Effect of Extrinsic Warming of Low-Osmolality CT Contrast Media (Iohexol 350) on Extravasations and Patient Reaction Rates: A Retrospective Study.

BACKGROUND. Extrinsic warming of iodinated CT contrast media to body temperature reduces viscosity and injection pressures. However, studies examining the effect of extrinsic warming on clinical adverse events are limited in number and provide conflicting results. Therefore, consensus practice recommendations have been sparse. OBJECTIVE. The purpose of this study is to compare rates of extravasation, allergic and allergiclike reactions, and physiologic reactions between iohexol 350 mg I/mL warmed to body temperature (37°C) versus this agent maintained at room temperature. METHODS. This retrospective study compared adult patients who received CT examinations using IV iohexol 350 that had either been warmed to body temperature or maintained at room temperature. At our institution, contrast media had historically been warmed to body temperature before a protocol change unrelated to this investigation. Information on the patient and CT examination was extracted from the electronic medical record. Adverse events, including extravasations, allergic and allergiclike reactions, and physiologic reactions, were compared between groups. RESULTS. A total of 3939 patients received contrast media warmed to body temperature before the protocol change; 3933 patients received contrast media at room temperature after the protocol change. The body temperature group experienced 11 (0.28%; 95% CI, 0.14-0.50%) adverse events, all extravasations; the allergic and allergic-like reaction rate was 0.00% (97.5% CI, 0.00-0.09%). The room temperature group experienced 17 (0.43%; 95% CI, 0.25-0.69%) adverse events: 13 (0.33%; 95% CI, 0.17-0.56%) extravasations and four (0.10%; 95% CI, 0.03-0.26%) allergic and allergiclike reactions. No physiologic reaction occurred in either group. The two groups were not different in terms of overall reaction rate (p = .19), extravasation rate (p = .69), allergic and allergiclike reaction rate (p = .06), or physiologic reaction rate (p > .99). Logistic regression adjusting for patient and CT characteristics (age, sex, conventional CT vs CTA, contrast media volume, injection location) showed no significant association of patient group and adverse reaction rate (odds ratio, 2.19; 95% CI, 0.68-7.00). Multivariable regression modeling showed an excess of 0.27 adverse events per 100 patients within the room temperature group, which is below a 0.6% noninferiority margin. CONCLUSION. The data suggest that maintaining iohexol 350 at room temperature is noninferior to warming the agent to body temperature before injection. CLINICAL IMPACT. The resources involved to prewarm iohexol 350 before injection may not be warranted.

Experimental system prototype of a portable, low-cost, C-scan ultrasound imaging device.

A system prototype of a future compact, low-cost medical ultrasound device is described and presented with experimental results. The prototype system consists of a 32 x 32 element, fully sampled 2-D transducer array and a printed circuit board (PCB) containing 16 custom "front-end" receive channel integrated circuits (ICs) with analog multiplexing and programmable logic. A PC that included a commercially available data acquisition card is used for data collection and analysis. Beamforming is performed offline using the direct sampled in-phase/quadrature (DSIQ) algorithm. Pulse-echo images obtained with the prototype are presented. Results from this prototype support the feasibility of a low-cost, pocket-sized, C-scan imaging device.

Cystic resolution: a performance metric for ultrasound imaging systems.

This paper describes a metric that can be used to characterize the resolution of arbitrary broadband coherent imaging systems. The metric is particularly suited to medical ultrasound because it characterizes scanner performance using the contrast obtained by imaging anechoic cysts of various sizes that are embedded in a speckle-generating background, accounting for the effect of electronic noise. We present the theoretical derivation of the metric and provide simulation examples that demonstrate its utility. We use the metric to compare a low-cost, handheld, C-scan system under development in our laboratory to conventional ultrasound scanners. We also present the results of simulations that were designed to evaluate and optimize various parameters in our system, including the f/# and apodization windows. We investigate the impact of electronic noise on our system and quantify the tradeoffs associated with quantization in the analog to digital converter. Results indicate that an f/1 receive aperture combined with 10-bit precision and a signal-to-noise ratio (SNR) of 0 dB per channel would result in adequate image quality.

Direct sampled I/Q beamforming for compact and very low-cost ultrasound imaging.

A wide variety of beamforming approaches are applied in modern ultrasound scanners, ranging from optimal time domain beamforming strategies at one end to rudimentary narrowband schemes at the other. Although significant research has been devoted to improving image quality, usually at the expense of beamformer complexity, we are interested in investigating strategies that sacrifice some image quality in exchange for reduced cost and ease in implementation. This paper describes the direct sampled in-phase/quadrature (DSIQ) beamformer, which is one such low-cost, extremely simple, and compact approach. DSIQ beamforming relies on phase rotation of I/Q data to implement focusing. The I/Q data are generated by directly sampling the received radio frequency (RF) signal, rather than through conventional demodulation. We describe an efficient hardware implementation of the beamformer, which results in significant reductions in beamformer size and cost. We present the results of simulations and experiments that compare the DSIQ beamformer to more conventional approaches, namely, time delay beamforming and traditional complex demodulated I/Q beamforming. Results that show the effect of an error in the direct sampling process, as well as dependence on signal bandwidth and system f number (f#) are also presented. These results indicate that the image quality and robustness of the DSIQ beamformer are adequate for low end scanners. We also describe implementation of the DSIQ beamformer in an inexpensive hand-held ultrasound system being developed in our laboratory.

A novel beamformer design method for medical ultrasound. Part I: Theory.

The design of transmit and receive aperture weightings is a critical step in the development of ultrasound imaging systems. Current design methods are generally iterative, and consequently time consuming and inexact. We describe a new and general ultrasound beamformer design method, the minimum sum squared error (MSSE) technique. The MSSE technique enables aperture design for arbitrary beam patterns (within fundamental limitations imposed by diffraction). It uses a linear algebra formulation to describe the system point spread function (psf) as a function of the aperture weightings. The sum squared error (SSE) between the system psf and the desired or goal psf is minimized, yielding the optimal aperture weightings. We present detailed analysis for continuous wave (CW) and broadband systems. We also discuss several possible applications of the technique, such as the design of aperture weightings that improve the system depth of field, generate limited diffraction transmit beams, and improve the correlation depth of field in translated aperture system geometries. Simulation results are presented in an accompanying paper.

A novel beamformer design method for medical ultrasound. Part II: Simulation results.

In the first part of this work, we introduced the minimum sum squared error (MSSE) technique of ultrasound beamformer design. This technique enables the optimal design of apertures to achieve arbitrary system responses. In the MSSE technique, aperture weights are calculated and applied to minimize the sum squared error (SSE) between the desired and actual system responses. In this paper, we present the results of simulations performed to illustrate the implementation and validity of the MSSE technique. Continuous wave (CW) and broadband simulations are presented to demonstrate the application of the MSSE method to obtain arbitrary system responses (within fundamental physical limitations of the system). We also describe CW and broadband simulations that implement the MSSE method for improved conventional depth of field (DOF) and for improved correlation DOF in translated aperture geometries. Using the MSSE technique, we improved the conventional DOF by more than 200% in CW simulations and more than 100% in broadband simulations. The correlation DOF in translated aperture geometries was improved by more than 700% in both CW and broadband simulations.