Blooming Artifact Research Articles

A preliminary study of super-resolution deep learning reconstruction with cardiac option for evaluation of endovascular-treated intracranial aneurysms.

To investigate the usefulness of super-resolution deep learning reconstruction (SR-DLR) with cardiac option in the assessment of image quality in patients with stent-assisted coil embolization, coil embolization, and flow-diverting stent placement compared with other image reconstructions. This single-centre retrospective study included 50 patients (mean age, 59 years; range, 44-81 years; 13 men) who were treated with stent-assisted coil embolization, coil embolization, and flow-diverting stent placement between January and July 2023. The images were reconstructed using filtered back projection (FBP), hybrid iterative reconstruction (IR), and SR-DLR. The objective image analysis included image noise in the Hounsfield unit (HU), signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and full width at half maximum (FWHM). Subjectively, two radiologists evaluated the overall image quality for the visualization of the flow-diverting stent, coil, and stent. The image noise in HU in SR-DLR was 6.99 ± 1.49, which was significantly lower than that in images reconstructed with FBP (12.32 ± 3.01) and hybrid IR (8.63 ± 2.12) (P < .001). Both the mean SNR and CNR were significantly higher in SR-DLR than in FBP and hybrid IR (P < .001 and P < .001). The FWHMs for the stent (P < .004), flow-diverting stent (P < .001), and coil (P < .001) were significantly lower in SR-DLR than in FBP and hybrid IR. The subjective visual scores were significantly higher in SR-DLR than in other image reconstructions (P < .001). SR-DLR with cardiac option is useful for follow-up imaging in stent-assisted coil embolization and flow-diverting stent placement in terms of lower image noise, higher SNR and CNR, superior subjective image analysis, and less blooming artifact than other image reconstructions. SR-DLR with cardiac option allows better visualization of the peripheral and smaller cerebral arteries. SR-DLR with cardiac option can be beneficial for CT imaging of stent-assisted coil embolization and flow-diverting stent.

Quantitative analysis of blooming artifact caused by calcification based on X-ray energy difference using computed tomography

Blooming artifacts caused by calcifications appearing on computed tomography (CT) images lead to an underestimation of the coronary artery lumen size, and higher X-ray energy levels are suggested to reduce the blooming artifacts with subjective visual assessment. This study aimed to evaluate the effect of higher X-ray energy levels on the quantitative measurement of adjacent pixels affected by calcification using CT images. In this two-part study, CT images were acquired from dual-energy CT scanners by changing the X-ray energy levels such as kilovoltage peak (kVp) and kilo-electron volts (keV). Adjacent pixels affected by calcification were measured using the brightened length, excluding the actual calcified length, as determined by the full width at third maximum. In a separate clinical study, the adjacent affected pixels associated with 23 calcifications across 10 patients were measured using the same method as that used in the phantom study. Phantom and clinical studies showed that the change in kVp (field of view [FOV] 300 mm: p = 0.167, 0.494, and 0.861 for vendors 1, 2, and 3, respectively) and keV levels (p = 0.178 for vendor 2) failed to reduce the adjacent pixels affected by calcification, respectively. Moreover, the change in keV levels showed different aspects of adjacent pixels affected by calcification in the phantom study (FOV 300 mm: no significant difference [p = 0.191], increase [p < 0.001], and decrease [p < 0.001] for vendors 1, 2, and 3, respectively). Quantitative measurements revealed no significant relationship between higher X-ray energy levels and the adjacent pixels affected by calcification.

Countering Calcium Blooming With Personalized Contrast Media Injection Protocols: The 1-2-3 Rule for Photon-Counting Detector CCTA.

