Dispersion of Heterogeneous Medium in Pulsatile Blood Flow and Absolute Pulsatile Flow Velocity Quantification.

Heterogeneous medium enhanced angiogr- ams are key diagnostic tools in clinical practice; the associated hemodynamic information is crucial for diagnosing cardiovascular diseases. However, the dynamics of such medium in physiological blood flow are poorly understood. Herein, we report a previously unnoticed dispersion pattern, which is a universal phenomenon, of a medium in pulsatile blood flow. We present a physical theory for studying the dispersion of a steadily injected heterogeneous medium into a thin tubular blood vessel in which the blood flow is pulsatile. In a thin tubular blood vessel, we demonstrate that variations of concentration associated with the heterogeneous medium obey a one-dimensional advection diffusion equation, and the diffusion has limited effect whenever a short vascular segment is considered. A distinct feature of the distribution of the medium in the axial distance-time plane is a "dilation-retraction" pattern. The time evolution signals at different axial positions exhibit distinct concentration waveforms. A numerical scheme is proposed for exploiting this information to estimate the pulsatile velocity. Artificial data are adopted to validate the scheme. Real X-ray angiography is also analyzed to support our theory and method. The theory is applicable whenever imaging protocols involve a heterogeneous medium in pulsatile flow.

Estimating Pulsatile Blood Flow Parameters from Digital Subtraction Angiography.

Digital subtraction angiography (DSA) is the gold standard for diagnosing vascular diseases. Much attention had been attracted on estimating blood flow velocity from DSA data, and many techniques to compute the mean flow velocity had been proposed. In this paper, we present a physical model that demonstrates how the pulsatile flow can affect the dispersion of the contrast medium delivered into the blood vessel. Using empirical mode decomposition and angiographic data of 4 patients, we then showed it is feasible to compute pulsatile flow related parameters from routine interventional angiographic acquisitions.Clinical Relevance- This is the first attempt to present a physical model and corresponding method to estimate pulsatile flow related parameters from routine angiographic acquisitions, and has potential to be used for real-time diagnostic and therapeutic monitoring during interventional procedures.

Estimating blood flow velocity using time-resolved 3D angiography and a derived physical law of contrast media.

OBJECTIVE: Four-dimensional (4D) digital subtraction angiography (DSA) offers a method for evaluating hemodynamics. It is, however, unclear how the delivered contrast medium interacts with the physiological blood flow, and how hemodynamic information may be inferred from the mixture of the contrast medium and blood. In this study, we present a theoretical explanation of contrast dynamics, and an accompanying algorithm for estimating blood flow velocity. APPROACH: We retrospectively recruited 23 patients who underwent both 4D DSA and magnetic resonance (MR) phase-contrast imaging. The 4D DSA-reconstructed contrast dynamics were first studied for the internal carotid arteries. Using physical laws governing fluid motion within a curved tube, we showed that the reconstructed contrast dynamics obeyed a simple advection equation. We then proposed an algorithm for estimating the contrast dynamics using angiographic data, and subsequently estimated the axial blood flow velocity using an advection equation. MAIN RESULTS: The estimated velocities were compared using three techniques: the Fourier technique, Lin's method, and MR phase contrast. Testing with noise-corrupted artificial data showed that the proposed algorithm was noise resistant. The velocities of 23 patients computed by 4D DSA using the proposed algorithm showed a moderate correlation with the MR phase contrast (r = 0.61), and good correlations with the other two techniques (r = 0.75 and r = 0.72). SIGNIFICANCE: The proposed algorithm and has been applied to blood vessel segments with poor signal-to-noise ratios and axial lengths of less than 3 cm, and has a physical basis for computing axial flow velocities using an advection equation. The results of the proposed algorithm are consistent with existing methods.

Fluoroscopic angiography quantifies delay in cerebral circulation time and requires less radiation in carotid stenosis patients: A pilot study.

