Autumn 2020

Issue Archive

Volume 29 – Autumn 2020

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Marc Zins, MD

Saint Joseph Hospital

Paris, France

Francois Legou, MD

Centre Cardiologique du Nord

Paris, France

IN PRACTICE

In pursuit of fast and consistent free-breathing abdominal MR exams

Marc Zins, MD

Saint Joseph Hospital

Paris, France

Francois Legou, MD

Centre Cardiologique du Nord

Paris, France

Since its introduction in 2004, LAVA has become a staple in many abdominal MR exams due to its enhanced image contrast and uniform fat suppression. HyperSense was introduced in SIGNA™Works in 2016 and was shown to go faster and improve image quality with higher spatial resolution. GE has now extended HyperSense into additional body sequences, including LAVA, LAVA Flex and DISCO.

More recent iterations of the sequence include: Turbo LAVA, a rapid accelerated 3D T1 dynamic sequence offering homogeneous fat suppression with shorter scan times, and LAVA Flex, a dynamic 3D T1-weighted technique that generates four contrasts (fat, water, in phase and out of phase) in one rapid acquisition. LAVA, LAVA-Flex and DISCO offer different fat suppressed contrasts and can be used with Auto Navigator for a free-breathing acquisition or with patient breath-hold. While breath-holding remains the gold standard in abdominal imaging, free-breathing with Navigator provide a complete package of options for clinical use. With the advent of compressed sensing and volumetric imaging, GE Healthcare is taking dynamic imaging – LAVA, LAVA Flex, DISCO – to the next level with the introduction of LAVA HyperSense‡ T1 for sequences and DISCO Star‡. Marc Zins, MD, Chairman of the Radiology Department at Saint Joseph Hospital, evaluated a prototype of LAVA HyperSense and Francois Legou, MD, radiologist at Centre Cardiologique du Nord (CCN), evaluated a prototype of DISCO Star at their respective facilities and shared their experience with SIGNA™ Pulse of MR.

LAVA HyperSense

At Saint Joseph Hospital, LAVA sequences are used in all liver and pancreas MR exams. According to Dr. Zins, the hospital will perform a pancreas MR exam for cystic lesion follow-up, to characterize a lesion incidentally detected on a CT exam, for assessment of chronic pancreatitis and for diagnosis and staging of pancreatic cancer. In the liver, an MR exam is generally performed for tumor staging or follow-up, liver cancer screening, post-ablation therapy or TACE assessment, and in cases where a lesion is incidentally found on a CT or ultrasound exam.

A prototype of LAVA HyperSense was installed on the Discovery™ MR750 at Saint Joseph Hospital in March 2018. Dr. Zins and his team tested different acceleration factors – using both ARC and HyperSense – and qualitatively evaluated image quality, including artifacts, blurring, lesion detection, reformat quality and the sharpness of organs and lesions. When used with other sequences, Saint Joseph Hospital typically uses a HyperSense factor of 1.3 to achieve a balance between higher spatial resolution and scan time.

The radiologists anticipate that their diagnostic confidence will improve due to the higher spatial resolution in the arterial phase sequences. In the example shown in Figure 1, the LAVA HyperSense prototype demonstrates improved in-plane resolution for the LAVA multi-arterial – three phases in one 25-second breath hold – without changing the scan time. Also, the reduction in breath-hold times may enable fewer breathing artifacts or failed acquisitions due to patients who couldn’t comply with breath holding.

Figure 1. In initial evaluations of the LAVA HyperSense prototype, in-plane resolution increased compared to LAVA without HyperSense with the same breath-hold time to improve early enhancement visualization and facilitate lesion contrast enhancement analysis. LAVA HyperSense (A) phase 1, (B) phase 2, and (C) phase 3, 1.5 x 1.5 x 3.6 mm, 25 sec., HyperSense factor of 1.3.

"LAVA HyperSense could become the new standard reference technique on post-contrast 3D GRE T1 sequences to obtain a better balance between spatial and temporal resolution," Dr. Zins says. "In an arterial axial LAVA HyperSense post-contrast sequence, we can reduce the slice thickness for an isotropic acquisition. In the reformats we’ve performed with the prototype, we did not detect loss of detail or a decrease in image quality."

Dr. Zins explains the pancreas is a tortuous organ and, therefore, evaluating it in different planes and views is often desired for diagnosis. A faster LAVA sequence enabled by HyperSense could assist the radiologist in their diagnosis by allowing for higher spatial resolution by using thinner slices when evaluating the relationship between an enhancing lesion and a pancreatic duct.

As with any sequence utilizing compressed sensing (HyperSense), Dr Zins says choosing the right factor is crucial to avoid image blurring. It’s only when the factor is too high that this issue occurs. "We have a high reproducibility of image quality with patients who can perform a good breath-hold."

In his evaluation, Dr. Zins was able to reduce breath-hold time by 25 percent using LAVA HyperSense compared to conventional LAVA.

With the shorter scan times from LAVA HyperSense, the clinical team could potentially utilize the time savings to obtain higher spatially resolved acquisitions. For example, in liver, biliary tract (gall bladder cancer and cholangiocarcinoma) and pancreas, it is important to capture excellent spatial resolution to look for tiny lesions with locoregional invasion.

Figure 2. Patient with a focal lesion in the pancreas head. With 3D isotropic LAVA and HyperSense, the (A, B, C) axial images, 1.7 x 1.5 x 1.4 mm, 25 sec., HyperSense factor of 1.3, can be reformatted to (D) coronal and (E) oblique reformats.

