Non-parametric deconvolution using Bézier curves for quantification of cerebral perfusion in dynamic susceptibility contrast MRI

Objective Deconvolution is an ill-posed inverse problem that tends to yield non-physiological residue functions R(t) in dynamic susceptibility contrast magnetic resonance imaging (DSC-MRI). In this study, the use of Bézier curves is proposed for obtaining physiologically reasonable residue functions in perfusion MRI. Materials and methods Cubic Bézier curves were employed, ensuring R(0) = 1, bounded-input, bounded-output stability and a non-negative monotonically decreasing solution, resulting in 5 parameters to be optimized. Bézier deconvolution (BzD), implemented in a Bayesian framework, was tested by simulation under realistic conditions, including effects of arterial delay and dispersion. BzD was also applied to DSC-MRI data from a healthy volunteer. Results Bézier deconvolution showed robustness to different underlying residue function shapes. Accurate perfusion estimates were observed, except for boxcar residue functions at low signal-to-noise ratio. BzD involving corrections for delay, dispersion, and delay with dispersion generally returned accurate results, except for some degree of cerebral blood flow (CBF) overestimation at low levels of each effect. Maps of mean transit time and delay were markedly different between BzD and block-circulant singular value decomposition (oSVD) deconvolution. Discussion A novel DSC-MRI deconvolution method based on Bézier curves was implemented and evaluated. BzD produced physiologically plausible impulse response, without spurious oscillations, with generally less CBF underestimation than oSVD.

Normal liver-to-heart transit time and shunt fraction after transplenic injection of 99MTC-pertechnetate in healthy cats

Portosystemic shunts (PSS) are rare vascular anomalies in cats. Transsplenic portal scintigraphy (TSPS) can aid in diagnosing PSS in cats. Although the actual performance of the scan remains the same between species, it is questionable whether the generally accepted transit time of seven seconds for small dogs can be applied to cats, thereby influencing shunt fraction (SF) calculation. In this study, normal mean transit time and SF were determined in a population of cats without PSS following two methods established in canine medicine. For both, the mean ± SD transit time was calculated as 6.75 ± 1.58 seconds and 7.40 ± 1.64 seconds respectively, without significant difference between both methods. The results confirmed the validity of the generally used transit time of seven seconds for SF calculation in cats. The average normal SF (± SD) for the cats in this study was 0.73 % (±0.74; range 0.11-2.48%).

Quantitative evaluation of hemodynamics after partial embolization of brain arteriovenous malformations

BackgroundTo explore the hemodynamic changes after embolization of arteriovenous malformations (AVMs) using quantitative digital subtraction angiography (QDSA).MethodsWe reviewed 74 supratentorial AVMs that underwent endovascular embolization and performed a quantitative hemodynamic analysis comparing parameters in pre- and post-operative DSA in correlation with rupture. The AVMs were further divided into two subgroups based on the embolization degree: Group I: 0%–50%, Group II: 51%–100%. In the intergroup analysis, we examined the correlations between embolization degree and hemodynamic parameter changes.ResultsA longer time to peak (TTP) of the main feeding artery (OR 11.836; 95% CI 1.388 to 100.948; P=0.024) and shorter mean transit time (MTT) of the nidus (OR 0.174; 95% CI 0.039 to 0.766; P=0.021) were associated with AVM rupture. After embolization, all MTTs were significantly prolonged (P<0.05). The full width at half maximum (FWHM) duration of the main feeding artery was significantly shortened (P<0.001), and several hemodynamic parameters of the main draining vein changed significantly (TTP: prolonged, P=0.005; FWHM: prolonged, P=0.014; inflow gradient: decreased, P=0.004; outflow gradient: decreased, P=0.042). In the subgroup analysis, several MTT parameters were significantly prolonged in both groups (P<0.05), and the MTT increase rate in Group II was greater than in Group I (P<0.05).ConclusionsEmbolization can significantly change the hemodynamics of AVMs, especially when an embolization degree >50% is obtained. Partial embolization may reduce the AVM rupture risk in hemodynamics perspective.