BACKGROUND: Quantitative digital subtraction angiography (DSA) facilitates in-room assessment of flow changes in various cerebrovascular diseases and improves patient safety. The purpose of this study was to compare the diagnostic accuracy of quantitative fluoroscopic angiography (FA) and DSA. METHODS: Twenty-two patients with >70% carotid stenosis according to NASCET criteria were prospectively included in the study. All patients received DSA and FA (ArtisZee, Siemens Healthcare, Forchheim, Germany) before and after carotid stenting in the same angiosuite. The regions of interest (ROIs) included the extracranial internal carotid artery (eICA), first segment of the middle cerebral artery (MCA1), and sigmoid sinus in the anterior-posterior view; cavernous portion of the ICA (cICA), parietal vein, and jugular vein in the lateral views. The time-to-peak (TTP) for all ROIs and cerebral circulation time (CCT) were measured from FA and DSA scans. TTP, CCT, and radiation doses from DSA were compared with those from FA. RESULTS: The mean age of the patients were 69 ± 9.5 years old. The average stenosis was 89.7% ± 7.8% before stenting and 31% ± 3.6% after stenting. No patient suffered from periprocedural stroke. The intermethod correlation for TTP for all ROIs except the eICA and cICA ranged from 0.46 to 0.65 before stenting and 0.57 to 0.73 after stenting, and that for CCT was 0.65 before stenting and 0.57 after stenting. The radiation doses were significantly lower for FA than for DSA regardless of views or periprocedural timing (p < 0.001). CONCLUSION: Stenosis facilitated the creation of a bolus by manual injection and therefore increased the accuracy of cerebral flow quantification in FA. Cerebral hemodynamic assessment by FA is quicker and associated with less radiation.

Evaluating cerebral hemodynamics using quantitative digital subtraction angiography and flat-detector computed tomography perfusion imaging: A comparative study in patients with carotid stenosis.

BACKGROUND: The efficacy of both quantitative digital subtraction angiography (QDSA) and flat-detector computed tomography perfusion (FD-CTP) is equivalent to that of magnetic resonance perfusion (MRP) in assessing perfusion deficits in carotid stenosis. This study evaluated the feasibility of using FD-CTP to monitor cerebral hemodynamics during carotid stenting. METHODS: Thirteen patients with extracranial carotid stenosis (>70%) were included. Both QDSA and two FD-CTP sessions were performed before and after carotid stenting. Cerebral circulation time (CCT) was defined as the difference between the time to peak (TTP) of the parietal vein and the cavernous internal carotid artery. For FD-CTP and MRP, regions of interest (ROIs) were placed in the middle cerebral artery territory at the basal ganglia level of both stenotic and contralateral hemispheres for measurement. The TTP ratio (rTTP) was defined as stenotic TTP divided by contralateral TTP; and ratio of cerebral blood volume (rCBV), ratio of mean transit time (rMTT), and ratio of cerebral blood flow (rCBF) were defined similarly. Both CCT and ratio perfusion parameters were compared during stenting. RESULTS: Before stenting, only rCBF (r = 0.73) and rTTP (r = 0.58) demonstrated correlations between FD-CTP and MRP; CCT correlated with only rMTT in MRP (r = 0.69). After stenting, only rCBF (r = 0.56) indicated a correlation between FD-CTP and MRP. Regarding cerebral flow after stenting, CCT (4.61 ± 1.6 s) was shortened, rMTT (1.12 ± 0.04) and rTTP (r = 1.05 ± 0.03) decreased, and rCBF (0.91 ± 0.16) increased significantly. CONCLUSION: FD-CTP provides a potentially more comprehensive hemodynamic assessment of parenchymal perfusion changes compared with QDSA during carotid stenting, but FC-CTP requires additional 18 min. FD-CTP confirmed that the normalization of cerebral hemodynamics began immediately and continued for 1-3 days.

In-room assessment of intravascular velocity from time-resolved rotational angiography in patients with arteriovenous malformation: a pilot study.

