Jan Menssen

Lateral frontal cortex oxygenation changes during translation and language switching revealed by non-invasive near-infrared multi-point measurements

The organisation of language in the brain of multilingual people remains controversial. Using a high temporal resolution 12-channel near-infrared continuous wave spectroscopy system, we have demonstrated that it is possible to monitor non-invasively, comfortably and, without the interferences due to intrinsic limitations of positron emission tomography (PET) and functional magnetic resonance imaging (fMRI), cortical oxygenation changes in the Brocas area in response to translation of short sentences and language switching. Eight Dutch students proficient in English translated aloud from their native language into English or vice versa or alternating (switching) short visually presented sentences. These tasks provoked, in the left inferior frontal cortex which includes the Brocas area, a consistent and incremental rise in oxyhaemoglobin accompanied by a smaller decrease in deoxyhaemoglobin. The investigated cortical areas surrounding the Brocas area showed no uniform and consistent oxygenation changes upon the three different translation tasks. These results confirm that Brocas area is involved in the translation process and its so called activation is unaffected by the direction of the translation. In addition, these results strengthen the role of near-infrared multi-point measurements as a powerful tool for investigating the spatial and temporal features of the cortical oxygenation changes during language processing.

Fetal Oxygenation in Chronic Maternal Hypoxia; What’s Critical?

For the study in an animal model of the consequences of chronic maternal hypoxia on several physiological variables (e.g., fetal ECG variability, fetal breathing patterns), as potential clinical indicators for insufficient oxygen supply to the fetus, the continuous availability of a reliable signal on fetal oxygenation is necessary. This signal is needed as a feedback for the control of maternal inspiratory oxygen fraction (F1O2) in the model. Theoretically, fetal arterial oxygen saturation is the indicator of choice for the observation of oxygen availability, assuming hemoglobin concentration is normal as well as constant. The development [1] of pulse oximetry as a non-invasive optical technique seemed promising for the application in fetal studies [2], especially in chronically instrumentated fetal lambs. To evaluate the possibilities of this technique, we tested pulse oximetry transducers, both in transmission and reflection mode, against blood gas analysis before, during and after periods of maternal hypoxia in sheep. From the results of the blood gas measurements we tried to find objective criteria to determine the onset of fetal endanger, induced by maternal hypoxia.

Fast 2-D ultrasound strain imaging: the benefits of using a GPU

Deformation of tissue can be accurately estimated from radio-frequency ultrasound data using a 2-dimensional normalized cross correlation (NCC)-based algorithm. This procedure, however, is very computationally time-consuming. A major time reduction can be achieved by parallelizing the numerous computations of NCC. In this paper, two approaches for parallelization have been investigated: the OpenMP interface on a multi-CPU system and Compute Unified Device Architecture (CUDA) on a graphics processing unit (GPU). The performance of the OpenMP and GPU approaches were compared with a conventional Matlab implementation of NCC. The OpenMP approach with 8 threads achieved a maximum speed-up factor of 132 on the computing of NCC, whereas the GPU approach on an Nvidia Tesla K20 achieved a maximum speed-up factor of 376. Neither parallelization approach resulted in a significant loss in image quality of the elastograms. Parallelization of the NCC computations using the GPU, therefore, significantly reduces the computation time and increases the frame rate for motion estimation.

The ductus arteriosus, pre- and post-ductal oxygen saturation measurements in fetal lambs

In the fetus, the arterial oxygen saturation (SaO2) in the ascending aorta is higher than in the descending aorta. We questioned whether this difference over the ductus arteriosus (delta SaO2) would change during hypoxaemia. Therefore, six chronically instrumented fetal lambs (119-126 days of gestation) were studied, by changing the inspired oxygen (FIO2) via a tracheal tube to the ewe. The SaO2 was measured intermittently every 15 min with blood samples obtained from the ascending and descending aorta, and continuously with 2 pulse oximeters at both sides of the ductus arteriosus. delta SaO2 was at a level of 3.4-5.3% and had a tendency to decrease at preductal SaO2 levels of 10-20% and at pH levels below 7.25. The precision of the pulse oximeters, expressed as standard deviation of the differences between sample SaO2 and pulse oximeter SaO2, was around 5.0% for the individual calibration curves. This precision was not enough to show details of the course of delta SaO2 between the blood samples. Our results show that there is no change in delta SaO2 across the ductus arteriosus.

