CT dose reduction factors in the thousands using X-ray phase contrast

Abstract

Phase-contrast X-ray imaging can improve the visibility of weakly absorbing objects (e.g. soft tissues) by an order of magnitude or more compared to conventional radiographs. Combining phase retrieval with computed tomography (CT) can increase the signal-to-noise ratio (SNR) by up to two orders of magnitude over conventional CT at the same radiation dose, without loss of image quality. Our experiments reveal that as the radiation dose decreases, the relative improvement in SNR increases. We show that this enhancement can be traded for a reduction in dose greater than the square of the gain in SNR. Upon reducing the dose 300 fold, the phase-retrieved SNR was still up to 9.6 ± 0.2 times larger than the absorption contrast data with spatial resolution in the tens of microns. We show that this theoretically reveals the potential for dose reduction factors in the tens of thousands without loss in image quality, which would have a profound impact on medical and industrial imaging applications.

On the “unreasonable” effectiveness of transport of intensity imaging and optical deconvolution

“…This explanation finally reconciles the apparent contradiction of this behaviour with the noise-resolution uncertainty principle [6]. It also provides a firm theoretical foundation for the SNR-boosting and resolution-preserving properties of the TIE-Hom method [8] of X-ray phase-contrast imaging that has been rapidly gaining popularity in recent years, particularly in view of its promising applications to medical and biomedical imaging [10,[29][30][31]. Some indications have been also given, of how some of these results generalise to other imaging systems which can be shown to perform optical deconvolutions.…”

“…The same will obviously be true for the SNR in the image plane It has been demonstrated in a number of recent publications [10,[29][30][31], that the application of the transformation inverse to TIE-Hom, eq. (12), may allow one to significantly reduce the noise variance in the image and boost SNR.…”

“…It has been demonstrated both theoretically [9] and experimentally [10] that the improvement factor can reach several hundreds (in the 3D case) without violating the TIE-Hom validity conditions. This in turn enables a reduction in the radiation dose by factors in the tens of thousands [10].…”

“…This in turn enables a reduction in the radiation dose by factors in the tens of thousands [10]. Therefore, the method has a potential to revolutionise biomedical X-ray imaging, in particular [10,[29][30][31].…”

“…Given this fundamental nature of the trade-off between the SNR and spatial resolution in any imaging or scattering experiments, it is very surprising that the reconstructive imaging method based on the so-called Homogeneous Transport of Intensity equation (TIE-Hom) [8] is able to comprehensively break the limit set by the noise-resolution uncertainty principle and increase SNR in the reconstructed images, sometimes by a factor of hundreds, without sacrificing spatial resolution [9,10]. One of the goals of the present work is to find a theoretical explanation for this apparent paradox.…”