Achieving PI-RADS-compliant prostate imaging at 1.5T

Over the last decade, multiparametric MR has become an indispensable tool in the early detection of prostate cancer. To help improve high-quality MR and reduce unnecessary biopsies and treatment for benign or subclinical cases, the American College of Radiology, the European Society of Urogenital Radiology and AdMeTech Foundation developed global clinical imaging guidelines, the Prostate Imaging Reporting and Data System (PI-RADS®)1.

It’s well known that PI-RADS® v2.1 revolves around diffusion and high-resolution T2 FSE MR imaging, with restricted diffusion and abnormal signal on T2 being some of the hallmarks of cancerous pathology. The PI-RADS® guidelines recommend 3.0T MR systems, as they can inherently achieve higher resolution and additional signal. Newer technologies such as AIR™ Coils, AIR™ Recon DL and MAGiC DWI make achieving PI-RADS® v2.1 compliant prostate imaging at 1.5T a game changer with improved image quality, shorter scan times and a better overall experience for the patient.

At radiomed (Wiesbaden, Germany), Christopher Ahlers, MD, Managing Partner, has always been a strong proponent of 3.0T MR, particularly for imaging the prostate. When the practice installed a SIGNA™ Pioneer 3.0T system in 2015, prostate exams were moved to the new system, and Dr. Ahlers saw a significant improvement in image quality as well as the ability to adhere to the PI-RADS® standards.

“I always felt that the gap in quality from 3.0T to 1.5T was so large that as long as we have 3.0T we shouldn’t consider imaging the prostate at 1.5T,” Dr. Ahlers says.

That was before radiomed installed a SIGNA™ Explorer 1.5T and the latest software from GE Healthcare, SIGNA™Works AIR™ IQ Edition, which includes AIR™ Recon DL, GE Healthcare’s deep-learning-based reconstruction solution designed to improve SNR and image sharpness, enabling shorter scan times.

In fact, Dr. Ahlers has seen a steady progression of image quality improvement and scan time reduction on SIGNA™ Explorer, beginning with AIR™ Recon in the previous version of software, then the upgrade to the new software and the introduction of AIR™ Recon DL. While the first advancement delivered a significant improvement in SNR and image quality, “recently switching to AIR™ Recon DL has provided a tremendous increase in image quality and a decrease in scan time,” he says.

As important, radiomed can acquire the multiparametric prostate exam that adheres to the PI-RADS® v2.1 guidelines on SIGNA™ Explorer with AIR™ Recon DL in approximately 17 minutes, which includes the two-minute additional T1 post-contrast series as required in Germany’s prostate MR guidelines2. While radiomed can obtain the same protocol with the added sequences on SIGNA™ Pioneer MR in just under 12 minutes, the quality between the two exams is comparable when using the latest software, he adds.

“There is still a gap in terms of quality and scan times between 3.0T and 1.5T in MR imaging, but it was never as small as it is now,” he adds.

Without AIR™ Recon DL, Dr. Ahlers says it would be difficult to adhere to a PI-RADS® v2.1 compliant exam due to the time needed to acquire the proper image resolution. For example, on a 1.5T system they followed the German guidelines2 for T2 resolution, 0.6 x 0.8 x 3.5 mm, to gain as much signal as possible. Now, with SIGNA™Works AIR™ IQ Edition, they can adhere to PI-RADS® v2.1 guidelines with 0.4 x 0.7 x 3 mm resolution (Figure 1).

Similarly, radiomed is using AIR™ Recon DL with MAGiC DWI to synthetically acquire high b-values. Diffusion can be a lengthy, time-consuming sequence. By combining these two technologies, Dr. Ahlers can acquire synthetic high b-values with significantly improved SNR and generate a very high-quality ADC (Figure 1B and 1C). The old protocol had a 2 x 2 x 4 mm voxel size in approximately five minutes. Now, by using MAGiC DWI and AIR™ Recon DL together, he can acquire a 1.7 x 1.7 x 3 mm voxel size in just over three minutes scan time with much improved image quality, which allows for the ability to match the slice thicknesses used for the T2s and dynamic contrast series (DCE).

“I am now confident to use our 1.5T SIGNA™ Explorer with AIR™ Recon DL for a good quality prostate exam. AIR™ Recon DL is paving the way for doing PI-RADS® v2.1 complaint prostate imaging on 1.5T,” Dr. Ahlers adds.

