Wearable technologies for active living and rehabilitation: Current research challenges and future opportunities.

This paper presents some recent developments in the field of wearable sensors and systems that are relevant to rehabilitation and provides examples of systems with evidence supporting their effectiveness for rehabilitation. A discussion of current challenges and future developments for selected systems is followed by suggestions for future directions needed to advance towards wider deployment of wearable sensors and systems for rehabilitation.

Workshop on using natural language processing applications for enhancing clinical decision making: an executive summary.

In April 2012, the National Institutes of Health organized a two-day workshop entitled 'Natural Language Processing: State of the Art, Future Directions and Applications for Enhancing Clinical Decision-Making' (NLP-CDS). This report is a summary of the discussions during the second day of the workshop. Collectively, the workshop presenters and participants emphasized the need for unstructured clinical notes to be included in the decision making workflow and the need for individualized longitudinal data tracking. The workshop also discussed the need to: (1) combine evidence-based literature and patient records with machine-learning and prediction models; (2) provide trusted and reproducible clinical advice; (3) prioritize evidence and test results; and (4) engage healthcare professionals, caregivers, and patients. The overall consensus of the NLP-CDS workshop was that there are promising opportunities for NLP and CDS to deliver cognitive support for healthcare professionals, caregivers, and patients.

Assessment of cardiac motion effects on the fiber architecture of the human heart in vivo.

The use of diffusion tensor imaging (DTI) for studying the human heart in vivo is very challenging due to cardiac motion. This paper assesses the effects of cardiac motion on the human myocardial fiber architecture. To this end, a model for analyzing the effects of cardiac motion on signal intensity is presented. A Monte-Carlo simulation based on polarized light imaging data is then performed to calculate the diffusion signals obtained by the displacement of water molecules, which generate diffusion weighted (DW) images. Rician noise and in vivo motion data obtained from DENSE acquisition are added to the simulated cardiac DW images to produce motion-induced datasets. An algorithm based on principal components analysis filtering and temporal maximum intensity projection (PCATMIP) is used to compensate for motion-induced signal loss. Diffusion tensor parameters derived from motion-reduced DW images are compared to those derived from the original simulated DW images. Finally, to assess cardiac motion effects on in vivo fiber architecture, in vivo cardiac DTI data processed by PCATMIP are compared to those obtained from one trigger delay (TD) or one single phase acquisition. The results showed that cardiac motion produced overestimated fractional anisotropy and mean diffusivity as well as a narrower range of fiber angles. The combined use of shifted TD acquisitions and postprocessing based on image registration and PCATMIP effectively improved the quality of in vivo DW images and subsequently, the measurement accuracy of fiber architecture properties. This suggests new solutions to the problems associated with obtaining in vivo human myocardial fiber architecture properties in clinical conditions.

In vivo cardiac diffusion-weighted magnetic resonance imaging: quantification of normal perfusion and diffusion coefficients with intravoxel incoherent motion imaging.

OBJECTIVES: Diffusion-weighted imaging (DWI) and the introduction of the intravoxel incoherent motion (IVIM) model have provided a unique method for evaluating perfusion and diffusion within a tissue without the need for a contrast agent. Despite its relevance, cardiac DWI has thus far been limited by low b values because of signal loss induced by physiological motion. The goal of this study was to develop a methodology for estimating IVIM parameters of in vivo cardiac magnetic resonance imaging using an efficient DWI acquisition framework. This was achieved by investigating various acquisition strategies (principal component analysis [PCA] filtering and temporal maximum intensity projection [PCATMIP] and single trigger delay [TD]) and fitting methods. MATERIAL AND METHODS: Simulations were performed on a synthetic dataset of diffusion-weighted signal intensity (SI) to determine the fitting method that would yield IVIM parameters with the greatest accuracy. The required number of b values to correctly estimate IVIM parameters was also investigated. Breath-hold DWI scans were performed for 12 volunteers to collect several TD values during diastole. Thirteen b values ranging from 0 to 550 s/mm were used. The IVIM parameters derived using the data from all the acquired TDs (PCATMIP technique) were compared with those derived using a single acquisition performed at an optimized diastolic time point (1TD). RESULTS: The main result of this study was that PCATMIP, when combined with a fitting model that accounted for T1 and T2 relaxation, provided IVIM parameters with less variability. However, an acquisition performed with 1 optimized diastolic TD provided results that were as good as those provided using PCATMIP if the R-R variability during the acquisition was sufficiently low (± 5%). Furthermore, the use of only 9 b values (that could be acquired in 2 breath-holds), instead of 13 b values (requiring 3 breath-holds), was sufficient to determine the IVIM parameters. CONCLUSIONS: This study demonstrates that IVIM is technically feasible in vivo and reports for the first time the perfusion fraction, f, and the diffusion coefficients, D and D*, for the cardiac DWI of healthy volunteers. Motion-induced signal loss, which is the main problem associated with cardiac DWI, could be avoided with the combined use of sliding acquisition during the cardiac cycle and image postprocessing with the PCATMIP algorithm. This study provides new perspectives for perfusion imaging without a contrast agent and demonstrates that IVIM parameters can act as promising tools to further characterize microvascular abnormalities or dysfunction.