Photon-counting detector computed tomography (PCD-CT) enables spectral data acquisition of CT angiographies allowing for reconstruction of virtual monoenergetic images (VMIs) in routine practice. Specifically, it has potential to reduce the blooming artifacts associated with densely calcified plaques. However, calcium blooming and iodine attenuation are inversely affected by energy level (keV) of the VMIs, creating a challenge for contrast media (CM) injection protocol optimization. A pragmatic and simple rule for calcium-dependent CM injection protocols is investigated and proposed for VMI-based coronary CT angiography with PCD-CT. A physiological circulation phantom with coronary vessels including calcified lesions (maximum CT value >700 HU) with a 50% diameter stenosis was injected into at iodine delivery rates (IDRs) of 0.3, 0.5, 0.7, 1.0, 1.5, 2.0, 2.5, and 3.0 g I/s. Images were acquired using a first-generation dual-source PCD-CT and reconstructed at various VMI levels (between 45 and 190 keV). Iodine attenuation in the coronaries was measured at each IDR for each keV, and blooming artifacts from the calcified lesions were assessed including stenosis grading error (as % overestimation vs true lumen). The IDR to achieve 300 HU at each VMI level was then calculated and compared with stenosis grading accuracy to establish a general rule for CM injection protocols. Plaque blooming artifacts and intraluminal iodine attenuation decreased with increasing keV. Fixed windowing (representing absolute worst case) resulted in stenosis overestimation from 77% ± 4% at 45 keV to 5% ± 2% at 190 keV, whereas optimized windowing resulted in overestimation from 29% ± 3% at 45 keV to 4% ± 1% at 190 keV. The required IDR to achieve 300 HU showed a strong linear correlation to VMI energy ( R2 = 0.98). Comparison of this linear plot versus stenosis grading error and blooming artifact demonstrated that multipliers of 1, 2, and 3 times the reference IDR for theoretical clinical regimes of no, moderate, and severe calcification density, respectively, can be proposed as a general rule. This study provides a proof-of-concept in an anthropomorphic phantom for a simple pragmatic adaptation of CM injection protocols in coronary CT angiography with PCD-CT. The 1-2-3 rule demonstrates the potential for reducing the effects of calcium blooming artifacts on overall image quality.

Influence of CBCT filters and contrast adjustments on peri-implant buccal bone thickness measurement and blooming expression.

To assess whether filter and contrast adjustments can improve the accuracy of CBCT in measuring the buccal bone thickness (BBT) adjacent to dental implants by reducing blooming artifacts. Homogeneous bone blocks with peri-implant BBT of 0.3mm, 0.5mm, and 1mm were scanned using the Orthophos SL system. Three dentists measured the BBT in 234 CBCT scans under different settings of contrast adjustments and 'Sharpen' filter activation. Additionally, implant diameter measurements were taken to assess blooming artifact expression. The differences between tomographic and actual measurements of BBT and implant diameter [(CBCT - actual) * 100 / actual] were subjected to Mixed ANOVA (α = 0.05). The group with the thinnest BBT (0.3mm) had the greatest difference between tomographic and actual measurements (79.9% ± 29.0%). Conversely, the 0.5mm (36.1% ± 38.4%) and 1mm (29.4% ± 12.3%) groups exhibited lower differences (p < 0.05). 'Sharpen' filter activation reduced blooming expression since it resulted in a lower difference for implant diameter (p < 0.05), but it did not influence BBT measurements (p = 0.673). Contrast settings had no impact on BBT (p = 0.054) or implant diameter measurements (p = 0.079). Although filter activation reduced blooming artifacts, neither filter nor contrast adjustments improved the accuracy of CBCT in measuring peri-implant BBT; actual BBT influenced this task. When assessing the peri-implant buccal bone plate in the CBCT system studied, dental surgeons may find it beneficial to adjust contrast and apply filters according to their preferences, since such adjustments were found to have no adverse effects on the diagnostic accuracy of this task. The use of the 'Sharpen' filter may lead to improved representation of implant dimensions.

Quantifying lumen diameter in coronary artery stents with high-resolution photon counting detector CT and convolutional neural network denoising.

Small coronary arteries containing stents pose a challenge in CT imaging due to metal-induced blooming artifact. High spatial resolution imaging capability is as the presence of highly attenuating materials limits noninvasive assessment of luminal patency. The purpose of this study was to quantify the effective lumen diameter within coronary stents using a clinical photon-counting-detector (PCD) CT in concert with a convolutional neural network (CNN) denoising algorithm, compared to an energy-integrating-detector (EID) CT system. Seven coronary stents of different materials and inner diameters between 3.43 and 4.72mm were placed in plastic tubes of diameters 3.96-4.87mm containing 20mg/mL of iodine solution, mimicking stented contrast-enhanced coronary arteries. Tubes were placed parallel with or perpendicular to the scanner's z-axis in an anthropomorphic phantom emulating an average-sized patient and scanned with a clinical EID-CT and PCD-CT. EID scans were performed using our standard coronary computed tomography angiography (cCTA) protocol (120kV, 180 quality reference mAs). PCD scans were performed using the ultra-high-resolution (UHR) mode (120×0.2mm collimation) at 120kV with tube current adjusted so that CTDIvol was matched to that of EID scans. EID images were reconstructed per our routine clinical protocol (Br40, 0.6mm thickness), and with the sharpest available kernel (Br69). PCD images were reconstructed at a thickness of 0.6mm and a dedicated sharp kernel (Br89) which is only possible with the PCD UHR mode. To address increased image noise introduced by the Br89 kernel, an image-based CNN denoising algorithm was applied to the PCD images of stents scanned parallel to the scanner's z-axis. Stents were segmented based on full-width half maximum thresholding and morphological operations, from which effective lumen diameter was calculated and compared to reference sizes measured with a caliper. Substantial blooming artifacts were observed on EID Br40 images, resulting in larger stent struts and reduced lumen diameter (effective diameter underestimated by 41% and 47% for parallel and perpendicular orientations, respectively). Blooming artifacts were observed on EID Br69 images with 19% and 31% underestimation of lumen diameter compared to the caliper for parallel and perpendicular scans, respectively. Overall image quality was substantially improved on PCD, with higher spatial resolution and reduced blooming artifacts, resulting in the clearer delineation of stent struts. Effective lumen diameters were underestimated by 9% and 19% relative to the reference for parallel and perpendicular scans, respectively. CNN reduced image noise by about 50% on PCD images without impacting lumen quantification(<0.3% difference). The PCD UHR mode improved in-stent lumen quantification for all seven stents as compared to EID images due to decreased blooming artifacts. Implementation of CNN denoising algorithms to PCD data substantially improved image quality.

