A ventilator for magnetic resonance imaging.

Duke University, Durham, North Carolina, United States
Investigative Radiology (Impact Factor: 4.45). 02/1986; 21(1):18-23. DOI: 10.1097/00004424-198601000-00003
Source: PubMed

ABSTRACT Breathing motion severely degrades the quality of magnetic resonance images (MRI) of the thorax and upper abdomen and interferes with the acquisition of quantitative data. To minimize these motion effects, we built an MRI compatible ventilator for use in animal studies. Solid state circuitry is used for controlling ventilation parameters. The ventilator can be triggered internally at frequencies of 0.1 to 30 Hz or it can be triggered externally such as by the MRI pulse sequence. When triggered by the scanner, ventilation is synchronized to occur between image data acquisitions. Thus, image data are obtained when there is no breathing motion and at a minimum lung volume when hydrogen density is maximum. Since the ventilator can be adjusted to operate at virtually any frequency from conventional to high frequency, ventilation can be synchronized to all commonly used repetition times (100 ms to 2000 ms or more; 600 to 30 breaths/min). Scan synchronous ventilation eliminates breathing motion artifacts from most imaging sequences (single and multiple spin echo and inversion recovery). Best image quality is obtained when scan synchronous ventilation is combined with cardiac gating. These methods are also useful for quantitative research studies of thoracic and abdominal organs.

  • [Show abstract] [Hide abstract]
    ABSTRACT: The alkylhalide 2-bromoethylamine hydrobromide (BEA) produces renal injury in rats that mimics analgesic-related renal injury in humans. Our purpose was to examine this injury, in vivo in rats, with magnetic resonance (MR) microscopy and correlate MR findings with findings from light microscopy of hematoxylin-eosin-stained sections. Rats (n = 48) were injected intravenously with BEA (150 mg/kg) or saline and imaged with MR 6, 48, and 336 hr later. The spin-spin relaxation time, T2, was measured from the cortex to the papilla. In other rats, we measured regional water content of the kidney. Renal injury was present 48 and 336 hr after BEA dosing based on increased renal organ weights, decreased urine specific gravity, and significant renal lesions (H & E). T2 was elevated in the inner stripe of the outer medulla in injured kidneys at 48 hr. The differences in T2 between cortex and outer medulla were also elevated 48 hr after BEA. In the inner medulla, there were no changes in T2 after BEA treatment. However, in all groups there were significant regional differences in T2. The value of T2 increased from outer to inner medulla and this gradient was directly correlated with water content. Thus, MR microscopy detected damage in the outer medulla after BEA injury but not the damage in the inner medulla. T2 appeared to reflect the water content in the different regions of the medulla. The noninvasive in vivo capability of MR microscopy, with its high sensitivity to tissue water, allows the toxicologist to monitor the progression and regression of toxic insult in the same animal. At present the technology is complicated. The precise and accurate measure of MR-sensitive parameters in live animals at microscopic resolution is difficult. However, as the technology matures, there will be significant improvements providing the toxicologist a unique in vivo tool.
    Fundamental and Applied Toxicology 05/1991; 16(4):787-797. DOI:10.1016/0272-0590(91)90164-Y
  • [Show abstract] [Hide abstract]
    ABSTRACT: To test the potential of 1.5 Tesla magnetic resonance imaging (MRI) for assessing the protein concentration of pleural effusions, five pleural fluid analogs (saline+0,2,4,6,8 g albumin/100 mL) and, for comparison, four saline dilutions of whole blood were evaluated in vitro. The relaxation rates (1/T1,1/T2) of albumin solutions were determined by 1.5 T spectroscopy (MRS) and correlated with albumin concentration (1/T1: slope 0.02, r+0.89, P<.05; 1/T2: slope 0.16, r = 0.997, P<.001). MRI studies of these solutions showed no significant correlation with 1/T1, but 1/T2 showed a positive correlation with albumin concentration (r = 0.98, P<.01). Both MRI relaxation rates were significantly correlated with blood concentration, and slopes were greater than for albumin solutions. These preliminary studies, demonstrating differences in correlation between relaxation rates and the concentration of albumin and blood, suggest that MRI has the potential for differentiating pleural effusions of different chemical composition. (C) Lippincott-Raven Publishers.
    Investigative Radiology 04/1987; 22(5). DOI:10.1097/00004424-198705000-00005 · 4.45 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Micro-CT is currently used in preclinical studies to provide anatomical information. But, there is also significant interest in using this technology to obtain functional information. We report here a new sampling strategy for 4D micro-CT for functional cardiac and pulmonary imaging. Rapid scanning of free-breathing mice is achieved with fast prospective gating (FPG) implemented on a field programmable gate array. The method entails on-the-fly computation of delays from the R peaks of the ECG signals or the peaks of the respiratory signals for the triggering pulses. Projection images are acquired for all cardiac or respiratory phases at each angle before rotating to the next angle. FPG can deliver the faster scan time of retrospective gating (RG) with the regular angular distribution of conventional prospective gating for cardiac or respiratory gating. Simultaneous cardio-respiratory gating is also possible with FPG in a hybrid retrospective/prospective approach. We have performed phantom experiments to validate the new sampling protocol and compared the results from FPG and RG in cardiac imaging of a mouse. Additionally, we have evaluated the utility of incorporating respiratory information in 4D cardiac micro-CT studies with FPG. A dual-source micro-CT system was used for image acquisition with pulsed x-ray exposures (80 kVp, 100 mA, 10 ms). The cardiac micro-CT protocol involves the use of a liposomal blood pool contrast agent containing 123 mg I ml(-1) delivered via a tail vein catheter in a dose of 0.01 ml g(-1) body weight. The phantom experiment demonstrates that FPG can distinguish the successive phases of phantom motion with minimal motion blur, and the animal study demonstrates that respiratory FPG can distinguish inspiration and expiration. 4D cardiac micro-CT imaging with FPG provides image quality superior to RG at an isotropic voxel size of 88 μm and 10 ms temporal resolution. The acquisition time for either sampling approach is less than 5 min. The radiation dose associated with the proposed method is in the range of a typical micro-CT dose (256 mGy for the cardiac study). Ignoring respiration does not significantly affect anatomic information in cardiac studies. FPG can deliver short scan times with low-dose 4D micro-CT imaging without sacrificing image quality. FPG can be applied in high-throughput longitudinal studies in a wide range of applications, including drug safety and cardiopulmonary phenotyping.
    Physics in Medicine and Biology 12/2011; 57(1):257-71. DOI:10.1088/0031-9155/57/1/257 · 2.92 Impact Factor