NHLBI SBIR/STTR Contract Topic

067 Transmit-receive Surface Array Coils for MRI of Patients with Internal Conductive Devices

(Fast-Track proposals will be accepted)

Number of anticipated awards: 1

Background

Magnetic resonance imaging (MRI) has the potential to guide non-surgical cardiovascular interventional procedures because it can visualize soft tissue, guide positioning of therapeutic devices, and assess treatment outcome, all without ionizing radiation. To ensure that such procedures can be carried out effectively and safely it is essential to have devices (catheters, guidewires, etc.) that have the appropriate mechanical properties and that are conspicuous (visible) on the MRI images. The only general way to ensure conspicuity is by making the devices active, i.e. by making the devices capable of receiving NMR signals. Unfortunately, such devices (with conductive structures) can heat up considerably in a standard MRI scanner and this is one of the current major obstacles for MRI guided interventions.

The problem of heating of conductive structures during MRI extends to other applications such as imaging of patients with pacemakers and implantable defibrillators. A solution to this problem would have wide implications for the ability to scan a growing population of patients with implanted devices.

It has become clear that one of the key causes of active device heating is electrical coupling between the main MRI scanner transmit system (the body coil) and the devices. This coupling can be eliminated (or greatly reduced) by using a surface coil transmit system, which uses much smaller transmission coils than the main body coil of the scanner. There are two competing constraints that make it challenging to implement such a solution: a) For this solution to be effective the RF transmission system should illuminate the smallest possible area needed to effectively guide the procedure, and b) It may be necessary to follow devices over relatively large distances in the body. To accommodate both of these constraints we envision a surface coil transmit-receive array consisting of a relatively large number of smaller coil elements (i.e. 32, or more elements) covering the entire torso front and back (from the groin to the neck region). The system should allow dynamic activation and deactivation of coil elements such that only a subset of the transmit elements in the region of interest are active at any given point in time.

Specifications

• The coil array should cover the entire torso approximately 35 cm wide by 60cm long and the area illuminated by the transmission system at any given time should be controllable down to a size of 15x15 cm.
• It has to be possible to use the system with an MRI scanner without parallel transmit capability, i.e. the system has to be driven by a single RF waveform specified by the sequence. The system could include additional amplifiers and control hardware and software as needed.
• It should be possible to turn elements on and off dynamically. We envision a programmable interface that can be controlled from the MRI sequence environment.
• Ideally, it would be possible to control the phase of the RF pulse in each individual transmit element. Element-by-element RF amplitude control would also be desirable to enable dynamic RF shimming as needed to accommodate different body shapes and also to mitigate device heating through more advanced techniques.
• Multiple receive elements (~16 elements) must be active within the illuminated area to enable parallel imaging acceleration.

The NHLBI currently uses 1.5T Siemens MRI systems and the proposed transmit-receive system must be compatible with these scanners (more details will be made available upon request).

Deliverables

Phase I should aim to provide a working prototype system that would allow a) MRI imaging with sufficient image quality to guide an interventional procedure , and b) comprehensive heating testing with interventional devices developed at the NHLBI. Heating test will be conducted in phantom and animal experiments at the NIH in collaboration with on-site scientists.

Phase II will incorporate design changes based on Phase I testing and deliver a complete transmit-receive system, which is safe for patient use. Specifically, the device should be eligible for designation as a “non-significant risk device” by FDA or the vendor is expected to obtain an “Investigational Device Exemption” from the FDA.

For more information, see the FY2012 Contract Solicitation or contact OTAC.

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Last Updated December 2011