OHSU

MRI

MRIThe magnetic resonance imaging (MRI) core provides ONPRC investigators with equipment and assistance to perform MRI exams of sedated NHP subjects.  As a satellite facility of the OHSU Advanced Imaging Research Center (AIRC), infrastructure and technical support exist to customize MRI investigations so that researchers can take advantage of the close similarity between human and NHP anatomy and physiology to develop new MRI research and diagnosis techniques and applications.

The ONPRC MRI building is a 2500 sq. ft. facility, housing a Siemens Magnetom Trio 3 T whole-body MR instrument.  In the fall of 2010, the MRI system was upgraded with Total imaging matrix (Tim) technology. 

The radio frequency (RF) transmitter unit contains one 35kW narrowband (1H) RF transmitter and one 8 kW broadband RF transmitter capable of covering 20‑128MHz. The instrument is equipped with a SONATA gradient coil set and a CASCADE gradient amplifier (2000V/500A for all three gradient axes). Together, they are capable of producing magnetic field gradients of ≥40 mT/m, with a slew rate of ≥200 T/(m*s), on all axes. The scanner is equipped with a wide array of RF coils; these include an integrated circularly polarized (CP) body coil, and transmit/receive (TR) CP specialized RF coils suitable for head, extremity, and wrist applications. Phased-array (PA) coils include a receive-only 12-channel head, and a 15-channel extremity (macaque head) coil.

The MRI facility is within 100 feet of the Animal Sciences Building to facilitate ease of access for NHP studies. A comprehensive MRI-compatible anesthesia delivery and physiological monitoring station is used to perform MRI measurements on NHP subjects while monitoring physiological parameters including respiration, arterial oxygenation, pulse rate, non-invasive blood pressure, respiration rate, end-tidal CO2 partial pressure, and ECG.

 

SERVICES

A. Magnetic resonance examination of sedated NHP subjects

In order to offer the ability to obtain MRI (or magnetic resonance spectroscopy, MRS) data from sedated NHP subjects to the wide pool of ONPRC scientific investigators, the ONPRC MRI core staff are capable of performing the following functions:

  1. Induction of anesthesia: Most NHP subjects are delivered to the MRI facility awake in portable cages. In this case, MRI core staff administer an initial anesthetic (such as ketamine, i.m.). Once unconscious, the subject is intubated and placed on inhaled anesthetic (isoflurane). Vital signs, arterial oxygenation, pulse rate, and end-tidal CO2 are monitored throughout the process of anesthesia induction.
  2. Positioning of animal within the MRI system: Depending on the application, there are several configurations possible for the MRI procedure. It is important to select an RF coil that maximizes sensitivity for each experiment. Once situated in the appropriate receiver on the MRI system table, physiological monitoring and control devices are attached to the study subject.
  3. Execution of the MRI protocol: Operator input is needed throughout an MRI exam, which typically lasts approximately one hour. Prior to the scan, the MRI exam protocol is designed. The operator guides the position of the acquired images relative to the subject position within the magnet, and makes adjustments to optimize image acquisition settings as needed.
  4. Monitoring the physiological status of the subject during the scan: Due to risks associated with sedation, one individual is needed to monitor the physiological status of the subject in the magnet at all times. Throughout the course of the MRI exam, this individual logs procedures associated with the MRI exam into the subjects history on the ONPRC IRIS database. Additionally, physiological indicators (at minimum pulse rate, arterial oxygenation, and respiration rate) are logged into the MRI facility database at regular intervals.
  5. Recovery from anesthesia: At the conclusion of the MRI exam, the subject is transferred from the magnet room to the animal preparation and recovery room. The subject is extubated, and its physiological status is monitored as it recovers from anesthesia. Once responsive, the animal is transferred to a portable cage, and monitored for at least 15 minutes before being returned to its home environment.
In the above, steps 3 and 4 occur simultaneously, therefore, a minimum of two individuals are needed to perform an MRI exam. For this reason, it is ONPRC MRI core policy that the investigator who requests the MRI scan provides a suitably trained individual to perform either step 3 or 4. A second purpose for this requirement is that individuals from the laboratory requesting the scan are present to ensure the appropriate execution of the MRI protocol.

B. Maintenance of a web-based calendar system/assurance of compliance with IACUC

Vincent Warren manages a web-based calendar system that ONPRC investigators access to reserve the MRI instrument. An approved institutional animal care and use committee (IACUC) protocol must be referenced in order for investigators to schedule MRI exams. After completion of the experiment, the calendar system is used to charge investigator accounts for use of the MRI instrument.

C. Safety and operator training sessions.

The AIRC staff offer monthly safety training sessions to familiarize ONPRC staff and scientists with the potential hazards of working in the presence of an MRI system, with its associated large magnetic field. Additionally, for researchers that are knowledgeable of the MRI procedures to be performed in their research quarterly MRI operator training is available through the AIRC staff.

D. Maintenance of the MRI system

Quality/assurance, management of a calendar system for scheduling the scanner, and billing responsibilities are shared between the ONPRC MRI core, and AIRC staff. These procedures conform to practices developed for the ONPRC MRI system, as well as three other MRI systems located on the OHSU main campus.

E. Hourly Scanner Fees

A table of the projected hourly scanner fees through the year 2014 is available to intramural investigators here.


CONTACTS

Christopher D. Kroenke, Ph D., Head

Technical Staff:

Vincent Warren,
The Advanced Imaging Research Center

MRI Safety Training (Required for access to the MRI facility):
Vincent Warren

MRI Operator Training:
Tom Barbara

FEEDBACK

Please send comments and suggestions to: AIRC_west@ohsu.edu