Abstract 15601: Optimal Virtual Monoenergetic Settings for Spectral Ct With a Dual-Layer Detector: A Breakthrough in Evaluating the Patency of the Coronary Arterial Lumen With a Metallic Stent in a Real-World Study

Introduction: Evaluation of the patency of a metallic stent in coronary arteries using CT is difficult because the metallic stent causes a blooming artifact. The CT values of metallic stents are influenced by tube kilovoltage (kV). Recent spectral CT with a dual-layer detector can generate CT images at any kiloelectron voltage (keV) (range: 40-200) after ordinary acquisition using virtual monoenergetic settings (VMS). Hypothesis: Using a new spectral CT, we can determine the optimal VMS for evaluating the patency of stents in coronary arteries. Methods: We performed enhanced 128 slice Spectral CT 7500 scans with a dual-layer detector in 35 patients with CAC who underwent implantation of a metallic stent in coronary arteries (tube voltage: 120 kV). After scanning, VMS images at various keV values were created from the spectral-based images. We measured the mean CT values of the metallic stent, coronary artery calcification (CAC), lumen in the left coronary artery (LCA), and fat tissue around the coronary arteries in the axial images at each keV in the early phase with contrast. Results: Lower keV values were associated with markedly increased mean CT values of the metallic stent and CAC. The CT values of the lumen in the LCA were moderately increased. Conversely, the CT values of fat tissue were slightly decreased. The greatest differences in mean CT values between the metallic stent and lumen in the LCA were observed at 40-50 keV, however, those between the metallic stent and CAC were observed at 110-180 keV. The optimal keV for achieving the best contrast between the CT values of the metallic stent, CAC, and the lumen in the LMA at each patient was influenced by age, male sex. Conclusions: The metallic stent, CAC, lumen of the LCA, and fat tissue exhibit unique characteristics. When conventional rather than spectral CT is used to evaluate the patency of a metallic stent in coronary arteries, it is necessary to determine the optimal tube voltage based on the age and male sex of the patient.

Abstract 15552: Optimal Virtual Monoenergetic Settings in Spectral Ct With a Dual Layer Detector: Breakthrough in Achieving Best Contrast Between Non Calcified and Calcified Plaques and Lumen in Coronary Arteries

Introduction: Non calcified plaque (NCP) in coronary arteries on CT is correlated with occurrence of acute coronary syndromes and coronary artery calcification (CAC) may occasionally be co-existed. CAC induces a blooming artifact, which magnifies the calcification versus its actual size. The CT values of NCP and CAC are influenced by tube kilovoltage (kV). Recent spectral CT with a dual-layer detector can generate CT images at any kiloelectron voltage (keV) (range: 40-200) after ordinary acquisition using virtual monoenergetic settings (VMS). Hypothesis: Using a new spectral CT, we can determine the optimal VMS settings for achieving best contrast between NCP, CAC and the lumen in coronary arteries. Methods: We performed enhanced 128 slice Spectral CT 7500 scans using a dual-layer detector in 42 patients with NCP and CAC on CT (tube voltage: 120 kV). After scanning, VMS images at various keV values were created from the spectral-based images. We measured the mean CT values of NCP and CAC, lumen in left main artery (LMA), and fat tissue around coronary arteries within a 1.0 mm2 circle in the axial images at each keV in early phase with a contrast. Results: Lower keV values were linked to only slightly increased mean CT values of NCP, but markedly increased mean CT values of CAC. The CT values of the lumen in the LMA were markedly increased. Conversely, the CT values of fat tissue were slightly decreased. The greatest differences in mean CT values between NCP and the LMA were observed at 40 keV. However, considering blooming artifact of CAC at 40 keV, the optimal keV for achieving the best contrast between the CT values of NCP and the lumen in the LMA was influenced by age, male sex. Conclusions: The NCP in coronary arteries, CAC, lumen of the LMA, and fat tissue exhibit unique characteristics. When conventional CT rather than spectral CT is used to evaluate the occurrence of NCP, it is necessary to determine the optimal tube voltage based on the age and male sex of the patient, CAC, and lumen of the LMA.