BACKGROUND: Time-resolved rotational angiography (t-RA) enables interventionists to better comprehend complex arteriovenous malformations (AVMs), thereby facilitating endovascular treatment. However, its use in evaluating hemodynamic changes has rarely been explored. OBJECTIVE: This study uses t-RA to estimate intravascular flow in patients with AVM to compare this with flow in the normal population. METHODS: Patients with available t-RA scans were prospectively categorized into one of three groups: hemorrhagic AVM, non-hemorrhagic AVM and control. Pulsatile time-density curves (TDCs) for C1, C6 and VOIMCA were used for amplitude and velocity estimation. C1 was at the cervical internal carotid artery (ICA), 2-3 cm below the carotid canal, C6 was at the paraclinoid segment of the ICA, and VOIMCA was at the junction of the first and second segment of the middle cerebral artery (MCA). A waveform amplitude ratio was defined as (peak - trough)/trough contrast intensity. VICA was defined as the distance between C6 and C1 divided by the time required for the wave to pass, and correspondingly, the average velocity of MCA (VMCA) was defined as the distance between C6 and VOIMCA divided by the duration for the same peak to travel from C6 and VOIMCA, AVM volume was estimated by MR angiography. RESULTS: Amplitude ratios AC1 and AC6, and average flow velocities VICA and VMCA were significantly larger in the non-hemorrhagic group than in the control group, while the hemorrhagic AVM group was not significantly different from the controls. VICA and VMCA showed moderate to good correlations with AVM volume (r=0.51 and 0.73, respectively). VMCA (33.0±9.1) was significantly lower than VICA (41.3±13.2) in the control group, but not in the two AVM groups. CONCLUSION: TDC waveform propagation derived from t-RA can quantify hemodynamic differences between AVM and the control group. t-RA provides both real-time anatomic and hemodynamic evaluation, and can thus potentially improve the interventional workflow.

Automatic flow analysis of digital subtraction angiography using independent component analysis in patients with carotid stenosis.

PURPOSE: Current time-density curve analysis of digital subtraction angiography (DSA) provides intravascular flow information but requires manual vasculature selection. We developed an angiographic marker that represents cerebral perfusion by using automatic independent component analysis. MATERIALS AND METHODS: We retrospectively analyzed the data of 44 patients with unilateral carotid stenosis higher than 70% according to North American Symptomatic Carotid Endarterectomy Trial criteria. For all patients, magnetic resonance perfusion (MRP) was performed one day before DSA. Fixed contrast injection protocols and DSA acquisition parameters were used before stenting. The cerebral circulation time (CCT) was defined as the difference in the time to peak between the parietal vein and cavernous internal carotid artery in a lateral angiogram. Both anterior-posterior and lateral DSA views were processed using independent component analysis, and the capillary angiogram was extracted automatically. The full width at half maximum of the time-density curve in the capillary phase in the anterior-posterior and lateral DSA views was defined as the angiographic mean transient time (aMTT; i.e., aMTTAP and aMTTLat). The correlations between the degree of stenosis, CCT, aMTTAP and aMTTLat, and MRP parameters were evaluated. RESULTS: The degree of stenosis showed no correlation with CCT, aMTTAP, aMTTLat, or any MRP parameter. CCT showed a strong correlation with aMTTAP (r = 0.67) and aMTTLat (r = 0.72). Among the MRP parameters, CCT showed only a moderate correlation with MTT (r = 0.67) and Tmax (r = 0.40). aMTTAP showed a moderate correlation with Tmax (r = 0.42) and a strong correlation with MTT (r = 0.77). aMTTLat also showed similar correlations with Tmax (r = 0.59) and MTT (r = 0.73). CONCLUSION: Apart from vascular anatomy, aMTT estimates brain parenchyma hemodynamics from DSA and is concordant with MRP. This process is completely automatic and provides immediate measurement of quantitative peritherapeutic brain parenchyma changes during stenting.

Quantitative Real-Time Fluoroscopy Analysis on Measurement of the Hepatic Arterial Flow During Transcatheter Arterial Chemoembolization of Hepatocellular Carcinoma: Comparison with Quantitative Digital Subtraction Angiography Analysis.