Perfusion CT detects alterations in local cerebral flow of glioma related to IDH, MGMT and TERT status

Background The aim of this study was to investigate the relationship between tumor biology and values of cerebral blood volume (CBV), cerebral blood flow (CBF), mean transit time (MTT), time to peak (TTP), permeability surface (PS) of tumor in patients with glioma. Methods Forty-six patients with glioma were involved in the study. Histopathologic and molecular pathology diagnoses were obtained by tumor resection, and all patients accepted perfusion computed tomography (PCT) before operation. Regions of interests were placed manually at tumor and contralateral normal-appearing thalamus. The parameters of tumor were divided by those of contralateral normal-appearing thalamus to normalize at tumor (relative [r] CBV, rCBF, rMTT, rTTP, rPS). The relationships of the parameters, world health organization (WHO) grade, molecular pathological findings were analysed. Results The rCBV, rMTT and rPS of patients are positively related to the pathological classification (P < 0.05). The values of rCBV and rPS in IDH mutated patients were lower than those IDH wild-type. The values of rCBF in patients with MGMT methylation were lower than those MGMT unmethylation (P < 0.05). The MVD of TERT wild-type group was lower than TERT mutated group (P < 0.05). The values of rCBV were significant difference in the four molecular groups divided by the combined IDH/TERT classification (P < 0.05). The progression free survival (PFS) and overall survival (OS) were significant difference in the four molecular groups divided by the combined IDH/TERT classification (P < 0.05). Conclusions Our study introduces and supports the changes of glioma flow perfusion may be closely related to its biological characteristics.

CT perfusion for response evaluation after interventional ablation of hepatocellular carcinoma: a prospective study

Background Computed tomography (CT) perfusion was found to be useful in assessing treatment response in a variety of cancers through the evaluation in the arterial perfusion changes. We investigated the performance of CT perfusion parameters for assessment of hepatocellular carcinoma (HCC) response to radiofrequency ablation (RFA) and trans-arterial chemoembolization (TACE). We conducted a prospective diagnostic test accuracy study that recruited 70 HCC patients who were scheduled to undergo TACE or RFA. For each dynamic CT scan acquisition, four single perfusion CT image maps were generated, including functional maps of blood flow (BF), blood volume (BV), mean transit time (MTT), and permeability surface (PS). Results In TACE-treated lesions, the BV achieved a sensitivity and specific of 100% and 83.3%, at a cutoff level of ≤ 122 ml/min/100 gm, for responders. Likewise, at a cutoff level of > 10 s, transit time had a sensitivity of 90.5% and specificity of 100%. At a cutoff level of ≤ 14 ml/min/100 gm, the PS had a sensitivity of 100% and specificity of 83.33% for responders. In RFA-treated lesions, at a cutoff level of ≤ 170 ml/min/100 gm and ≤ 11 ml/100 gm, the BF and BV had a sensitivity of 100% and specificity 100%, respectively, for responders. At a cutoff level of ≤ 11 ml/min/100 gm, PS had a sensitivity 77.27% and specificity 80%. Conclusions The present study confirms the feasibility of CT perfusion for assessment of response to TACE and RFA among patients with HCC.

Cerebral perfusion imaging: Hypoxia-induced deoxyhemoglobin or gadolinium?

Assessment of resting cerebrovascular perfusion measures (mean transit time, cerebral blood flow and cerebral blood volume) with magnetic resonance imaging currently requires the intravascular injection of the dynamic susceptibility contrast agent gadolinium. An initial comparison between hypoxia-induced deoxyhemoglobin and gadolinium was made for these measures in six healthy participants. A bolus of deoxyhemoglobin is generated in the lung via transient hypoxia induced by an available computer-controlled gas blender technology employing sequential gas delivery (RespirAct). We hypothesised and confirmed perfusion measures from both susceptibility contrast agents would yield similar spatial patterns of cerebrovascular perfusion measures. We conclude that hypoxia-induced deoxyhemoglobin, an endogenously, non-invasively generated, non-allergenic, non-toxic, recyclable, environmentally innocuous molecule, may be suitable to become the first new magnetic resonance imaging susceptibility contrast agent introduction since gadolinium.

