Photon-counting CT as good as MRI for evaluating hepatic steatosis

"The findings could provide additional and valuable clinical data from many CT (computed tomography) exams that are done each day in busy radiology departments, particularly in obese patients at risk of disease caused by the abnormal accumulation of live fat," the researchers wrote in their study.

The study showed that PCCT provides accurate liver fat fraction quantification, which could improve patients' outcomes by detecting fatty liver disease in earlier stages and providing an opportunity for early treatment initiation.

There has been a rise in hepatic steatosis incidence, which is linked to many health problems, including liver cirrhosis and fibrosis, coronary artery disease, diabetes, and metabolic syndrome. It is typically diagnosed by liver biopsy, an invasive procedure that doesn't allow repetition to monitor the disease's progression or patient's response to treatment. MRI can be used to assess hepatic steatosis but requires unique imaging sequences -- which prolong exam time, can be challenging for larger patients or those with claustrophobia and is not easily accessible.

In this scenario, PCCT could be helpful. Studies have reported that single-energy CT corresponds well to MR spectroscopy and MRI for assessing hepatic steatosis, but the basis for fat quantification is Hounsfield units dependent on the patient size, CT scanner and the absence or presence of iodine-based contrast. On the other hand, PCCT shows promise for fat quantification more accurately as it measures the energy of photons in the x-ray beam differently than conventional CT.

Against the above background, Fides Regina Schwartz from Duke University Health System in Durham, NC, and colleagues aimed to compare liver fat quantification between MRI and photon-counting CT.

Imaging of a cylindrical phantom with inserts comprising six oil-iodine mixtures (0, 10, 20, 30 and 50% fat + 3 mg/mL iodine) and of oil (0, 10, 20, 30, 50 and 100%) was done with a PCCT and a 1.5T MRI system. An IRB-approved prospective clinical assessment included 12 obese patients with known fatty liver disease.

Patients underwent a same-day abdomen clinical MRI and PCCT. Calculation of liver fat fractions was done in four segments (I, II, IVa and VII) using in- and opposed-phase on MRI and iodine-fat tissue decomposition analysis in PCCT. A comparison was made between CT and MRI Fat fractions.

The study revealed the following findings:

· Phantom results revealed no significant differences between the known fat fractions or iodine compared to PCCT-measured concentrations and no statistically notable difference between known and MRI-measured fat fractions.

· The mean fat signal fraction in patients measured on PCCT and MRI was 12.0 ± 9.0% and 13.1 ± 9.9%, respectively, with an average difference of 1.1 ± 1.9% between the modalities.

"The first experience demonstrated promising accuracy of liver fat fraction quantification for PCCT in patients with obesity," the researchers wrote. "This method may improve opportunistic screening for CT in the future."

Preliminary analysis in an obese patient population revealed a good correlation of fat fraction analysis between PCCT and MRI, with an average difference of 1.1% between methods.

Reference:

The study titled "Liver Fat Quantification in Photon Counting CT in head to head comparison with clinical MRI – first experience" was published in the European Journal of Radiology.

DOI: https://doi.org/10.1016/j.ejrad.2023.110734