Overcoming the challenges of implants

Fairfax MRI Center, part of Fairfax Radiology Consultants (FRC), began using 1.5T MR to image prostate patients with MR-Conditional pacemakers, implantable cardioverter defibrillators, intracranial leads and hip implants. This is significant since the increase in susceptibility artifacts at 3.0T in these patients near the area of interest can obscure pathology. Additionally, some MR-Conditional implants are incompatible at 3.0T.

When Fairfax MRI Center and FRC upgraded its SIGNA™ Artist 1.5T with GE’s latest software, SIGNA™Works AIR™ IQ Edition, the practice could image the prostate at 1.5T with the speed and resolution required for the PI-RADS® v2.1 guidelines and overcome the challenges of problematic implants in less time.

“With newer techniques using AIR™ Recon DL that allow us to increase our resolution, the image quality we are seeing at 1.5T is really excellent,” says Melany Atkins, MD, Medical Director at Fairfax MRI Center. “Now with AIR™ Recon DL, we’ve been able to achieve all the PI-RADS® v2.1 criteria – higher resolution, thinner slice thickness and smaller field-of-view — in 14 minutes, 58 seconds at 1.5T,” Dr. Atkins says. That is nearly a 50% reduction in total scan time for prostate MR at FRC.

Having access to both 1.5T and 3.0T in their practice allows Fairfax MRI Center to move patients to different scanners if needed. In one recent case, a patient was scheduled for a prostate MR exam on the SIGNA™ Architect 3.0T. It was identified that the patient had an MR-Conditional hip implant, making the exam almost nondiagnostic due to the increase of blooming susceptibility artifact. In fact, on the FOCUS DWI, the artifact was so significant the prostate was not recognizable (Figure 2).

The center was able to move the patient to the SIGNA™ Artist 1.5T and easily fit him into the schedule because the use of AIR™ Recon DL for all exams has shortened scan times, making it easier to accommodate add-on patients. In this particular patient, Dr. Atkins explains there was a lesion that was identified on the critical FOCUS DWI series at 1.5T that was completely unrecognizable on the 3.0T exam (Figure 2). This sort of finding can change the course of the treatment plan for the patient.

FRC typically includes two diffusion sequences — FOCUS and MUSE — and 3D T2 Cube that is used for treatment planning purposes. Even with these additions, scan time is 23 minutes, well below the practice’s prior scan times of just over 30 minutes.

“I love MUSE, but there are times when we want that small field-of-view with FOCUS,” she adds. Plus, an added benefit is higher quality ADC with more information that she can compare the two diffusion sequences, which increases clinical confidence.

MAGiC DWI is also utilized for both FOCUS and MUSE to acquire both 1400 and 2000 b-values with good image quality. By using AIR™ Recon DL with MAGiC DWI, FRC has shortened each critical diffusion sequence by 40%.

All around better patient care

Reducing scan times is good for the reading radiologist, the patient and the practice. There is less artifact due to patient or respiratory motion, organ blur or rectal gas and shorter scan times are more comfortable for the patient and more efficient for the practice. There’s another key benefit for patients, and potentially technologists, by using AIR™ Recon DL and the AIR™ AA Coil: FRC no longer uses an endorectal coil.

“I don’t know who is happier, our patients or our technologists,” Dr. Atkins says.

During her training, Dr. Atkins was reminded of the increase in signal with an endorectal coil. However, this coil can lead to susceptibility artifacts from the barium or air in the balloon.

“With the gains from using AIR™ Recon DL, AIR™ Coil and improvements in diffusion, we really don’t need the endorectal coil anymore,” she adds. “From start to finish, everyone is happier without it.”

Now, prostate patients feel like they are getting a blanket placed on top of them with the AIR™ AA Coil. They are also easier for the technologists to use.

“Everyone loves the AIR™ Coils and AIR™ Recon DL because the image quality is fantastic,” Dr. Atkins adds.

Increasing patient access helps grow the practice

Since 2015, Nakul Gupta, MD, Assistant Professor of Clinical Radiology and Director of MRI at Houston Methodist, has seen the demand for prostate MR imaging grow exponentially, from a handful of cases now up to a dozen or more each day. Urologists, he says, are increasingly accepting of both the radiologist’s interpretive abilities and the power of prostate MR to provide the information needed for patient diagnosis and disease management.

“Urologists see the value in prostate MR,” he adds. That acceptance is largely due to advancements in multiparametric MR imaging and new technologies that help propel the use of 1.5T MR in prostate imaging, allowing broader patient selection.

Dr. Gupta recalls that five years ago, the practice would occasionally perform a prostate MR exam at 1.5T in extenuating circumstances, such as the presence of MR-Conditional implants or devices, or in a patient with hip arthroplasties. However, there was a significant decrease in image quality on both the T2 and diffusion sequences.

