Suitability of the Openly Accessible 3D Printed Prosthetic Hands for War-Wounded Children.

The field of rehabilitation and assistive devices is being disrupted by innovations in desktop 3D printers and open-source designs. For upper limb prosthetics, those technologies have demonstrated a strong potential to aid those with missing hands. However, there are basic interfacing issues that need to be addressed for long term usage. The functionality, durability, and the price need to be considered especially for those in difficult living conditions. We evaluated the most popular designs of body-powered, 3D printed prosthetic hands. We selected a representative sample and evaluated its suitability for its grasping postures, durability, and cost. The prosthetic hand can perform three grasping postures out of the 33 grasps that a human hand can do. This corresponds to grasping objects similar to a coin, a golf ball, and a credit card. Results showed that the material used in the hand and the cables can withstand a 22 N normal grasping force, which is acceptable based on standards for accessibility design. The cost model showed that a 3D printed hand could be produced for as low as $19. For the benefit of children with congenital missing limbs and for the war-wounded, the results can serve as a baseline study to advance the development of prosthetic hands that are functional yet low-cost.

Characterizing coronary motion and its effect on MR coronary angiography--initial experience.

PURPOSE: To characterize coronary artery motion as a prescan procedure to select the optimum scan setting that will produce high-resolution images. MATERIALS AND METHODS: A 2D real-time scan was used to image the major coronary arteries during breath-holding and free-breathing conditions. With the use of the 2D images, motion displacement of each artery was measured along three axes. Motion data obtained from a computer simulation were used to estimate point-spread functions (PSFs) associated with different high-resolution spiral acquisition strategies, including real-time, cardiac-gated, and respiratory-gated acquisitions. The simulation output determined the optimum acquisition and scan parameters that would produce the highest-spatial-resolution images of the coronary arteries. The effects of heart rate (HR), extended breath-holding, and number of slices per heart cycle were also investigated. RESULTS: Substantial variations in coronary motion occur among individuals, which directly influences the optimum parameters for a high-resolution scan. Lower HRs and longer breath-holds yield substantially increased spatial resolution. The maximum number of slices per heart cycle can also be determined to minimize slice-to-slice distortion. CONCLUSION: The results suggest that to obtain high-resolution coronary images, one should perform a prescan coronary-motion characterization for each individual so that the scan parameters can be optimized before data acquisition.

Evaluating contrast kinetics by acquiring 2D images during 3D contrast-enhanced MR angiography.

PURPOSE: To monitor contrast kinetics by acquiring multiple 2D images during 3D contrast-enhanced magnetic resonance angiography (CE MRA). MATERIALS AND METHODS: A 2D real-time autotriggering tool was integrated into a 3D sequence, enabling it to run multiple times during 3D acquisition. Several dummy scans were applied after each transition to maintain the steady state condition of both sequences. The number of the acquired 2D images and their distribution can be adjusted. Each 2D image was saved along with its associated timing. Contrast signal variations over time were plotted, reflecting selective signal measurement over an artery and vein from the saved 2D images. RESULTS: Different contrast kinetics timings were calculated from the resulting plot. Contrast arrival time to the internal cerebral artery was 13.2 +/- 1.2 seconds and the peak arterial to peak venous (at the confluence of sinuses) enhancement was 6.7 +/- 0.6 seconds. The observed timing could be used for 3D sequence optimization; the saved 2D images are useful in detecting and characterizing vascular abnormalities. CONCLUSION: Integrating 2D and 3D sequences into one sequence to monitor contrast kinetics through the neurovasculature is feasible without the need for extra injections or reduced spatial resolution. The technique can also be used in different parts of the body to extract useful clinical information.

High-resolution imaging of the intracranial arterial and venous systems following a single contrast injection.

PURPOSE: To generate two separate three-dimensional (3D) high spatial resolution images of the intracranial arterial and venous systems using a single contrast injection. MATERIALS AND METHODS: A 3D contrast-enhanced (CE) magnetic resonance angiography (MRA) acquisition was modified to create two separate k-space data sets to encode the arterial and venous enhancement signals individually after contrast agent injection. Following an automated detection of contrast arrival, the central k-space views corresponding to the arterial phase were acquired for the first eight seconds. A full elliptical-centric acquisition was then acquired for the venous phase and the missing views in the periphery of the first k-space data set were copied from the venous phase. A total of 18 patients underwent this study. Image quality, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) were determined in both intracranial systems. RESULTS: Two 3D image sets were generated for the arterial and venous intracranial systems. Both sets have high quality images that are clinically diagnostic. SNR and CNR were high in both sets, so that all the major vessels were visible. CONCLUSION: This technique provides images with high spatial resolution for both arterial and venous intracranial systems using a single contrast injection.

Optimization of 3D contrast-enhanced pulmonary magnetic resonance angiography in pediatric patients with congenital heart disease.

