The Broadened Horizons with Higher Image Quality and Higher Acceleration Delivered by Deep Learning Reconstruction on the 1.5T MRI System

Improved examination workflow with AI-based solutions such as Ceiling Camera-assisted positioning based on a Deep Learning algorithm

Since 2009, Shiga General Hospital has been designated as a Prefectural Cancer Care Hospital. Since 2018, the hospital name has been changed from the former "Shiga Prefectural Medical Center for Adult Diseases" to reflect its expanded mission to provide comprehensive medical care focusing not only on lifestyle-related diseases but also on a variety of other diseases. At Shiga General Hospital, the Department of Radiology is composed of 4 physicians and 31 radiologic technologists for diagnosis and examinations, who are assigned to specific sections according to modality, such as CT and PET. In the MRI section, a radiologist, 3 radiologic technologists and a nurse perform about 32 examinations per day using a 1.5T MRI system Vantage Fortian and a 3T MRI system from another manufacturer. Approximately one-half of the MRI examinations focus on the head and neck, including follow-up examinations for neurovascular diseases and for the detection of brain metastases. The other half include the spine, MRCP and a variety of other examinations. Examinations of all parts of the body are performed for every clinical department and for every diagnostic objective.

Vantage Fortian was launched by Canon Medical Systems in February 2022 as a 1.5T MRI system with AI-driven technologies to improve image quality and streamline examination workflows. Meanwhile, Shiga General Hospital was planning to replace their previous 1.5T system from another manufacturer. Mr. Chatani explains that the most important criteria to select a new MRI system was image quality. At that time, DLR technologies for MRI were being launched by several different manufacturers. Therefore, the hospital focused on MRI systems with DLR, having expectations for higher-resolution or higher-acceleration imaging. The candidates for new MRI system were narrowed down to three systems, including one from Canon Medical Systems. After arranging several site visits to see the actual systems, Vantage Fortian was ultimately decided on. Mr. Chatani is impressed that Advanced intelligent Clear-IQ Engine (AiCE), which is one of the DLR technologies from Canon Medical Systems, can be flexibly applied to almost all the pulse sequences for 2D and 3D acquisition on Vantage Fortian. He also thinks highly of the system because AiCE allows the retrospective reconstruction for previously acquired images.
AiCE is a DLR technology for adaptive noise reduction in images, which enables the ability to extract and remove more selectively noise components from the signal compared with conventional denoising methods, e.g., smoothing filters. The noise reduction level can be selected in five levels and adjusted to achieve the desirable image quality even after acquisition. Mr. Chatani notes that it was easy to adjust image quality based on advice from radiologists soon after the replacement with Vantage Fortian, because the noise reduction level can be retrospectively adjusted without additional acquisition to achieve the desirable image quality. He also adds that most of the hospital's protocols for Vantage Fortian have already been fully optimised, thanks to the flexibility of AiCE.

There are two different methods with AiCE to benefit from the adaptive noise reduction: one is for high-resolution imaging without extending the scan time, the other is for high-acceleration imaging maintaining the image quality. In terms of the former, AiCE allows to acquire 1 mm-slice 2D images for examinations of the small extremities such as the finger and the wrist joints. According to Mr. Chatani, it previously took a long scan time even to acquire 3 mm-slice 2D images on the previous system, but AiCE enables to acquire thinner-slice and higher-resolution images without extending the scan time on Vantage Fortian as well as their 3T system. In contrast, for spine examinations, the highly-accelerated protocols are adopted maintaining the same spatial resolution as the previous. Mr. Chatani says that when sagittal T1- and T2-weighted images and axial T2-weighted images are acquired in the spine examinations, AiCE reduces the total scan time by more than 5 minutes on Vantage Fortian compared with the previous system. Nevertheless, the image quality is comparable to that acquired on their 3T system. He notes that AiCE greatly broadens the options for higher image quality or higher acceleration in MRI examinations depending on the situation.
Furthermore, Fast 3D mode, which is one of the acceleration techniques for 3D acquisition, has been used to accelerate head MRA in combination with AiCE. The combination allows to acquire higher-resolution MRA images without extending the scan time and improves the depiction of vascular structures, Mr. Chatani also says that the combined use of AiCE and Fast 3D mode permits to acquire high-resolution MRA images on Vantage Fortian in almost the same scan time as on their 3T system. Due to inflow effects in MRA, there are generally differences of the depiction of vascular lesions, e.g., microaneurysms and vascular stenosis, between 1.5T and 3T systems. Hence, their 3T system would often be employed in these cases. However, Vantage Fortian has recently compensated for their 3T system in the examinations for those cases. Dr. Yusaku Moribata, Head of the Department of Diagnostic Radiology, observes that Vantage Fortian provides improved overall image quality. Especially in head MRA, it allows blood vessels to be clearly depicted and the morphological characteristics of aneurysms to be precisely evaluated. In addition to head MRA, neck MRA is often requested by the Department of Neurosurgery. Large FOV images for neck MRA are usually required including the upper section of the aortic arch, but the combination of AiCE and Fast 3D mode enables to acquire them in a short scan time of about 2 minutes. Other than Fast 3D mode, Vantage Fortian incorporates a variety of acceleration techniques such as Compressed SPEEDER, all of which can be used in combination with AiCE. Mr. Chatani observes that as an added value of AiCE, the combination with various acceleration techniques reduces the scan time while maintaining the image quality, and that results in minimising motion artifacts generated by uterine peristalsis in gynecological examinations. Mr. Chatani is amazed by the fact that AiCE allows to perform routine gynecological examinations without using radial sampling to correct body motion artifacts, which typically affects overall image contrast unlike Cartesian sampling.

