These images were acquired with an investigational device. PD T2 T2 FLAIR T1 MAP T1 FLAIR PSIR T1 New Technology Allows Multiple Image Contrasts in a Single Scan MR exams can be time consuming. A typical neurological MR scan can take approximately 30-45 minutes per patient. Consequently, there is a need for increased efficiency, to improve productivity and expand the use of MR globally. Image compilation technology is being explored as a method for allowing clinicians to capture multiple image contrasts in a single scan the goal being generating quantitative T1, T2, STIR, T1-FLAIR, T2-FLAIR, and PDweighted images in far less the total time it would take to acquire each contrast separately. The time saved could allow clinicians to scan more patients each day. In addition to helping save time, image compilation technology could also boost the quality of the images. For example, after the images have been acquired, if the contrast could be adjusted by manipulating TR, TE, and TI values, this could help to ensure that details aren t missed. An approach to image compilation One approach to image compilation technology relies on using a 2D FSE multi-dynamic, multi-echo (MDME) sequence with an interleaved sliceselective 120 degrees saturation RF pulse and multi-echo acquisition. In this approach, the saturation acts on a slice n, whereas the acquisition acts on This article discusses technology in development that represents ongoing research and development efforts. These technologies are not products and may never become products. These technologies are not for sale, are not CE marked, and are not cleared or approved by the FDA, Health Canada or other regulatory authorities for commercial availability. GEHEALTHCARE.COM/MR 6 Academic Issue SPRING 2015
Equation 1. Equation 2. Equation 3. a slice m, where n and m are different slices of the planned stack of slices. As such, the effective delay time between saturation and acquisition of each particular slice can be controlled by the choice of n and m. There are four different choices of n and m performed (four dynamics), resulting in four different delay times (TI). This is done automatically and requires no user interaction. The number of echoes of the acquisition is fixed to two, at two different echo times. Hence the result of each MDME acquisition is eight (complex) images per slice (4 saturation delays at 2 echo times). For the MDME sequence, the user can choose the field of view, matrix size, bandwidth, slice thickness, slice gap, and acceleration factor. The Echo Train Length (ETL: the number of 180 degree RF pulses) can be chosen within a range of 10-16. The repetition time (TR) has a minimum value of 4000 ms. The echo times (TE) are automatically chosen, approximately at 20 and 95 ms. The resulting real and imaginary images of the sequence are displayed for the user, but these are not intended to be diagnostic, rather as a quality check for motion artifacts. The MDME images all exhibit different effects of the T1 relaxation and T2 relaxation of the imaged tissues. The image compilation technology algorithm does a least-square fit on the signal intensity S of each pixel of the eight images per slice and calculates the T1 and T2 relaxation values. Additionally, it calculates the proton density (PD) and the amplitude of the B 1 field according to Equation 1 (see above), where A is an overall intensity scaling factor taking into account the coil sensitivity, the RF chain amplification and the voxel volume, α is the applied 90 degrees excitation flip angle, and q is the applied 120 degrees saturation pulse angle. Making synthetic images Once T1, T2, and PD values are known, normal MR images can be recreated, or synthesized, by calculating the expected signal intensity S, as a function of TE, TR, and, if applied, an inversion pulse with inversion delay time TI. The same Equation 1 is used for this, where A is set to 1, B 1 is set to 1, and α is set to 90 degrees. For T1-weighted and T2-weighted FSE images, q is set to zero and Equation 1 simplifies to Equation 2 (see above). For inversion recovery IR-FSE images, such as FLAIR, q is set to 180 degrees and Equation 1 simplifies to Equation 3 (see above). In Equation 3 the signal S can become negative. Typically the absolute value is provided unless the user chooses the PSIR option, which keeps the sign. After the examination has been completed, MR images are traditionally examined manually in order to make GESIGNAPULSE.COM 7 Academic Issue SPRING 2015
A single MR quantification scan of approximately 5-6 minutes delivers six contrasts which is significantly shorter than the total time taken to acquire each contrast separately using conventional techniques. Dr. Marcel Warntjes sure adequate images have been obtained. If the contrast settings were not optimal, the patient may have to be recalled for another scanning session. With the new technique, an approach to image compilation technology developed by Marcel Warntjes, PhD, the radiologist can easily choose or change the contrast, even after completing the scan, by changing the effective acquisition parameters and generating their contrast of choice. Quantitative images can be synthesized at any combination of TR, TE, and TI values for maximum flexibility. If a radiologist chooses the contrast but a colleague doesn t like it and wants to look at another, the change can be made without additional scan time, offers Dr. Warntjes, founder and CTO of SyntheticMR AB in Linköping, Sweden. An additional potential benefit of the technology is the short scan times that may make it possible to use MR as an optimized visualization tool for neurological exams. The fast examination of this technology might be useful to exclude pathology or for quick patient follow up. Further, for those who are interested in additional information, this technology can be used for image segmentation, which can be useful for visualizing diseases such as Multiple Sclerosis or dementia. Image compilation technology can provide quantitative information while allowing radiologists to still obtain conventional images. The mix could allow them to be confident with the result while reviewing the quantitative information from the brain, Dr. Warntjes explains. Challenges and differences Dr. Warntjes says that while the technology is designed for ease of use, there are some challenges in applying it. The industry should be aware that this is a new way of acquiring MR images. The synthetic images are very similar to conventional, but they are not the same. They are acquired in a different way, so image artifacts will