Nippon Koukan Hospital (Tokyo) installed a SIGNA™ Voyager and upgraded a 12-year-old 1.5T MR to SIGNA™ Explorer in May 2018. While many hospitals may opt to implement one 3.0T MR and one 1.5T MR, Kenji Ogawa MD, PhD, Director, Department of Radiology, believed a two 1.5T MR department would best meet the hospital and patient needs.
MR exams account for 7 percent of all radiology imaging studies at Nippon Koukan Hospital. Since the hospital is focused on sports medicine, the most common applications are spine (30 percent) and orthopedics (21 percent), with the majority of the latter being knee exams. Gastrointestinal MR exams are also commonly employed.
A key factor in Dr. Ogawa’s decision to select SIGNA™ Voyager was SIGNA™Works, including key sequences such as PROPELLER MB, the HyperWorks suite, VIBRANT Flex, IDEAL IQ and MR Touch.
Dr. Ogawa believes the applications on SIGNA™ Voyager are of such high quality that he didn’t need to move to 3.0T MR. Plus, with the SIGNA™ Explorer upgrade, he was able to further extend advanced MR imaging capabilities in the department in a fiscally responsible way.
Advanced apps
On SIGNA™ Voyager, Dr. Ogawa is very impressed by PROPELLER MB, HyperSense and HyperCube. The high scanning speed of HyperSense and HyperCube, coupled with high-resolution matrix imaging, were important for the department to maximize scanning efficiency. HyperSense is an advanced, iterative reconstruction technique for accelerating the acquisition. By utilizing HyperSense, Dr. Ogawa found that he can image the posterior fossa and surrounding areas with high resolution and he can shorten the MR angiography (MRA) scan time in the brain. He has the added advantage of using 3D Cube to reconstruct sagittal and coronal images from an axial acquisition as well as shorten acquisition times with HyperSense.
Having two 1.5T MR systems is easier to manage within the department, particularly in terms of protocol standardization. In terms of functionality, SIGNA™ Voyager offers equivalent applications to those found on a 3.0T system with the added benefit that there is a lower susceptibility to MR-Conditional metal implants or devices, therefore less noticeable metal artifacts, in 1.5T compared to 3.0T.”Dr. Kenji Ogawa
“The reconstructed coronal and sagittal images are clear and such good quality that they don’t look like they were reformatted from the axial plane,” he adds.
Figure 1.
Using HyperSense with a factor of 1.5 and ARC with a factor of 2 have decreased T2 Cube and T2 FLAIR exam times by approximately 30 percent at Nippon Koukan Hospital. (A) Axial T2 Cube FLAIR, 0.9 x 1.2 x 2.6 mm, 2 NEX, 5:04 min. and (B) axial T2 Cube FLAIR with HyperSense, same acquisition in 3:28 min. (C) Axial T2w Cube, 0.9 x 0.9 x 2.6 mm, 2 NEX, 5:26 min. and (D) axial T2w Cube with HyperSense, same acquisition in 3:31 min.
The impact
Most notable is the substantial improvement in image quality and shorter scan times. With the prior system, the technologists often chose to optimize scan time because even if they increased scan time to enhance image quality, the benefit in SNR was minimal. Also, it was important for department scheduling to maintain consistent exam times across all MR systems.
“MR is all about signal and you need to decide how you are going to use it — for better image quality, faster scan times or a combination of both,” Dr. Pechet explains. With the new hardware, he estimates a better than 20% improvement in SNR, but the new pulse sequences and software are also much better.
This package of new hardware and software — new digital receive chain, coils, sequences and reconstruction technology — is absolutely key in Dr. Pechet’s opinion. This required protocol development, particularly since there were many capabilities and several new sequences that Shields had not previously used.
The team started with longer scan times and patient slot times, initially at one hour. As the protocols were improved, the scan times decreased and they compressed the schedule. Dr. Pechet worked with GE applications specialist Jorge Forero to refi ne protocols, and in many cases develop new protocols for sequences they had not previously used, so that each was 80% optimized. Then they moved to the next one.
As a pilot site, Shields Brockton had on-site GE support, which Dr. Pechet acknowledges won’t be available to every site. However, the sequence development work that he and Forero completed will be available to subsequent sites and users.
Figure 2.
HyperSense can also be used to increase spatial resolution with the same scanning time. (A, B) TOF-MRA, 0.8 x 1.3 x 1.0 mm, 4:45 min. and (C-E) TOF-MRA with HyperSense, 0.7 x 0.9 x 1.0 mm, 4:32 min.
Figure 3.
PROPELLER MB helps preserve tissue contrast regardless of weighting while also reducing motion artifacts and providing a more signal rich image. C-spine images: (A) axial T2w FSE, 0.7 x 0.7 x 5 mm, 2:03 min.; (B) axial T2w PROPELLER MB, 0.6 x 0.6 x 5 mm, 2:21 min.; (C) axial T1w FSE, 0.7 x 0.8 x 5 mm, 2:05 min.; and (D) axial T1w PROPELLER MB, 0.6 x 0.6 x 5 mm, 3:01 min.
Figure 4.
PROPELLER MB in the female pelvis. (A) Axial T2w PROPELLER, 1:13 min.; (B) coronal T1w PROPELLER, 2:53 min.; (C) sagittal T2w PROPELLER, 3:01 min.; (D) axial T2w FatSat PROPELLER, 2:48 min.; (E) axial DW-EPI, b1000, 2:44 min.; and (F) coronal T2w PROPELLER, 3:01 min.
