Matteo Lenge

Comparison of carotid artery blood velocity measurements by vector and standard Doppler approaches.

Although severely affected by the angle dependency, carotid artery peak systolic velocity measurements are widely used for assessment of stenosis. In this study, blood peak systolic velocities in the common and internal carotid arteries of both healthy volunteers and patients with internal carotid artery stenosis were measured by two vector Doppler (VD) methods and compared with measurements obtained with the conventional spectral Doppler approach. Although the two VD techniques were completely different (using the transmission of focused beams and plane waves, respectively), the measurement results indicate that these techniques are nearly equivalent. The peak systolic velocities measured in 22 healthy common carotid arteries by the two VD techniques were very close (according to Bland-Altman analysis, the average difference was 3.2%, with limits of agreement of ± 8.6%). Application of Bland-Altman analysis to comparison of either VD technique with the spectral Doppler method provided a 21%-25% average difference with ± 13%-15% limits of agreement. Analysis of the results obtained from 15 internal carotid arteries led to similar conclusions, indicating significant overestimation of peak systolic velocity with the spectral Doppler method. Inter- and intra-operator repeatability measurements performed in a group of 8 healthy volunteers provided equivalent results for all of the methods (coefficients of variability in the range 2.7%-6.9%), even though the sonographers were not familiar with the VD methods. The results of this study suggest that the introduction of vector Doppler methods in commercial machines may finally be considered mature and capable of overcoming the angle-dependent overestimation typical of the standard spectral Doppler approach.

High-frame-rate 2-D vector blood flow imaging in the frequency domain

Conventional ultrasound Doppler techniques estimate the blood velocity exclusively in the axial direction to produce the sonograms and color flow maps needed for diagnosis of cardiovascular diseases. In this paper, a novel method to produce bi-dimensional maps of 2-D velocity vectors is proposed. The region of interest (ROI) is illuminated by plane waves transmitted at the pulse repetition frequency (PRF) in a fixed direction. For each transmitted plane wave, the backscattered echoes are recombined offline to produce the radio-frequency image of the ROI. The local 2-D phase shifts between consecutive speckle images are efficiently estimated in the frequency domain, to produce vector maps up to 15 kHz PRF. Simulations and in vitro steady-flow experiments with different setup conditions have been conducted to thoroughly evaluate the methods performance. Bias is proved to be lower than 10% in most simulations and lower than 20% in experiments. Further simulations and in vivo experiments have been made to test the approachs feasibility in pulsatile flow conditions. It has been estimated that the computation of the frequency domain algorithm is more than 50 times faster than the computation of the reference 2-D cross-correlation algorithm.

Plane-wave transverse oscillation for high-frame-rate 2-D vector flow imaging

Transverse oscillation (TO) methods introduce oscillations in the pulse-echo field (PEF) along the direction transverse to the ultrasound propagation direction. This may be exploited to extend flow investigations toward multidimensional estimates. In this paper, the TOs are coupled with the transmission of plane waves (PWs) to reconstruct high-framerate RF images with bidirectional oscillations in the pulse-echo field. Such RF images are then processed by a 2-D phase-based displacement estimator to produce 2-D vector flow maps at thousands of frames per second. First, the capability of generating TOs after PW transmissions was thoroughly investigated by varying the lateral wavelength, the burst length, and the transmission frequency. Over the entire region of interest, the generated lateral wavelengths, compared with the designed ones, presented bias and standard deviation of -3.3 ± 5.7% and 10.6 ± 7.4% in simulations and experiments, respectively. The performance of the ultrafast vector flow mapping method was also assessed by evaluating the differences between the estimated velocities and the expected ones. Both simulations and experiments show overall biases lower than 20% when varying the beam-to-flow angle, the peak velocity, and the depth of interest. In vivo applications of the method on the common carotid and the brachial arteries are also presented.

Structural brain abnormalities in the common epilepsies assessed in a worldwide ENIGMA study.

Structural MRI abnormalities are inconsistently reported in epilepsy. In the largest neuroimaging study to date, Whelan et al. report robust structural alterations across and within epilepsy syndromes, including shared volume loss in the thalamus, and widespread cortical thickness differences. The resulting neuroanatomical map will guide prospective studies of disease progression.

A new method for 2D-vector blood flow imaging based on unconventional beamforming techniques

Conventional Ultrasound (US) Doppler methods for blood flow imaging are limited to velocity estimations only in the axial direction, i.e. along the beam direction. Transverse oscillations (TO) methods extend blood investigations towards multidimensional estimates, and detailed descriptions of complex and fast blood flows are achievable by high frame-rate (HFR) imaging methods. In this work, TO are coupled with plane-waves (PWs) to reconstruct radio-frequency (RF) images with bi-directional oscillations in the pulse-echo field. The achieved RF images are exploited by a 2D phase-based displacement estimator to produce 2D-vector flow maps. A preliminary simulation study confirmed the capability of the method to produce the designed oscillations in the RF pulse-echo fields as well as the possibility to obtain 2D-vector maps with errors lower than 10% in many different conditions.

