Ross D. Venook

Dual in vivo magnetic resonance evaluation of magnetically labeled mouse embryonic stem cells and cardiac function at 1.5 t

Cell therapy has demonstrated the potential to restore injured myocardium. A reliable in vivo imaging method to localize transplanted cells and monitor their restorative effects will enable a systematic investigation of this therapeutic modality. The dual MRI capability of imaging both magnetically labeled mouse embryonic stem cells (mESC) and their restorative effects on cardiac function in a murine model of acute myocardial infarction is demonstrated. Serial in vivo MR detection of transplanted mESC and monitoring of the mESC‐treated myocardium was conducted over a 4‐week period using a 1.5 T clinical scanner. During the 4‐week duration, the mESC‐treated myocardium demonstrated sustained improvement of the left ventricular (LV) ejection fraction and conservation of LV mass. Furthermore, no significant difference of their restorative effects on the cardiac function was created by the magnetic labeling of mESC. Thus, in vivo MRI enables simultaneous detection of transplanted mESC and their therapeutic effect on the injured myocardium. Magn Reson Med 2006.

Prepolarized magnetic resonance imaging around metal orthopedic implants.

A prepolarized MRI (PMRI) scanner was used to image near metal implants in agar gel phantoms and in in vivo human wrists. Comparison images were made on 1.5‐ and 0.5‐T conventional whole‐body systems. The PMRI experiments were performed in a smaller bore system tailored to extremity imaging with a prepolarization magnetic field of 0.4 T and a readout magnetic field of 27–54 mT (1.1–2.2 MHz). Scan parameters were chosen with equal readout gradient strength over a given field of view and matrix size to allow unbiased evaluation of the benefits of lower readout frequency. Results exhibit substantial reduction in metal susceptibility artifacts under PMRI versus conventional scanners. A new artifact quantification technique is also presented, and phantom results confirm that susceptibility artifacts improve as expected with decreasing readout magnetic field using PMRI. This proof‐of‐concept study demonstrates that prepolarized techniques have the potential to provide diagnostic cross‐sectional images for postoperative evaluation of patients with metal implants. Magn Reson Med.

Magnetic resonance imaging with T1 dispersion contrast.

Prepolarized MRI uses pulsed magnetic fields to produce MR images by polarizing the sample at one field strength (∼0.5 T) before imaging at a much lower field (∼50 mT). Contrast reflecting the T1 of the sample at an intermediate field strength is achieved by polarizing the sample and then allowing the magnetization to decay at a chosen “evolution” field before imaging. For tissues whose T1 varies with field strength (T1 dispersion), the difference between two images collected with different evolution fields yields an image with contrast reflecting the slope of the T1 dispersion curve between those fields. Tissues with high protein content, such as muscle, exhibit rapid changes in their T1 dispersion curves at 49 and 65 mT due to cross‐relaxation with nitrogen nuclei in protein backbones. Tissues without protein, such as fat, have fairly constant T1 over this range; subtracting images with two different evolution fields eliminates signal from flat T1 dispersion species. T1 dispersion protein‐content images of the human wrist and foot are presented, showing clear differentiation between muscle and fat. This technique may prove useful for delineating regions of muscle tissue in the extremities of patients with diseases affecting muscle viability, such as diabetic neuropathy, and for visualizing the protein content of tissues in vivo. Magn Reson Med 2006.

An Optically Coupled System for Quantitative Monitoring of MRI-Induced RF Currents Into Long Conductors

The currents induced in long conductors such as guidewires by the radio-frequency (RF) field in magnetic resonance imaging (MRI) are responsible for potentially dangerous heating of surrounding media, such as tissue. This paper presents an optically coupled system with the potential to quantitatively measure the RF currents induced on these conductors. The system uses a self shielded toroid transducer and active circuitry to modulate a high speed light-emitting-diode transmitter. Plastic fiber guides the light to a photodiode receiver and transimpedance amplifier. System validation included a series of experiments with bare wires that compared wire tip heating by fluoroptic thermometers with the RF current sensor response. Validations were performed on a custom whole body 64 MHz birdcage test platform and on a 1.5 T MRI scanner. With this system, a variety of phenomena were demonstrated including cable trap current attenuation, lossy dielectric Q-spoiling and even transverse electromagnetic wave node patterns. This system should find applications in studies of MRI RF safety for interventional devices such as pacemaker leads, and guidewires. In particular, variations of this device could potentially act as a realtime safety monitor during MRI guided interventions.