Coronary artery wall imaging in mice using osmium tetroxide and micro-computed tomography (micro-CT).

The high spatial resolution of micro-computed tomography (micro-CT) is ideal for 3D imaging of coronary arteries in intact mouse heart specimens. Previously, micro-CT of mouse heart specimens utilized intravascular contrast agents that hardened within the vessel lumen and allowed a vascular cast to be made. However, for mouse coronary artery disease models, it is highly desirable to image coronary artery walls and highlight plaques. For this purpose, we describe an ex vivo contrast-enhanced micro-CT imaging technique based on tissue staining with osmium tetroxide (OsO(4) ) solution. As a tissue-staining contrast agent, OsO(4) is retained in the vessel wall and surrounding tissue during the fixation process and cleared from the vessel lumens. Its high X-ray attenuation makes the artery wall visible in CT. Additionally, since OsO(4) preferentially binds to lipids, it highlights lipid deposition in the artery wall. We performed micro-CT of heart specimens of 5- to 25-week-old C57BL/6 wild-type mice and 5- to 13-week-old apolipoprotein E knockout (apoE(-/-) ) mice at 10 µm resolution. The results show that walls of coronary arteries as small as 45 µm in diameter are visible using a table-top micro-CT scanner. Similar image clarity was achieved with 1/2000th the scan time using a synchrotron CT scanner. In 13-week-old apoE mice, lipid-rich plaques are visible in the aorta. Our study shows that the combination of OsO(4) and micro-CT permits the visualization of the coronary artery wall in intact mouse hearts.

3 Tesla turbo-FLASH magnetic resonance imaging of deglutition.

OBJECTIVES/HYPOTHESIS: In this article we describe a methodology for obtaining high-quality dynamic magnetic resonance imaging (MRI) sequences of the swallow sequence in healthy volunteers. The study includes comparison to previous work done in our lab using a 1.5 Tesla (T) magnet. STUDY DESIGN: Case series. METHODS: Three healthy volunteers underwent turbo-fast low angle shot MRI at 3T while swallowing liquid boluses delivered via intravenous tubing to the oral cavity. Imaging was performed in the sagittal and axial planes. RESULTS: Imaging provided by this sequence provided high temporal resolution, with the ability to depict deglutition in the axial and sagittal planes. Comparison with imaging at 1.5 T demonstrated benefits in temporal resolution and signal-to-noise. Anatomic information provided differed from comparative videofluoroscopy. CONCLUSIONS: MRI of swallowing using the described technique is reliable and provides a unique evaluation of the swallowing sequence.

Low b-value diffusion-weighted cardiac magnetic resonance imaging: initial results in humans using an optimal time-window imaging approach.

OBJECTIVES: Diffusion-weighted imaging (DWI) using low b-values permits imaging of intravoxel incoherent motion in tissues. However, low b-value DWI of the human heart has been considered too challenging because of additional signal loss due to physiological motion, which reduces both signal intensity and the signal-to-noise ratio (SNR). We address these signal loss concerns by analyzing cardiac motion during a heartbeat to determine the time-window during which cardiac bulk motion is minimal. Using this information to optimize the acquisition of DWI data and combining it with a dedicated image processing approach has enabled us to develop a novel low b-value diffusion-weighted cardiac magnetic resonance imaging approach, which significantly reduces intravoxel incoherent motion measurement bias introduced by motion. MATERIALS AND METHODS: Simulations from displacement encoded motion data sets permitted the delineation of an optimal time-window with minimal cardiac motion. A number of single-shot repetitions of low b-value DWI cardiac magnetic resonance imaging data were acquired during this time-window under free-breathing conditions with bulk physiological motion corrected for by using nonrigid registration. Principal component analysis (PCA) was performed on the registered images to improve the SNR, and temporal maximum intensity projection (TMIP) was applied to recover signal intensity from time-fluctuant motion-induced signal loss. This PCATMIP method was validated with experimental data, and its benefits were evaluated in volunteers before being applied to patients. RESULTS: Optimal time-window cardiac DWI in combination with PCATMIP postprocessing yielded significant benefits for signal recovery, contrast-to-noise ratio, and SNR in the presence of bulk motion for both numerical simulations and human volunteer studies. Analysis of mean apparent diffusion coefficient (ADC) maps showed homogeneous values among volunteers and good reproducibility between free-breathing and breath-hold acquisitions. The PCATMIP DWI approach also indicated its potential utility by detecting ADC variations in acute myocardial infarction patients. CONCLUSIONS: Studying cardiac motion may provide an appropriate strategy for minimizing the impact of bulk motion on cardiac DWI. Applying PCATMIP image processing improves low b-value DWI and enables reliable analysis of ADC in the myocardium. The use of a limited number of repetitions in a free-breathing mode also enables easier application in clinical conditions.

