The scanner, a 3.0 Tesla X750 GE Discovery, was installed in April 2009. Equipped with the most powerful gradients found in the industry, new water-cooled gradient amplifier and 64-bit data pipeline with dual blade processing. Custom pulse sequences are developed using GE's EPIC software development package. Brain imaging studies (fMRI, structural and DTI) are done using either a quadrature birdcage coil, 8-channel array head coil, or 16-channel array head coil.
Visual stimulation 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 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.
Auditory stimulus is presented using a pneumatic headphone system (Avotec). 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 lab has two head stabilizing methods: 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), and Ethernet connectivity. Controlling the Biopac is the software, AcqKnowledge. This software is an interactive program that lets lab members instantly view, measure, analyze, and transform the incoming data.
The MRI facilities are supported by a full-time physicist, imaging technologists, and research staff.
The laboratory houses a complete PET research facility, complementing the previously established PET research labs under the Medical Physics department. The scanning facilities consist of a Siemens ECAT EXACT HR+ PET scanner and its adjacent control room, subject prep room, and blood metabolite analysis lab. A dedicated particle accelerator (see below) and radiochemistry lab support the imaging experiments. The PET scanner room is also equipped with a positional computer monitor for performing computer tasks during the acquisition of the scans.
The EXACT HR+ scanner consists of 4 detector rings of 72 BGO blocks per ring. Each block contains an 8 x 8 array of discrete detector elements with dimensions of 4.39 x 4.05 x 30 mm3, providing 63 contiguous 2-D image planes through an axial field of view (FOV) of 15.5 cm and a patient port diameter of 56.2cm. The rings are separated by extendable tungsten septa for acquisition in both 2D and 3D modes. The transaxial intrinsic resolution of this scanner is 4.3 mm FWHM, and axial intrinsic resolution is 4.7 mm FWHM in the center of the field of view. Reconstructed spatial resolution for a head-shaped object is in a nearly isotropic resolution of 6mm FWHM throughout the entire region of the brain.
Data acquisition and processing is performed using the ECAT v7.2.2 software. For most research brain imaging applications, the data are acquired in 3D mode following a 3 minute transmission scan in 2D mode. The data are reconstructed using either filtered back projection or iterative algorithms, using brain mode sinogram trimming, zoom = 2.8, and a 4mm Gaussian filter to a reconstructed image of 128 x 128 x 63 voxel matrix (pixel size = 1.84mm x 1.84mm x 2.43mm ). The reconstructed data are also corrected for the attenuation of annihilation radiation (using segmented attenuation maps), scanner normalization and scatter radiation.
The microPET P4 small animal scanner (Siemens, Knoxville, TN) creates images with 6 microliter volumetric resolution. It is used routinely for in vivo PET brain imaging of rhesus macaques and rats. Stereotactic head holders are provided along with electronic vitals monitoring and isoflurane anesthesia equipment. In the scanner, scintilator crystals are arranged in 32 rings of 332 elements each, which provides 7.8 cm axial and 19 cm transaxial field of view with 2% sensitivity. Detector modules consisting of 8x8 arrays of 2.2 mm x 2.2 mm x 10 mm lutetium oxyorthosilicate (LSO) crystals are coupled to position sensitive photomultiplier tubes.
The LSO crystals have good light output and fast time response permitting 26% energy resolution and 3.2 ns timing resolution. Energy and timing windows are user selectable and typically set at 350 - 750 keV and 6 ns, respectively. Data are acquired in 3D list mode with the time and crystal pair position recorded for each coincidence event. Normalization and transmission scans are performed using a mechanism that carries a point source on a helical path. Lists are histogrammed into sinograms with post hoc dynamic framing. Sinograms are corrected for accidental coincidences and scaled to correct for radioactive decay and deadtime. Images are typically generated using filtered back projection (FBP) or ordered subset expectation maximization (OSEM) algorithms with 2D rebinning of the 3D sinograms. During reconstruction, histograms are normalized for detector sensitivity, and transmission-based attenuation and scatter corrections are applied.
Since most of the commonly used PET tracers have a short radioactive half-life, on-site production of the radioactive isotopes is required. The dedicated accelerator, a National Electrostatics Corporation 9SDH-2 electrostatic tandem accelerator, is adjacent to to the PET scanner and radiochemistry lab. It is capable of accelerating >100uA of protons or deuterons to 7 MeV with fine beam shaping and positioning capabilities, with high yield targetry systems for 11C, 13N, 14O, 18F, and newly developed PET radioisotopes such as 17F.
A research chemistry lab with dual fume hoods and a class 10,000 clean room with class 100 laminar flow hood are available for radiotracer production and radiopharmaceutical preparation. The lab is well equipped for continuous (in-line) production and delivery of short lived tracers. The facility includes separate animal handling and transport accommodations, including appropriate air handling considerations. Other support resources include: a fully equipped machine shop; developmental and diagnostic electronics apparatus; a clean stainless steel transfer line network for specialty gases and liquids, including radioactive and corrosive materials; and ample bench space for cutting edge instrumentation development and repair.
Our lab has extensive collaborations with the accelerator facilities in Medical Physics and the new WIMR facility, which can provide us with additional PET tracers. These facilities specialize in synthesizing large amounts of high specific activity PET neuroligand tracers.
To acclimate patients to the unique environment of the MRI scanner, the lab houses a simulator room. This room has a mock MRI scanner (non-magnetic), another Avotec fiber optic goggle system, and auditory system with two control computers. A motion detection system (based upon linear accelerometers) with video feedback is available for training subjects to not move in the scanner. 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.