MRI

The MR750 scanner has a main magnetic field strength of 3 Tesla and is equipped with fast water-cooled gradients (slew rate of 200 mT/ms, peak amplitude 50mT/m, 100% duty cycle) used for spatial encoding.  The MR 750 has 32 receive channels for improved multi-coil signal detection.  Currently quadrature head and extremity coils, 8 and 16 channel head coils and a surface coil are available.  We are awaiting delivery on a 32 channel coil from Nova Instruments which will provide increased SNR and parallel imaging capabilities.  The image reconstruction engine consists of two blade processors capable of reconstructing parallel image acquisitions during the scanning session allowing the operator to assess image quality in near real time.  The scanner has the ability to run in research mode, allowing modified research sequences both from in-house and external collaborators to be used in addition to the standard GE pulses sequences already provided.   Real-time AFNI is used to monitor head motion in real-time.  Synchronization and triggering signals are logged by the Biopac system described below.

Stimulus presentation can be delivered by using an advanced fiber optic goggle system (Avotec), the high resolution Visuastim XGA system (Resonance Technology), or using back-projection with an LCD projector and a screen at the end of the patient table.  The Avotec fiber optic goggles are interfaced with SensoMotoric Instruments eye tracking system (sampling rate of 50 Hz). This eye tracking system yields four different analyses: percentage analysis, pictorial analysis, order of object vs. time, and pupil diameter vs. time.  

MRI auditory stimulus is presented using a pneumatic headphone system (Avotec) or the SereneSound system (Resonance Technology) that creates a frequency response of 40 Hz to 40 kHz.  All auditory stimuli are presented through a digital equalizer that is optimized for tone and clarity. 

Stabilizing patients to minimize head movement is critical for MRI studies.  The Brain Imaging Core has three head stabilizing methods: bite bars, vacuum pillow, and foam inserts.   

Collection of peripheral, physiological measures in the MRI are done using the Biopac MP150 system. The MP150 system provides high resolution (16 bit), variable sample rates for analog and calculation channels, 16 analog inputs and two analog outputs, digital I/O lines (automatically control other TTL level equipment), and 16 online calculation channels. The MP150 System provides high-speed acquisition (400 kHz aggregate) via an Ethernet connection to a host computer.  AcqKnowledge, the Biopac control and analysis software package, is used to control the acquisition and can be used for data analysis.  

Electrodermal activity is acquired in the MRI using the Biopac amplifier and two 6mm Ag-AgCL non-polarizable electrodes placed on the tips of the second and third fingers. 

Facial electromyography is acquired in the MRI using the Biopac amplifier and two 3mm Ag-AgCL non-polarizable electrodes placed over the right or left corrugator supercilli muscle (small narrow pyramidal muscle at the medial end of the eyebrow beneath the frontalis and obicularis oculi); zygomatic corrugator muscle activity is recorded via two electrodes over the right or left cheek muscle with a third electrode applied over the ipsilateral mastoid to serve as an electrical ground. 

Electrocardiogram activity is acquired in the MRI using the Biopac amplifier and three Ag-AgCl lead electrodes, using Einthoven’s triangle potential measurement strategy.

Blood oxygen saturation levels are acquired in the MRI using the Biopac amplifier and a receiving photodiode.  The amplifier transmits two wavelengths of light via LEDs through a pulsating vascular bed (finger).

Skin temperature is acquired in the MRI using the Biopac amplifier and a thermistor transducer.  This amplifier includes a lower frequency response selection switch that permits either absolute (DC) or relative (via a 0.05 highpass filter) temperature measurement.

Carbon Dioxide gas analysis is done in the MRI using the Biopac amplifier and a gas sampling interface kit.  This amplifier records varying carbon dioxide concentration levels employing a single beam infrared, single wavelength, measurement technique.

Respiration data is acquired in the MRI using the Biopac amplifier and a respiration transducer to measure abdominal or thoracic expansion and contraction.

Blood pressure is collected in the MRI using Magmedix’s non invasive Tesla blood pressure manometer.  Diastolic, mean, and heart rate can be acquired.  This monitor can be used on neonates, pediatric, and adult subjects (Adults:  Heart Rate: 30-220 BPM, Systolic NBP: 40-260 mmHg, Mean NBP: 20-200 mmHg, Diastolic NBP: 20-200 mmHg, Static Cuff Accuracy +/- 3mmHg).

In addition, respiration and pulse oximetry data collected by the scanner can be acquired via a serial interface.

To acclimate patients to the unique environment of the MRI scanner, the Brain Imaging Core of the IDDRC houses a simulator room. This room has a mock MRI scanner, another Avotec fiber optic goggle system with eye tracking, and auditory system with two control computers.   This room is used to introduce subjects to the identical experimental procedures that they will experience in the actual scanner.  This is done to ensure subject comfort and data quality.