Interobserver reproducibility of contrast-enhanced ultrasound in diabetic nephropathy

Objective: To investigate the interobserver reproducibility of contrast-enhanced ultrasound (CEUS) in patients with diabetic nephropathy. Methods: A total of 40 patients with diabetic nephropathy were enrolled in this retrospective study. We measured peak intensity (PEAK), time-to-peak (TP), area under the curve (AUC) and mean transit time (MTT) of renal CEUS in each patient. Each parameter was performed by two independent observers. The interobserver reproducibility was assessed using intraclass correlation coefficients (ICCs) with 95% confidence intervals (CIs) and Bland–Altman plots by mean difference with 95% limits of agreement (LOAs). Results: The parameters of the left and right kidneys showed moderate or good reliability. The best was the left kidney AUC parameters (ICC,0.945),with a 95% CI of 0.896–0.971.The Bland–Altman plots showed that the mean differences between the right renal parameters (PEAK, TP, AUC and MTT) obtained between the observers 1 and 2 were −6.63%,2.54%,−11.30%,−2.22%, and the 95% LOAs are −30.78 to 17.52%, −30.15 to 35.23%, −43.95 to 21.35%, −44.50 to 40.06%. While the left ones were −2.89%, 0.32%, −8.26%, 1.25% , and the 95% LOAs were −38.50 to 32.72%, −31.98 to 32.62%, −57.89 to 41.37%, −37.21 to 39.71%, respectively. Conclusion: Quantitative CEUS can show good interobserver reproducibility, which is better for the right kidney. It seems necessary to establish standardized techniques for obtaining contrast-enhanced quantitative analysis of renal blood perfusion. Advances in knowledge: Quantitative assessment of renal perfusion by CEUS in patients with diabetic nephropathy provides diagnostic information. Furthermore, renal perfusion assessment in patients with diabetic nephropathy using CEUS has good reproducibility.

Velocity Obstacles and Emergent Rules-of-the-Air for Autonomous Drone Traffic Management

As the use of unmanned aerial vehicles (UAVs) becomes ever more widespread there is a growing need to develop traffic management and flight rules, in particular for autonomous UAVs or where the predicted traffic densities far exceed those of traditional manned aviation. Inspired by the current rules of the air and multi-agent systems (e.g., pedestrians and swarm robotics) we outline a set of flight rules for autonomous UAVs that consist of waypoint following and conflict avoidance schemes. These flight rules are then explored in small,pairwise simulations and thus refined to allow a UAV to choose from three potential avoidance behaviors based on it and its neighbors velocities and positions. Finally we compare the original and modified flight rules in larger scale simulations modelling two streams of UAV traffic crossing at a point. We show that the modified rules significantly reduce the mean transit time by reducing the impact of UAVs avoiding other UAVs from the same stream.

Velocity Obstacles and Emergent Rules-of-the-Air for Autonomous Drone Traffic Management

As the use of unmanned aerial vehicles (UAVs) becomes ever more widespread there is a growing need to develop traffic management and flight rules, in particular for autonomous UAVs or where the predicted traffic densities far exceed those of traditional manned aviation. Inspired by the current rules of the air and multi-agent systems (e.g., pedestrians and swarm robotics) we outline a set of flight rules for autonomous UAVs that consist of waypoint following and conflict avoidance schemes. These flight rules are then explored in small,pairwise simulations and thus refined to allow a UAV to choose from three potential avoidance behaviors based on it and its neighbors velocities and positions. Finally we compare the original and modified flight rules in larger scale simulations modelling two streams of UAV traffic crossing at a point. We show that the modified rules significantly reduce the mean transit time by reducing the impact of UAVs avoiding other UAVs from the same stream.