Doppler flow phantom failure detection by combining empirical mode decomposition and independent component analysis with short time Fourier transform

<p class="Abstract">Nowadays, objective protocols and criteria for the monitoring of phantoms failures are still lacking in literature, despite their technical limitations. In such a context, the present work aims at providing an improvement of a previously proposed method for the Doppler flow phantom failures detection. Such failures were classified as low frequency oscillations, high velocity pulses and velocity drifts. The novel objective method, named EMoDICA-STFT, is based on the combined application of the Empirical Mode Decomposition (EMD), Independent Component Analysis (ICA) and Short Time Fourier Transform (STFT) techniques on Pulsed Wave (PW) Doppler spectrograms. After a first series of simulations and the determination of adaptive thresholds, phantom failures were detected on real PW spectrograms through the EMoDICA-STFT method. Data were acquired from two flow phantom models set at five flow regimes, through a single ultrasound (US) diagnostic system equipped with a linear, a convex and a phased array probe, as well as with two configuration settings. Despite the promising outcomes, further studies should be carried out on a greater number of Doppler phantoms and US systems as well as including an in-depth investigation of the proposed method uncertainty.</p>

Three-dimensional printed flow phantom model of the carotid artery in preterm infants for training and research

The aim of this study was to perform flow volume measurements with Doppler ultrasound using novel 3D printed flow phantom models of carotid artery in preterm infants with varying characteristics. Clinical data from cerebral blood flow measurements using Doppler ultrasound of the right common carotid artery from premature newborn infants were used to produce a 3D printed Doppler flow phantom model with three different vessel diameters; 0.158 cm, 0.196 cm and 0.244 cm. Leading edge to centre was used to measure vessel diameter. Two observers performed flow volume measurements using continuous and pulsatile flow. Agreement between observers was examined using Bland-Altman plots. 24 measurements were performed. 18 (75%) measurements were performed using continuous flow. Pulsatile flow measurements were performed on lumen diameter of 0.244 cm only using physiological rates. Bland-Altman analysis for continuous flow measurements for observer 1 and 2 were -0.007 (95%LOA -4.3 to 4.3) ml/min and 3.2 (95%LOA -2.7 to 9.1) ml/min. Bias for pulsatile flow measurements for observer 1 and 2 were 1.5 (95%LOA -0.8 to 3.8) ml/min and 4.6 (0.7 to 8.5) ml/min respectively. Inter and intra-observer reliability was excellent for majority of measurements. The mean coefficient of variation for inter observer diameter measurements was 1.2% and intra observer measurements were between 1.5% to 3.9% for both observers. Flow volume measurements performed using 3D printed materials resulted in realistic echogenicities mimicking biological tissues. Validity and reliability studies, within and between, observers showed acceptable results. Researchers and clinicians can use this model for further training and simulation.

Effect of decreased contrast injection flow rate on aortic enhancement in 80-KV peak CT with contrast dose reduction

Background Effect of decreased injection flow rate of contrast agent at the same iodine dose and delivery rate on aortic enhancement has not been clearly elucidated. Purpose To evaluate the effect of decreased injection flow rate of contrast agent on aortic peak enhancement in a dynamic flow phantom and on aortic enhancement in clinical dynamic 80-kVp computed tomography (CT) with contrast dose reduction. Material and Methods In the dynamic flow phantom experiment, the effect of a decreased injection flow rate at the same total iodine dose and delivery rate on simulated aortic peak enhancement was evaluated. In the clinical retrospective study, we searched 312 patients with renal dysfunction who underwent an 80-kVp abdominal dynamic CT with 40% reduction of contrast agent from a standard 120-kVp protocol and measured the aortic enhancement at the level of the hepatic hilum. Independent predictors for aortic enhancement were determined by multiple linear regression analysis, and after adjustment of significant predictors, independent variables for acquiring optimal aortic enhancement, ≥300 HU, were determined by multiple logistic regression analysis. Results In the phantom experiment, decreased flow rate showed a significant but small descent effect (6%–9%) on simulated aortic peak enhancement. In the multiple linear regression analysis, only age was an independent predictor of aortic enhancement; there was no independent predictor for optimal age-adjusted aortic enhancement of ≥300 HU. Conclusions Decreased injection flow rate had a small influence on aortic enhancement in vitro but had no significant effect on the aortic enhancement in clinical dynamic 80-kVp CT.

Comparison of a Portable and Non-Portable Ultrasound Machine in the Evaluation of Children with Sickle Cell Disease: A Pilot Study

Background: Transcranial color Doppler (TCCD) ultrasound is used to identify children with sickle cell disease (SCD) at high risk of developing stroke. There is anecdotal evidence to suggest that different ultrasound equipment can give different blood flow velocities. The purpose of this study was to compare two different TCCD ultrasound machines. Methods and Results: A flow phantom was used to compare PSV measurements from a Philips IU-22 and Zonare Z-One ultrasound machine. Twenty-five children with SCD (aged between 2 and 16 years) attending the outpatient clinic at St. Mary’s Hospital, Imperial College Healthcare NHS Trust, as part of the NHS Sickle Cell & Thalassaemia (SC&T) screening program were studied. The two ultrasound machines compared the TAMM velocities in the middle cerebral artery and stroke risk categorization. PSV measurements using a flow phantom were underestimated by Philips IU-22 (31%) and Zonare Z-One (53%). TAMM velocities varied considerably between machines, with a poor agreement in stroke risk categorization. As a result, three children identified at increased risk of stroke by Philips IU-22 were not identified by Zonare Z-One. Conclusion: Two ultrasound machines were found to underestimate PSV using a flow phantom. The two ultrasound machines were shown to positively correlate, and this was statistically significant. However, there was variation in the TAMM velocities recorded by the machines which resulted in the different categorization of the stroke risk of a small number of the subjects. This pilot study confirms the feasibility and clinical significance of this investigation.