Blooming artifact reduction using different cone-beam computed tomography software to analyze endodontically treated teeth with intracanal posts.

The appearance of high-density root obturating materials, such as gutta-percha and intracanal posts, on cone-beam computed tomography (CBCT) scans is substantially different from that seen in the specimen. This study evaluated the effectiveness of different CBCT software in the reduction of blooming artifacts when examining teeth with intracanal posts. The sample included 42 human single-rooted teeth with two types of posts: G1 - low-fusion alloy posts; G2 - gold alloy posts. CBCT scans were obtained using two scanners, PreXion 3D Elite® and Carestream 9000C 3D®. First, the posts were measured using a digital micrometer (standard reference, control). Post diameters were determined using the Blooming Artifact Reduction (BAR) tool of the e-Vol DX software and of the PreXion3D Image Analysis System. Statistical data were evaluated using the van Der Waerden nonparametric analysis of variance and, after that, normalized data were analyzed using the Tukey test. The level of significance was set at α=5%. There were no significant differences (p>0.05) between the diameters of intracanal posts on the CT scans when the e-Vol DX was used, or when these results were compared with those obtained using a micrometer. There were significant differences in post diameters determined using the PreXion3D Image Analysis System when compared with the e-Vol DX and the micrometer values (p<0.05). The use of the e-Vol DX BAR filter eliminated blooming artifacts. There were no dimensional changes in the CBCT images of the low-fusion and gold alloy intracanal posts using the e-Vol DX BAR filter.

Intratumoral microhemorrhage detection on susceptibility-weighted imaging can help in preoperative differentiation of cerebellopontine angle vestibular schwannomas from meningiomas: Correlation with pathology findings

Objectives: In this study, we aimed to evaluate whether intratumoral microhemorrhage detection on susceptibility-weighted imaging (SWI) could help in preoperative differentiation of cerebellopontine angle (CPA) vestibular schwannomas (VSs) from meningiomas. Patients and Methods: A total of 75 patients (32 males, 43 females; mean age: 45.5±16.7 years; range, 17 to 68 years) consisting of 61 VSs and 14 meningiomas located in the CPA cistern were retrospectively analyzed. All patients underwent contrast-enhanced magnetic resonance imaging (MRI) using the SWI sequence. All images in our study were obtained with a 12-channel phased-array head coil on a 1.5-Tesla clinical scanner. The presence of intratumoral microhemorrhages on SWI sequence was evaluated by demonstrating blooming artifacts as punctate hypointense regions. Both magnitude and phase-contrast images were used to verify microhemorrhages. All patients in our patient cohort underwent surgery and resected tumor specimens were evaluated by pathology. Results: All VS cases in our cohort exhibited multiple hypointense small foci causing blooming artifact on magnitude and processed SWI images. In the meningioma population, typical MRI signal intensity characteristics, including an intense homogenous contrast enhancement, were observed. In all the meningioma cases, except for one, there was no blooming artifact due to intratumoral hemorrhage within the mass lesions on SWI images. In only one meningioma case, SWI revealed hypointense microhemorrhages within the mass lesion. Following surgical procedures and tumor resections, pathology specimens were evaluated and absence or presence of intratumoral microhemorrhages were detected. These results were significantly correlated with the SWI findings. We obtained 100% sensitivity, 92.8% specificity, and 98.6% accuracy in terms of differentiating VSs from meningiomas located in the CPA cistern by using the SWI sequence. Conclusion: Meningiomas and VSs are the two most common masses of the CPA cistern and, in some cases, it seems to be difficult to reach an accurate diagnosis with conventional MRI sequences. The SWI can be helpful to solve this problem by demonstrating whether intratumoral microhemorrhages are present or not within mass lesions and, thus, can help to assume a probable accurate diagnosis prior to surgery

Potential of a New Cone-Beam CT Software for Blooming Artifact Reduction.