manifest themselves in a slightly different manner. For example, according to Dr. Warntjes, post-contrast imaging with synthetically generated T1-weighted images will not have the same appearance as a conventional T1-weighted spin echo image. Enhancing lesions will still enhance, but the vessels will appear dark, because the MDME acquisition is a black blood sequence. Thus, if there are no enhancing lesions, it may be difficult to tell whether the synthetic T1-weighted was pre- or post-contrast. He continues by noting that other differences include the technique s sensitivity to motion, which can result in an enhancement of edges in brain structures. It can be prone to ghosting artifacts due to blood and CSF flow and fitting errors due to partial volume effects that may be visible in the resulting images. Potential impact Dr. Warntjes says that the new technology is engineered to provide significant productivity benefits. A single MR quantification scan of approximately 5-6 minutes delivers six contrasts which is significantly shorter than the total time taken to acquire each contrast separately using conventional techniques. Also, scanner settings are designed to match exactly between scans, allowing for accurate comparison between examinations. The synthetic images can also be matched with previous, conventional protocols, potentially increasing the ability to compare or potentially reducing the need to recall patients. Additionally, flexibility could offer a productivity benefit. According to Dr. Warntjes, If the images turned out to be a little different than anticipated, another kind of contrast might be warranted that would not have been acquired conventionally. In that case, the patient would need to be recalled. But now, any contrast can be regenerated, because there s total freedom of setting the image acquisition parameters afterward. He continues, The technique is designed to be flexible and to help adjust the images so they are more uniform across different hospitals and systems. GEHEALTHCARE.COM/MR 8 Academic Issue SPRING 2015
Marcel Warntjes, PhD, is the founder and CTO of SyntheticMR AB in Linköping, Sweden. Furthermore, standardization could become a reality as radiologists would observe exactly the same type of MR image from different scanners even from another hospital. Dr. Warntjes provides a different example. Even within the same modality, if a patient is large and the tech changes the number of slices, it might have an impact on the contrast. The B 1 field homogeneity might also have an impact. That issue does not exist with Image Compilation Technology there s more standardization and uniformity. Dr. Warntjes and the SyntheticMR team cite important advantages for pediatric patients, as well. Because the brains of very young children change rapidly, it s a challenge to say in advance what kind of protocol should be run and to make an optimal contrast. It often requires a radiologist on site to ensure that the images are acceptable. With this technology, clinicians can run the scans, and later the sequence contrast can be recreated and optimized to that specific child. It can make pediatric scanning more predictable and reliable because clinicians are not bound to the original protocol. Next steps According to Dr. Warntjes, the obvious next step is segmentation, using quantitative maps to characterize tissue. Tissue segmentation can provide more accurate patient follow up than we see today. For productivity, he believes scan time can be made faster by better tuning the acquisition. But there is a certain limit to that. I don t think we ll ever get to less than 5 minutes for a high-resolution image. We could possibly get to 2-3 minutes for lower resolution, but clinically it may not be feasible. When asked if the technology has reached the maximum in terms of productivity enhancements, he responds, No, we are just beginning there s much more to come. For example, we re looking into an even faster synthetic scan process of capturing all the contrast images, and then one by one, the clinician would replace them with high-resolution conventional images. If everything goes well, the result is the normal protocol. If everything does not go well, and the patient does not cooperate, there s a backup plan because the images not captured could be regenerated. Additionally, Dr. Warntjes and his team are investigating other uses, such as for the spine, knee, and prostate, atherosclerosis, and breast imaging, as well as the possibility of 3D. Currently, MR is about generating many different images that vary in contrast. These images are subjectively interpreted, generally without quantitative support. My goal is to improve MR with a single, rapid scan that generates a range of reproducible images, with flexible image contrast that does not require rescanning. Standardized, rapid MR scanning could decrease MR examination time and costs significantly, Dr. Warntjes concludes. Marcel Warntjes, PhD, is the founder and CTO of SyntheticMR AB in Linköping, Sweden. He was born and educated in the Netherlands and holds a post doctorate in physics. SyntheticMR AB was founded in Linköping, Sweden in 2007 in order to commercialize a new MR processing methodology. GESIGNAPULSE.COM 9 Academic Issue SPRING 2015
Application of synthetic MR on a patient with malignant glioma The following (Figure 1 and Figure 2) demonstrate an example of the images that can be obtained using the Image Compilation Technology. These are from a patient with malignant glioma who received an MR examination using the synthetic MR technique. References Details of the MDME sequence are further described by Warntjes et al. Magnetic Resonance Imaging 60; 320-329 (2008). The concept of synthetic MRs described by Bobman et al. AJNR 6:265-269 (1985) and the signal equations for synthetic MR images are described by Maera et al. Magnetic Resonance in Medicine 54:241 245 (2005). These images were acquired with an investigational device. These images were acquired with an investigational device. Figure 1. On the left panel the axial images were processed with image compilation technology (investigational): FLAIR (TR/TE/TI = 12000/100/2600 ms), T2w (TR/TE = 4500/100 ms), T1w (TR/TE = 500/10 ms), and T1w post-gd (TR/TE = 500/10 ms). On the right panel are the conventional images: a coronal and sagittal reformat of a T1w BRAVO, diffusion weighted imaging (b=1000), and ADC map. Figure 2. R1 map on a scale 0-2.5 s-1, left pre-gd, right post-gd. The T1w enhancing areas show values up to 3 s-1 after GD contrast. GEHEALTHCARE.COM/MR 10 Academic Issue SPRING 2015