Figure 3. Patient with an auto immune pancreatitis, associated with cholangitis (stenosis, red arrow). A 3D isotropic volume was acquired in the same acquisition time as a 2D acquisition with LAVA HyperSense. (A) Acquisition plane, 1.7 x 1.5 x 1.4 mm, 30 sec., HyperSense factor of 1.3, (B, C) reformats and (D) axial DWI b800. With the coronal and oblique reformations of the LAVA Hypersense, the radiologist can review the normal portion (green arrow) of the pancreas around the lesion (yellow arrow).

Figure 4. (A) Coronal LAVA HyperSense and (B) coronal SSFSE T2, 1.3 x 1.6 x 2.4 mm, 3:00 min.

"Before HyperSense, a highly resolved sequence required a long breath-hold duration, which was not feasible for patients and not acceptable in our clinical routine," Dr. Zins explains. "With a navigated dynamic 3D T1 sequence, it can be difficult to manage the timing of the arterial phase due to the patient’s condition (poor cardiac output, for instance) making it challenging to characterize liver and pancreatic lesions."

DISCO Star

Each week, CCN performs approximately 30 abdominal MR exams on both the SIGNA™ Premier 3.0T and the SIGNA™ Artist 1.5T systems, with nearly two-thirds on the former. The primary indication is for liver and bile duct, small bowel and pancreas assessments. A dynamic 3D T1 sequence is the go-to acquisition for most of these exams.

In addition to imaging the pancreas for suspected cancer, MR is also used at CCN for a differential diagnosis of autoimmune pancreatitis. Liver MR exams are generally utilized to determine extension of colorectal cancer, bile duct pathologies and to characterize lesions detected on X-ray or ultrasound, including hepatocellular carcinoma (HCC).

Dr. Legou was excited to work with the DISCO Star prototype on SIGNA™ Artist because of the potential to provide a solution to respiratory motion in MR imaging of the liver and pancreas – some of the most demanding MR exams. Previously with the navigated sequence, the timing of the arterial phases may not always be consistent due to the patient’s condition or ability to comply, making it difficult to characterize liver and pancreas lesions. From his initial evaluation of DISCO Star, Dr. Legou believes it can provide a consistent acquisition of the arterial phase during free breathing for good image quality without relying on patient cooperation or trackers or navigators.

"DISCO Star could help us detect and characterize many types of lesions in the liver where multiple differential diagnoses can be observed with very specific enhancement patterns," Dr. Legou explains. It is important to detect small lesions early in order to change the patient care pathway at the earliest possible disease stage.

"In my initial assessment of the DISCO Star prototype, the overall image quality was quite good in terms of spatial resolution, contrast and SNR, and I believe it will impact my diagnostic confidence thanks to the ability to precisely assess lesion perfusion."

Dr. Francois Legou

With DISCO Star, Dr. Legou was able to achieve consistent temporal resolution on a free-breathing, dynamic scan, around 10 seconds per phase, without compromising spatial resolution, which can be kept around 1.5 × 1.5 × 3.6 mm. It is important to find the best compromise between spatial and temporal resolution to avoid streaking artifacts.

He adds, "Based on our experience with the DISCO Star prototype, we anticipate it could allow for higher temporal resolution without sacrificing spatial resolution. Most important, this could be accomplished without patient breath hold."

Figure 5. Patient with liver metastases. (A-D) DWI b400, 1.5 x 1.5 x 3.6 mm, 26 sec. for 3 arterial phases, HyperSense factor of 1.3.

Figure 6. Multi-arterial phases improve early enhancement visualization and facilitate lesion contrast enhancement analysis. HyperSense is designed to reduce scan time without changing image quality. (A, B) LAVA without Hypersense in 25 sec. compared to (C, D) LAVA with HyperSense in 17 sec., a 25 percent reduction in breath-hold time. Acquisition voxel was 1.3 x 1.6 x 2.4 mm.

The ability to deliver free-breathing abdominal exams is important due to the wide array of patient conditions, including those with sleep apnea or dyspnea, a condition where the patient does not inspire and expire at the same level leading to motion artifacts, as well as in pediatric and elderly populations. Dr. Legou believes that DISCO Star could simplify the workflow and enable reproducible exams regardless of the technologist’s expertise.

Dr. Legou says the need for an MR sequence that is robust to motion and adaptable to young and old patients is greatly needed. In addition to motion management due to respiration, abdominal MR imaging can be compromised by peristalsis and cardiac shading. Often, contrast media is required, adding the additional challenge of combining both high-temporal and high-spatial resolution in order to detect small lesions that can wash-in and wash-out very quickly.

"In my opinion, DISCO Star could help answer these challenges at the same time," he says.

Figure 7. Dynamic DISCO Star enables visualization of progressive enhancement in a typical angioma case. (A-E) DISCO Star, phases 1, 3, 5, 7, 9 of (F) the DISCO Star acquisition; (G) LAVA Flex breath hold without contrast; (H) LAVA portal phase, breath hold; and (I) ADC map.

Figure 8. A 43-year-old man with liver hemangioma. (A) Axial T2 FatSat PROPELLER; (B) high ACD; (C) LAVA, late injected phase, 3 min.; (D) DISCO Star native axial plane; (E) DISCO Star sagittal reformat; and (F) DISCO Star coronal reformat. 1.5 x 1.6 x 2.8 mm, 10 temporal phases + Mask, 11.4 sec.phase temporal resolution, 3:22 min.

Figure 9. Excellent visualization of distal intrahepatic bile duct (C, arrow). 3D MRCP acquisition shows multiple stenoses of pancreas main duct. (A-C) DISCO Star, 1.5 x 1.6 x 2.8 mm, 10 temporal phases, 11.7 sec./phase, 3:19 min., (D) DWI b800 and (E) 3D MRCP.