This study evaluated the dimensions of intraradicular posts using a new cone beam CT (CBCT) software, and verified the potential of blooming artifact reduction. Sixty-three single-rooted human teeth were shaped, obturated, prepared for intracanal post placement and distributed into three groups: G1: anatomically customized prefabricated glass fiber posts; G2: low-fusion alloy posts; G3: gold alloy posts. After post fabrication and luting with RelyX U200®, specimens were sectioned axially at 9 mm from the root apex, and markings were made on the root surfaces (X-, Y- and Z-axes). The dimensions of the original posts (control group) were measured using a digital micrometer. CBCT scans of the teeth were obtained using a PreXion 3D Elite® scanner. Posts were measured on CBCT scans using DICOM files and the e-Vol DX software. A specific filter, Blooming Artefact Reduction (BAR), was developed to analyze intracanal posts. Statistical data were evaluated using the Van de Waerden nonparametric analysis of variance and, after that, normalized data were analyzed using the Tukey test. The level of significance was set at α = 5%. The measures of the anatomical prefabricated, low-fusion alloy and gold alloy intracanal posts obtained using the e-Vol DX CBCT software and a micrometer were not significantly different (p>0.05). The use of the BAR filter of the e-Vol DX software application did not induce any dimensional differences on CBCT scans of intracanal posts when compared with measurements made with a micrometer on original posts. The use of the BAR filter eliminated blooming artifacts.

Unilateral Nonvisualization of a Transverse Dural Sinus on Phase-Contrast MRV: Frequency and Differentiation from Sinus Thrombosis on Noncontrast MRI.

Unilateral decreased/nonvisualization of a transverse dural sinus on MRV poses a diagnostic dilemma when gadolinium administration is contraindicated. We determined the frequency of unilateral decreased/nonvisualization of the transverse dural sinus and the performance of pregadolinium MR imaging sequences in diagnosing transverse sinus thrombosis in the presence of unilateral decreased/nonvisualization on phase-contrast MRV. We conducted a retrospective review of consecutive 3D phase-contrast MRV (VENC, 30 cm/s) and routine brain imaging (noncontrast sagittal T1, axial T2, FLAIR, DWI, GRE, and postgadolinium 3D-MPRAGE images) performed during a 3-year period for a total of 208 patients. Nonvisualization of a transverse dural sinus was defined as ≥50% nonvisualization of the transverse sinus caliber versus the contralateral side on MRV. Noncontrast imaging findings were considered abnormal when hyperintense signal was present on T2, FLAIR, T1, and DWI, and there were T2* blooming artifacts on GRE and DWI. Postgadolinium 3D-MPRAGE was used to confirm the diagnosis of transverse sinus thrombosis. Nonvisualization of a transverse dural sinus was observed in 72/208 (34.6%) patients on MRV; 56/72 (77.8%) were without transverse sinus thrombosis, and 16/72 (22.2%) patients had transverse dural sinus thrombosis. Nonvisualization of a transverse dural sinus was seen in 56/192 (29.2%) patients without transverse sinus thrombosis and 16/16 (100%) with transverse sinus thrombosis. Abnormal findings on DWI (transverse sinus hyperintense signal or T2* blooming artifact) are 93.8% sensitive and 100.0% specific for transverse sinus thrombosis. Other noncontrast MR imaging sequences ranged from 56.3%-68.8% sensitive and 91.1%-100.0% specific. Nonvisualization of a transverse dural sinus is a frequent phenomenon on phase-contrast MRV. DWI can be effectively used to exclude sinus thrombosis when nonvisualization of a transverse dural sinus is a diagnostic conundrum on phase-contrast MRV and contrast-enhanced studies are contraindicated.

Effect of a calcium deblooming algorithm on accuracy of coronary computed tomography angiography