PURPOSE: To quantify the arterial flow change during transcatheter arterial chemoembolization (TACE) for hepatocellular carcinoma (HCC) using digital subtraction angiography, quantitative color-coding analysis (d-QCA), and real-time subtraction fluoroscopy QCA (f-QCA). MATERIALS AND METHODS: This prospective study enrolled 20 consecutive patients with HCC who had undergone TACE via a subsegmental approach between February 2014 and April 2015. The TACE endpoint was a sluggish antegrade tumor-feeding arterial flow. d-QCA and f-QCA were used for determining the relative maximal density time (rTmax) of the selected arteries. The rTmax of the selected arteries was analyzed in d-QCA and f-QCA before and after TACE, and its correlation in both analyses was evaluated. RESULTS: The pre- and post-TACE rTmax of the embolized segmental artery in d-QCA and f-QCA were 1.59 ± 0.81 and 2.97 ± 1.80 s (P < 0.001) and 1.44 ± 0.52 and 2.28 ± 1.02 s (P < 0.01), respectively. The rTmax of the proximal hepatic artery did not significantly change during TACE in d-QCA and f-QCA. The Spearman correlation coefficients of the pre- and post-TACE rTmax of the embolized segmental artery between d-QCA and f-QCA were 0.46 (P < 0.05) and 0.80 (P < 0.001). Radiation doses in one series of d-QCA and f-QCA were 140.7 ± 51.5 milligray (mGy) and 2.5 ± 0.7 mGy, respectively. CONCLUSIONS: f-QCA can quantify arterial flow changes with a higher temporal resolution and lower radiation dose. Flow quantification of the embolized segmental artery using f-QCA and d-QCA is highly correlated.

Finding the optimal deconvolution algorithm for MR perfusion in carotid stenosis: Correlations with angiographic cerebral circulation time.

PURPOSE: The aim of our study is to explore the impacts of different deconvolution algorithms on correlations between CBF, MTT, CBV, TTP, Tmax from MR perfusion (MRP) and angiography cerebral circulation time (CCT). METHODS: Retrospectively, 30 patients with unilateral carotid stenosis, and available pre-stenting MRP and angiography were included for analysis. All MRPs were conducted in a 1.5-T MR scanner. Standard singular value decomposition, block-circulant, and two delay-corrected algorithms were used as the deconvolution methods. All angiographies were obtained in the same bi-plane flat-detector angiographic machine. A contrast bolus of 12mL was administrated via angiocatheter at a rate of 8mL/s. The acquisition protocols were the same for all cases. CCT was defined as the difference between time to peak from the cavernous ICA and the parietal vein in lateral view. Pearson correlations were calculated for CCT and CBF, MTT, CBV, TTP, Tmax. RESULTS: The correlation between CCT and MTT was highest with Tmax (r=0.65), followed by MTT (r=0.60), CBF (r=-0.57), and TTP (r=0.33) when standard singular value decomposition was used. No correlation with CBV was noted. CONCLUSIONS: MRP using a singular value decomposition algorithm confirmed the feasibility of quantifying cerebral blood flow deficit in steno-occlusive disease within the angio-room. This approach might further improve patient safety by providing immediate cerebral hemodynamics without extraradiation and iodine contrast.

Prolonged Cerebral Circulation Time Is the Best Parameter for Predicting Vasospasm during Initial CT Perfusion in Subarachnoid Hemorrhagic Patients.

PURPOSE: We sought to imitate angiographic cerebral circulation time (CCT) and create a similar index from baseline CT perfusion (CTP) to better predict vasospasm in patients with subarachnoid hemorrhage (SAH). METHODS: Forty-one SAH patients with available DSA and CTP were retrospectively included. The vasospasm group was comprised of patients with deterioration in conscious functioning and newly developed luminal narrowing; remaining cases were classified as the control group. The angiography CCT (XA-CCT) was defined as the difference in TTP (time to peak) between the selected arterial ROIs and the superior sagittal sinus (SSS). Four arterial ROIs were selected to generate four corresponding XA-CCTs: the right and left anterior cerebral arteries (XA-CCTRA2 and XA-CCTLA2) and right- and left-middle cerebral arteries (XA-CCTRM2 and XA-CCTLM2). The CCTs from CTP (CT-CCT) were defined as the differences in TTP from the corresponding arterial ROIs and the SSS. Correlations of the different CCTs were calculated and diagnostic accuracy in predicting vasospasm was evaluated. RESULTS: Intra-class correlations ranged from 0.96 to 0.98. The correlations of XA-CCTRA2, XA-CCTRM2, XA-CCTLA2, and XA-CCTLM2 with the corresponding CT-CCTs were 0.64, 0.65, 0.53, and 0.68, respectively. All CCTs were significantly prolonged in the vasospasm group (5.8-6.4 s) except for XA-CCTLA2. CT-CCTA2 of 5.62 was the optimal cut-off value for detecting vasospasm with a sensitivity of 84.2% and specificity 82.4. CONCLUSION: CT-CCTs can be used to interpret cerebral flow without deconvolution algorithms, and outperform both MTT and TTP in predicting vasospasm risk. This finding may help facilitate management of patients with SAH.