Atropine-induced polymorphic ventricular tachycardia: a rare and bygone occurrence revisited.

Atropine is commonly a used pre anesthetic medication. A 22-year-old female with history of unexplained recurrent syncope during electrophysiology developed inducible ventricular arrhythmias when 0.5 mg of atropine was injected intravenously to improve this Wenckebach. There is a significant change in the autonomic influence on the heart prior to idiopathic ventricular tachycardia and this seems to result mainly from decreased vagal activity.

Extrinsic multiecho phase-contrast SSFP: evaluation on cardiac output measurements.

Multiecho phase-contrast steady-state free precession (PC-SSFP) is a recently introduced sequence for flow quantification. In this multiecho approach, a phase reference and a velocity-encoded readout were acquired at different echo times after a single excitation. In this study, the sequence is validated in vitro for stationary flow. Subsequently, the sequence was evaluated on cardiac output measurements in vivo for through-plane flow in comparison to regular single gradient echo velocity quantification [phase-contrast spoiled gradient echo (PC-GE)]. In vitro results agreed with regular flow meters (RMS 0.1 cm/s). Cardiac output measurements with multiecho PC-SSFP on 10 healthy subjects gave on average the same results as the standard PC-GE. However, the limits of repeatability of PC-SSFP were significantly larger than those of PC-GE (2 l/min and 0.5 l/min, respectively, P=.001). The multiecho approach introduced some specific problems in vivo. The difference in echo times made the velocity maps sensitive for water-fat shifts and B(0)-drifts, which in turn made velocity offset correction problematic. Also, the addition of a single bipolar gradient cancelled the flow compensated nature of the SSFP sequence. In combination with the prolonged TR, this resulted in flow artifacts caused by high and pulsatile through-plane flow, affecting repeatability. Given the significantly lower repeatability of PC-SSFP, cardiac output in turn is less reliable, thus impairing the use of multiecho PC-SSFP.

A rare and unusual cause of PSA (prostate-specific antigen) elevation: sarcoidosis of the prostate.

Sarcoidosis and prostate cancer are 2 separate conditions that are more prevalent among the African American population. However, sarcoidosis of the prostate is a very rare clinical entity. Its association with prostate cancer is described in clinical case series. The use of PSA (prostate specific antigen) test for screening prostate cancer may be associated with false-positive results in this patient population. We report a patient who had an elevated PSA but had a biopsy proven to be sarcoidosis of the prostate gland.

Real-time myocardial segmentation using coupled active geometric functions.

Myocardial segmentation is essential for quantitative evaluation of cardiac functional images. As imaging techniques advance, 3D and 4D image data have become available. These data can provide clinically important cardiac dynamic information at high spatial or temporal resolution. However, the enormous amount of information contained in these data has also raised a challenge for traditional image analysis algorithms in terms of efficiency and clinical workflow. In this context, an automated real-time myocardial segmentation framework based on coupled Active Geometric Functions was proposed and tested on 414 frames of Phase Train Imaging data, a real-time cardiac MR imaging technique, with an average temporal resolution of 2 ms. The performance of myocardial segmentation was visually and quantitatively validated. Implemented in Matlab(c), the current method takes less than 1.2 ms per cardiac phase, allowing realization of true real-time online segmentation.

Theory, technique, and practice of magnetic resonance angiography.

Magnetic resonance angiography (MRA) is now a widely accepted technique used to characterize vascular pathology such as stenosis, dissection, fistula, and aneurysms. Magnetic resonance techniques are increasingly driving clinical decision making by vascular physicians. The physics behind MRA can contribute to the general understanding and interpretation of the anatomic images. We seek to provide a window into how magnetic resonance images are generated, which techniques may be employed, and the potential advantages and limitations of various techniques and to discuss the future role MRA may have for the vascular physician.

Phase contrast using multiecho steady-state free precession.

Conventional phase-contrast (PC) MRI is limited in the temporal resolution (typically 50 ms) that can be achieved, due to the need to implement bipolar velocity encoding gradients. PC using steady-state free precession (SSFP) has recently been developed to acquire PC data at higher rates without sacrificing contrast-to-noise ratio (CNR). This work presents two multiecho SSFP PC implementations that can be used to increase the time efficiency of PCSSFP. Both approaches (extrinsic and intrinsic) enable reference image lines to be acquired within the same TR as the flow-encoded lines, thus minimizing the scan time and permitting TR-equivalent temporal resolutions. Both approaches have been implemented and tested successfully on human volunteers at 1.5T and 3T. While the intrinsic approach is useful for encoding higher velocity flows in-plane, the extrinsic implementation can be used for studying a wider range of encoding velocities for flow in the imaging plane and through the imaging plane.