BackgroundCoronary artery calcification is a significant contributor to reduced accuracy of coronary computed tomographic angiography (CTA) in the assessment of coronary artery disease severity. The aim of the current study is to assess the impact of a prototype calcium deblooming algorithm on the diagnostic accuracy of CTA. Methods40 patients referred for invasive catheter angiography underwent CTA and invasive catheter angiography. The CTA were reconstructed using a standard soft tissue kernel (CTASTAND) and a deblooming algorithm (CTADEBLOOM). CTA studies were read with and without the deblooming algorithm blinded to the invasive coronary angiogram findings. Sensitivity, specificity, accuracy, positive predictive value and negative predictive value for the detection of stenosis ≥50% or ≥70% were evaluated using quantitative coronary angiography as the reference standard. Image quality was assessed using a 5-point scale, and the presence of image artifact recorded. ResultsAll studies were diagnostic with 548 segments available for evaluation. Image score was 3.64 ± 0.72 with CTADEBLOOM, versus 3.56 ± 0.72 with CTASTAND (p = 0.38). CTADEBLOOM had significantly less calcium blooming artifact than CTASTAND (12.5% vs. 47.5%, p = 0.001). Based on a 50% stenosis threshold for defining significant disease, the Sensitivity/Specificity/PPV/NPV/Accuracy were 65.9/84.9/27.6/96.6/83.4 for CTADEBLOOM and 75.0/81.9/26.6/97.4/81.4 for CTASTAND using a ≥50% threshold. CTADEBLOOM specificity was significantly higher than CTASTAND (84.9% vs. 81.5%, p = 0.03), with no difference between the algorithms in sensitivity (p = 0.22), or accuracy (p = 0.15). These results remained unchanged when a stenosis threshold of ≥70% was used. Interobserver agreement was fair with both techniques (CTADEBLOOM k = 0.38, CTASTAND k = 0.37). ConclusionIn this proof of concept study, coronary calcification deblooming using a prototype post-processing algorithm is feasible and reduces calcium blooming with an improvement of the specificity of the CTA exam.

Comparative evaluation of cone beam CT and micro-CT on blooming artifacts in human teeth filled with bioceramic sealers.

To assess blooming artifacts caused by root canal sealers in CBCT images compared with those that appeared in micro-CT scan images used as references. Thirty freshly extracted human mandibular central incisors were used. Root canals were prepared with nickel titanium files with an ISO size 40/0.06 taper and filled with a single cone (40/0.06 taper) and three different sealers. The samples were divided into the following three groups with 10 roots each: (I) AH Plus sealer; (II) Sure Seal Root; and (III) Total BC sealer. Teeth were scanned with the same voxel sizes (0.2mm) in different CBCT devices and the micro-CT images were acquired as reference images. Significantly different results in terms of blooming artifacts were detected between CBCT and micro-CT images, as well as among the CBCTs images. The canals filled with AH Plus sealer showed more blooming artifacts than those filled with bioceramic sealers (p < 0.05). Additionally, the worst blooming artifact was observed when the images were acquired with lower kilovoltage peak. The appearance of blooming artifacts is dependent on sealer and CBCT, and their effects are significantly worse than they are in micro-CT images. The differential effect of different sealers and distinct CBCT protocols should be further investigated to enable the use of bioceramic sealers without a significant impact on post-treatment imaging. Root canal sealers showed a different extent of blooming artifact in CBCT images. Hence, researchers and clinicians should be aware of these artifacts before conducting endodontic evaluations using CBCT images.

Blooming Artifact Reduction in Coronary Artery Calcification by A New De-blooming Algorithm: Initial Study

The aim of this study was to investigate the use of de-blooming algorithm in coronary CT angiography (CCTA) for optimal evaluation of calcified plaques. Calcified plaques were simulated on a coronary vessel phantom and a cardiac motion phantom. Two convolution kernels, standard (STND) and high-definition standard (HD STND), were used for imaging reconstruction. A dedicated de-blooming algorithm was used for imaging processing. We found a smaller bias towards measurement of stenosis using the de-blooming algorithm (STND: bias 24.6% vs 15.0%, range 10.2% to 39.0% vs 4.0% to 25.9%; HD STND: bias 17.9% vs 11.0%, range 8.9% to 30.6% vs 0.5% to 21.5%). With use of de-blooming algorithm, specificity for diagnosing significant stenosis increased from 45.8% to 75.0% (STND), from 62.5% to 83.3% (HD STND); while positive predictive value (PPV) increased from 69.8% to 83.3% (STND), from 76.9% to 88.2% (HD STND). In the patient group, reduction in calcification volume was 48.1 ± 10.3%, reduction in coronary diameter stenosis over calcified plaque was 52.4 ± 24.2%. Our results suggest that the novel de-blooming algorithm could effectively decrease the blooming artifacts caused by coronary calcified plaques, and consequently improve diagnostic accuracy of CCTA in assessing coronary stenosis.

