A Ventilator for Magnetic Resonance Imaging

Duke University, Durham, North Carolina, United States
Investigative Radiology (Impact Factor: 4.44). 02/1986; 21(1):18-23. DOI: 10.1097/00004424-198601000-00003
Source: PubMed


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.

7 Reads
  • Source
    • "However, it produces a big overshot due to the system react delay. When is large and is close to , the voltage output decays quickly and progressively decreases as approaches when (1) The effects of various combinations of a heating rate are shown in Fig. 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.
    IEEE Transactions on Biomedical Engineering 12/1997; 44(11):1107-13. DOI:10.1109/10.641338 · 2.35 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Optimization of the contrast-to-noise ratio (CNR) is described for microcirculation magnetic resonance (MR) imaging techniques based on flow-compensated/flow-dephased sequences, both with and without even-echo rephasing. The authors present the most advantageous manner of applying flow-dephased gradients, such that dephasing is maximal while diffusion losses are minimal. The theoretical considerations include phase, diffusion, echo time, and bandwidth in the determination of the optimal parameters for microcirculation imaging. Studies in phantoms consisting of stationary and flowing copper sulfate in Sephadex columns demonstrate the validity of the calculations. Optimized in vivo images of a rat stroke model demonstrate the potential of the flow-compensated/flow-dephased technique and the importance of optimizing CNR.
    Journal of Magnetic Resonance Imaging 1(1):39-46. · 3.21 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Magnetic resonance imaging sequences utilizing limited flip angles and gradient echoes yield rapid (less than 2 min) dynamic images of the cardiovascular system. These images contain both accurate anatomical and functional information. Using a gradient refocused acquisition in the steady state (GRASS) in the CINE mode, we studied the relationship between gradient echo signal intensity and velocity of steady and pulsatile flow in a phantom simulating medium to large vessels. Images were acquired on a 1.5 Tesla system (repetition time = 21 ms, echo time = 12 ms, flip angle = 30 degrees). Data from each pulse interval were sorted in 16 images. Signal intensities from flow tube lumina and surrounding stationary water jacket were used to calculate contrast ratios which were compared to velocity measurements made with electromagnetic (EM) flow probes outside the magnet room. During steady flow, signal intensity contrast ratios increased with increasing flow and in a 10 mm thick slice, reached a peak at 48 cm/s, and declined for velocities up to 90 cm/s. Changes in instantaneous velocity during pulsatile flow correlated well (r greater than .88) with signal intensity changes up to a maximum mean velocity of 17 cm/s. Total signal intensity from the lumen for an "R to R" interval correlated extremely well (r greater than .97) with mean pulsatile flow velocities up to 30 cm/s. The excellent correlation between gradient echo signal intensity and actual flow velocities suggests that this imaging sequence might be useful for evaluating normal and pathologic flow phenomena.
    Magnetic Resonance Imaging 02/1987; 5(6):475-82. DOI:10.1016/0730-725X(87)90382-1 · 2.09 Impact Factor
Show more

Similar Publications