Advances in MRI tagging techniques for determining regional myocardial strain.

MRI of the heart with magnetization tagging provides a potentially useful new way to assess cardiac mechanical function, through revealing the local motion of otherwise indistinguishable portions of the heart wall. Although still an evolving area, tagged cardiac MRI is already able to provide novel quantitative information on cardiac function. Exploiting this potential requires developing tailored methods for both imaging and image analysis. In this article, we review some of the progress that has been made in developing imaging methods for tagged cardiac MRI.

High-resolution imaging reveals a limit in spatial resolution of blood flow measurements by microspheres.

Density of 15-microm microspheres after left atrial application is the standard measure of regional perfusion. In the heart, substantial differences in microsphere density are seen at spatial resolutions <5 ml, implying perfusion heterogeneity. Microsphere deposition imaging permits a superior evaluation of the distribution pattern. Therefore, fluorescent microspheres (FMS) were applied, FMS deposition in the canine heart was imaged by epifluorescence microscopy in vitro, and the patterns were observed compared with MR images of iron oxide microspheres (IMS) obtained in vivo and in vitro. FMS deposition in myocardial slices revealed the following: 1) a nonrandom distribution, with sequentially applied FMS of different color stacked within the same vessel, 2) general FMS clustering, and 3) rather large areas devoid of FMS (n = 3). This pattern was also seen in reconstructed three-dimensional images (<1 nl resolution) of FMS distribution (n = 4). Surprisingly, the deposition pattern of sequentially applied FMS remained virtually identical over 3 days. Augmenting flow by intracoronary adenosine (>2 microM) enhanced local microsphere density, but did not alter the deposition pattern (n = 3). The nonrandom, temporally stable pattern was quantitatively confirmed by a three-dimensional intermicrosphere distance analysis of sequentially applied FMS. T2-weighted short-axis MR images (2-microl resolution) of IMS revealed similar patterns in vivo and in vitro (n = 6), as seen with FMS. The observed temporally stable microsphere patterns are not consistent with the notion that microsphere deposition is solely governed by blood flow. We propose that at high spatial resolution (<2 microl) structural aspects of the vascular network dominate microsphere distribution, resulting in the organized patterns observed.

Rapid-motion-perception based cardiac navigators: using the high flow blood volume as a marker for the position of the heart.

Navigators have been developed as one of the many approaches to reducing motion artifacts due to respiration. A typical navigator approach applies a pencil-beam style profile crossing the diaphragm to track the superior-inferior (SI) motion of the diaphragm, and subsequently applying correlations to determine the heart location. This approach necessitates a priori knowledge of the correlation coefficients between heart and diaphragm motion, a variable parameter among patients. This paper presents an alternative navigator method based on Rapid Motion Perception (RaMP). This method acquires profiles of the ventricular blood volume based on its high flow velocity. The position of the blood volume is a direct representation of the position of the heart. This method allows cardiac navigation in two orthogonal directions simultaneously, eliminates the need to obtain correlations to the diaphragm motion, and increases tracking reliability for individual patients. A prospective version of RaMP navigators has been implemented on a clinical 1.5 T scanner, and preliminary tests on human volunteers show that this method can successfully track the heart position over the entire respiratory period. This navigation scheme is tested for predicting superior-inferior and anterior-posterior (AP) motion of the heart for breath-hold and free breathing conditions. Bland-Altman plots comparing the motion predicted by the navigators and that computed from single-shot images immediately following the navigators, show that the accuracy of this method is +/- 1.43 mm in the SI direction and +/- 0.84 mm in the AP direction. The RaMP navigator is suited for real-time tracking of the bulk translational motion of the heart.

Does binding of Gd-DTPA to myocardial tissue contribute to late enhancement in a model of acute myocardial infarction?

The long-lasting signal enhancement by Gd-DTPA in areas of myocardial infarction has been conventionally explained by low perfusion and an enhanced Gd distribution volume. To test whether binding of Gd to myocardial constituents is an additional factor contributing to this effect, Gd-DTPA was allowed to equilibrate between homogenized porcine myocardial tissue and physiological saline. The relaxation rate (1/T(1)) of homogenate samples (n = 61) increased in proportion (r(2) = 0.98) to the Gd concentration (0.025-0.5 mM) of the surrounding medium, with no evidence for augmented uptake. The diffusion-limited uptake was only slightly more rapid than the subsequent Gd-release. The amount of Gd released was in line with all of the Gd-DTPA in the homogenate participating in water proton relaxation. The data from this acute myocardial infarction model do not support the notion that Gd-DTPA binding in the early stages of myocardial damage contributes to delayed enhancement.