Magnetic Resonance Imaging (MRI) is one of the most powerful tools in modern medicine, allowing to see detailed images of the body’s internal structures without invasive procedures MRI radiographers play a critical role in ensuring accurate imaging results while putting patients at ease. This includes steps like calibrating, localiser scanning, acquiring, and post-processing the image. Today, we take a deep dive into the first three steps — patient preparation, screening, and positioning — that every MRI radiographer should master to perform successful scans and avoid potential risks.
Patient preparation consists of two parts: 1) before the patient arrives at the MRI department, 2) after the patient arrives at the MRI department.
Before the patient arrives at the MRI department:
After the patient arrives at the MRI department:
Patients entering an MRI suite for a diagnostic exam are screened for potential contraindications. They present the MRI safety questionnaire, and provide a detailed medical history before the MRI procedure about operations, implanted or removable medical devices (fig. 1), allergies, medical conditions (e.g. CKD) and possibility of pregnancy (for women patients).
Fig. 1 Implanted and removable medical devices may be harmful during the MRI scan and/or may interfere with the MR examination. For safety purposes, medical implants and devices that might be used in the MRI environment have been classified into three groups since 2005 by the American Society for Testing and Materials (ASTM) International (Standard F2503-20): 1) MR Safe, 2) MR Conditional, 3) MR Unsafe
Because MRI is a powerful magnet (the main magnetic field of a 1.5T system is about 30,000 times the strength of the earth's magnetic field), patients should ideally remove all clothing (fig. 2) and anything containing metal (e.g. piercings, jewelry, metal dentures, personal effects etc.) and change into a gown before the start of the examination. However small leftover metal pieces may still be pulled by the magnetic force, cause distortions in the image, or, depending on the RF energy deposition, heat up and cause burns.
Fig. 2 Some clothing may contain metal even when not apparent. This figure shows a second-degree burn after MRI examination from invisible metallic microfibres in clothing (Copyright: Frank G. Shellock, PhD, www.MRIsafety.com).
In MRI, proper patient positioning is vital in order to obtain good image quality and appropriate diagnosis (fig. 3). In general, the patient is placed on the MRI table, usually in the supine position with the head first. Feet first positioning minimises claustrophobic reactions and should be considered (when applicable). Receiver imaging coils are arranged around the region of interest (head, knee, etc.) and a key anatomic structure (such as glabella or iliac crests) is identified as a landmark using laser guidance, and this is correlated with table position by pressing the isocentre button on the gantry. If ECG or respiratory gating is required, then these devices are attached before the start of the MRI exam.
Fig. 3 Knee MRI patient positioning. The patient is placed on the MRI table in the supine position with the feet first. Dedicated or flex coils are used for knee MRI. The knee coil should be placed as close as possible to the center of the MRI table. The patient's knee is then inserted with a slight bend (about 15 degrees). The patella is aligned to the center of the coil. Pads are used for knee fixation and immobilisation (Here: Multipads)(Copyright: Pearl Technology).
Of course, some patients may be uncooperative, debilitated or in pain and cannot hold still during the MRI exam. Because of this, radiographers need to be creative sometimes and think outside of the box. Figure 4 shows an alternative lumbar spine MRI positioning in a patient who could not lie down in the supine (or prone) position due to severe lower back pain.
Fig. 4 Lumbar spine MRI with the patient placed on lateral decubitus position. The patient could not lie down in the supine or prone position due to severe lower back pain. Acceptable MR image quality can be noted within just 10 minutes of scanning time (for 5-sequences protocol).
Patient positioning aids (e.g. pads, cushions) should always be used because they enable an optimum and comfortable patient placement, positioning and fixation (fig. 3, fig. 5). Furthermore, they can help in eliminating image artifacts (e.g. motion artifacts) and providing efficient and high-quality MR imaging.
Fig. 5 Lumbar spine MRI patient positioning. The patient is placed on the MRI table in the supine position with the head or feet first. Feet first positioning minimises claustrophobic reactions and should be considered (when applicable). Cushions under the head and legs provide extra comfort to the patient, while non-conducting pads should be used in order to avoid contact with the wall of the scanner bore (here: PearlFit Cushions and MR Safety Pads)(Copyright: Pearl Technology)
While MRI technology and techniques are improving, many of the safety concerns remain the same as when first established. For example, improper patient positioning cannot only lead to low-quality MRI exams, but can also cause RF-induced thermal burns. Patient thermal burns and heating are the most frequently reported adverse event, accounting for 59% of MRI incidents to the Food and Drug Administration (FDA). Patient thermal injuries are preventable (fig. 6) and to prevent a thermal burn, the MRI radiographer should:
Fig. 6 “Do's and Don'ts” to prevent most skin burns in MRI. Figure shows a typical patient with a shoulder coil in place (Baker C. et al 2024, https://doi.org/10.1002/jmrs.800).
Fig. 7 Non-conducting MR Safety Pads in practice (Copyright: Pearl Technology AG)
Another safety concern is the acoustic noise. The MRI radiographer should always provide hearing protection during the patient positioning because the acoustic noise generated by the MRI scanners can range anywhere from 80-140 dB. The patients are strongly urged to use the earplugs and headphones provided to them, otherwise the noise levels may affect patients’ hearing. The International Electrotechnical Commission (IEC) requires that ear protection should reduce exposure levels in MRI to below 99 dB. The typical foam earplugs provide approximately 25 dB of noise reduction.
The answer is simple and straightforward: the MRI radiographer/technologist. Tasks like protocol and image quality optimisation are very important BUT patient preparation and positioning should always be the radiographer’s priority. Preparation, positioning and communication with the patient are crucial for obtaining high-quality MRI exams.
Author: Christos Tsiotsios, MSc