Neurological MRI: Trends in Contrast Utilization
At RAYUS Radiology in Minneapolis, Minnesota, neuroradiologist Blake A Johnson, MD, FACR, has noticed several clinical trends in magnetic resonance imaging (MRI) in recent years. One is that shorter exam times seem to be on the rise. “There’s a desire to shorten the overall acquisition time, not only for throughput, but for patient comfort, which is directly linked to patient satisfaction,” said Dr. Johnson.
He’s also noticed a growing recognition of the value of applying artificial intelligence (AI) tools to image acquisition and postprocessing. “More AI products are being approved by the FDA and utilized for enhancing diagnostic sensitivity and improving workflow for radiologists using diagnostic and volumetric quantification tools for stroke, for example. AI enhances image acquisition, processing, initial diagnostic triaging, and more,” he said.
The importance of contrast in neuro MR imaging
Another trend Dr. Johnson has observed is the necessity of the use of gadolinium-based contrast agents (GBCAs), which he feels are critical in neurological MRI studies to optimize diagnostic value. In any imaging study, the goal is to visualize and differentiate abnormal and normal tissue. Contrast is an essential tool in that process.1
In neuro MRI, contrast agents are often needed when assessing small metastatic lesions without perifocal edema. Once contrast is added, the difference in tissue enhancement can help differentiate the abnormal tissue versus normal tissue.1 “If they all have similar relaxation properties, they’re going to look the same on an MR study without contrast,” he said. “In that setting, the only way you’re going to accurately detect the tumor is to administer an MR contrast agent.”2
Dr Johnson noted that some vascular and perfusion studies3 also rely on contrast, and some treatment protocols require it. These include susceptibility perfusion exams, multiple sclerosis surveillance, and MR angiography. “There are instances where you can’t compromise on the use of contrast, including tumors assessment, border delineation and MS surveillance studies,” he said.
Concerns over nephrogenic systemic fibrosis (NSF) and the potential for gadolinium deposition4 have led the neuroimaging community to strive for administering contrast less frequently or at lowest recommended dose. However, the use of contrast must be balanced against diagnostic utility.
“It only makes sense to use less contrast if you aren’t sacrificing diagnostic quality of the study,” he said. “To compromise the quality of the study by either not giving contrast or giving too little contrast is not acceptable. If you decide to give contrast, you need to give enough contrast agent to make it a high-quality exam that doesn't compromise on contrast resolution and diagnostic confidence.”
The role of contrast in patient management
The choice of contrast agent can also affect the radiologist’s ability to get the right diagnosis the first time.
“A precise diagnosis is necessary to direct effective treatment, and a timely diagnosis is often necessary for a satisfactory patient outcome. In all cases, accuracy is critical. You want to make that diagnosis because you can’t treat something if you don’t have a precise diagnosis,” he explained.
Dr Johnson believes getting a correct diagnosis quickly should be the primary concern for radiologists focused on a patient-centric model of providing patients with the optimal care. “I don’t know any clinician who doesn’t rely on imaging for diagnoses. It’s critical for radiology to provide the right exam the first time and optimize that exam to make a high-confidence diagnostic study,” he said.
This is particularly important when assessing malignant tumors. “Contrast agents help us delineate the tumor’s margins and the extent of the lesion, which are extremely important in terms of treatment,” he explained.
The value of a high relaxivity GBCA in neuroimaging
Relaxivity is defined as “a measure of the sensitivity of the contrast agent”5 and is one of the properties that radiologists consider when selecting a GBCA. The higher the relaxivity of the agent, the more conspicuous the lesion.2
Thus, “you get higher contrast resolution in enhancing tissue versus non-enhancing tissue at the same dose, so your image quality goes up and your diagnostic certainty goes up. You want an agent that optimizes relaxivity,” stated Dr Johnson.2
Further, for GBCAs with similar distribution, a GBCA with higher relaxivity would provide equivalent contrast enhancement at a lower dose when compared to a lower relaxivity GBCA.5
Dr Johnson noted that relaxivity is linked to some of the most important elements of MRI. “It can help to improve diagnostic accuracy, and image with lower doses,” he said.
Dr. Johnson also believes high relaxivity can help further reduce contrast dose while achieving optimal imaging results, which could level the playing field between high- and low-field scanners. “In general, you get better contrast enhancement with high relaxivity, you get better signal-to-noise, and you can back off on your acquisition time and dose, and achieve a similar signal to noise at the same field strength,” he said.
Editor’s note: Applied Radiology Publisher Kieran Anderson recently spoke with Blake A Johnson, MD, FACR, the national medical director, director of neuroimaging, and director of regenerative medicine with Medical Scanning Consultants, PA. Dr Johnson also provides professional physician services at RAYUS Radiology in Minneapolis, Minnesota. He is a member of the Applied Radiology Editorial Advisory Board and an editor of the journal’s neuroradiology section. This article is based on their conversation.
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- Ibrahim MA, Hazhirkarzar B, Dublin AB. Gadolinium Magnetic Resonance Imaging. 2022 Jul 4. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan–. PMID: 29494094.Retrieved August 5, 2022, from https://pubmed.ncbi.nlm.nih.gov/29494094/.
- Maravilla KR, Maldjian JA, Schmalfuss IM, et al. Contrast enhancement of central nervous system lesions: Multicenter intraindividual crossover comparative study of two MR contrast agents. Radiology. Retrieved August 10, 2022, from https://pubmed.ncbi.nlm.nih.gov/16801373/.
- Goldfarb JW, Hochman MG, Kim DS, Edelman RR. Contrast-enhanced MR angiography and perfusion imaging of the hand. Am J Roentgenol. 2001; 177(5):1177-1182. Retrieved August 5, 2022, from https://www.ajronline.org/doi/10.2214/ajr.177.5.1771177.
- American College of Radiology (ACR) Committee on Drugs and Contrast Media. ACR Manual on Contrast Media, 2021. Available at: https://www.acr.org/ Clinical-Resources/Contrast-Manual. Accessed December 31, 2021.
- Jacques V, Dumas S, Sun, W-C, Troughton J S, Greenfield MT, Caravan P. (2010, October). High-relaxivity magnetic resonance imaging contrast agents. part 2. optimization of inner- and second-sphere relaxivity. Investig. Radiol. Retrieved August 10, 2022, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3024144/