THE EFFECT OF INCREASING ACQUISITION SPEED ON OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY IMAGES: A Qualitative and Quantitative Analysis.

PURPOSE: To evaluate the effect of two different A-scan rates on qualitative and quantitative parameters on optical coherence tomography angiography images in a clinical setting. METHODS: Subjects undergoing a comprehensive ophthalmic examination were scheduled for optical coherence tomography angiography imaging using a new SPECTRALIS device allowing for 85 and 125 kHz scan rate. Consecutive registered 20° × 20° optical coherence tomography angiography images using both speeds were acquired using the follow-up tool. The acquisition time and the quality values of each scan were extracted and analyzed. The image quality was also graded in pairs by two independent graders. RESULTS: Two-hundred and one eyes of 128 consecutive patients (67 males, 52.3%) were included. Mean acquisition time significantly decreased from 56.92 ± 24.6 seconds on the 85 kHz images to 39.39 ± 15.5 seconds on the 125 kHz images (P < 0.001). The percentage change in acquisition time showed a mean decrease of 28.47%. Mean Q value significantly decreased from 32.97 ± 2.8 dB on the 85 kHz images to 31.43 ± 2.6 dB on the 125 kHz images (P < 0.001). Overall, 92.5% of images were graded as equal or better at 125 kHz A-scan rate. CONCLUSION: The use of optical coherence tomography angiography in daily clinical practice may require higher A-scan rates for an optimal workflow. Increased speed may also reduce image sensitivity and thus image quality could be compromised. In this study, 125 kHz scan rate using SPECTRALIS showed significant benefit with reduction on the acquisition time and no clinically significant differences on image quality analysis. Further studies evaluating qualitative and quantitative data in specific retinal conditions and using other devices are required to confirm these results.

Proton magnetic resonance imaging with para-hydrogen induced polarization.

A major challenge in imaging is the detection of small amounts of molecules of interest. In the case of magnetic resonance imaging (MRI) their signals are typically concealed by the large background signal of e.g. the body. This problem can be tackled by hyperpolarization which increases the NMR signals up to several orders of magnitude. However, this strategy is limited for (1)H, the most widely used nucleus in NMR and MRI, because the enormous number of protons in the body screens the small amount of hyperpolarized ones. Here, we describe a method giving rise to high (1)H MRI contrast for hyperpolarized molecules against a large background signal. The contrast is based on the J-coupling induced rephasing of the NMR signal of molecules hyperpolarized via PHIP and it can easily be implemented in common pulse sequences. We discuss several scenarios with different or equal dephasing times T(2)* for the hyperpolarized and thermally polarized compounds and verify our approach by experiments. This method may open up unprecedented opportunities to use the standard MRI nucleus (1)H for e.g. metabolic imaging in the future.