A Ventilator for Magnetic Resonance Imaging

ArticleinInvestigative Radiology 21(1):18-23 · February 1986with8 Reads
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.
    • "We performed phantom studies to validate the accuracy of the phase selection in our FPG implementation. We constructed a phantom consisting of a plastic container filled with a dense liquid soap solution, in which we immersed a balloon connected to a mechanical ventilator system (Hedlund et al., 1986). We adjusted the exhalation/inhalation ratio of the ventilator to set the inflation/deflation cycle of the balloon at a rate of 200 cycles/minute. "
    [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.
    Full-text · Article · Dec 2011
    • "The nature of the design and control of this valve allows us to generate a wide variety of breathing patterns that can be accurately synchronized to image acquisition. The current ventilator is based on one described earlier (Hedlund et al. 1986a) and has been subsequently modified for the small animal (Hedlund et al. 1996; Shattuck et al. 1997). Our current ventilator (Hedlund et al. 2000a,b) is shown schematically inFigure 3 . "
    [Show abstract] [Hide abstract] ABSTRACT: This review emphasizes some of the challenges and benefits of in vivo imaging of the small animal lung. Because mechanical ventilation plays a key role in high-quality, high-resolution imaging of the small animal lung, the article focuses particularly on the problems of ventilation support, control of breathing motion and lung volume, and imaging during different phases of the breathing cycle. Solutions for these problems are discussed primarily in relation to magnetic resonance imaging, both conventional proton imaging and the newer, hyperpolarized helium imaging of pulmonary airways. Examples of applications of these imaging solutions to normal and diseased lung are illustrated in the rat and guinea pig. Although difficult to perform, pulmonary imaging in the small animal can be a valuable source of information not only for the normal lung, but also for the lung challenged by disease.
    Full-text · Article · Feb 2002
    • "The effects of various combinations of a heating rate are shown inFig. 4. Animal and Imaging Study: Animals (rats 140–350 g, guinea pigs 250–550 g, ferrets 250–300 g, and mice 25–40 g) were anesthetized with methohexital sodium, intubated with an endotracheal tube, and maintained on a MR-compatible ventilator with isoflurane anesthesia [3], [7]. More detailed description of animal preparation methods can be found in several publications [8]–[12]. "
    [Show abstract] [Hide abstract] ABSTRACT: A temperature control system consisting of a thermistor, signal processor, and computer algorithm was developed for magnetic resonance (MR) microscopy of small live animals. With control of body temperature within +/- 0.2 degree C of the set point, heart rate is stabilized and, in turn, repetition time (TR) during cardiac-gated studies is less variable. Thus, image quality and resolution are improved.
    Full-text · Article · Dec 1997
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