Free-breathing liver imaging using DISCO with Auto Navigator

MR imaging is routinely used for non-invasively evaluating the liver. Improvements in both diffusion-weighted sequences and hepatocyte-specific contrast agents have improved the detection of both primary and secondary (metastatic) lesions.

However, many patients are unable to perform breath-holds due to the extent of their liver disease and side effects of cancer treatments. This inability to hold their breath for approximately 15 seconds can impact image quality and in some cases render the MR study insufficient for radiologist diagnosis and evaluation of patient treatment.

Recent advances in MR imaging sequences offer a free-breathing option for patients who cannot hold their breath, even though they have a regular, stable breathing pattern, capturing high quality images without a breath-hold. Auto Navigator is a free-breathing technique that combats respiratory motion and includes an automatic tracker placement for enhanced workflow. More importantly, it is compatible with all the typical sequences used for liver imaging, including T2 PROPELLER MB, FSE and DWI, as well as the critical dynamic T1 sequences, such as LAVA, LAVA Flex and DISCO.

The navigator tracker is automatically placed over the right hemidiaphragm and synchronizes with the patient’s breathing pattern to reduce respiratory ghosting artifacts. Acceptance window and threshold levels can be adjusted during the acquisition, which helps eliminate failures due to changes in the patient’s respiratory cycle, especially as the patient begins to relax in the MR bore.

Combining Auto Navigator with DISCO delivers excellent image quality with a free-breathing, dynamic scan without sacrificing resolution.

Patient history

A 70-year-old man was referred to MR for evaluation of hepatocellular carcinoma (HCC) after surgery, targeted therapy and biliary duct prosthesis.

Procedure

Axial LAVA Flex with Auto Navigator replaced a breath-hold sequence because the patient could not hold his breath longer than seven seconds. Free-breathing DISCO with Auto Navigator was also employed to provide high temporal and high spatial resolution. For the dynamic T1, DISCO captured six view-shared arterial phases at 14 seconds per phase and six phases delayed, non-view shared at 46 seconds.

DWI with high b-values may help provide additional information for the evaluation of lesions while the SIGNA™ Artist Total Digital Imaging (TDI) provided adequate signal-to-noise ratio (SNR).

MR findings

Patient had an increase in unresectable HCC lesions despite targeted therapy. Biliary duct dilatation was also noted despite prosthesis.

Discussion

Without the availability of the Auto Navigator free-breathing protocol, the exam quality would have been insufficient for the radiologist to evaluate patient treatment and detect the new lesions due to the patient’s poor breathing pattern and inability to hold their breath. DISCO with Auto Navigator allowed the radiologist to examine hepatic contrast enhancement with high-resolution images (2.2 mm, 320 × 224 matrix, two arterial phases, three venous phases and late enhancement to 5 minutes). Additionally, TDI enabled high signal and high-resolution imaging so we could acquire DWI with a b-value of 1000, 5 mm slice thickness and good SNR.

DISCO with Auto Navigator delivers simplicity of prescription, high spatial resolution and good temporal resolution allowing contrast enhancement analysis on arterial, portal and late phases. DISCO Flex is easy to use and minimizes the technologist’s concern regarding enhancement timing. The addition of Auto Navigator and respiratory trigger offer a comprehensive free-breathing protocol that provides images without breathing artifacts for high-quality abdominal imaging.