Feasibility of imaging superficial palmar arch using micro-ultrasound, 7T and 3T magnetic resonance imaging

Fabricating Novel PDMS Vessels for Phantoms in Photoplethysmography Investigations

This paper introduces a novel technique for the development of custom polydimethylsiloxane (PDMS) vessels for use in phantom technologies. The method involves continuous dip coating of commercial silicone tubes with rapid curation in a single controlled process. The technique accommodates the production of different vessel diameters, wall thicknesses (56 µm-80 µm) and mechanical properties. Clear phantoms were fabricated to compare the commercial silicone tubes against the customs vessels. A pulsatile fluidic pump (BDCLabs, CO, USA) driven by a computer controlled linear motor generated the pulsatile flow through the phantom. The resulting flow profile, using the custom vessels, simulates human blood flow and the detected contact PPG signal from the phantom closely resembles the morphology of in vivo PPG waveforms with signal-to-noise ratios of 38.16 dB and 40.59 dB, compared to the closest commercially-available tubing at 5.38 dB and 10.59 dB for the red and infrared wavelengths respectively. The rigidity and thick walls of commercial silicone tubes impede the expansion of the tubing under systolic pressure. This technique eliminates this common limitation in phantom development.

Novel Polydimethylsiloxane (PDMS) Pulsatile Vascular Tissue Phantoms for the In-Vitro Investigation of Light Tissue Interaction in Photoplethysmography

Currently there exists little knowledge or work in phantoms for the in-vitro evaluation of photoplethysmography (PPG), and its' relationship with vascular mechanics. Such phantoms are needed to provide robust, basic scientific knowledge, which will underpin the current efforts in developing new PPG technologies for measuring or estimating blood pressure, blood flow and arterial stiffness, to name but a few. This work describes the design, fabrication and evaluation of finger tissue-simulating pulsatile phantoms with integrated custom vessels. A novel technique has been developed to produce custom polydimethylsiloxane (PDMS) vessels by a continuous dip-coating process. This process can accommodate the production of different sized vessel diameters (1400-2500 µm) and wall thicknesses (56-80 µm). These vessels were embedded into a mould with a solution of PDMS and India ink surrounding them. A pulsatile pump experimental rig was set up to test the phantoms, where flow rate (1-12 L·min-1), heart rate (40-120 bpm), and total resistance (0-100% resistance clamps) could be controlled on demand. The resulting flow profiles approximates human blood flow, and the detected contact PPG signal (red and infrared) from the phantom closely resembles the morphology of in-vivo PPG waveforms with signal-to-noise ratios of 38.16 and 40.59 dB, for the red and infrared wavelengths, respectively. The progress made by this phantom development will help in obtaining new knowledge in the behaviour of PPG's under differing flow conditions, optical tissue properties and differing vessel stiffness.

Initial Experience With Staging Rectal Adenocarcinoma Using 7T Magnetic Resonance Imaging

BACKGROUND

Magnetic resonance imaging (MRI) has become the preferred method for local staging of rectal cancer. Current MRI technology, operating at 1.5-3 T, results in incorrectly reported tumor depth and therefore inaccurate staging in one-third of individuals. Inaccurate staging can result in suboptimal treatment in patients with rectal cancer and can submit them to unnecessary treatments. The Medical College of Wisconsin Center for Imaging Research houses one of approximately twenty experimental 7 T MRIs worldwide capable of imaging the human pelvis. We present our initial experience with this novel imaging technique for the human rectum.

METHODS

This was a prospective observational trial conducted at a single institution. Patients diagnosed with rectal cancer and who underwent low anterior resection or abdominoperineal resection between July 2015 and July 2017 were included. Excised rectal specimens were suspended in a saline-filled container and imaged by MRI at 7T. Tumor depth and lymph node status were determined by a single radiologist who was blinded to the pathologic results. These MRI interpretations were then compared with the pathologic stage.

RESULTS

Seven of the 10 patients received neoadjuvant chemoradiation. When using the T1-weighted volumetric interpolated breath-hold examination-flex fat-suppressed sequences, radiologic and pathologic interpretation was identical regarding tumor depth in 7 of 10 patients (70%). Nodal status was correctly interpreted by 7T MRI in 8 of 10 patients (80%). Lymph nodes as small as 2 mm were able to be correctly characterized as harboring malignancy.

CONCLUSIONS

We have demonstrated that 7T MRI of the rectum ex vivo has a strong correlation with histologic results. With its superior signal-to-noise ratio and spatial resolution, 7T MRI holds promise in more accurately staging rectal cancer and may be useful in correctly categorizing response to neoadjuvant therapy.