Three-dimensional prepolarized magnetic resonance imaging using rapid acquisition with relaxation enhancement

Prepolarized MRI (PMRI) with pulsed electromagnets has the potential to produce diagnostic quality 0.5‐ to 1.0‐T images with significantly reduced cost, susceptibility artifacts, specific absorption rate, and gradient noise. In PMRI, the main magnetic field cycles between a high field (Bp) to polarize the sample and a homogeneous, low field (B0) for data acquisition. This architecture combines the higher SNR of the polarizing field with the imaging benefits of the lower field. However, PMRI can only achieve high SNR efficiency for volumetric imaging with 3D rapid imaging techniques, such as rapid acquisition with relaxation enhancement (RARE) (FSE, TSE), because slice‐interleaved acquisition and longitudinal magnetization storage are both inefficient in PMRI. This paper demonstrates the use of three techniques necessary to achieve efficient, artifact‐free RARE in PMRI: quadratic nulling of concomitant gradient fields, electromotive force cancelation during field ramping, and phase compensation of CPMG echo trains. This paper also demonstrates the use of 3D RARE in PMRI to achieve standard T1 and fat‐suppressed T2 contrast in phantoms and in vivo wrists. These images show strong potential for future clinical application of PMRI to extremity musculoskeletal imaging and peripheral angiography. Magn Reason Med, 2006.

Automatic tuning of flexible interventional RF receiver coils.

Microcontroller‐based circuitry was built and tested for automatically tuning flexible RF receiver coils at the touch of a button. This circuitry is robust to 10% changes in probe center frequency, is in line with the scanner, and requires less than 1 s to tune a simple probe. Images were acquired using this circuitry with a varactor‐tunable 1‐inch flexible probe in a phantom and in an in vitro porcine knee model. The phantom experiments support the use of automatic tuning by demonstrating 30% signal‐to‐noise ratio (SNR) losses for 5% changes in coil center frequency, in agreement with theoretical calculations. Comparisons between patellofemoral cartilage images obtained using a 3‐inch surface coil and the surgically‐implanted 1‐inch flexible coil reveal a worst‐case local SNR advantage of a factor of 4 for the smaller coil. This work confirms that surgically implanted coils can greatly improve resolution in small‐field‐of‐view (FOV) applications, and demonstrates the importance and feasibility of automatically tuning such probes. Magn Reson Med, 2005.

The Impact of Postgraduate Health Technology Innovation Training: Outcomes of the Stanford Biodesign Fellowship

Stanford Biodesign launched its Innovation Fellowship in 2001 as a first-of-its kind postgraduate training experience for teaching biomedical technology innovators a need-driven process for developing medical technologies and delivering them to patients. Since then, many design-oriented educational programs have been initiated, yet the impact of this type of training remains poorly understood. This study measures the career focus, leadership trajectory, and productivity of 114 Biodesign Innovation Fellowship alumni based on survey data and public career information. It also compares alumni on certain publicly available metrics to finalists interviewed but not selected. Overall, 60% of alumni are employed in health technology in contrast to 35% of finalists interviewed but not selected. On leadership, 72% of alumni hold managerial or higher positions compared to 48% of the finalist group. A total of 67% of alumni reported that the fellowship had been “extremely beneficial” on their careers. As a measure of technology translation, more than 440,000 patients have been reached with technologies developed directly out of the Biodesign Innovation Fellowship, with another 1,000,000+ aided by solutions initiated by alumni after their training. This study suggests a positive impact of the fellowship program on the career focus, leadership, and productivity of its alumni.

In vitro assessment of bacterial colonisation rates of goat umbilical cord segments using three embodiments of a novel neonatal umbilical catheter protection device

Introduction Central line-associated bloodstream infections (CLABSIs) in neonates with umbilical catheters occur at a rate that is 5 times higher than CLABSIs in adults with central catheters. No device currently exists tailored to the unique constraints umbilical catheters pose. The current study examined the natural progression of bacterial colonisation in goat umbilical cords and the relationship between embodiments of a novel neonatal umbilical catheter protection device and bacterial colonisation rates. The authors hypothesise that device venting is required to minimise bacterial colonisation in the unique umbilical stump environment. Methods The natural progression of bacterial colonisation in goat umbilical cord segments was studied by examining bacterial colonisation rates each day over 7 days. To understand the relationship between protection and bacterial colonisation, umbilical catheters were placed in goat umbilical cord segments and secured with 1 of 3 embodiments of a novel umbilical catheter protection device, which offered varying degrees of venting. After a 7-day period of incubation, colony counts were compared. Results Bacterial load was largest when umbilical cord segments were fresh and subsequently decreased over time. Further, bacterial colonisation rates showed a statistically significant difference between device embodiments (F(2,9)=4.26, p<0.05), with the non-vented embodiment showing the highest bacterial colonisation rate. Conclusions A device to better stabilise and protect umbilical catheters in order to reduce bloodstream infections in neonates is greatly needed. The current experiments confirm the hypothesis that completely enclosed, or non-vented, protection device will have increased bacterial growth.