Digital Subtraction Angiography Projections Research Articles

Abstract WP11: Semi-automated Quantitative Assessment of Reperfusion in Acute Ischemic Stroke Patients

Introduction: Accurate assessment of brain reperfusion during endovascular treatment helps determining whether adjuvant intervention is necessary. The gold standard for reperfusion scales are the modified and extended Treatment in Cerebral Ischemia (mTICI and eTICI) scale. However, these scales are coarse and highly dependent on the observer, which may result in imprecise rating of reperfusion status. In this study, we developed a semi-automated quantitative reperfusion measure (qTICI) that was based on eTICI methodology using deep learning. Methods: Digital subtraction angiography (DSA) images of 67 acute ischemic stroke patients with proximal occlusions were collected from the MRCLEAN registry, including only patients who were eTICI graded by an independent core lab and had follow-up 90 days-modified Rankin Scale (mRS) scores. Both DSA projections, anteroposterior and lateral, were used. We trained a patch-based multi-path convolutional neural network to segment the perfusion area. The ground truths of perfusion segmentation were constructed using heuristic, intensity thresholding after vessel removal, which were inspected for their accuracy by a neuroradiologist. The target downstream territory was manually segmented based on the treated occlusion location by two neurointerventionalists. qTICI was formulated as a ratio between the area of perfusion and target downstream territory. We compared performance between qTICI and eTICI in relation with functional outcome, dichotomized as favorable (mRS 0-2) and unfavorable outcome (mRS 3-6). Results: Our study showed that the multi-path convolutional neural network was able to reproduce the ground truth perfusion segmentation with an average Dice score of 0.91. qTICI correlated significantly with eTICI (p<0.001) and the ordinal 90-days mRS (p<0.05). qTICI had comparable discriminative power to distinguish between favorable and unfavorable functional outcome (AUC = 0.80) with eTICI (AUC = 0.81). Conclusions: qTICI provided a quantitative and semi-automated perfusion assessment with strong association with functional outcome.

New vessels formation in young strokes with isolated steno-occlusive MCA.

ObjectiveNew vessels formation (NVF) along the steno‐occlusive middle cerebral artery (MCA) is often observed in digital subtraction angiography (DSA) imaging. In the study, we aim to explore the clinical relevance of NVF in young ischemic stroke patients with isolated middle cerebral artery (MCA) stenosis.MethodsWe retrospectively reviewed the digital subtraction angiography (DSA) images of 93 young ischemic stroke patients (age ≤ 45 years old) in our center from January 2006 to June 2016. All the patients were diagnosed with isolated steno‐occlusive middle cerebral artery (MCA) disease.NVF was defined as new vessels formation along the stenotic MCA on anteroposterior DSA projection. The association between NVF and functional outcome was analyzed.ResultsThe prevalence of NVF was 0 in moderate stenosis, 15.8% in severe stenosis, and 53.7% in MCA occlusions. The presence of NVF had a strong correlation with the severity of MCA stenosis (r = 0.467, p < 0.001). Compared to patients without NVF, patients with NVF were more likely to suffer an unfavorable functional outcome (6.2% vs. 21.4%, p = 0.061) at 3 months. Univariate logistic regression analysis showed that NVF was associated with unfavorable outcome [Odds Ratio (OR) = 4.159, 95% confidence intervals (CI) = (1.072, 16.137), p = 0.039].ConclusionsThis study demonstrated that NVF were associated with poor clinical outcome in young ischemic stroke patients who were diagnosed with isolated steno‐occlusive MCA.

Correlation Between Contrast Time-Density Time on Digital Subtraction Angiography and Flow: An inVitro Study.

