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Real-time Video Projection in an MRI for Characterization of Neural Correlates Associated with Mirror Therapy for Phantom Limb Pain
Chapters
Summary April 20th, 2019
We present a novel combined behavioral and neuroimaging protocol employing real-time video projection for the purpose of characterizing the neural correlates associated with mirror therapy within the magnetic resonance imaging scanner environment in leg amputee subjects with phantom limb pain.
Transcript
The overall goal of this procedure is to more accurate characterize the neural correlates of mirror therapy in phantom limb pain patients, that is, PLP patients. This is accomplished by the following steps. Step one.
Ensure that the participant does not have any known contraindications to MRI scanning and provide a pre-recorded audio to make sure that they are able to understand and follow the instructions provided during the scanning procedure. Step two. Position the patient as comfortably as possible in the scanner bed, where he or she should be lying supine with a single-piece MRI-compatible horizontal mirror between his or her legs.
This mirror should be supported by a triangular stand to avoid contact with any part of the patient's body. Step three. Place an MRI-compatible digital camera on an adjustable tripod stand near the patient's intact leg to provide real-time video transmission.
Step four, the final step. Begin with an anatomical MRI and adjust the machine settings to each patient and then, while the functional MRI scan is being performed, play the recording to the patient, instructing him or her to complete the specific behavioral tasks. Ultimately, the mirror attached to the MRI coil will allow patients to watch the mirrored leg movements in real time without moving their heads.
For this protocol, you will need the following items. An MRI scanner, two MRI-compatible mirrors, a large one to place between the patient's legs, as well as a small one to place on the head coil. Additionally, you'll need sandbags, an MRI-compatible digital camera, a tripod for the camera, a computer-controlled system, and a monitor to place in the back of the scanner bore.
Before proceeding to the MRI, it is critical to make sure the patient has no known contraindications to MRI scanning, for example, metal implants, aneurysm clips, or severe claustrophobia. Initially, you will explain to the patients exactly what they should expect during the experimental procedure. The patients will then listen to a recording with instructions to follow during the scan.Mirror.
Patients may first practice during a mock scan to become familiar with the tasks as well as the scanner environment. The mock scanner is similar in every way to the real MRI scanner but without the active magnet. Before entering the scanner room, patients must remove their prostheses as well as any metal objects they might be wearing on their heads or bodies, for example, watches or jewelry.
The MRI technician will make sure the patients have no metal that might put them at risk. All patients are transported to the scanner room using an MRI-safe wheelchair to avoid falling out. After that, the patients will transfer themselves to the MRI scanner bed.
After the patient is lying comfortably in a supine manner on the scanner bed, a single-piece MRI-compatible horizontal mirror is placed between his or her legs. An adjustable arm is then positioned to point the camera at the mirrored leg. The large mirror is positioned between the legs at an angle of about 45 degrees, depending on the patient's height and amputation level.
The goal is to cover the stump and make it invisible to the video camera. Sandbags are used to keep the mirror at the correct angle. A smaller mirror is positioned on the head coil, angled at 45 degrees at eye level.
This mirror allows the patient to visualize the mirrored leg image directly, without moving their head while lying completely inside the scanner bore. An MRI-compatible digital camera is mounted on a tripod stand near the intact leg. This camera will transmit real-time video images of the mirrored leg movements to a computer control system that then projects the video to a monitor near the patient's head so he or she can view the mirrored leg movements.
The patient will undergo a four-minute anatomical scan first followed by four runs of functional acquisitions while he or she performs the tasks. Each run lasts six minutes. During the scans, the patient wears sound-isolating MRI-compliant headphones which emit a series of auditory cues, instructing the patient to perform the given behavioral task.
The following commands are used. One, leg, two, mirror, and three, rest. Additionally, the investigator says start and end at the beginning and end of the experimental run.
The patient has already been instructed on hearing the word leg to follow the tapping sound presented in the audio. With the eyes closed, he or she will tap the foot at a rate of one tap per two seconds for a total of 10 taps in 20 seconds.Leg. On hearing the second command, mirror, the patient has to continue tapping his or her foot at the same rate, this time, while looking at the display showing the mirrored image of the two legs.
Again, this would be at a rate of 10 taps in 20 seconds.Mirror. On hearing the third command, rest, the patient should stop moving his or her foot and lie motionless with both eyes closed.Rest. Data is collected in a single session for each patient and the entire scanning procedure lasts approximately 30 minutes.
The investigators take note of any unwanted movements. Between the runs, they can ask the patients to keep the right pace and do the correct movements. After the procedure is finalized, the data is transferred to an encrypted flash drive and stored in a secure location in the facility.
A longitudinal analysis design is used, comparing baseline and post-treatment data. The FSL software package and processing stream will be applied. Volumes with motion above 0.9 millimeters in any direction are identified with FSL's motion outlier detection processing stream and mathematically scrubbed from the final analysis.
If more than 25%of the volumes are designated for removal, the whole acquisition is excluded from the total data set. A region of interest ROI analysis is used. The primary ROI is defined structurally using Freesurfer's Desikan Atlas of the primary sensory motor cortex and refined with a subject-specific functional activation during the leg versus stress condition at the baseline scan.
This ROI is then reflected on the homologous area of the other hemisphere, that is, ipsilateral primary sensory motor representation of the intact lower limb. The secondary ROI is the entire bilateral occipital visual cortex as defined by the anatomical Desikan Atlas. Patients reported that the experience is immersive and the video image is life-like.
Therefore, this real-time video projection process can generate the sensations associated with conventional mirror therapy. We expect that the leg condition, that is, the foot-tapping task, will lead to robust activation of the sensory motor cortex representing the intact leg compared to the rest condition. However, we also expect to see a less-pronounced activation of the sensory motor leg area representing the amputated leg.
The mirror condition also shows robust contralateral as well as some ipsilateral activation of the cortical leg sensory motor area compared to the rest condition. Additionally, robust cortical activation is seen posteriorly in the visual cortical areas associated with viewing the mirrored leg. The activation pattern is described to represent the baseline condition, that is, prior to beginning therapy.
These initial responses serve to define regions of interest, ROIs, and allow for comparisons after the therapeutic protocol is completed in each individual. After watching this video, you should have an adequate and sufficient understanding of the necessary steps required to set up all the equipments to perform your therapy inside the MRI scanner. This protocol describes a novel physical procedure that allows investigators to more accurately characterize the neural correlates associated with mirror therapy in individuals with phantom limb pain.
We could answer additional questions regarding brain organization after a limb amputation following the steps of this protocol using other neurophysiological measurements or imaging techniques. A challenge associated with this approach is the risk of generating excessive head motion artifacts, given that the leg must be moved repeatedly inside the scanner. Excessive head motion can compromise image data quality.
In this regard, it's important to plan ahead and implement a variety of strategies to mitigate this possibility. These include training the participant in a mock scanner to carry out the task without excessively moving their head, making sure that the head is secure yet comfortably restrained, and implementing motion detection correction strategies during the acquisition and data analysis phases respectively. Given the method to implementing the experimental set-up is relatively simple, this approach may allow the evaluation of the mirror therapy effects not only in limb amputees but also in other conditions, such as stroke or spinal cord injury where mirror therapy is already commonly used in clinical practice.
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