Diameter measurements in three-dimensional printed flow phantom model of the carotid artery in preterm infants

Diameter form an integral part of blood flow measurement. This study aimed to explore different three-dimensional (3D) printed materials to develop flow phantom models of the carotid artery in preterm newborn infants and to investigate ideal diameter measurement points using ultrasound that reflected accurate lumen diameter measurement. Cerebral blood flow measurements data using Doppler ultrasound of the right common carotid artery from 21 randomly selected preterm infants were used to produce a 3D printed Doppler flow phantom model with three different vessel diameters. Diameters were measured by multiple observers blinded to phantom vessel characteristics and each other’s measurements. 9 measurement points were studied. Agreement between observers, inter and intra observer reliability and coefficient of variation (CoV) was examined. Of the 63 diameter measurements, 45 (71%) were performed on flow phantoms with vessel diameter of 0.196 cm. Bland-Altman plots revealed that measurement performed using leading edge to centre (mean bias 1.8% {95%LOA -4.1% to 7.7%}) and centre to trailing edge (mean bias 1.1% {95%LOA -5.4% to 7.8%}) resulted in the most accurate lumen diameter measurements. Inter and intra-observer reliability was excellent. The mean CoV for inter observer measurements was 1.7% and intra observer measurements was 1.6% and 1.8% for each observer. We successfully produced a 3D printed flow phantom model of the carotid artery in preterm infants and identified two measurement methods that result in reliable and accurate lumen diameter measurement. Researchers and clinicians can use this information for further studies involving ultrasound diameter measurements in small calibre vessels.

Development of an MRI-Guided Approach to Selective Internal Radiation Therapy Using Holmium-166 Microspheres

Selective internal radiation therapy (SIRT) is a treatment modality for liver tumours during which radioactive microspheres are injected into the hepatic arterial tree. Holmium-166 (166Ho) microspheres used for SIRT can be visualized and quantified with MRI, potentially allowing for MRI guidance during SIRT. The purpose of this study was to investigate the MRI compatibility of two angiography catheters and a microcatheter typically used for SIRT, and to explore the detectability of 166Ho microspheres in a flow phantom using near real-time MRI. MR safety tests were performed at a 3 T MRI system according to American Society for Testing of Materials standard test methods. To assess the near real-time detectability of 166Ho microspheres, a flow phantom was placed in the MRI bore and perfused using a peristaltic pump, simulating the flow in the hepatic artery. Dynamic MR imaging was performed using a 2D FLASH sequence during injection of different concentrations of 166Ho microspheres. In the safety assessment, no significant heating (ΔTmax 0.7 °C) was found in any catheter, and no magnetic interaction was found in two out of three of the used catheters. Near real-time MRI visualization of 166Ho microsphere administration was feasible and depended on holmium concentration and vascular flow speed. Finally, we demonstrate preliminary imaging examples on the in vivo catheter visibility and near real-time imaging during 166Ho microsphere administration in an initial patient case treated with SIRT in a clinical 3 T MRI. These results support additional research to establish the feasibility and safety of this procedure in vivo and enable the further development of a personalized MRI-guided approach to SIRT.

A Micro-flow Phantom for Superficial Micro-vasculature Imaging

Visualization of cutaneous micro-vasculatures is a powerful approach assisting in the diagnosis of skin vascular disorders. These minute structures can be visualized by high-frequency ultrasound (HFUS) using ultrafast Doppler imaging. Ultrasound flow phantoms have been used as assessment tools to evaluate the performance of the ultrasound imaging system, however, to optimize the imaging system for visualization of micro-structures, flow phantom with micro-channels is required which are usually difficult to fabricate. Here, we design a simple approach for micro-flow phantom which is easy to fabricate and cast for detection of micro-circulation in superficial micro-structures. The proposed approach features (i) the micro-channels of 200-micron at the depth of 4 mm (ii) casted in the cryogel mixture of Poly-vinyl alcohol (PVA) and (iii) infused at flow speed of 30 mm/s using infusion pump. Visualization of micro-flow channel in power Doppler image obtained by HFUS ultrafast Doppler imaging reveals that the proposed micro-flow phantom could serve as a viable assessment tool for optimizing the system for in-vivo cutaneous micro-vasculature imaging.

A preliminary study on an image analysis based method for lowest detectable signal measurements in Pulsed Wave Doppler ultrasounds

<span lang="EN-GB">Nowadays, Doppler system performance evaluation is a widespread issue because a shared worldwide standard is still awaited. Among the recommended Doppler test parameters, the lowest detectable signal could be considered mandatory in Quality Control (QC) protocols for Pulsed Wave (PW) Doppler. Such parameter is defined as the minimum signal level that can be clearly distinguished from noise and therefore, it is considered as related to PW Doppler sensitivity. The present study focuses on proposing and validating a novel image analysis based method for the estimation of the Lowest Detectable Signal in the spectrogram image (LDS_IMG), namely Automatic Doppler Sensitivity Measurement Method (ADSMM), as well as to compare its results with the outcomes retrieved from the Naked Eye Doppler Sensitivity Method (NEDSM), based on the mean judgment of three independent observers. Data have been collected from a Doppler flow phantom, through three ultrasound systems for general purpose imaging, equipped with two linear array probes each and with two configuration settings. Results are globally compatible among the proposed methods, US systems and settings. Further studies could be carried out on a higher number of US diagnostic systems, Doppler frequencies and observers, as well as with different probe and phantom models.</span>