Digital subtraction angiography (DSA) provides an excellent anatomic characterization of cerebral vasculature, but hemodynamic assessment is often qualitative and subjective. Various clinical algorithms have been produced to semiquantify flow from the data obtained from DSA, but few have tested them against reliable flow values. An arched flow model was created and injected with contrast material. Seventeen injections were acquired in anterior-posterior and lateral DSA projections, and 4 injections were acquired in oblique projection. Image intensity change over the angiogram cycle of each DSA run was analyzed through a custom MATLAB code. Time-density plots obtained were divided into 3 components (time-density times, TDTs): TDT10%-100% (time needed for contrast material to change image intensity from 10% to 100%), TDT100%-10% (time needed for contrast material to change image intensity from 100% to 10%), and TDT25%-25% (time needed for contrast material to change from 25% image intensity to 25%). Time-density index (TDI) was defined as model cross-sectional area to TDT ratio, and it was measured against different flow rates. TDI10%-100%, TDI100%-10%, and TDI25%-25% all correlated significantly with flow (P < 0.001). TDI10%-100%, TDI100%-10%, and TDI25%-25% showed, respectively, a correlation coefficient of 0.91, 0.91, and 0.97 in the anterior-posterior DSA projections (P < 0.001). In the lateral DSAprojection, TDI100%-10% showed a weaker correlation (r= 0.57; P= 0.03). Also in the oblique DSA projection, TDIs correlated significantly with flow. TDI on DSA correlates significantly with flow. Although invitro studies might overlook conditions that occur in patients, this method appears to correlate with the flow and could offer a semiquantitative method to evaluate the cerebral blood flow.

Time-resolved 3D rotational angiography: display of detailed neurovascular anatomy in patients with intracranial vascular malformations

PurposeThe purpose of this pilot study was to demonstrate the applicability of time-resolved three-dimensional (3D) reconstructions from 3D digital subtraction angiography (DSA) rotational angiography (RA) datasets (four-dimensional (4D) DSA) to...

A 2D driven 3D vessel segmentation algorithm for 3D digital subtraction angiography data

Cerebrovascular disease is among the leading causes of death in western industrial nations. 3D rotational angiography delivers indispensable information on vessel morphology and pathology. Physicians make use of this to analyze vessel geometry in detail, i.e. vessel diameters, location and size of aneurysms, to come up with a clinical decision. 3D segmentation is a crucial step in this pipeline. Although a lot of different methods are available nowadays, all of them lack a method to validate the results for the individual patient. Therefore, we propose a novel 2D digital subtraction angiography (DSA)-driven 3D vessel segmentation and validation framework. 2D DSA projections are clinically considered as gold standard when it comes to measurements of vessel diameter or the neck size of aneurysms. An ellipsoid vessel model is applied to deliver the initial 3D segmentation. To assess the accuracy of the 3D vessel segmentation, its forward projections are iteratively overlaid with the corresponding 2D DSA projections. Local vessel discrepancies are modeled by a global 2D/3D optimization function to adjust the 3D vessel segmentation toward the 2D vessel contours. Our framework has been evaluated on phantom data as well as on ten patient datasets. Three 2D DSA projections from varying viewing angles have been used for each dataset. The novel 2D driven 3D vessel segmentation approach shows superior results against state-of-the-art segmentations like region growing, i.e. an improvement of 7.2% points in precision and 5.8% points for the Dice coefficient. This method opens up future clinical applications requiring the greatest vessel accuracy, e.g. computational fluid dynamic modeling.

