Angiographic parametric imaging (API) is a quantitative imaging method which uses digital subtraction angiography (DSA) to calculate biomarkers related to hemodynamics. This method has been used for neurovascular disease diagnosis and treatment outcome predictions in clinical settings but results are regarded with caution since derived biomarkers are strongly correlated with contrast injection parameters. This study aimed to assess utilization of truncated singular value decomposition (TSVD) in correcting API maps across various injection rates. Digital angiography data was collected using two neurovascular phantoms embedded in a simulated flow loop. Contrast volumes of 5 and 10 mL along with injection rates of 5, 10, 15, and 20 mL/sec were utilized during testing. API maps were generated with baseline and stenosis models using gamma variate fitting along with TSVD of the arterial input of the phantom. Surrogate regional blood flow (sRBF) and regional blood volume (sRBV) maps indicate consistent values across varying injection rates along with decreases in flow and volumes following introduction of a stenosis (Baseline: sRBF=53.3±4.20 arbitrary volume units (AVU)/min, sRBV=2.66±0.14 AVU, Stenosis: sRBF=28.6±3.78 AVU/min, sRBV=1.75±0.45 AVU). Mean transit time (MTT) and time of maximal residue function (Tmax) maps indicate consistent and decreasing parameter values respectively as injection rates increase along with increases in each parameter in the presence of a stenosis (Baseline: MTT=0.72±0.14 sec, Tmax=1.36±0.14 sec, Stenosis: MTT=0.94±0.13 sec, Tmax=1.71±0.18 sec). This study indicates TSVD has the potential to normalize API parameter maps across various injection rates potentially allowing for the implementation of API in ischemic stroke diagnosis and treatment.
Purpose: Intracranial aneurysm (IA) treatment using flow diverters (FDs) has become a widely used endovascular therapy with occlusion rates between 70 to 90 percent resulting in reduced mortality and morbidity. This significant variation in occlusion rates could be due to variations in patient anatomy, which causes different flow regimes in the IA dome. We propose to perform detailed in-vitro studies to observe the relation between the FD geometrical properties and IA hemodynamics changes. Materials and Methods: Idealized and patient-specific phantoms were 3D-printed, treated with FDs, and connected into a flow loop where intracranial hemodynamics were simulated using a programmable pump. Pressure measurements were acquired before and after treatment in the main arteries and IA domes for optimal and sub-optimal diameter sizing of the FD when compared with the main artery. The 3D-printed phantoms were scanned using a micro-CT to measure the ostium coverage, calculate the theoretical FD hydraulic resistance, and study its effect on flow. Results: The pressure differences between arteries and the IA dome for optimal FDs’ diameter with a hydraulic resistance of 3.4 were ~7 mmHg. When the FD was undersized, the hydraulic resistance was 4.2 and pressure difference increased to ~11 mmHg. Conclusion: 3D-printing allows development of very precise benchtop experiments where pressure sensors can be embedded in vascular phantoms to study hemodynamic changes due to various therapies such as IA treatment with FDs. In addition, precise imaging, such as micro-CT can be used in order to evaluate complex deployment geometries and study their correlation with flow.
Purpose: 3D-printing of patient-specific phantoms such as the mitral valve (MV) is challenging due to inability of current imaging systems to reconstruct fine moving features and 3D printing constraints. We investigated methods to 3D-print MV structures using ex-vivo micro-CT. Materials and Methods: A dissected porcine MV was imaged using micro-CT in diastole, using a special fixation holder. The holder design was based on a patient ECG gated cardiac CT scan using as reference points the papillary muscles and annulus. Next the micro-CT volume was segmented and 3D-printed in various elastic materials. We tested different postprocessing techniques for support material removal and surface coatings to preserve the MV integrity. To test the error a Cloud Comparison of the porcine valve-mesh file and the valve-mesh file from the patient ECG gated cardiac CT scan was performed. Results: Best results for the 3D-printed models were achieved using TangoPlus poly-jet material with a Objet Eden printer. The error computation yielded a 2.6mm deviation-distance between the two aligned valves indicating adequate alignment. The post-processing methods for support removal were challenging and required 24+ hours sample-emersion in slow agitating sodium hydroxide baths. Conclusions: The most challenging part for MV manufacturing is 3D volume acquisition and the post-printing methods during support cleaning. We developed methods to circumvent both, the imaging and the 3D-printing challenges and to ensure that the final phantom includes the fine chordae and valve geometry. Using these solutions, we were able to create complete MV structures which could benefit medical research and device testing.
Purpose: 3D printed (3DP) patient specific vascular phantoms provide the ability to improve device testing and to aid in the course of treatment of vascular disease, while reducing the need for in-vivo experiments. In addition to accurate vascular geometric reproducibility, such phantoms could allow simulation of certain vascular mechanical properties. We investigated various 3DP designs to allow simulation of physiological transmural pressure on phantom vasculature. Materials and Methods: A transparent compliance chamber was created using an Eden260V printer (Stratasys) with VeroClear and acrylic to accommodate 3DP patient specific vascular phantoms. The patient vascular geometries were acquired from a CT angiogram (Aquilion ONE, Canon Medical) and segmented using Vitrea workstation (Vital Images). The segmented geometry was manipulated in Autodesk Meshmixer and 3D printed using Agilus. The phantom was integrated in the compliance chamber and connected to a pump which simulated physiologic pulsatile flow waveforms. Compliance of the vessels was varied by filling the chamber with various levels of liquid and air. This setup allowed controlled expansion of the 3DP arteries, as a function of the liquid level while a programmable pump simulated the blood flow through the vascular network. The pressure within the vessels was measured for various compliancy settings while physiological flow rates were simulated through the arteries. Results: A neurovascular phantom was placed in the chamber and amount of artery expansion diameter was controlled by changing the liquid level in the compliance chamber. Artery patency and contrast flow were demonstrated using x-ray angiography. The pressures in the left and the right internal carotid artery increased from 98mmHg to 104mmHg and from 96mmHg to 102mmHg, respectively, while maintaining the same flow rates. Conclusions: 3D printed patient specific neurovascular phantoms can be manipulated through using of a compliance chamber in order to establish physiologically relevant hemodynamic conditions.
Four-dimensional computed tomography perfusion (CTP) provides the capability to validate angiographic parametric imaging (API) when locating infarct core. Similar results between these two methods could indicate API can be used to determine whether infarct core has changed following reperfusion procedures. CTP data from 20 patients treated for ischemic strokes was retrospectively collected and loaded into a Vitrea software to locate cerebral infarct tissue. The CTP data was then used to simulate anteroposterior (AP), lateral, and planar digital subtraction angiograms (DSA) for each time period through the perfusion scan. These simulated DSA sequences were used to generate API maps related to mean transit time (MTT), bolus arrival time (BAT), time to peak (TTP), area under the curve (AUC), and peak height (PH) parameters throughout the brain. Contralateral hemisphere comparisons of these values were conducted to determine infarct regions. The infarct regions from the Vitrea and API software were compared using a region of interest overlay method. For all patients, contralateral hemisphere percent differences of 40% for MTT, 20% for BAT, 35% for TTP, 55% for AUC, and 50% for PH are consistent with infarct regions. Using these percentages, the accuracy of API in labeling infarct tissue for the AP, lateral, and planar views is 84%, 70%, and 78% respectively. API conducted on CTP data from stroke patients successfully identified infarct tissue using AP and planar DSA’s. Lateral DSA studies indicate future work is necessary for improved results. This validates API is a feasible method for locating infarct core after reperfusion procedures.
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