An integrated system for the evaluation of flow Mediated Dilation

An integrated system capable of estimating either the stimulus (wall shear rate change) and the effect (diameter change) in Flow Mediated Dilation (FMD) ultrasound investigations is presented. The FMD integrated system consists of a modified ULA-OP research platform and a post-processing software. The ULA-OP provides a real-time visual feedback on the positioning of the ultrasound probe on the artery of interest. Both B-mode images and blood velocity profiles can be checked during the entire exam so that the operator continuously controls the morphology and the hemodynamics of the region of interest. In addition, ULA-OP is used to acquire the raw I/Q demodulated data. These are post-processed through a Matlab® platform to estimate the arterial diameter and the wall shear rate changes. Experimental examples are reported.

Frequency-domain high frame-rate 2D vector flow imaging

Conventional ultrasound flow imaging systems are limited to estimate only the axial component of blood velocity. In this work, a method to produce 2D vector Doppler maps is proposed and experimentally tested. The local displacements between consecutive high frame-rate (HFR) radio-frequency (RF) images are estimated in the frequency domain. Each image is subdivided in partially overlapped matching blocks, and the average local displacements in a block are calculated from the difference of spectral phases in consecutive frames. The method has been tested by simulations and experiments by using the ULA-OP research scanner. Preliminary in-vivo tests have been conducted and an example of the femoral vessels of a healthy volunteer is presented. The performance of the method are evaluated through the relative error bias and standard deviation, presenting values lower than 10% in standard conditions.

Multi-channel Raw-Data Acquisition for Ultrasound Research

Ultrasound is widely used in diagnostic applications where novel methods and techniques are continuously developed and proposed. The test of new techniques often requires the access to the raw echo-data saved from each of the multiple elements which compose the modern array probes. Given the high number of receiving elements and the high Analog-to-Digital sampling rate, tens of GB of data are typically generated in few seconds. Only a small number of research instruments are equipped to save raw data, but the saved quantity is often not sufficient. In this paper we describe a memory board that, coupled to the Ultrasound Advanced Open Platform (ULA-OP), can save up to 36 GB of data, sampled at 50 MHz, from 64 probe elements. Two novel applications developed by using the data from this board are discussed as well.

Relationships Between Morphologic and Functional Patterns in the Polymicrogyric Cortex

Polymicrogyria is a malformation of cortical folding and layering underlying different cognitive and neurological manifestations. The polymicrogyric cortex has heterogeneous morphofunctional patterns, qualitatively described at magnetic resonance imaging (MRI) by variable severity gradients and functional activations. We investigated the link between abnormal cortical folding and cortical function in order to improve surgical planning for patients with polymicrogyria and intractable epilepsy. We performed structural and functional MRI on 14 patients with perisylvian polymicrogyria and adopted surface-based methods to detect alterations of cortical thickness (CT) and local gyrification index (LGI) compared with normal cortex (30 age-matched subjects). We quantitatively assessed the grade of anatomic disruption of the polymicrogyric cortex and defined its relationship with decreased cortical function. We observed a good matching between visual analysis and morphometric measurements. CT maps revealed sparse clusters of thickening, while LGI maps disclosed circumscribed regions of maximal alteration with a uniformly decreasing centrifugal gradient. In polymicrogyric areas in which gyral and sulcal patterns were preserved, functional activation maintained the expected location, but was reduced in extent. Morphofunctional correlations, evaluated along cortico-cortical paths between maximum morphologic alterations and significant activations, identified an interindividual threshold for LGI (z-value = -1.09) beyond which functional activations were no longer identifiable.

Hemicerebellitis can drive handedness shift

BackgroundHemicerebellitisis a rare acquired condition, typical of the pediatric age. A residual switched handedness may develop after remission of acute cerebellar symptoms.Case presentationHerein we describe a motor functional MRI studyperformed in a 35-year old girl who had switched to left-handedness after acute right hemicerebellitis in childhood. During left hand tapping, we observed activation in the right primary sensori-motor cortex, right supplementary motor area and left superior cerebellum. During right hand tapping bilateral activations of primary sensori-motorcortex and superior cerebellum including the vermis and activation of the right supplementary motor area were observed. We speculate that during right hand tapping both the ipsilateral and contralateralpre-central gyri and the ipsilateral cerebellum would be engaged in order to recover the tapping internal model of action. From this perspective the ipsilateral pre-central gyrus might serve as are transmission station of information from the healthy cerebellum to the contralateral pre-central gyrus.ConclusionSelective damage of the right half of the cerebellum due to hemicerebellitis in childhood can drive shift of lateralized hand functions in the cerebrum.