SPECIAL ASPECTS OF DIAGNOSTIC IMAGING FOR RADIOSURGERY OF ARTERIOVENOUS MALFORMATIONS

Radiosurgery can be considered a well-established option for the treatment of arteriovenous malformations (AVMs). The exact application of the therapeutic dose is based on the availability of imaging data sets with superior image quality that can be superimposed using an image fusion algorithm. For follow-up studies, the quantitative comparison of the respective image data sets also plays an important role. Until now, digital subtraction angiography (DSA) has been a mandatory tool for treatment planning and follow-up procedures. The aim of this study was to investigate whether a suitable computed tomographic (CT) and/or magnetic resonance (MR) angiography procedure can replace DSA and, if so, in which cases. For 34 AVM patients, various MR data sets were used together with the stereotactically localized CT and DSA data sets for treatment planning. To define the AVM nidus precisely, all available MR data sets were fused onto the CT data set by the use of an automatic image fusion algorithm. The nidus was outlined in both localized DSA projections, resulting in the DSA target volume. Subsequently, the DSA target volume was adapted by inclusion of the available CT/MR data sets (localized and/or fused, slice by slice), resulting in the final target volume. Finally, both volumes were compared and analyzed. For precise comparison purposes, all available digital follow-up studies were fused. In all cases, the thin-slice MR data sets (1-mm slice width) that included T1-weighted series and time of flight angiographies have been precisely fused onto the stereotactically localized treatment planning CT. The final target volume was compared with the DSA target volume as follows. In 19 cases, the final target volume was larger than the DSA target volume; in six cases, it was smaller; and in five cases, it was approximately equal. The difference was significant (Wilcoxon test, difference <0.0001; t test, t = 3.01; P > 0.005). In four cases, outlining the AVM was not possible without DSA. In five patients, a two- or three-vessel DSA was needed because there were different AVM compartments. In cases in which a previous partial embolization had been undergone by the patient, the use of superimposed CT sets with and without contrast medium was important to define the completely embolized partial volumes that were not subject to treatment. The inclusion of the DSA images enabled a better identification of those arterialized veins that did not belong to the nidus. In six cases, the follow-up MR studies showed contrast enhancements overlapping the AVM nidus as a result of brain-blood barrier disturbances (T1-weighted series with contrast). In seven cases, perifocal reactions were primarily observed (T2-weighted series) 12 months after treatment with rather low clinical relevance. By integrating all available imaging modalities, the exact three-dimensional definition of the AVM nidus was safely realized for all patients. Stereotactic DSA data acquisition remains a crucial tool for safe nidus definition in radiosurgery treatment planning and cannot, therefore, be discarded at present. It is recommended that a quantitative comparison of all MR follow-up studies be established.

Assessment of the uterine artery before uterine arterial embolization: Comparison of unenhanced 3D water‐excitation sensitivity‐encoding time‐of‐flight (WEST) and gadolinium‐enhanced 3D sensitivity‐encoding water‐excitation multishot echo‐planar (SWEEP) MR angiography

To compare unenhanced 3D water-excitation sensitivity-encoding time-of-flight (WEST) and gadolinium-enhanced 3D sensitivity-encoding water-excitation multishot echo-planar (SWEEP) MR angiography (MRA) with regard to conspicuity of uterine arteries in correlation with digital subtraction angiography (DSA). Eleven consecutive patients with symptomatic uterine fibroids underwent 2 types of MRA before uterine arterial embolization (UAE). From these MRA an interventional radiologist predicted the optimal degrees for oblique DSA projections to reveal uterine arterial origins. Qualitatively, three independent observers reviewed two types of MRA assessing the conspicuity of uterine arterial origins and descending portions using a 3-point scale. Quantitatively, the visualized uterine arteries were measured from their orifice to the end of their descending portions. At UAE, knowing the optimal degrees from MRA, the uterine arterial origins were clearly visualized on all first oblique DSA projections. Mean conspicuity levels of the uterine arterial origins and descending portions were significantly higher and mean length of the visualized uterine arteries was significantly longer for unenhanced WEST MRA than for gadolinium-enhanced SWEEP MRA. Unenhanced 3D-WEST MRA was superior to gadolinium-enhanced 3D-SWEEP MRA in demonstrating uterine arteries. The optimal degrees for DSA projections to reveal uterine arterial origins could be accurately predicted using this noninvasive technique.

