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Free-breathing DWI in MR

For many patients in emergent situations or who have chronic conditions, breath-holds can be difficult. Traditionally, patients having a magnetic resonance imaging (MRI) scan may have to hold their breath. This is because the patient's respiratory motion can interfere with the quality of the scan. The team at Addenbrooke's hospital in Cambridge, UK may have the solution for patients having hepatobiliary lesions who are unable to hold their breath.

Imaging of cholangiopathies1

David Bowden, FRCR, is a Consultant Hepatobiliary and Gastroenterology Radiologist at Addenbrooke's hospital, part of the Cambridge University Hospitals NHS Foundation Trust. As a radiologist, Bowden has experience with imaging patients with possible hepatobiliary lesions and other cholangiopathies (or liver diseases).

The importance of correctly determining these lesions is critical because of the high cost and associated toxicity of cancer treatment. High-quality imaging is often important for the surveillance of the development of malignancy in the liver. In order to find an adequate method of medical imaging for such cases, the team at Addenbrooke's hospital turned to MRI.

MRI can be especially useful when trying to get a clear image of liver diseases, because it can provide detailed images of the soft tissue and organ structures within the body. One particular technique used during certain MRI scans, diffusion weighted imaging (DWI), could help increase the sensitivity for detecting lesions and sometimes even characterizing them.

DWI relies on the Brownian motion of water molecules to create detailed MR images. Throughout the scan, the scanner the patient lays inside of sends pulse sequences that change the magnetic field of the super-conducting magnet. The radiologist observes the changes in water molecules as they align to the magnetic field during the pulse sequences and relax after. They can then calculate the apparent diffusion coefficient (ADC).

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Free-breathing exams1

Conventional DWI required breath-holds in order for the patient to undergo the scan an avoid motion artifacts. However, when a patient has trouble with holding their breath, the images may be marred with the distortions from the respiratory motion. Bowden and his team have found that certain DWI techniques may allow for imaging in such patients, including free-breathing, respiratory and navigator triggered acquisitions.

Navigator triggered DWI can track the motion of the diaphragm during a free-breathing exam. This motion will then trigger the data acquisition for the ideal parts of the respiratory cycle. This can help to reduce the motion artifacts related to respiratory motion.

As a result, radiologists may have increased confidence in the consistency of the scan and in the ability to detect lesions. In particular, the team believes this will be an important discovery to use with the left liver to mitigate cardiac motion and in the right liver to reduce the degradation due to the closeness to the lung parenchyma. The team also feels that this technique could be important for lesion detection in patients unable to undergo contrast enhanced MRI due to renal dysfunction. The team at Addenbrooke's hospital found that using this technique helped with identifying lesions that may have been missed on conventional MRI.1

Diffusion weighted imaging during magnetic resonance imaging, especially when the scan is free-breathing, may help with the detection of lesions in the liver that may have otherwise been missed. Because patients may have trouble holding their breath, the free-breathing aspect can lead to better images with the gating of respiratory motion. David Bowden and his team at Addenbrooke's hospital have already seen the benefit of the techniques with at least two patients.

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Reference:

Free-breathing navigator-echo triggered diffusion-weighted imaging in the evaluation of hepatobiliary disease. SIGNA Pulse of MR. http://www.gesignapulse.com/signapulse/spring_2019/MobilePagedArticle.action?articleId=1488824&app=false. Last accessed September 23, 2019.