Ultrahigh-field MRI @ 7T

An exciting development in clinical research is that cutting-edge MR centers are pushing the boundaries by investigating the feasibility and clinical value of 7-tesla MRI for imaging neurodegenerative and neuroinflammatory diseases. Here, increasing the field strength helps to gain signal-to-noise ratio, contrast-to-noise ratio, and spatial resolution, which are all currencies of diagnostic image quality.

In particular, enhanced spatial resolution can help to advance the capabilities of imaging subtle focal cerebral lesions. A recent study demonstrated in a side-by-side analysis that MPRAGE MRI at 7 tesla depicted 82% more subtle multiple sclerosis (MS) lesions than MPRAGE MRI at 1.5 tesla due to the enhanced T1 contrast and the high spatial resolution.1

These improvements can be also put to clinical use to detect lesions at an earlier stage of disease progression, if not prior to the onset of clinical symptoms. This capability has been demonstrated by MR microscopy of animal models, using an effective resolution (pixel per anatomy) currently approached in humans with 7-tesla MRI.2 Also, it offers means for differential diagnosis.

Cerebral lesions morphology derived from 7-tesla exams differentiates Susac syndrome (an orphan disease that needs to be considered in the differential diagnostic workup of various neurological disorders) from MS, according to a recent clinical study. This study demonstrated that white matter and callosal lesion morphology in Susac syndrome differs significantly from MS plaques in terms of a perivascular localization, the presence of a hypointense ring, and the frequency of CSF-isointense lesions, as illustrated in figure 2.3

Also, the (super)linear relationship between magnetic field strength and sensitivity for susceptibility effects in T2*-weighted imaging, together with the enhanced spatial resolution, can substantially enhance the detection of anatomical details of MS plaques.

At the same time, this research is paralleled by pioneering explorations into human stroke imaging and imaging microbleeds at 7 tesla. Stroke lesions visible at 3 tesla can all be detected at 7 tesla.5 Improved spatial resolution at 7 tesla helps to reveal more anatomical detail and pathophysiological characteristics of ischemic lesions, which pays off for imaging microinfarcts. These findings encourage further exploration into the diagnostic benefits that 7-tesla MRI may offer for neurology and neuroradiology.

t is no secret that the feasibility of 7-tesla MRI is not limited to the brain, but also can be beneficial for musculoskeletal and cardiac imaging. The requirements of cardiac MR at 7 tesla inspired recent advances in multichannel radiofrequency (RF) coil technology. This includes the move from cardiac optimized RF coils equipped with four transmit/receive channels only to 16 TX/RX channels configurations,6 and even 32 TX/RX channel versions.7

It has been shown that a larger number of elements, in conjunction with a 2D RF coil-array design, can improve image quality, as well as accelerated imaging performance.8 All these efforts culminated in images of the beating heart with a spatial resolution that is by an order of magnitude superior to that routinely available at 1.5 tesla.

These improvements offer detailed insights into cardiac anatomy and might provide means for a better understanding of the myocardial microstructure. Recognition of the benefits of the many channel RF coil configurations should help to eventually lead to a 7-tesla body RF coil design, though this is, for the moment, merely a vision. It is nonetheless a vision that offers the potential to inspire a further push toward body imaging at 7 tesla.

2D CINE FLASH images of the beating human heart

2D CINE FLASH images of the beating human heart

Set of six (top and bottom) 2D CINE FLASH images of the beating human heart derived at systole from a series of 12 short-axis views ranging from the apex to the base of the heart (in-plane resolution [1 x 1] mm2, slice thickness of 4 mm, acceleration factor = 2, GRAPPA). A 2D 16-channel transmit/receive radiofrequency coil array was used for signal transmission and reception.6 The images illustrate that a rather uniform intensity distribution was obtained across the entire heart.6

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