Application of color-coded digital subtraction angiography in treatment of indirect carotid-cavernous fistulas: initial experience.

BACKGROUND: Parametric-colored digital subtraction angiography using Tmax is almost a routine angiographic imaging procedure, currently. The current feasibility study is aimed to using the imaging to monitor treatment effects while embolizing indirect carotid-cavernous fistulas (CCF). METHODS: Ten patients with CCFs receiving embolization and 40 patients with normal circulation time were recruited. Their color-coded DSAs were used to define the Tmax of selected intravascular ROIs. A total of 19 ROIs in the internal carotid artery (ICA) (cervical segment of ICA in AP view (I0), cavernous segment of ICA in AP view (I1), supraclinoid segment of ICA in AP view (I2) and cervical segment of ICA in lateral view (I0'), cavernous portion of ICA in lateral view (IA), supraclinoid portion of ICA in lateral view (IB)), ACA (first segment of anterior cerebral artery, second segment of anterior cerebral artery (A1, A2)), middle cerebral vein (MCA) first segment of MCA ((M1), second segment of MCA (M2)), frontal vein (FV), parietal vein (PV), superior sagittal sinus (SSS), sigmoid sinus (SS), internal jugular vein (JV), fistula, superior ophthalmic vein (SOV), inferior petrosal vein (IPS), and MCV were selected. Relative Tmax was defined as the Tmax at selected ROIs minus Tmax at I0 or I0'. An intergroup comparison between the normal and treatment groups and pre- and post-treatment comparison of the peri-therapeutic rTmax for the treatment group were performed. RESULTS: rTmax's for the normal group were as follows: Anterior-posterior view: I1: 0.16, I2: 0.32, A1: 0.31, M1: 0.35, SSS: 6.16, SS: 6.56, and MCV: 3.86 seconds. Lateral view: IA: 0.05, IB: 0.20, A2: 0.53, M2: 0.95, FV: 4.84, PV: 5.12, IPS: 4.62, JV: 6.81, and MCV: 3.86 seconds. Before embolization, rTmax of the IPS, SS, and JV for the treatment group were shortened (p < 0.05). No rTmaxs for any arterial ROIs in the fistula group were significantly different. After embolization, the rTmaxs for all venous ROIs returned to normal except for two which were partially obliterated. CONCLUSION: This postprocessing method does not require extra radiation exposure and contrast media. It facilitates real-time hemodyamic monitoring and may help determining the endpoint of embolization, which increases patient safety.

The Relationship between Carotid Artery Diameter and Percentage of Stenosis.

In order to understand percentage of stenosis from the residual lumen of the carotid artery, we explored the relationship between the residual diameter at the carotid stenosis, its stenosis percentage and the size of the internal carotid artery. Diameters of 103 carotid arteries of Taiwan residents were retrospectively measured from digital subtraction angiograms. Severe cases of near occlusion with the angiographic string sign, and cases with tandem lesions or intracranial occlusion were excluded. Of the total 103 carotid arteries, 22 (21%) had one or both of the following signs of reduced distal arterial caliber: (1) obvious narrowing of the distal carotid artery; (2) the caliber of the cervical internal carotid artery was smaller than the caliber of the corresponding external carotid artery. That the diameter of the distal carotid artery was smaller when the stenosis was greater at the site of minimal lumen was true in the group of patients with signs of reduced distal caliber and in the group of patients without such signs. Therefore, reduced distal caliber may be present in patients without such signs. After excluding cases with at least one of the above signs of reduced distal arterial caliber, the relation between percentage of stenosis (y) and the absolute value of the diameter at the stenosis (x) can be represented by the formula: y = 96.83-18.27 x. From our data, a diameter of 2 mm is about 60% stenosis and 1.5 mm is 70% stenosis. According to this formula, we can estimate percentage of carotid stenosis using residual diameter at the site of minimal lumen obtained from other imaging modalities, such as carotid Doppler, CT angiogram or MR angiogram.