum coherence imaging of the human brain.

The first intermolecular zero-quantum coherence (iZQC) MR images of the human brain at 4T are presented. To generate iZQC images, a modified echo-planar imaging pulse sequence was used which included an additional 45 degrees RF pulse and a correlation gradient. The observability and nonconventional contrast of human brain iZQC images at 4T is demonstrated. Axial images are presented for various pulse sequence parameters, and a zero-quantum relaxation map is obtained.

Brain↗

PubMed2000

Detection and localization of pulmonary air leaks using laser-polarized (3)He MRI.

Pulmonary air leaks were created in the lungs of Yorkshire pigs. Dynamic, 3D MRI of laser-polarized (3)He gas was then performed using a gradient-echo pulse sequence. Coronal magnitude images of the helium distribution were acquired during gas inhalation with a voxel resolution of approximately 1.2 x 2.5 x 8 mm, and a time resolution of 5 sec. In each animal, the ventilation images reveal focal high-signal intensity within the pleural cavity at the site of the air leaks. In addition, a wedge-shaped region of increased parenchymal signal intensity was observed adjacent to the site of the air leak in one animal. (3)He MRI may prove helpful in the management of patients with pulmonary air leaks.

Administration, Inhalation↗

PubMed1999

Pulmonary perfusion: respiratory-triggered three-dimensional MR imaging with arterial spin tagging--preliminary results in healthy volunteers.

The authors used a spin-tagging method of magnetic resonance perfusion imaging to measure pulmonary perfusion in eight healthy volunteers with use of a respiratory-triggered three-dimensional pulse sequence. The average signal intensity (SI) decrease upon arterial labeling was 24%. The perfusion SI increased by 21% after exercise (P = .02). Focal blood flow abnormalities were observed in a patient with chronic obstructive pulmonary disease.

Adult↗

PubMed1998

MR imaging contrast enhancement based on intermolecular zero quantum coherences.

A new method for magnetic resonance imaging (MRI) based on the detection of relatively strong signal from intermolecular zero-quantum coherences (iZQCs) is reported. Such a signal would not be observable in the conventional framework of magnetic resonance; it originates in long-range dipolar couplings (10 micrometers to 1 millimeter) that are traditionally ignored. Unlike conventional MRI, where image contrast is based on variations in spin density and relaxation times (often with injected contrast agents), contrast with iZQC images comes from variations in the susceptibility over a distance dictated by gradient strength. Phantom and in vivo (rat brain) data confirm that iZQC images give contrast enhancement. This contrast might be useful in the detection of small tumors, in that susceptibility correlates with oxygen concentration and in functional MRI.

Animals↗

PubMed1998

MRI of hyperpolarized 3He gas in human paranasal sinuses.

In this study, MRI of hyperpolarized 3He gas in human paranasal sinuses is presented. Helium images were obtained at 1.5 T, using a surface coil and a 2D, fast gradient-echo sequence with a nominal constant flip angle of 12 degrees. Coronal images of 20-mm thick slices were generated and compared with proton images of the corresponding sections. The images enable visualization of the paranasal sinuses and the nasal cavity, suggesting a potential use of this method not only in identifying the anatomical configuration of these pneumatic spaces, but also in assessing sinus ventilation.

Adult↗

PubMedDate not supplied

Proton T1rho-dispersion imaging of rodent brain at 1.9 T.

Detection of H2(17)O with proton T1rho-dispersion imaging holds promise as a means of quantifying metabolism and blood flow with MRI. However, this technique requires a priori knowledge of the intrinsic T1rho dispersion of tissue. To investigate these properties, we implemented a T1rho imaging sequence on a 1.9-T Signa GE scanner. A series of T1rho images for different locking frequencies and locking durations were obtained from rat brain in vivo and compared with 5% (wt/vol) gelatin phantoms containing different concentrations of (17)O ranging from .037% (natural abundance) to 2.0 atom%. Results revealed that, although there is considerable T1rho-dispersion in phantoms doped with H2(17)O, the T1rho of rat brain undergoes minimal dispersion for spin-locking frequencies between .2 and 1.5 kHz. A small degree of T1rho dispersion is present below .2 kHz, which we postulate arises from natural-abundance H2(17)O. Moreover, the signal-to-noise ratios of T1rho-weighted images are significantly better than comparable T2-weighted images, allowing for improved visualization of tissue contrast. We have also demonstrated the feasibility of proton T1rho-dispersion imaging for detecting intravenous H2(17)O on a live mouse brain. The potential application of this technique to study brain perfusion is discussed.

Animals↗