MRI Resources

The Center for Image Acquisition (CIA):
Siemens Magnetom 3T Prisma & Siemens Magnetom 7T MRI

The Center for Imaging Acquisition will house a Siemens Magnetom Prisma, a new 3 Tesla MRI scanner and a Siemens Magnetom 7T MRI scanner. The MAGNETOM Prisma 3T includes unparalled simultaneous 80mT/m @ 200T/m/s gradients, a new, high end gradient system that delivers high gradient amplitudes and fast switching capabilities in a combination that is currently truly innovative. The Siemens Magnetom 7T MRI system is an investigational device. Both MRI scanners are at the leading edge for neuroimaging

Siemens Magnetom 3T MRI scanner.
Figure 1. Siemens Magnetom 3T MRI scanner.

The Magnetom Prisma 3T MRI is a high performance 3T based on the Trio system. It allows for unparalled simultaneous 80mT/m @ 200T/m/s gradients. It’s 60 cm bore diameter allows for magnet homogeneity at 40 cm DSV – 0.2 ppm. With 64 – 128 channel receive it is really the ultimate MRI scanner for neuroimaging. High performance gradients will allow for human connectomics. The Prisma offers as standard Diffusion Spectrum Imaging up to 514 diffusion directsions allowing characterization of crossing fibers. Higher resolution DTI with it’s reduced field of view – ZOOMit DTI for isotopic DTI. Higher SNR will also allow for reproducible 3D ASL perfusion and improved resting state fMRI data.

The new Magnetom Prisma is also FDA approved now for clinical imaging. This is important to allow the data acquisition for patients with neurological diseases. This includes but is not limited to patients with Alzheimer’s Disease, Parkinson’s Disease, Multiple Sclerosis, Stroke, Brain Tumor patients. The key part of this scanner which is unique are the powerful XR Gradients, which have a strength of 80 milliTesla per meter (mT/m) combined with a 200T-per-meter-per-second (T/m/s) slew rate. Furthermore, it employs advanced homogeneity and shimming functions for optimal MRI data acquisition. This will be critical for reproducibility in longitudinal studies of patients and subjects over time such as those being studied by the USC ADRC and ADNI.

hcpThe Human Connectome Project is already working on methods for improving mapping the Connectome such as Multi-shell HARDI reconstructed with a Fiber Orientation Density methodology. This will be enhanced having the gradient performance of the 3T Prisma.

The USC Siemens 7T MRI consists of a magnet system which generates the basic magnetic field. The electrical and mechanical shim are integrated in the gradient coil. The magnet comprises the superconducting magnet including the system for cooling (interface for helium fill/refill, cold head), energizing (current probe) and monitoring the magnet during operation. In addition, it includes the cabling up to the point where the external lines are connected. The system consists of an actively shielded highly homogeneous superconducting magnet (7.0 Tesla) housed in a 830 mm horizontal room temperature bore, low-loss helium cryostat. Field shimming is primarily accomplished using superconducting shim coils. Final shimming is performed with a small number of passive shims. The system is supplied with a helium level monitor and an emergency quench heater control unit. A two-stage 4.2 K cryo refrigerator cooling system is employed, consisting of two independent cryocooler systems that eliminate the static cryogenic consumption.

Gradients & RF Receiver Technology The gradient system essentially consists of a Gradient Power Amplifier (GPA) and a Gradient Coil (GC), both water cooled to sustain a high duty cycle. The Magnetom 7T uses the GPA model as is used on other Magnetom systems. The gradient coil SC72 is based on established technology and has been optimized to operate in the 7T magnet environment. The gradient coil includes the full set of 5 second order electrical shim coils to adjust B0 homogeneity for patient and each measurement volume. The Siemens RF receiver technology is currently 32 channels receive and the USC 7T includes a Nova Medical 32 channel head coil. The system also has an 8–channel RF transmit array. 3rd order shims provide four out of the seven possible 3rd order shims that built into the SC72 gradients, along with 2nd 4-fold SPS cabinet, wiring for 3rd order shim, electric infrastructure expansion, SW interface to drive additional 3rd order shims.

Figure 3. Siemens Magnetom 7T

USC – Siemens Magnetom 7T system The Siemens 7T is an actively shielded whole body highly homogeneous superconducting magnet. Construction has begun and the delivery date is slated for 2016.