Pancreas Allografts: Comparison of Three-dimensional Rotational Angiography with Standard Digital Subtraction Angiography

To define the role of three-dimensional (3D) rotational angiography (RA) for the evaluation of pancreas allografts and compare 3D RA to standard digital subtraction angiography (DSA). DSA and 3D RA were performed in patients with vascular abnormalities diagnosed on contrast medium-enhanced magnetic resonance (MR) angiography. Patency of the allograft vasculature, confidence in the ability to make a therapeutic decision, and value of the study for definition of the optimal projection for an intervention was assessed on a graded scale. Seventeen standard DSA projections (mean, 3.4; range, 2-6) and 10 3D RA images (mean, 2; range, 1-3) were obtained in five patients. An average iodinated contrast agent dose of 14.4 mL (range, 8-22 mL) was administered for DSA. An average CO2 dose of 54 mL (range, 0-120 mL) was administered for 3D RA. Five 3D RA procedures were timed for the arterial phase and five were timed for the arterial and venous phases. Average contrast agent doses were 17.6 mL (range, 11-22 mL) for arterial 3D RA and 24.4 mL (range, 16-34 mL) for arterial- and venous-phase 3D RA. Of 68 vascular segments available for direct comparison of patency, complete concordance was present in 96%. There was no difference in the reviewers' diagnostic confidence (10 +/- 0 for both techniques). Three-dimensional RA was considered significantly superior for planning the optimal projection for intervention (10 +/- 0 for 3D RA vs 7.2 +/- 1.6 for DSA; P = .0052). Three-dimensional RA of pancreatic allografts is feasible and does not differ in accuracy from conventional DSA. It provides similar reviewer confidence in the ability to make an accurate treatment decision, but its key advantage is its superior ability to define the optimal projection for planned endovascular interventions.

Three-dimensional time-of-flight MR angiography at 3 T compared to digital subtraction angiography in the follow-up of ruptured and coiled intracranial aneurysms: a prospective study

Since digital subtraction angiography (DSA) carries a low risk of morbidity, and is associated with patient discomfort and higher cost, our objective was to determine whether high-resolution 3-D time-of-flight MR angiography (TOF-MRA) at 3 T may replace DSA in the follow-up of patients after coiling of an intracranial aneurysm. This prospective study included 50 consecutive patients with a ruptured and subsequently coiled intracranial aneurysm. All patients were followed up at a mean of 14 months after coiling with DSA and high-resolution 3-D TOF-MRA at 3 T generating 0.02 mm3 isotropic voxels. One examiner used DSA and TOF-MR angiograms to assess the need for and risk of retreatment; these data were used to calculate intermodality agreement. Another two examiners independently assessed aneurysm occlusion by DSA and TOF-MRA according to the Raymond scale; these data were used to calculate interobserver agreement. Discrepancies between DSA and TOF-MRA were found in three patients (intermodality agreement kappa=0.86). While DSA indicated complete aneurysm occlusion, TOF-MRA showed small neck remnants in the three patients. Coils on all DSA projections obscured these three neck remnants. Interobserver agreement was higher for DSA (kappa=0.82) than for TOF-MRA (kappa=0.68), which was in part due to the complexity of the information provided by TOF source images and reconstructions. 3-D TOF-MRA at 3 T is not only an adjunctive tool but is ready to replace DSA in the follow-up of patients with previously coiled intracranial aneurysms. Additional DSA may only be performed in complex and not clearly laid out aneurysms.

Overestimation of carotid artery stenosis with magnetic resonance angiography compared with digital subtraction angiography

