At Kurashiki Central Hospital (KCH) in Japan, the MRI staff is always looking for ways to improve image quality and to scan faster. As one of the goals of faster scanning, they mention improving the MRI examination for patients, for instance by reducing breath hold duration and overall scanning time. This can make it easier for patients to comply, which in turn benefits the imaging results. An additional aim is to gain time for the MRI technologists, to relieve the pressure of their high workload and to give them more time to attend to their patients.
When the staff at Kurashiki heard about Compressed SENSE, they were eager to learn about its capabilities, and what these could mean for their staff workload and patient comfort. KCH is a general hospital that scans approximately 110 patients a day using seven MRI systems. Compressed SENSE was first installed on their Ingenia 1.5T scanner. The staff quickly appreciated substantial decreases in scan times and decreases in breath hold requirements, without having to compromise on image quality.
The Compressed SENSE technology allows users to accelerate their 2D and 3D sequences by up to 50%.1 The staff at KCH has noticed reduced noise in many Compressed SENSE images in different anatomies, allowing them to increase the spatial resolution. “We are now using Compressed SENSE for almost all of our sequences in brain, spine and abdominal examinations,” says technologist Masayuki Kumashiro, PhD.
According to KCH diagnostic radiologist Dr. Takashi Koyama, Compressed SENSE is extensively used in brain and spine examinations. Both of which require high quality images, and it is possible to obtain excellent quality images even when using higher Compressed SENSE factors (C-SENSE factors) for decreasing scan times.
Brain protocols were the first to be converted to Compressed SENSE, according to MRI technologist Sachi Fukushima. “We started with comparing the image quality of Compressed SENSE with our original SENSE images in five cases of brain imaging. For 2D images for instance, we looked for possible changes in contrast and structural details when changing from a SENSE factor of 2.0 to a C-SENSE factor of 2.4. We also examined image quality obtained with different denoising parameters.” This convinced the Kurashiki team that image quality would not suffer by switching from SENSE to Compressed SENSE.
According to Fukushima, the high spatial resolution desired in brain and spine, used to typically require quite long scan times, but now the speed provided by Compressed SENSE may be traded for increased spatial resolution when necessary.
“For several brain examinations we use Compressed SENSE for faster1 scanning, using C-SENSE factors from 2.0 to 3.5 for 2D and 3D protocols (except EPI diffusion). High resolution sequences such as TOF and 3D usually take the longest, but with Compressed SENSE we obtain really good quality, even when using a higher C-SENSE factor for decreasing scan time as compared to images with SENSE.”
“In the 3D TOF MR angiography sequence, we decided to use a C-SENSE factor of 3.5, after carefully examining the quality of the inflow signal and the detailed structure of the cerebral blood vessels using this higher factor. Compressed SENSE also allows us to use more 3D sequences instead of 2D sequences, providing higher resolution and allowing us to perform reformatting (MPR) in different orientations,” says Fukushima.
The KCH team has already changed most of their Ingenia 1.5T spine ExamCards by incorporating Compressed SENSE into their 2D TSE, mDIXON TSE, FFE, and 3D sequences.
“Previously with SENSE, our 2D mDIXON TSE scans required relatively long scan times. But now, with Compressed SENSE, we have reduced these scan times while maintaining a high SNR, because the Compressed SENSE technology helps reduce noise,” says Dr. Koyama.
“Because the faster scanning with Compressed SENSE saves us time, we can sometimes add a sequence to obtain high quality spine images in the same time slot for confident diagnoses. And in cervical spine exams, a 2D sequence is sometimes replaced by a 3D protocol, which provides us more information as it can be reformatted in different orientations. Compressed SENSE allows us to easily add this 3D sequence in the timeslot,” says Fukushima
“Incorporating Compressed SENSE in common spine sequences, such as mDIXON, 3D SpineVIEW and eTHRIVE, can substantially reduce the scanning time of these sequences, while maintaining adequate spatial resolution, resulting in high quality, multiple contrasts, multiple orientations,” says Dr. Koyama.
