When Can MRI Replace CT in Musculoskeletal Imaging?
For many musculoskeletal imaging scenarios, the standard protocol is an MRI and an additional CT scan. For trauma like a shoulder or wrist injury there may be soft tissue damage, best seen with MRI, and possible bone fractures that may be better visible on CT. Rather than schedule imaging on two machines, which adds complexity for both patient and clinician and increases cost, it is now possible to produce CT-like bone fracture detection images with a radiation-free MRI scan. This “CT-like MRI” is accomplished with zero echo time (ZTE) or ultra-short echo time (UTE) MRI sequences.
Alexandra Gersing, MD, PhD, and her collaborators in the Musculoskeletal Quantitative Imaging research group (MQIR) saw the potential to expand ZTE beyond initial musculoskeletal trials in the head and neck. The members of MQIR have conducted studies using CT-like MRI to detect bone fractures in the spine or hand and to diagnose trauma, bone tumors, or osteoporosis. These CT-like MRI images have great potential for many patients such as radiation-sensitive young athletes with shoulder trauma, bone tumor patients burdened by radiation accumulation, or even patients with loosening metal implants.
Image Processing Highlights Fractures
Deep learning image reconstruction algorithms make CT-like MRI imaging possible and practical. The algorithms originally developed to eliminate skeletal interference when imaging soft tissue can be inverted to provide precise images of the bones they were intended to mask. The physician only needs to order an extra ZTE scan sequence for the area of interest during an already scheduled clinical MRI, with no additional cost.
Gersing said, “I think there is going to be a lot of growth in this field within the next five years,” noting that she and her colleagues are now further investigating CT-like MRI to supplement CT readings in certain anatomical regions, such as the shoulder and knee.
AI Differentiates Bone Tumors and Osteoporosis
Currently it often requires a combination of CT and MRI to diagnose cases of bone pain that could be caused by bone tumors or by osteoporosis fractures. These patients and those confirmed to have bone tumors have many CT imaging sessions and can suffer from radiation accumulation. The proper scan protocol can combine MRI with CT-like MRI, for a high resolution of interior trabecular bone and the cortical bone to effectively visualize bone tumors.
Gersing’s team also developed an automated decision support tool to make this identification and differentiation easier. The tool has excellent detection of bone fractures with underlying osteoporosis in the spine and is efficient at differentiating them from other pain sources. Gersing and her colleagues envision applying such a tool to routine CT scans, enabling earlier detection of bone health problems before they are symptomatic.
Zero Echo Time MRI is FDA cleared in the USA and is used on several 3T scanners at UCSF as well as at certain other specialized medical centers.
Dr. Gersing acknowledges collaborators Sharmila Majumdar, Thomas Link, Daehyun Yoon, Drew Lansdown, Kevin McGill, Georg Feuerriegel, and Jonathan Friedman.
Reference
Foreman SC, Schinz D, El Husseini M, Goller SS, Weißinger J, Dietrich AS, Renz M, Metz MC, Feuerriegel GC, Wiestler B, Stahl R, Schwaiger BJ, Makowski MR, Kirschke JS, Gersing AS. Deep Learning to Differentiate Benign and Malignant Vertebral Fractures at Multidetector CT. Radiology. 2024 Mar;310(3):e231429. doi: 10.1148/radiol.231429. PMID: 38530172.