Contrast kinetics were studied in the main pulmonary artery (MPA) and ascending aorta (AAo) of 12 children with congenital heart disease. This information was used to optimize the timing of data acquisition for contrast-enhanced MR angiography in these vessels. To reduce contrast-agent dosage in these fragile patients, contrast enhancement was measured during routine diagnostic 3D magnetic resonance (MR) angiography instead of using test-bolus methods. This was possible by acquiring 2D cross-sectional images of the MPA and AAo during the 3D scan. Time-to-peak in the MPA and AAo was 4.9 +/- 2.2 and 6.1 +/- 2.2 s, respectively, while the transit time between the two vessels was 4.5 +/- 0.6 s. A point-spread-function analysis showed that intravascular signal strength was maximized if data acquisition began 4.7 +/- 2.3 s after the first arrival of contrast in the MPA and 5.6 +/- 2.3 s in the AAo. Little signal loss and artifact resulted when longer acquisition delays were used because contrast-agent clearance was slow. Based on these results, MR angiography of both the MPA and the AAo in children with congenital heart disease can be performed using elliptic-centric k-space sampling and a trigger delay of 7.9 s after contrast arrival in the AAo (i.e., time-to-peak signal strength in the AAo plus one SD to account for intersubject variability).

Pulsatile motion effects on 3D magnetic resonance angiography: implications for evaluating carotid artery stenoses.

In-plane carotid artery motion during a 3D MR angiography (MRA) scan can significantly degrade the resulting image resolution. This study characterizes the effect of cardiac pulsatility on 3D contrast-enhanced (CE) MRA with elliptical centric acquisitions using a point-spread function (PSF) analysis. Internal carotid artery (ICA) motion was collected from volunteers and patients using both MR and ultrasound (US) scans. After measuring the carotid artery motion displacement, a simulation was performed which calculated the blurring effects for three different protocols: nongated and two different cardiac gating schemes. The motion sensitivity of each protocol was evaluated for different spatial resolutions. The selection of optimal imaging parameters for a given scan time was investigated. The final results showed that cardiac-gated acquisitions only over a limited region of k-space high spatial frequencies are more time-efficient than cardiac gating for the entire k-space, as it allows for higher resolutions to be achieved and for capturing the arterial phase with low spatial frequencies. Selecting the optimal gating parameters depends directly on the motion characteristics of each individual. Our initial clinical experience is presented, and the need for a real-time tool that characterizes motion behavior for each individual as a prescan protocol is discussed.

Optimized spiral imaging for measurement of myocardial T2 relaxation.

Microcirculation oxygen levels and blood volumes should be reflected in measurements of myocardial T(2) relaxation. This work describes the optimization of a spiral imaging strategy for robust myocardial T(2) measurement to minimize the standard deviation of T(2) measurement (sigmaT(2)). Theoretical and experimental studies of blurring at muscle/blood interfaces enabled the derivation of parameter sets which reduce sigma T(2) to the level of 5%. T(2) relaxation mapping within healthy volunteers provided estimation of residual sigmaT(2) within the optimized technique. The standard deviation in T(2) measurement across regions of interest (ROIs) in different locations is about 9%. The standard deviation in T(2) measurement in an ROI across different time points is about 5%.

Vessel contrast at three Tesla in time-of-flight magnetic resonance angiography of the intracranial and carotid arteries.

The effects of the increased field strength of 3T on blood vessel contrast in three-dimensional time-of-flight (TOF) MR angiography (MRA) of the intracranial and carotid arteries was evaluated. Bloch equation simulations based on measured longitudinal relaxation times suggested superior blood-to-background contrast might be expected at 3T over 1.5T when using typical 3D TOF MRA parameters. A 15-volunteer study found that 3T was preferable over 1.5T for visualising distal intracranial vessels and the carotid arteries, by providing superior background suppression and excellent fat suppression. The combination of improved background suppression and improved signal-to-noise at 3T, enabled high resolution intracranial 3D TOF MRA with voxel volumes as small as 0.14 mm(3) to be acquired.

Application of magnetization transfer at 3.0 T in three-dimensional time-of-flight magnetic resonance angiography of the intracranial arteries.

PURPOSE: To apply magnetization transfer (MT) at 3.0 T in three-dimensional time-of-flight magnetic resonance angiography of the intracranial arteries. MATERIALS AND METHODS: This study was performed on phantoms and seven volunteers to determine the effects of MT at 3.0 T. By using a modulated MT approach and an altered phase encode order, the specific absorption rate (SAR) was kept below 3 W/kg over any 8-second time period. RESULTS: For a 20-degree flip angle and 36 msec repetition time, the background suppression at 3.0 T was improved with MT by 52 +/- 5% for white matter and 40 +/- 8% for grey matter, making the distal intracranial vasculature significantly more discernible. CONCLUSIONS: MT at 3.0 T can significantly improve background suppression in 3D time-of-flight magnetic resonance angiography (MRA) of the intracranial arteries without exceeding SAR guidelines.