Vantage Fortian incorporates a variety of features to streamline its examination workflow, including Ceiling Camera-assisted positioning solution, in which a camera manufactured by Canon on the ceiling of the scan room detects the target position and moves the patient table into the magnetic center. The Intelligent Monitor on the gantry shows the patient on the table, and the operator can perform coil set-up while referring to the guidelines indicating the detected target position. At Shiga General Hospital, the Ceiling Camera-assisted positioning has been the most useful for the prostate examinations with the 16ch Flex SPEEDER coil, whose high-density element design makes it possible to acquire high-SNR images with localised coil sensitivity. However, the coil is so small that even if there is a slight error between a targeted position and a landmarked position with laser marking, it could lead to the target deviating from the region covered with the localised coil sensitivity during examinations for small anatomies such as the prostate. Before using the Ceiling Camera, the patient positioning in case of prostate examinations would often vary slightly depending on the operator's experience and the patient's physical characteristics. However, recently, it has been easier to perform the patient positioning and coil set-up with the Ceiling Camera, because the 16ch Flex SPEEDER coil just has to be set on patients referring to the detected position shown on the Intelligent Monitor. That results in more accurate and consistent positioning in prostate examinations. Mr. Chatani also points out another advantage of the positioning solution. During the ongoing coronavirus pandemic, it is also beneficial to be able to perform the patient positioning while minimising physical contact. In addition, the positioning solution prevents unnecessary repositioning caused by manual-landmark errors depending on the operator’s experience. Thus, the examination workflow has been streamlined, allowing medical staff to have plenty of time to explain the examinations to patients.

Vantage Fortian incorporates a variety of unique reconstruction technologies not only for adaptive noise reduction, i.e., AiCE, but also for artifact reduction, which includes those for motion artifact reduction, i.e., Iterative Motion Correction (IMC), and for distortion correction in diffusion-weighted images (DWI). In particular, Reverse encoding Distortion Correction (RDC) DWI minimises distortion caused by susceptibility effects and eddy currents in DWI. RDC DWI is mostly used for head examinations at their hospital to reduce the distortion of DWI at the base of the brain caused by the presence of air, which enhances susceptibility effects. It is available and useful in all imaging planes, especially in direct acquisition of coronal and sagittal planes for DWI. Thin-slice coronal DWI for head examinations are sometimes requested by the Department of Neurosurgery to evaluate the lesions in the brain stem, where the distortion is likely to be generated in DWI. Mr. Chatani adds that the examinations are performed with greater confidence thanks to RDC DWI, although that was not the case with the previous system.

Moreover, mUTE (minimized acoustic noise utilising UTE) sequences can be used for metal artifact reduction in head MRA, especially in case of the follow-up after coil embolisation, allowing to acquire DSA-like 4D MRA images to evaluate hemodynamics without contrast enhancement and radiation exposure as added values.

The higher-resolution and -accelerated imaging and streamlined examination workflows delivered by Vantage Fortian are expected to lead to even higher reliability and efficiency in MRI examinations.
(Interview conducted on November 15, 2022)

This article is a translation of the INNERVISION magazine, Vol.38, No.1, 2023.

Disclaimer: Deep Learning technology is used in the design stage of the image reconstruction processing. The system itself does not have self-learning capabilities.
The contents of this report include the personal opinions of the authors based on their clinical experience and knowledge.