Automated 3D ultrasound elastography of the breast: a phantom validation study

In breast cancer screening, the automated breast volume scanner (ABVS) was introduced as an alternative for mammography since the latter technique is less suitable for women with dense breasts. Although clinical studies show promising results, clinicians report two disadvantages: long acquisition times (>90 s) introducing breathing artefacts, and high recall rates due to detection of many small lesions of uncertain malignant potential. Technical improvements for faster image acquisition and better discrimination between benign and malignant lesions are thus required. Therefore, the aim of this study was to investigate if 3D ultrasound elastography using plane-wave imaging is feasible. Strain images of a breast elastography phantom were acquired by an ABVS-mimicking device that allowed axial and elevational movement of the attached transducer. Pre- and post-deformation volumes were acquired with different constant speeds (between 1.25 and 40.0 mm s(-1)) and by three protocols: Go-Go (pre- and post-volumes with identical start and end positions), Go-Return (similar to Go-Go with opposite scanning directions) and Control (pre- and post-volumes acquired per position, this protocol can be seen as reference). Afterwards, 2D and 3D cross-correlation and strain algorithms were applied to the acquired volumes and the results were compared. The Go-Go protocol was shown to be superior with better strain image quality (CNRe and SNRe) than Go-Return and to be similar as Control. This can be attributed to applying opposite mechanical forces to the phantom during the Go-Return protocol, leading to out-of-plane motion. This motion was partly compensated by using 3D cross-correlation. However, the quality was still inferior to Go-Go. Since these results were obtained in a phantom study with controlled deformations, the effect of possible uncontrolled in vivo tissue motion artefacts has to be addressed in future studies. In conclusion, it seems feasible to implement 3D ultrasound quasi-static elastography on an ABVS-like system and to reduce scan times within one breath-hold (~10 s) by plane-wave acquisitions.

Intracranial pressure and fetal heart rate in a hydrocephalic fetus during labor

Intra-uterine pressure (IUP), intracranial pressure (ICP) and fetal heart rate (FHR) were simultaneously recorded during labor in a severely hydrocephalic fetus. After cephalocentesis, 600 ml of liquor cerebrospinalis was drained. ICP exceeded IUP, but the increase in ICP was less than the increase in IUP during most of the contractions. The FHR showed marked decelerations during uterine contractions and changed gradually into a persistent bradycardia. The pathophysiology of fetal heart rate patterns during labor is discussed and the literature has been reviewed.

Reflectance Pulse Oximetry

Continuous fetal heart rate (FHR) monitoring is used to assess the fetal condition during labour. Unfortunately, FHR patterns are not always easy to interpret, with low sensitivity and specificity as consequence. Other continuous methods for fetal surveillance have been proposed during labour (e.g. transcutaneous pO2 and pCO2, and pH-monitoring), but are not widespread used.

Real-time noninvasive optical imaging of exercising muscle and brain upon cognitive stimuli

The monitoring of a single muscle location does not reflect the heterogeneity of the muscle groups activation during exercise. In the past, measurements of oxygen consumption (VO2) at single muscle locations could be carried out non-invasively by near-infrared continuous wave spectroscopy (NIRCWS) at rest or during isometric contractions. In the present study, human regional quadriceps (vastus lateralis and rectus femoris) VO2 was investigated at rest and during maximal voluntary contractions using a 12- channel NIRCWS system with an acquisition time of 0.1 s.

Effect of Bladderbox Alarms During Venoarterial Extracorporeal Membrane Oxygenation on Cerebral Oxygenation and Hemodynamics in Lambs

To determine the effects of bladderbox alarms during venoarterial extracorporeal membrane oxygenation (va-ECMO) on cerebral oxygenation and hemodynamics, six lambs were prospectively treated with va-ECMO and bladderbox alarms were simulated. Changes in concentrations of oxyhemoglobin (ΔcO2Hb), deoxyhemoglobin (ΔcHHb), and total Hb (ΔctHb) were measured using near infrared spectrophotometry. Fluctuations in Hb oxygenation index (ΔHbD) and cerebral blood volume (ΔCBV) were calculated. Heart rate (HR), mean arterial pressure (MAP), blood flow in the left carotid artery (Qcar), and central venous pressure (CVP) were registered. Bladderbox alarms were simulated by increasing the ECMO flow or partially clamping the venous cannula and resolved by decreasing the ECMO flow, unclamping the cannula, or intravascular volume administration. CBV, HbD, MAP, and Qcar decreased significantly during bladderbox alarms, whereas HR and CVP increased. After the bladderbox alarms, CBV and HbD increased significantly to values above baseline. For HbD, this increase was higher during intravascular volume administration. MAP, Qcar, and CVP recovered to preexperiment values but increased further with volume administration. HR was increased at the end of our measurements. We conclude that Bladderbox alarms during va-ECMO treatment result in significant fluctuations in cerebral oxygenation and hemodynamics, a possible risk factor for intracranial lesions.

4D strain imaging using single and dual probe acquisitions of a patient specific carotid bifurcation phantom

Atherosclerosis in the carotid artery (CA) elevates the risk for cerebral events. Strain imaging has demonstrated to be a technique capable of identifying plaque composition. For strain imaging of carotid cross-sections, compound techniques have been developed to solve the poor strain estimation quality perpendicular to the ultrasound beam direction. This study assesses the performance of radial and circumferential strain imaging in 4D derived from multi-plane acquisitions with a single transducer with and without compounding and using two orthogonally placed transducers.