Figure 5.
FSE Flex delivers homogenous FatSat images in a single scan, even in the presence of MR Conditional implants such as fixation hardware. These images are post-surgery in a patient who had fixation hardware affixed in the L4/5 vertebrae in the lumbar spine. (A) Sagittal T2w, 0.9 x 1.1 x 5 mm, 2:13 min.; (B) sagittal T1w, 0.9 x 1.1 x 5 mm, 2:50 min.; (C) sagittal T2w FatSat, 1.1 x 1.1 x 5 mm, 1:59 min.; and (D) sagittal T2w FSE Flex, 1.1 x 1.1 x 5 mm, 3:11 min.
PROPELLER MB (Multi-shot Blade) combines multiple blades together to achieve shorter TEs and improved motion correction for true T1 and proton density (PD) contrast imaging. It is compatible with Auto Navigator, shim volumes, sat bands and ASPIR.
The impact of PROPELLER MB is especially noticeable in pelvic and cervical spine examinations. I believe the PROPELLER MB image is the best in the pelvis, where I can clearly see the edges of a lesion. When I first saw the image quality, I noticed it was completely different and improved from before. The cervical spine image with PROPELLER MB is by far the best I’ve seen, and I believe the female pelvis has benefited the most from this sequence.”Dr. Kenji Ogawa
Another key area of improvement is the 2-point DIXON FSE Flex for excellent fat suppression. Dr. Ogawa says it has helped address the issue of fat remaining on the edge of the image, making it more difficult and stressful for the radiologists to read through the image for a confident diagnosis. This was particularly an issue in orthopedic patients with certain MR-Conditional metal implants.
“Until now, the effect of fat suppression was sometimes poor due to metal artifacts from implants,” Dr. Ogawa explains. “In addition, uniform fat suppression can also be a challenge in breast imaging. Now, fat suppression has become particularly uniform, especially in the rim of the breast, such as the chest wall.”
The dynamic breast protocol at Nippon Koukan Hospital now includes VIBRANT Flex. However, one disadvantage is that fat suppression in a normal shoulder without any physical findings sometimes appears black, “because the fat suppression is too effective,” says Dr. Ogawa. “Even with this, the images of the shoulder and elbow have clearly improved with SIGNA™ Voyager.”
Dr. Ogawa attributes some of the improvement in FatSat on SIGNA™ Voyager to the 70 cm bore. He can position the patient in the center of the bore and patients seem to be more comfortable.
Since SIGNA™ Explorer and SIGNA™ Voyager have a similar suite of SIGNA™Works applications, Dr. Ogawa doesn’t see much difference in the images. All MR elastography (MRE) exams are performed on SIGNA™ Voyager, so he knows which scanner was used in that case. In most other instances, he cannot easily recognize on which scanner an MR exam was conducted.
Addressing liver disease with MR Touch and IDEAL IQ
Even though the incidence of viral hepatitis and overall liver disease and liver cancer in Japan has dropped in the last decade,1 it remains a health issue. The incidence of hepatic cirrhosis, both alcoholic and non-alcoholic steatohepatitis, continue to increase in Japan.2 Ultrasound elastography is commonly used in Japan, however, the technique is highly operator dependent and may not be reproducible.
Figure 6.
Liver imaging with MRE (MR Touch) and IDEAL IQ. (A, F) In-phase; (B, G) out-of-phase; (C, H) IDEAL IQ, (C) fat fraction 9%, (H) fat fraction 0.6-2.6%; (D,I) MRE and T2w SSFSE fused images; and (E, J) MRE wave images.
Figure 7.
IDEAL IQ delivers quantitative measurements of iron and fat content. (A) Axial in-phase and (B) axial out-of-phase at 1.25 x 2.5 x 7 mm, 14 sec.; and (C) fat fraction with IDEAL IQ, 2.75 x 2.75 x 8 mm, 19 sec.
MR Touch is reproducible across exams and provides relative stiffness data of the liver, which may help with the assessment of liver fibrosis. IDEAL IQ is included in patients with fatty liver disease to obtain quantitative measurements of iron and fat content.
The department has been collecting MRE data since the implementation of SIGNA™ Voyager and Dr. Ogawa believes the technique will become a point of distinction and strength for the hospital.
With two specialists in liver medicine at the hospital, Dr. Ogawa sees liver imaging as an area of potential growth in terms of patient volume and attracting specialists. He is hopeful for the possibility of conducting joint research with other academic hospitals in the near future.
The unique quantification provided by IDEAL IQ and the relative stiffness data of MR Touch are very good. Quantitative analysis will be important to the future of MR imaging.”Dr. Kenji Ogawa
Dr. Ogawa is hopeful that continued improvements in tissue characterization, including deposition of metals, as well as time resolution, will further extend diagnostic capabilities. While it can be difficult for radiologists to read through some artifacts, he believes that completely removing artifacts with image processing is not as important as correcting movement with tools such as PROPELLER MB. Some artifacts, such as respiratory-induced artifacts in the lower abdomen, are to be expected when reading these types of images.
He adds, “I think that MR will benefit us and our patients more with improvements in quantitation and temporal resolution of images.”
References
- Institute for Health Metrics and Evaluation. Japan. Available at: https://www.healthdata.org/japan.
- Kang JH, Matsui T. Changing Etiology in Liver Cirrhosis in Sapporo, Japan. Euroasian J Hepatogastroenterol. 2018 Jan-Jun; 8(1): 77–80.
