Week 3 - Jiahao

This week I visited Weill Cornell Imaging Center for outpatient practice to observe MR scanning procedure around the control room. The Imaging Center is located at the 3rd floor on 1305 York Avenue, including different kinds of diagnostic imaging examination, X-ray, CT, MRI, PET, etc. During my observation, I visited at one PET/MR scanning room which is a state-of-the-art simultaneous PET/MR device for a co-registered imaging exam.

The outpatient imaging center has two MR devices, both with 3T scanner manufactured by Siemens. Before my visit to the scanner, I completed the online MR safety training class by New York-Presbyterian Hospital. The MR scanning practice is conducted in the specific place which can be classified into four areas. Zone 1 and 2 are usually for patients to wait and be notified with any clinical or safety-related concerns. Zone 3 is the control room where technicians operate the machine and Zone 4 is the MR scanning room located the machine and other appliances for examination. Patients come to the front desk for inquiry of their exam orders by appointment. Then they wait in the waiting room outside of the scanning room which is decorated with care until they are called by physicians to get into the examination areas. Before the scanning, patients are being asked with any safety-related concerns in different ways for several times, in terms of any ferromagnetic materials, implants with MR compatibility, etc. After that, patients are required to change their clothes, enter into the control room, again communicate with the technicians before they finally get into the scanning room.

3T PET/MR scanning room at Weill Cornell Imaging

3T MR scanning room at Weill Cornell Imaging

I visited the 3T PET/MR which can be used for simultaneous PET/MR imaging as well as normal MR clinical practice. The scanner volume for participants is smaller than the other 3T MR scanner. Due to its simultaneous imaging, both MR coil receptors and PET gamma detectors are implemented into the machine. I encountered three cases the time I was in the control room. The first one is a patient getting whole body to thigh PET/MR scan along with MR Gadolinium contrast. The scan went on for a really long time around 1h. Since the main focus on the scan was around the patient's neck, it was required for the patient to keep his mouth and neck still as much as possible without swallowing action during each step of scan which usually lasted for around 2-4min. This was to avoid any possible motion artifacts causing defects in the images and was even hard for patients with pain in their head or neck. The technician communicated with the patient every time he finished one step scan in order to tell him how long the next step would take as well as get to know how the patient was feeling and whether everything went on well. After that several scans were made until 7:00pm.

During the scanning, technicians will exam the result in order to do any post-processing protocols using the platform provided by Siemens. The platform provides a great variety of functions for post-processing. In terms of the PET/MR, the fusion images of both attenuation correction maps by PET and different weighted images by MR are made prior before sending the results to radiologists for reading and examination. However, during my visit, an unexpected artifact arose when the AC map was calculated for PET/MR fusion images, where a huge circular artifact occurred in several slices in the air area where there should be no signals. After several efforts using different source images together with different tissue type filters, this artifact was finally removed from the offline attenuation-coefficient map and fusion images were corrected. Other post-processing also included brain vessel 3D segmentation for MR angiography during my visit.

Another interesting observation was for the contrast MR exam. Gad-MR is commonly used for contrast enhancement for T1 weighted imaging for vasculature and other parts. The whole injection process is automatically monitored during the scan. Usually pre-contrast and post-contrast imaging are both required for comparison. Gad contrast takes effect for not a long time. The automated syringe guarantees precise timing and controlled rate of injection.

It was really excited for me to see the whole scanning processes. Communicating with the technicians as well as observing how they work greatly inspired me to think about how my own research related with MR imaging clinics. Most of the work involves post-processing which is tightly related with my work, with the only difference that I use general MATLAB or Python to do image analysis and signal processing while technicians use the commercial software by the imaging company such as Siemens. However, it tells me to take care of any post-processing procedure, when making it commercialized or applied to hospital, thinking about any possible condition and giving corresponding solution to verify the algorithm robustness as well as the compatibility.