“In addition, fast sequences generally make it easier for patients to stay motionless throughout the scans, so it also helps us in that way.”
Dr. Koyama says that he used to believe that high resolution MRI at 1.5T required long scan times, and SNR was low. “With Compressed SENSE, however, it is possible to acquire high quality images, even with higher Compressed SENSE factors, so in a quite short time.”
“In breast scanning, high resolution is important to help me identify very small mammary lesions, so, we need high spatial resolution in 2D T1- and T2-weighted images, as well as a short scan time. Compressed SENSE has allowed us to increase spatial resolution, which benefits our diagnostic confidence.”
While breath holds are vital for image quality in many abdominal MRI scans, commonly used breath hold times of around 25 seconds or more can be challenging, for instance when a patient is sick, in pain or stressed. Failed breath holds can decrease image quality and add to scan time.
KCH technologist Fukushima recognizes the impact of Compressed SENSE on breath hold times. “Before we started using Compressed SENSE, some high resolution 3D examinations used to require long breath holds, because when scan times were shortened, images would often become noisy in the center of the body. But now, Compressed SENSE allows us to further decrease scan times without that increased noise.”
Dr. Koyama particularly focused on reducing breath hold times in abdominal MRI, as these patients often need to perform many breath holds in one examination. “In liver scans we were able to shorten our scanning time – and thus reduce breath hold time – from 22 to 13 seconds by using a higher C-SENSE factor. Since shorter breath hold times make it easier for patients to comply, we saw breath holding failures largely disappeared, allowing the exam to be finished smoothly.”
Dr. Koshi Miyake, cardiologist, explains that scanning of patients with cardiac arrhythmia can be challenging, as scanning times can become very long due to the varying heart rate. So his most important motive to implement Compressed SENSE in cardiac MRI exams was to reduce the burden of breath holds for the patient, while maintaining high image quality. He hopes this can also help to reduce motion caused by the difficulty for patients to hold their breath.
“Compressed SENSE has now been implemented in all cardiac exams. Thanks to the acceleration, fewer breath holds are now needed, or breath hold times are shortened. This reduces the burden of the exam for cardiac patients, without affecting the quality of information required for cardiac function analyses,” he says. “Because it’s easier for patients to comply with the breath hold times”
“In our previous cardiac cine sequence, we were acquiring two slices during one breath hold. With Compressed SENSE, we increased this to four slices per breath hold. It is also possible to shorten scanning time using a C-SENSE factor 6 without sacrificing image quality.”
The KCH staff would definitely recommend Compressed SENSE to peers at other institutions. They advise new users to start using it in brain and spine imaging first, as these are the easiest protocols to switch.
According to Dr. Kumashiro, “The most important reason for us to acquire Compressed SENSE has been to achieve higher image quality and make examinations easier for patients by reducing breath hold scan time and examination time. The shorter scan times achieved with Compressed SENSE relieve the stress of a tight work schedule for the MR staff. Technologists can spend the gained time on increasing the image quality, or to take more time for patient preparation and dealing with safety aspects.”
“After seeing the improvements that Compressed SENSE brought to the scanning on Ingenia 1.5T, we decided to also acquire Compressed SENSE for two additional MRI scanners,” he concludes.
In this MRI exam of pelvis in a patient with myoma, Compressed SENSE is used to accelerate individual sequences and thus the entire examination on Ingenia 1.5T.
Compressed SENSE allowed for a decrease in scan time for the T2 TSE from 3:38 to 1:46 minutes. The Compressed SENSE images in this case show fewer motion artifacts than the images from the previous protocol with SENSE.
In 3D PelvisVIEW, the Compressed SENSE images have a higher and isotropic spatial resolution with a scan time similar to the SENSE sequence. The improved spatial resolution and better contrast in the myometrium of the uterus allowed radiologist Dr. Koyama to confidently diagnose the cancerous lesion in the uterus.
The use of Compressed SENSE accelerates scanning times and increases spatial resolution in 3D PelvisVIEW.