Metal artifact reduction in MRI-based cervical cancer intracavitary brachytherapy

Magnetic resonance imaging (MRI) plays an increasingly important role in brachytherapy planning for cervical cancer. Yet, metal tandem, ovoid intracavitary applicators, and fiducial markers used in brachytherapy cause magnetic susceptibility artifacts in standard MRI. These artifacts may impact the accuracy of brachytherapy treatment and the evaluation of tumor response by misrepresenting the size and location of the metal implant, and distorting the surrounding anatomy and tissue. Metal artifact reduction sequences (MARS) with high bandwidth RF selective excitations and turbo spin-echo readouts were developed for MRI of orthopedic implants. In this study, metal artifact reduction was applied to brachytherapy of cervical cancer using the orthopedic metal artifact reduction (O-MAR) sequence. O-MAR combined MARS features with view angle tilting and slice encoding for metal artifact correction (SEMAC) to minimize in-plane and through-plane susceptibility artifacts. O-MAR improved visualization of the tandem tip on T2 and proton density weighted (PDW) imaging in phantoms and accurately represented the diameter of the tandem. In a pilot group of cervical cancer patients (N = 7), O-MAR significantly minimized the blooming artifact at the tip of the tandem in PDW MRI. There was no significant difference observed in artifact reduction between the weak (5 kHz, 7 z-phase encodes) and medium (10 kHz, 13 z-phase encodes) SEMAC settings. However, the weak setting allowed a significantly shorter acquisition time than the medium setting. O-MAR also reduced susceptibility artifacts associated with metal fiducial markers so that they appeared on MRI at their true dimensions.

Intracranial Posterior Circulation Large Artery Thrombi Visualized Using Susceptibility-Weighted MRI.

To identify thrombi in patients with posterior circulation large artery occlusion using susceptibility-weighted magnetic resonance imaging (MRI). All patients hospitalized with intracranial posterior circulation occlusion from January 2003 to September 2013 were included. MRI and computed tomography angiography were reviewed to determine the presence of arterial occlusion and identify thrombi. Eighty-one patients were analyzed to investigate susceptibility vessel sign (SVS) that was identified as blooming artifact (BA) on T2*-weighted gradient echo imaging. We identified 21 of 63 (33.3%) patients with BA in symptomatic patients, and 1 of 18 (5.6%) in the asymptomatic group with significant difference (P = .019). BAs were found in 6 of 10 (60.0%) patients with cardioembolism, 5 of 13 (38.5%) with dissection, 9 of 34 (26.5%) with large artery atherosclerotic disease, and 1 of 6 (16.7%) with undetermined cause. Identifying SVS may be useful in exploring the fresh thrombi and the mechanism of posterior circulation stroke.

Extensive blooming artifact predicts no recanalization after intravenous thrombolysis.

Hemosiderin exhibits a stronger T2 shortening effect than deoxyhemoglobin. The extent of the 'blooming artifact' may therefore reflect a composition of different iron forms. Our aim was to investigate the relationship between extent of susceptibility vessel sign (SVS) width beyond the lumen and middle cerebral artery (MCA) recanalization. Clinical and imaging data from consecutive acute ischaemic stroke patients with MCA occlusion who underwent susceptibility-weighted imaging (SWI) before intravenous thrombolysis were examined. The source images of magnitude and angiography were used to obtain the width of SVS and MCA at the interface, respectively. The presence of MCA SVS was observed in 64 patients on initial SWI scans and recanalization was observed in 30 (46.9%) patients. The overestimation ratio of thrombus width on SWI was an acceptable predictor for no recanalization [odds ratio 1.360 per 0.1; 95% confidence interval (CI) 1.093-1.691; P = 0.006]. The optimal cut-off point was identified at 1.943, and this yielded a sensitivity of 67.6% and a specificity of 86.7%. Extensive blooming artifact, defined as overestimation ratio ≥2, independently predicted no recanalization (odds ratio 9.687, 95% CI 1.974-47.545; P = 0.005) and unfavorable outcome (odds ratio 4.916, 95% CI 1.049-23.051; P = 0.043). The extent of SVS width beyond the lumen might reflect the content of hemosiderin. An extreme overestimation ratio might indicate aged thrombus, which may be resistant to thrombolysis.