Three-dimensional time-of-flight (3D TOF) magnetic resonance angiography (MRA) is generally considered to overestimate the degree of stenosis in the internal carotid artery (ICA) in comparison with the reference standard intraarterial digital subtraction angiography (DSA). We evaluated whether the degree of stenosis was more accurately assessed with 3D TOF MRA if corresponding projections on MRA and DSA were compared instead of comparison of maximal stenosis at MRA with maximal stenosis at DSA. From February 1997 to December 1999, we included 186 symptomatic and 17 asymptomatic consecutive patients suspected of having carotid artery stenosis on the basis of clinical presentation and screening with duplex ultrasound scan examination. All patients subsequently underwent DSA and MRA imaging. From each ICA, 12 maximum intensity projections with 3D TOF MRA and two or three projections with DSA were obtained. First, we compared the maximal stenosis at MRA with the maximal stenosis at DSA. Subsequently, we used the stenosis at MRA measured on the projection corresponding with the DSA projection that showed the maximal stenosis. For both strategies, the mean differences in stenosis and sensitivity and specificity for assessment of severe stenosis (70% to 99%) were calculated and compared. The MRA and DSA images of 354 ICAs could be compared. The sensitivity and specificity of MRA with the projection that showed the maximal stenosis were 92.6% (95% CI, 85.3% to 97.0%) and 82.7% (95% CI, 78.1% to 87.3%), respectively. The sensitivity and specificity with the MRA projection, corresponding with the DSA projection showing the maximal stenosis, were 88.3% (95% CI, 81.8% to 94.8%) and 89.6% (95% CI, 85.9% to 93.3%), respectively. The mean difference between maximal stenosis at MRA and DSA was 7.5% (95% CI, 5.2% to 9.9%). The mean difference between stenosis at MRA and DSA in corresponding projections was 0.4% (95% CI, -2.0% to 2.7%). If corresponding MRA and intraarterial DSA projections are compared, 3D TOF MRA does not overestimate carotid stenosis.

3D reconstruction of the encapsulating contour of arteriovenous malformations for radiosurgery using digital subtraction angiography

Purpose: Treatment planning for radiosurgery depends on the precise definition of radiation target volumes. For vascular pathologies such as arteriovenous malformations (AVM), the most usual technique remains standard X-ray projection imaging, most often carried out under stereotactic conditions. To further benefit from the advantages of two-dimensional digital subtraction angiography (DSA), the authors have developed a method for determining the three-dimensional shape of arteriovenous malformations from two views. Methods and Materials: After correction of image intensifier distortion and calibration of both views, the 3D shape of the AVM was determined from two DSA projections using epipolarity geometry. The AVM-encapsulating contour was modeled by triangulation of a stack of almost parallel ellipses. The method was technically validated using artificial targets in a skull phantom. Clinical validation was carried out on 10 patients who were examined using both conventional angiography under stereotactic conditions (SX-ray) and DSA. Results: There was excellent agreement between the artificial target volumes measured with SX-ray and with DSA. The correspondence between AVM volumes found for patients was not as good as with the phantom. Conclusions: The different image characteristics of the two modalities lead to some differences in AVM estimations. However, the results were sufficiently satisfactory to justify routine use of this AVM modeling technique for radiosurgery planning.

Localization of cerebral arterovenous malformations using digital angiography.

Since 1989 we performed stereotactic radiotherapy treatments of cerebral arterovenous malformations (AVM), estimating three-dimensional (3-D) localization and shape of target volumes by the Leksell stereotactic helmet on two orthogonal radiographic projections. Due to the limitations of this method, we developed a new technique for the localization of the target volume using digital subtraction angiography (DSA) and digital image processing. To achieve this result we first developed a method to correct nonlinear distortion of DSA images using spatial relocation of image pixels based on a calibration grid. We then developed an algorithm for localization of the target volume using two independent DSA projections. Target volume coordinates in the helmet system are calculated using two DSA acquisitions taken with a free angle (approximately 90 degrees), one in the AP and the other in the LL direction. The helmet can be freely positioned between the x-ray source and the image plane. The projections of eight reference points inserted in the helmet at a known location, are used to calculate the transformation matrix between the two coordinate systems. We performed numerical and experimental validation of the system. A hypothetical random error (up to 2 mm) on image coordinates of the reference points allowed to determine that the error in target localization was less than 0.2 mm. Using DSA images of target points with a known location within a phantom, the error between calculated and actual location was, on average, 0.30+/-0.13 mm (mean+/-SD), with a maximum error of 0.49 mm. The results of numerical and experimental validations show that the system we have developed allows fast and accurate localization of the center of the target volume and it is suitable for efficient guiding during stereotactic radiosurgery of AVM.