“In the T2 sequences, we would try to overcome loss of SNR by using more signal averages or PROPELLER, which helped,” Dr. Gupta explains. “But with diffusion, it was really challenging to overcome that SNR loss. Definitely, 1.5T diffusion without an endorectal coil was only borderline diagnostic.”

Now, with the SIGNA™ Artist upgrade to SIGNA™Works AIR™ IQ Edition featuring AIR™ Recon DL and the AIR™ AA Coil, it’s an entirely different story. Knowing the benefits of having their MR scanners on the same software, Houston Methodist also did a software upgrade for their Discovery™ MR750 3.0T system, which has breathed new life into their scanner fleet.

“It is definitely practical to use surface coils for prostate imaging at 1.5T now,” he adds. Being able to avoid using an endorectal coil is not trivial for the patient or the technologists.

Also, the ability to perform PI-RADS® v2.1 complaint prostate exams may also impact patient access. In general, there are more 1.5T MR systems installed worldwide than 3.0T. For a practice, the ability to accommodate prostate patients on a 1.5T system also means more flexibility in scheduling and potentially less time to wait for an appointment.

Dr. Gupta says facilities with only 1.5T systems can confidently provide high-quality prostate MR exams if they are using AIR™ Recon DL, AIR™ AA Coils and the latest software from GE Healthcare. And, for sites that have both 3.0T and 1.5T MR systems, they can confidently move exams to the lower Tesla strength with these technologies, if necessary, to accommodate a broader base of patients. This is especially useful considering that the average age of a prostate cancer patient is 66 years and the average range of patients undergoing hip replacements is between 50-70 years old, with a median of 65 years.3,4

This becomes significantly important depending on the stage of the prostate cancer. Some low-risk groups can take an observational or watchful-waiting approach driven by the patient’s symptoms for the next steps, whereas with other intermediate risk groups an active surveillance route with routine follow-up for blood tests and imaging is preferred5. If a patient has a hip implant during that time, it will make it very difficult to obtain a diagnostic exam, which could result in a biopsy. Having the ability to offer a non-invasive procedure for these patients improves compliance for following up long term.

“Any time you can have an exam not restricted to a certain machine, that’s definitely an operational benefit,” Dr. Gupta says.

With AIR™ Recon DL and the AIR™ AA Coil, Dr. Gupta can achieve the multiparametric PI-RADS® v2.1 T2 sequences with 3 mm slices and 0.4 mm resolution in-plane, as well as high b-value diffusion sequences using MAGiC DWI to synthesize the b-1400 values or higher.

“Using these technologies, we get sufficient SNR at b-800 values with the appropriate slice thickness and resolution requirements,” he adds. “Then, being able to use that acquisition to generate any higher b-value in the image is quite helpful at 1.5T, where it is harder to acquire those values natively due to SNR limitations. With the combination of AIR Recon DL and MAGiC DWI, these synthesized high b-values on 1.5T look very close to the natively acquired high b-values on 3.0T. You may need additional signal averages at 1.5T, but, nonetheless the scan times are very reasonable.”

In diffusion, FOCUS helps with imaging smaller field-of-views and reduces some of the distortion related to rectal gas.

“There may be a potential benefit of using 1.5T versus 3.0T in prostate imaging for decreased susceptibility artifact from rectal gas,” Dr. Gupta says (Figure 3). “So, there is potentially another hidden benefit that really hasn’t been explored by performing prostate MR at 1.5T.”

References

1. American College of Radiology. Prostate & Data System (PI-RADS). Available at: https://www.acr.org/Clinical-Resources/Reporting-and-Data-Systems/PI-RADS.
2. Franiel T, Asbach P, Beyersdorff D, et al. Board of the Deutsche Röntgengesellschaft e. V. (DRG); Board member of the Professional Association of German Radiologists (BDR). mpMRI of the Prostate (MR-Prostatography): Updated Recommendations of the DRG and BDR on Patient Preparation and Scanning Protocol. Rofo. 2021 Jul;193(7):763-777. English, German. doi: 10.1055/a-1406-8477.
3. American Cancer Society. Risk of prostate cancer. Available at: https://www.cancer.org/cancer/prostate-cancer/about/key-statistics.html.
4. Crawford RW, Murray DW. Total hip replacement: indications for surgery and risk factors for failure. Ann Rheum Dis. 1997;56(8):455-457. doi:10.1136/ard.56.8.455.
5. American Cancer Society. Observation or Active Surveillance for Prostate Cancer. Available at: https://www.cancer.org/cancer/prostate-cancer/treating/watchful-waiting.html.