4 Reasons Why MRI is Used to Guide Focused Ultrasound

Harnessing soundwaves to heal disease

For today’s mother-to-be, one of the fun parts of being pregnant is coming home from a prenatal exam with a “photo” (ultrasound image) of the fetus. The image is generated by sending soundwaves (at a frequency above the range a human can hear) through the abdomen, and then capturing the waves that bounce back. Software translates these echoes into a picture on a monitor. The picture can then be printed so the woman can proudly show off her budding offspring. This use of ultrasound (abbreviated as US) is 100% safe for both mom and baby-to-be.

US can also be used at a different frequency to ablate (destroy) diseased tissues in the body. Ablation US is not the same as harmless imaging US. Ablation US waves can be harnessed from different directions to simultaneously focus on a target in the body, where they create destructive heat at the meeting point. This is called Focused Ultrasound (FUS). With no surgical incisions, and no exposure to radiation, a single outpatient treatment can accurately ablate a problem area, even one as small as a grain of rice. How is such accuracy and effectiveness possible? The secret is imaging – but it has to be the right type.

Ultrasound imaging didn’t work

It took many years for FUS to “reach wide application in the clinic. The main reason for this has been the lack of a way to monitor procedures.” Initially, x-rays and ultrasound (like the modality used for fetal imaging) were tried. They were okay in terms of knowing where to focus the ultrasound beams, but they weren’t adequate to the task of monitoring tissue changes during ablation and confirming results.

Magnetic resonance imaging has 4 benefits

Magnetic resonance imaging (MRI) proved to excel in combination with FUS. There are four reasons why, and each of them is a great benefit to both doctor and patient.

1. Identification – MRI produces high resolution images of soft tissues, making it the optimal method for identifying the target to be treated. It also identifies adjacent anatomic landmarks; for example, using FUS to deaden very small structures in the brain requires locating them in relation to nearby “landmarks”. MRI can also define tissue characteristics.
2. Planning – Once the target to be ablated is identified, MRI creates 3-dimensional maps that enable doctors to plan precise delivery of FUS beams. Sophisticated software is used to help calculate the strength of the FUS and the duration of each “blast”.
3. Monitoring treatment – No matter how thorough the advance planning, there has to be a way to track exactly what the FUS waves are accomplishing in real time. By using a highly sensitive technology called thermography, MRI reveals exactly what is being treated by tracking temperature changes in tissues. This also reveals the precise zone of ablation so ensure that adjacent structures are not affected.
4. Confirming treatment effect – Immediately after treatment, another MRI scan is performed to evaluate how the tissue has changed and, in the case of ablating a cancerous tumor, make sure that the tumor’s blood supply was also destroyed (no blood flow).

These are the four reasons that have established MRI as the imaging of choice for use with FUS.

MRgFUS at the Sperling Neurosurgery Associates

Currently, the Sperling Neurosurgery Associates offers FDA-approved Neuravive, a treatment for essential tremor (ET) using MRI-guided FUS, or MRgFUS. In this case, a tiny part of the thalamus in the brain is precisely ablated so it no longer relays tremor messages to the brain’s motor center. By interrupting the transmission, the hand tremors stop. Thanks to the amazing power of MRI, this outpatient procedure is safe, accurate, and durably effective. For more information, visit our website.