MRI retrospective respiratory gating and cardiac sensing by CW Doppler radar: A feasibility study.

OBJECTIVE: This study investigates the feasibility of non-contact retrospective respiratory gating and cardiac sensing using continuous wave Doppler radar deployed in an MRI system. The proposed technique can complement existing sensors which are difficult to apply for certain patient populations. METHODS: We leverage a software-defined radio for continuous wave radar at 2.4 GHz to detect in-vivo respiratory and cardiac timescrolled signals. In-bore radar signal demodulation is verified with full electromagnetic simulations, and its functionality is validated on a test bench and within the MR bore with four normal subjects. Radar sensing was compared against well-known references: electrocardiography on a test bench, system bellows, and pulsed plethysmography sensors with in the MRI bore. RESULTS: The feasibility of noncontact cardiac rate sensing, dynamic breathing sequence synchronization, and in-bore motion correction for retrospective respiratory gating applications was demonstrated. Optimal radar front-end system arrangement, along with spectral isolation and narrow bandwidth of operation, enable MRI-compatible and interference-free motion sensing. The signal-to-noise-ratio degradation by the radar integration was within 4.5% on phantom images. CONCLUSION: We confirmed that in-bore retrospective motion correction using CW Doppler radar is feasible without MRI system constraints. SIGNIFICANCE: Non-contact motion correction sensing in MRI may provide better patient handling and through put by complementing existing system sensors and motion correction algorithms.

Radiation dose reduction and improvement of image quality in digital chest radiography by new spatial noise reduction algorithm.

PURPOSE: To evaluate the image quality of low-dose chest digital radiographic images obtained with a new spatial noise reduction algorithm, compared to a conventional de-noising technique. MATERIALS AND METHODS: In 69 patients, the dose reduction protocol was divided into A, B, and C test groups- 60% (n = 22), 50% (n = 23), and 40% (n = 24) of the baseline dose. In each patient, baseline dose radiographs were obtained with conventional image processing while low-dose images were acquired with new image processing. A set of baseline and low-dose radiographic images per patient was evaluated and scored on a 5-point scale over seven anatomical landmarks (radiolucency of unobscured lung, pulmonary vascularity, trachea, edge of rib, heart border, intervertebral disc space, and pulmonary vessels in the retrocardiac area) and three representative abnormal findings (nodule, consolidation, and interstitial marking) by two thoracic radiologists. A comparison of paired baseline and low-dose images was statistically analyzed using a non-inferiority test based on the paired t-test or the Wilcoxon signed-rank test. RESULTS: In A, B, and C test groups, the mean dose reduction rate of the baseline radiation dose was 63.4%, 53.9%, and 47.8%, respectively. In all test groups, the upper limit of the 95% confidence interval was less than the non-inferiority margin of 0.5 every seven anatomical landmarks and three representative abnormal findings, which suggested that the image quality of the low-dose image was not inferior to that of the baseline dose image even if the maximum average dose reduction rate was reduced to 47.8% of the baseline dose. CONCLUSION: In our study, an image processing technique integrating a new noise reduction algorithm achieved dose reductions of approximately half without compromising image quality for abnormal lung findings and anatomical landmarks seen on chest radiographs. This feature-preserving, noise reduction algorithm adopted in the proposed engine enables a lower radiation dose boundary for the sake of patient's and radiography technologist's radiation safety in routine clinical practice, in compliance with regulatory guidelines.

Characterization of Arabidopsis thaliana FLAVONOL SYNTHASE 1 (FLS1) -overexpression plants in response to abiotic stress.

Flavonoids are an important group of secondary metabolites that are involved in plant growth and contribute to human health. Many studies have focused on the biosynthesis pathway, biochemical characters, and biological functions of flavonoids. In this report, we showed that overexpression of FLS1 (FLS1-OX) not only altered seed coat color (resulting in a light brown color), but also affected flavonoid accumulation. Whereas fls1-3 mutants accumulated higher anthocyanin levels, FLS1-OX seedlings had lower levels than those of the wild-type. Besides, shoot tissues of FLS1-OX plants exhibited lower flavonol levels than those of the wild-type. However, growth performance and abiotic stress tolerance of FLS1-OX, fls1-3, and wild-type plants were not significantly different. Taken together, FLS1 can be manipulated (i.e., silenced or overexpressed) to redirect the flavonoid biosynthetic pathway toward anthocyanin production without negative effects on plant growth and development.

Radiofrequency current source (RFCS) drive and decoupling technique for parallel transmit arrays using a high-power metal oxide semiconductor field-effect transistor (MOSFET).

A radiofrequency current source (RFCS) design using a high-power metal oxide semiconductor field effect transistor (MOSFET) that enables independent current control for parallel transmit applications is presented. The design of an RFCS integrated with a series tuned transmitting loop and its associated control circuitry is described. The current source is operated in a gated class AB push-pull configuration for linear operation at high efficiency. The pulsed RF current amplitude driven into the low impedance transmitting loop was found to be relatively insensitive to the various loaded loop impedances ranging from 0.4 to 10.3 ohms, confirming current mode operation. The suppression of current induced by a neighboring loop was quantified as a function of center-to-center loop distance, and was measured to be 17 dB for nonoverlapping, adjacent loops. Deterministic manipulation of the B(1) field pattern was demonstrated by the independent control of RF phase and amplitude in a head-sized two-channel volume transmit array. It was found that a high-voltage rated RF power MOSFET with a minimum load resistance, exhibits current source behavior, which aids in transmit array design.