Just as Sharp: MRI Scans at Triple the Speed
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What if there were a way to triple the speed of MRI scans without losing resolution? At the Clinical Trials on Alzheimer’s Disease conference, held October 29 to November 1 in Madrid, Miguel Rosa-Grilo of University College London presented just such an option. By leveraging recent advances in scanning technology, his group cut the time needed for diagnostic structural MRIs by two-thirds, with no measurable loss of quality. Shown side-by-side comparisons of scans done by the new versus old methods, scientists in Madrid could not tell the difference. Adopting the new method could make scanning easier on patients and help remove a bottleneck in Alzheimer’s diagnosis and care, Rosa-Grilo suggested.
- New MRI technology allows diagnostic scans to be done in one-third the time.
- Images are nearly indistinguishable from those done by standard protocols.
- Fast scans could resolve bottlenecks in patient care.
Clifford Jack of the Mayo Clinic in Rochester, Minnesota, agreed the field needs to move in this direction. He noted that fast MRI scans using a similar protocol are being tested in ADNI4 and the Standardized Centralized Alzheimer’s & Related Dementias Neuroimaging (SCAN) study, as well.
“Speeding up MR exams will be necessary to accommodate increased throughput as a new stream of patients receiving AD treatment places increasing demands on radiology departments,” Jack wrote to Alzforum (comment below).
Spot the Difference? T1-weighted scans of a 59-year-old with posterior cortical atrophy, done by standard and fast protocols. Which is which? (Answer at bottom.) [Courtesy of Miguel Rosa-Grilo.]
In Alzheimer’s, MRI scans are needed not only for diagnosis, but also to monitor for ARIA, the most concerning side effect of amyloid immunotherapy. The large number of required scans can limit how many patients a site can treat. In addition, long scan times can be hard on patients. Some have trouble tolerating the claustrophobia of the machine or lying motionless for long.
To speed things up, Rosa-Grilo, working with Nick Fox at UCL, turned to Wave-Controlled Aliasing in Parallel Imaging. Developed in 2015 by scientists at Massachusetts General Hospital, Wave-CAIPI uses multiple coils arranged around a patient’s head to perform parallel imaging in three-dimensional space, speeding up acquisition (Bilgic et al., 2015).
Rosa-Grilo incorporated Wave-CAIPI into the diagnostic scanning protocol used at UCL’s memory clinic. It comprises four sequences: T1-weighted 3D, T2-weighted 2D, T2-weighted 3D, and 3D FLAIR imaging. The entire protocol takes nearly 18 minutes to complete. By adding Wave-CAIPI, Rosa-Grilo shortened this to 6.5 minutes.
A FLAIR for Speed. Three-dimensional FLAIR imaging of a 74-year-old with vascular cognitive impairment, done by both protocols. Which is which? (Answer at bottom.) [Courtesy of Miguel Rosa-Grilo.]
Was the faster imaging as reliable? To test this, the scientists recruited 90 patients who came to the clinic for diagnosis, scanning them with both the old and new protocols in the same session. In this group, 21 percent turned out to have AD, 38 percent other pathologies, and 41 percent no pathology. Three neuroradiologists independently assessed their scans in a blinded fashion.
The result? The radiologists assessed the fast and standard scans of each patient nearly identically on multiple measures, including detecting the presence of medial temporal lobe atrophy, posterior cortical atrophy, microbleeds, and white-matter hyperintensities. The type of scan made no difference in how likely radiologists were to clear AD patients for amyloid immunotherapy. Moreover, the variability between how a given rater assessed a fast versus standard scan of the same patient was smaller than the variability between how different raters assessed those scans. Because use of the fast scan introduced less variability than did changing raters, fast scans are no worse than standard ones, Rosa-Grilo concluded.
Finding Microhemorrhages. Susceptibility-weighted imaging to detect microbleeds (arrows) in a 60-year-old with cerebral amyloid angiopathy, done by both protocols. Which is which? (Answer at bottom.) [Courtesy of Miguel Rosa-Grilo.]
To illustrate his point, Rosa-Grilo showed several examples of fast versus standard scans of the same patient, and asked the audience to guess which was which. In general, the audience was unable to tell. Can you do better?
The findings suggest that the fast protocol can be used for diagnosing AD and assessing treatment eligibility, Rosa-Grilo said. He noted that it remains to be shown whether the fast protocol will work for monitoring ARIA, as well. Jack, for one, believes it will. “Although ARIA was not specifically evaluated, the imaging exam described by Rosa-Grilo and colleagues includes both FLAIR and gradient echo sequences and thus should be useful for detection of ARIA,” he wrote. Rosa-Grilo is now testing this.
Other scientists agreed the advance has potential. Some noted that fast scans may save less time in routine clinical care than they did in this study, because of the required check-in, undressing, and redressing time each patient needs for these appointments. Still, Jonathan Schott of Queen Square Institute of Neurology, London, who works with Fox and Rosa-Grilo, estimated that the new technology might bring the current 30-minute time slots their clinic now schedules for diagnostic scans down to 15 minutes.
Schott noted another advantage: Because scanning is so rapid, it would be possible to quickly redo the sequence if the patient moved during the procedure. That would help scientists capture better data.—Madolyn Bowman Rogers
Answers: 1. Fast scan on left. 2. Fast scan on right. 3. Fast scan on right.
References
Paper Citations
- Bilgic B, Gagoski BA, Cauley SF, Fan AP, Polimeni JR, Grant PE, Wald LL, Setsompop K. Wave-CAIPI for highly accelerated 3D imaging. Magn Reson Med. 2015 Jun;73(6):2152-62. Epub 2014 Jul 1 PubMed.
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Comments
Mayo Clinic
At the recent CTAD meeting, Grilo and colleagues at UCL described an ultra-fast MRI protocol consisting of four core imaging sequences. Using the advanced imaging methods, a complete MR exam including all four sequences could be accomplished in around 6½ minutes with no apparent loss in diagnostic quality. This represents a 63 percent reduction in imaging time compared to standard acquisition methods. As the authors point out, speeding up MR exams will be necessary to accommodate increased throughput as a new stream of patients receiving AD treatment places increasing demands on radiology departments.
In addition, since every patient requires a number of safety MRIs, decreasing time per exam is needed to reduce patient burden. Although ARIA was not specifically evaluated, the imaging exam described by Grilo and colleagues includes both FLAIR and gradient echo sequences and thus should be useful for detection of ARIA .
It is useful to know that both the ADNI 4 and SCAN (Standardized Centralized Alzheimer’s & Related Dementias Neuroimaging) studies offer ultra-fast imaging as part of the protocols for scanners that have this capability. A difference is that, for a variety of reasons, ADNI and SCAN employ only product imaging sequences (series), i.e., sequences that have received regulatory approval for clinical use. In contrast, the sequences used in the abstract by Grilo were a work in progress, i.e., not yet approved for clinical use.
Nonetheless, investigating ultra-fast, highly efficient imaging as an important new direction that the MR field must take is common to ADNI 4, SCAN, and the work of the UCL group. In fact, several of the UCL coauthors on the Grilo abstract are coinvestigators in the ADNI MR Core.
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