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MR guidance provides detailed soft tissue images during interventional pain treatment

Best Practice
Retzlaff, Sebastian, Dr. 360 MRT Praxis für offene Kernspintomografie • Germany

The 360 MRT Practice for Open MRI (Schwerin, Germany) has been performing MR-guided

periradicular interventional pain therapy since May 2011. Focusing on musculoskeletal MRI, with some

neuro and abdominal work, the practice scans more than 10 patients a day on its Panorama HFO.

Sebastian Retzlaff, MD, the founder of this private practice, says he is one of the first physicians to use open MRI instead of CT in periradicular therapy (PRT) procedures. He says he appreciates the detailed soft tissue images, as well as the lack of radiation.

“The standard modality is CT-guided PRT, but personally, I strongly prefer MRI for this purpose. Unlike with CT, we can really see the nerve root on MR images, and the control of the needle tip is excellent. Also, in a young patient, for instance a woman still in her childbearing years, we might not want to use CT because of that accumulated dosage.”

“With the Panorama’s openness, reaching the patient is easy in patients of any size. And the image quality is very good,” he adds.

Dr. Retzlaff performs this PRT procedure in patients with lumbar radicular pain, but he excludes patients with unspecific low back pain. “I only use it in patients with a compression of at least one or two well-defined nerve roots.”

PRT begins and ends with MRI

Dr. Retzlaff starts with MR imaging prior to the PRT process. “We begin with diagnostic lumbar MRI, and then we proceed with a physical examination. It’s important to determine whether there is nerve root compression.” The treatment itself generally begins the next day. With the patient lying on the symptomatic side in the magnet, a localizer sequence is performed first to find the proper segment. When the best path for the needle is determined, Dr. Retzlaff finds the proper puncture point using the in-room monitor and his outstretched index fingers, and marks it on the skin. This is enabled by the system’s real-time interactive package. The patient is slid slightly out of the magnet while the skin is disinfected and a sterile covering is placed on the back. The needle, the Invivo 22 G puncture needle, is inserted approximately 1 cm at the marker and the patient is moved into magnet again. Under MR guidance the needle is then pushed forward to the neuroforamen, the iliosacral joint space or facet joint. When MR images show that the targeted position is reached, the patient is moved slightly out of the magnet again, and an injection is given.

 Marking the proper puncture point on the skin Inserting the puncture needle outside of the magnet
Marking the proper puncture point on the skin
Inserting the puncture needle outside of the magnet
 Pushing the needle forward under MR fluoroscopic guidance Documentation of correct needle tip position
Pushing the needle forward under MR fluoroscopic guidance
Documentation of correct needle tip position

Performing this application requires interactive MR software, an in-room monitor and an MR-compatible needle.

Visualizing the needle

“During the procedure I want to follow the needle in the tissue. I want to see the vertebrae, the joints, the neuroforamen, the nerve roots, the muscles and so on, in addition to visualizing the needle position,” says Dr. Retzlaff. “Remember that the metal needle does not create MR signal, but is visible thanks to the well-defined ‘artifact’ it creates. With gradient echo sequences being very sensitive to this kind of artifact, the artifact would be much too large and the nerve root and the surrounding structures could not be visualized with the needle, which may be 2-3 cm in the images – much too large to meet a small nerve root of 2-3 mm in diameter. So, we need a very fast interactive sequence that is not too sensitive for metal artifacts. We use a turbo spin echo sequence, which makes the needle very visible, without influencing the surrounding structure. Sometimes it helps to switch readout gradient direction.

The interactive MR fluoroscopy sequence used for the real-time visualization is T1TSE interactive, TR 600 ms, TE 10 ms, slice thickness 5.0 mm, in-plane resolution 0.89 x 2.53 mm, TSE factor 36, scan time 3.0 seconds, NSA 1, CLEAR. The coil used is ST Multi Purpose L.

Practical experience

“It takes some practical skill to give the needle the right direction in the initial placement when the patient is outside the gantry,” says Dr. Retzlaff. “Then, MRI Fluoroscopy provides one slice or two slices in perpendicular orientations with a refresh rate of 3 seconds. The MR technologist needs to learn which slice position and orientation the radiologist needs to see while navigating the needle through the neuroforamen. The procedure now typically takes 10 to 15 minutes. We’re still in the learning curve, so it will become even shorter.”

“The team at the University Clinic of* Magdeburg has much more experience on these interventional procedures on the Panorama – I learned this procedure from them,” Dr. Retzlaff adds.

Dr. Retzlaff says he wouldn’t use anything but MR for PRT. “I think use of MR guidance will grow for PRT and many other interventional procedures.”

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Oct 9, 2012

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Best Practice
Panorama HFO
Body, interventional, Interventional, Lumbar spine, MR fluoroscopy, MR-guided interventions, ST multi porpose L coil

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