Thrombus Characteristics Are Related to Collaterals and Angioarchitecture in Acute Stroke

We have theorized that clots with stasis are longer. We therefore explored the relationship between thrombus imaging characteristics on noncontrast computed tomography (NCCT) and magnetic resonance imaging (MRI) with clot length and pial collaterals on baseline computed tomography angiography (CTA). Prospective study of acute ischemic stroke patients (2005-2009) from Keimyung University. Patients with known stroke symptom onset time, baseline CTA, MRI, and with M1-Middle Cerebral Artery (MCA)±intracranial internal carotid artery (ICA) occlusions were included. Clot length and pial collaterals were measured on baseline CTA. A total of 104 patients (mean age 65.1±12.28 years, 56.7% male, median baseline National Institutes of Health Stroke Scale 13) with intracranial ICA + MCA (n=50) or isolated M1-MCA (n=54) occlusions were included. Hyperdense sign on NCCT had a median clot length of 42.3 mm versus 29.5 mm when hyperdense negative (p=0.02). Clots showing blooming artifact on gradient recall echo MRI had a median length of 39.1 mm versus 24.5 mm without blooming (p=0.005). Patients with poor baseline collaterals on CTA had longer clots than those with intermediate/good collaterals (median clot length 49.4 mm vs 34.9 mm vs 20.5 mm respectively, p<0.001). In censored logistic regression modeling, clot length was an independent predictor of hyperdense sign (p=0.05) and of the presence of blooming artifact (p=0.006). Clot length and baseline collateral status are independent predictors of clot hyperdensity on NCCT and blooming artifact on gradient recall echo. Longer clots are more likely to be hyperdense and to bloom more, probably because portions of these clots are freshly formed locally due to of stasis of blood around the original clot. This stasis could be because of poor collaterals and inefficient angio-architecture within the cerebral arterial tree.

Optimizing Image Contrast Display Improves Quantitative Stenosis Measurement in Heavily Calcified Coronary Arterial Segments on Coronary CT Angiography: A Proof-of-Concept and Comparison to Quantitative Invasive Coronary Angiography

Blooming artifact from calcified plaques often renders measurement of stenosis impossible on coronary computed tomographic angiography (CTA). We sought to evaluate the impact of modifying window level on reducing blooming artifact, and its impact on stenosis quantification. We analyzed 125 calcified segments from 53 patients who underwent CTA and invasive coronary angiography (ICA). Segmental stenosis on CTA was measured using three window settings: width of 1000 Hounsfield units (HU) and level of 200 HU ("default"), 1500/200 HU ("widened"), and width and level based on the mean HU of the calcified plaque and pericoronary fat ("calcium-specific"). Segmental stenosis on ICA was quantified by a blinded experienced reader. ICA found ≥50% stenosis in 30 segments. Displaying segments with widened and calcium-specific settings improved overall accuracy of detecting ≥50% stenosis (P's < 0.001) by increasing the rate of accurately quantifying <50% stenosis (P's < 0.001), and improved correlation of stenosis quantification to ICA (P's < 0.05). There was no difference in stenosis quantification accuracy between widened and calcium-specific window settings. Limits of agreement between CTA stenosis quantification and ICA narrowed with widened and calcium-specific settings. We showed for the first time that in calcified segments, widening display window width significantly improved CTA quantification of stenosis compared to ICA.

CT and MRI Early Vessel Signs Reflect Clot Composition in Acute Stroke

The purpose of this study was to provide the first correlative study of the hyperdense middle cerebral artery sign (HMCAS) and gradient-echo MRI blooming artifact (BA) with pathology of retrieved thrombi in acute ischemic stroke. Noncontrast CT and gradient-echo MRI studies before mechanical thrombectomy in 50 consecutive cases of acute middle cerebral artery ischemic stroke were reviewed blinded to clinical and pathology data. Occlusions retrieved by thrombectomy underwent histopathologic analysis, including automated quantitative and qualitative rating of proportion composed of red blood cells (RBCs), white blood cells, and fibrin on microscopy of sectioned thrombi. Among 50 patients, mean age was 66 years and 48% were female. Mean (SD) proportion was 61% (±21) fibrin, 34% (±21) RBCs, and 4% (±2) white blood cells. Of retrieved clots, 22 (44%) were fibrin-dominant, 13 (26%) RBC-dominant, and 15 (30%) mixed. HMCAS was identified in 10 of 20 middle cerebral artery stroke cases with CT with mean Hounsfield Unit density of 61 (±8 SD). BA occurred in 17 of 32 with gradient-echo MRI. HMCAS was more commonly seen with RBC-dominant and mixed than fibrin-dominant clots (100% versus 67% versus 20%, P=0.016). Mean percent RBC composition was higher in clots associated with HMCAS (47% versus 22%, P=0.016). BA was more common in RBC-dominant and mixed clots compared with fibrin-dominant clots (100% versus 63% versus 25%, P=0.002). Mean percent RBC was greater with BA (42% versus 23%, P=0.011). CT HMCAS and gradient-echo MRI BA reflect pathology of occlusive thrombus. RBC content determines appearance of HMCAS and BA, whereas absence of HMCAS or BA may indicate fibrin-predominant occlusive thrombi.