Free-breathing pediatric abdominal MR using DL-based reconstruction with motion compensation

by Christian Kellenberger, MD, Professor of Pediatric Radiology and Radiologist-in-Chief, University Children’s Hospital Zürich, Zürich, Switzerland

Christian Kellenberger, MD

University Children’s Hospital Zürich Zürich, Switzerland

MR is the preferred advanced cross-sectional imaging technique for the pediatric abdomen in a number of scenarios due to its high diagnostic potential and the lack of ionizing radiation compared with CT. Beyond the standard abdominal MR exams, typical applications include: MR enterography to visualize intra- and extraluminal bowel pathology; MR cholangiopancreatography to depict pancreatic and biliary abnormalities; and MR urography for functional and structural evaluation of the kidneys and urinary tracts.

Acquiring MR images in the pediatric abdomen is challenging due to varying patient size and the patient’s inability to perform breathhold, resulting in motion artifacts. Motion compensation techniques can improve image quality and employing PROPELLER is a very useful sequence in this respect. PROPELLER enables free-breathing abdominal imaging in children with reduced motion artifact that may occur from both breathing and bowel peristalsis, while providing T1 and T2 contrast. However, a compromise in resolution (both slice thickness and in-plane resolution) might be necessary in order to preserve SNR and reduce scan time, especially in cases where sedation is required. Recent advances in deep-learning-based reconstruction, such as AIR™ Recon DL, have shown very compelling evidence that it is indeed possible to preserve and improve image quality, both in terms of SNR and spatial resolution, while reducing scan time in conventional Cartesian 2D acquisitions. After upgrading our Discovery™ MR750 3.0T and our Discovery™ MR450 1.5T systems to SIGNA™ Premier and SIGNA™ Artist, respectively, both systems were fully equipped with AIR™ Recon DL and AIR™ Coil technology. Our institution was involved in the clinical evaluation of the extension of AIR™ Recon DL to the PROPELLER acquisition (e.g., AIR™ Recon DL PROPELLER) as the first pediatric site to assess the clinical utility of the technique for abdominal imaging in children.

Figure 1. T2-weighted PROPELLER images obtained on SIGNA™ Artist 1.5T on a 2-month-old female presenting with non-bilious vomiting. (A-C) Conventional reconstruction and (D-F) AIR™ Recon DL PROPELLER reconstructed images using the same raw data are shown. Fifty-one 4 mm slices were acquired in 1:43 min. to cover the entire abdomen without respiratory triggering. AIR™ Recon DL images present less noise and decreased blurring of the tissue boundaries, thus allowing for sharper delineation of the visceral organs, such as the liver, spleen, adrenals, bowel or the “mesenteric whirl,” as well as the small structures: hepatic vasculature, spinal cord and (A, D) nerve roots, (B, E) renal collecting system and (C, F) the mesenteric lymphatic malformation where the septations are clearly visible.

Case 2

A 7-year-old female, follow-up MR after neuroblastoma treatment (Figure 2). Figure 2A and 2D are the previous scans of the same patient from 2017 prior to the upgrade to SIGNA™ Artist.

Case 1

A 2-month-old female presenting with non-bilious vomiting: mesenteric lymphatic malformation and incomplete midgut volvulus (Figure 1).

Figure 2. (A-C) T2-weighted and (D-F) T1-weighted images obtained at 1.5T on a 7-year-old girl as part of a follow-up evaluation after neuroblastoma treatment. (A, D) Previous scan of the same patient from 2017 (Discovery™ MR450, 32-channel cardiac coil) and SIGNA™ Artist upgrade acquisition with (B, E) conventional reconstructions and (C, F) AIR™ Recon DL PROPELLER images using the same raw data. In particular, (D) respiratory compensated T1-weighted spin echo was replaced by (F) T1-weighted AIR™ Recon DL PROPELLER with no respiratory triggering, which shows superior motion robustness with minimal respiratory artifacts in a shorter acquisition time: (F) 68 slices in 4:24 min. versus (D) 51 slices in 6:44 min. (F) Note the sharper delineation of moving structures, such as small bowel (peristalsis) or intraspinal nerve roots (CSF pulsation). Also, AIR™ Recon DL PROPELLER enables higher resolution images, (0.7 x 0.7 mm² in plane versus 0.9 x 1.1 mm²).

Conclusion

AIR™ Recon DL PROPELLER images present less noise and decreased blurring of the tissue boundaries with sharper delineation of visceral organs and small structures. In particular, T1 AIR™ Recon DL PROPELLER is the best T1-weighted method we have encountered for removing respiratory artifacts in free-breathing children. It performs better than conventional spin echo with signal averaging (multiple NEX) or respiratory compensation, while enabling higher resolution and thinner slices in a shorter acquisition time. Moving structures, such as the small bowel with peristalsis or intraspinal nerve roots with pulsation, are sharply delineated.

AIR™ Recon DL PROPELLER improves the image quality of abdominal MR in children, with the potential to obtain higher spatial resolution and simultaneously shorten imaging time.