High Field MRI

High field MRI’s use powerful magnetic fields to quickly generate extremely high-resolution images. Because high field MRI’s also scan very quickly, they are excellent for visualizing physiological processes in addition to structural tissue.

Early MRI’s were based on 0.35 and 0.5 Tesla magnets, which were quickly replaced by 1.5 Tesla magnets by the late 1980’s. Higher power magnets yield relatively lower signal-to-noise ratio, which in turn can translate into higher resolution imaging and/or reduced imaging time. By the 1990’s, advances in producing homogeneous magnetic fields and robust signal reception radiofrequency arrays, as well as mechanisms and procedures to ensure patient safety, led to the introduction of high field MRI’s based on 3.0 Tesla magnets, which offered significant improvements in image resolution. Ultra-high field MRI’s are now being introduced which use magnets of up to 7.0 Tesla.

Significantly, high field MRI facilitate new functional MRI techniques which use blood-oxygen level contrast, angiography and other techniques to map muscle oxygenation and muscle function. Ultra-high field MRI also has relatively greater sensitivity to low-gamma nuclei, enabling assessment of sodium physiology and phosphorus metabolites.

Ultra-high field MRI enables studies of human joints such as knees and wrists, since it produces high resolution images of cartilage, which cannot be imaged by conventional MRI due to its small size. Evaluation of joints is further enhanced by ultra-high field MRI’s ability to evaluate cartilage biochemistry via sodium MRI and gadolinium-enhanced MRI. Bone micro-architecture studies also generate metrics for structural alterations associated with bone disorders such as osteoporosis. Sodium MRI supports physiological assessment of muscle as well by providing information about the sodium-potassium pump and ion balance.

High field and ultra-high field MRI offer great promise in the field of brain imaging. A 3.0 Tesla MRI’s provide spatial resolution as low as 200 µm, enabling imaging of blood flow within the vessels of the brain. At 7.0 Tesla, resolution of 50 µm may allow detection of senile plaques such as those associated with early stages of Alzheimer’s disease. At very high magnetic fields, MRI’s could be used to detect biochemical reactions as well as very small lesions, facilitating diagnosis and early treatment of early stage cancers, myocardial infarctions, diabetes and other metabolic disorders.

Explaining the MRI Receiver

What is the MRI Receiver’s Role?

An RF MRI receiver is used to process the signals from the MRI receiver coils. Most modern MRI systems have six or more MRI receivers to process the signals from multiple coils. The signals range from approximately 1MHz to 300MHz, with the frequency range highly dependent on applied-static magnetic field strength. The bandwidth of the received signal is small, typically less than 20kHz, and dependent on the size of the gradient field.

A traditional MRI receiver configuration has a low-noise amplifier followed by a mixer. The mixer combines the signal of interest to a low-frequency IF frequency for conversion by a high-resolution, low-speed, 12-bit to 16-bit analog-to-digital converter (ADC). In this receiver architecture, the ADCs used have relatively low sample rates below 1MHz. Because of the low-bandwidth requirements, ADCs with higher 1MHz to 5MHz sample rates can be used to convert multiple channels by time-multiplexing the receive channels through an analog multiplexer into a single ADC.

With the introduction of higher-performance ADCs, newer MRI receiver architectures are now possible. High-input bandwidth, high-resolution 12-bit to 16-bit ADCs with samples rates up to 100MHz can also be used to directly sample the signals, thus eliminating the need for analog mixers in the receive chain.

What are the Basic Elements of an MRI Receiver?

The basic elements of an analog MRI receiver chain are a pre-amplifier, a one- or two-staged modulator, aquadrature-phase-sensitive detector, low pass filters, two second-stage audio amplifiers with variable gain, and two analog-to-digital converters. As a result, the MRI receiver is very similar to a conventional superheterodyne radio receiver.

What to Look for in MRI Receivers When Purchasing

When dealing with MRI scanner receivers, it is important to take a good look at the signal-to-noise ratio and the bandwidth. In general, a wider bandwidth includes more noise. Decreasing the bandwidth by a factor of 4 results in an increase in the signal-to-noise ratio by a factor of 2 (less noise in the image).

When decreasing the bandwidth, we gain a better signal quality. However, there are also some trade-offs:

• the chemical shift artifact increases.
• longer echo time (TE) means some reduction.
• longer echo time means that fewer slices can be fitted into the repetition time (TR) period.

In the signal-to-noise ratio however, the overall effect of the reduction of the bandwidth is an improvement in the signal-to-noise ratio.
The initial bandwidth of the MRI signal produced by the MRI scanner is a function of the special encoding readout gradient strength, and the chemical shift.

Where to Buy MRI Scanner Receivers

MedWOW, the global medical equipment portal, specializes in imaging equipment, including an impressive selection of MRI scanner receivers. Currently, there is a broad selection of MRO scanner receivers for both stationary and mobile MRI units from GE Healthcare, Siemens, Marconi, Picker and Toshiba. MedWOW’s revolutionary search engine allows you to browse their catalogue in a number of ways, so finding the MRI scanner receiver you need is a simple procedure. You can filter by manufacturer, make, model, condition, location, year manufactured, Seller’s business type and more. So, when buying or selling MRI scanner receivers, MedWOW is a good place to find a varied selection at competitive prices, as well as safe and protected transactions.