HYPR: constrained reconstruction for enhanced SNR in dynamic medical imaging

Abstract

During the last eight years our group has developed radial acquisitions with angular undersampling factors of several hundred that accelerate MRI in selected applications. As with all previous acceleration techniques, SNR typically falls as least as fast as the inverse square root of the undersampling factor. This limits the SNR available to support the small voxels that these methods can image over short time intervals in applications like time-resolved contrast-enhanced MR angiography (CE-MRA). Instead of processing each time interval independently, we have developed constrained reconstruction methods that exploit the significant correlation between temporal sampling points. A broad class of methods, termed HighlY Constrained Back PRojection (HYPR), generalizes this concept to other modalities and sampling dimensions.

Undersampled radial MR acquisition and highly constrained back projection (HYPR) reconstruction: Potential medical imaging applications in the post‐Nyquist era

“…To facilitate this, one can break the image into a matrix of subregions in which the composite information is integrated until motion is detected, at which point the composite image is reset. In this motion-adaptive version of HYPR (HYPR-MA) (49), SNR can be significantly increased in regions where motion is not excessive while maintaining spatial resolution at the cost of SNR in regions of greater motion. Figure 10 illustrates the application of this concept to a cardiac wall motion study using an undersampling factor of 20.…”

“…The hypothesis is that the increased SNR might permit the use of higher-frequency transducers that provide more resolution at the expense of increased attenuation and that new acoustic windows, for example through the skull, might be possible (49). Figure 23 shows a comparison of the raw data from a clinical Doppler ultrasound scanner before any spatial or temporal averaging algorithms were applied.…”