Less Noise, Greater Contrast: 1.5T MRI Is Going Strong
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| Using the Cube sequence on the GE Signa HD 1.5T MR scanner, hospitals such as Hays Medical Center in Hays, Kan., can obtain gapless, 3D high-definition, high-contrast image data in one scan. |
Imaging flexibility
Within the University of Michigan Health System (UMHS), no stranger to cutting edge technology and research, 1.5T MRI is a tried-and-true imaging technique for a variety of applications. UMHS has an Achieva 1.5T MRI from Philips Healthcare installed at its East Ann Arbor offsite facility as well as at the C.S. Mott Children’s Hospital. And the reason they stick with 1.5T rather than making a switch to 3T is based on flexibility, says Suresh K. Mukherji, MD, chief of neuroradiology and head & neck radiology.
“1.5T gives us the flexibility to image all types of patients who come in, including cardiac, neuro, musculoskeletal and abdomen cases,” he says. UMHS had the option to purchase a 3T, but since, in those two areas it would be the only magnet, it made more sense to install a 1.5T, since 3T has more inherent artifacts than conventional 1.5T scanners.
“Before you spend the money on an MRI [system], and it’s going to be your only magnet, make sure it has the type of diagnostic information for all types of studies you want to perform,” says Mukherji. As the historical workhorse, 1.5T is “the tried and true magnet for MRI.”
Expanded imaging options
In Northwestern Kansas, Hays Medical Center (HMC) is focused on being the best tertiary care center in the United States. The 194-bed hospital is moving closer toward its goal with the GE Signa HDxt 1.5T MRI. Each year, HMC performs approximately 2,600 MRI exams.
The hospital upgraded in March 2008 from 9.0 to 14.0 HDx software, which meant they went from a basic MR scanner to a high definition (HD) scanner. Just a few weeks ago, the t software release was added that included new sequences which enable a single 3D volume scan as well as fat suppression, according to Christy Gillogly MRI supervisor. “We went pretty quickly from not having too many options to having a lot,” she says.
One expanded capability with the new software is Bravo, a 3D brain volume sequence that creates images in 3 to 4 minutes. Additionally, they can perform diffusion weighted imaging (DWI) on all brain sequences, typically for stroke detection.
“So along with mapping provided in back parameters in post processing in DWI, you can stage the age of the stroke, whether old, new or evolving and that helps in treating a patient within a three-hour window,” Gillogly says.
One new feature that radiologists really like is the 8-channel body coil because it has improved images for abdomen work. “Previously, we had a smaller torso array coil but in comparison to this channel, the wow factor is more information and better resolution,” she adds.
HMC is just scratching the surface of the potential applications of the Cube and Ideal sequences, Gillogly says she knows the potential they hold. Ideal is designed to help overcome fat saturation failures by providing a typical water saturation image, fat saturation image and an in-phase and out of phase sequence all in one four minute acquisition. “This will help reduce artifact and help characterize tissues better,” she says.
Cube replaces several slice-by-slice, plane-after-plane 2D acquisitions with a single 3D volume scan, to give a plethora of information for evaluating even the smallest lesions. “You can easily reconstruct high-definition, sub-millimeter-resolution images from a single acquisition into any plane you desire—without gaps and with the same resolution as the original plane in which it was acquired,” she concludes.
Here to stay
As MRI manufacturers continue to improve upon the design and features of 1.5T scanners, adding new coil technology, faster sequences and new gradients, the clinical workhorse will continue to maintain its standard of care, even as 3T comes galloping in from behind.
| 1.5T fMRI sheds light on schizophrenia |
| Researchers at the McGovern Institute for Brain Research at Massachusetts Institute of Technology in Cambridge, Mass., have used functional MRI (fMRI) to reveal how schizophrenia may blur the boundary between internal and external realities by over-activating a brain system that is involved in self-reflection, causing an exaggerated internal focus. Investigators scanned subjects using fMRI, both while resting and while performing easy or hard memory tasks, using a Siemens Sonata 1.5T MRI system. A sagittal localizer scan was performed for placement of slice, followed by a coronal T2-weighted sequence to rule out unexpected neuropathological findings. Two sagittal 3D magnetization prepared gradient echo (MPRAGE) sequences were collected for anatomical localization. The researchers were interested in the default system—a network of brain regions whose activity is suppressed when people perform demanding mental tasks. The network includes the medial prefrontal cortex and the posterior cingulate cortex, regions that are associated with self-reflection and autobiographical memories and which become connected into a synchronously active network when the mind is allowed to wander. To image the brain’s default regions, researchers needed to see where blood flow would go during the tests, which is what fMRI allowed. So why use 1.5T versus 3T? “With 3T, there is signal drop out or susceptibility artifacts that you can address by doing various post processing and correction, but the regions of the brain critical to our study were simply put, easier to image on 1.5T due to less artifact,” says Susan Whitfill-Gabrieli, research scientist and first author of the study, which was published in the Jan. 19 advance online issue of the Proceedings of the National Academy of Science (PNAS). Gabrieli and colleagues discovered that the default system in schizophrenia patients was both hyperactive and hyperconnected during rest, and it remained so as they performed the memory tasks. In other words, patients were less able than healthy control subjects to suppress the activity of the network during the task. The less the suppression and the greater the connectivity, the worse they performed on the hard memory task, and the more severe their clinical symptoms. “We think this may reflect an inability of people with schizophrenia to direct mental resources away from internal thoughts and feelings and toward the external world in order to perform difficult tasks,” Gabrieli says. The hyperactive default system also could help to explain hallucinations and paranoia by making neutral external stimuli seem inappropriately self-relevant. For instance, if brain regions whose activity normally signifies self-focus are active while listening to a voice on television, the person may perceive that the voice is speaking directly to them. Future applications of fMRI would be in predicting treatment outcomes, predicting treatment efficacy and enabling real-time neuro feedback, Gabrieli concludes. |