Image Quality of Virtual Monochromatic Reconstructions of Noncontrast CT on a Dual-Source CT Scanner in Adult Patients

Rationale and Objectives To evaluate the image quality of virtual monochromatic images (VMI) reconstructed from dual-energy dual-source noncontrast head CT with different reconstruction kernels. Materials and Methods Twenty-five consecutive adult patients underwent noncontrast dual-energy CT. VMI were retrospectively reconstructed at 5-keV increments from 40 to 140 keV using quantitative and head kernels. CT-number, noise levels (SD), signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) in the gray and white matter and artifacts using the posterior fossa artifact index (PFAI) were evaluated. Results CT-number increased with decreasing VMI energy levels, and SD was lowest at 85 keV. SNR was maximized at 80 keV and 85 keV for the head and quantitative kernels, respectively. CNR was maximum at 40 keV; PFAI was lowest at 90 (head kernel) and 100 (quantitative kernel) keV. Optimal VMI image quality was significantly better than conventional CT. Conclusion Optimal image quality of VMI energies can improve brain parenchymal image quality compared to conventional CT but are reconstruction kernel dependent and depend on indication for performing noncontrast CT

Virtual monochromatic dual-energy CT reconstructions improve detection of cerebral infarct in patients with suspicion of stroke

Purpose: Early infarcts are hard to diagnose on non-contrast head CT. Dual-energy CT (DECT) may potentially increase infarct differentiation. The optimal DECT settings for differentiation were identified and evaluated. Methods: One hundred and twenty-five consecutive patients who presented with suspected acute ischemic stroke (AIS) and underwent non-contrast DECT and subsequent DWI were retrospectively identified. The DWI was used as reference standard. First, virtual monochromatic images (VMI) of 25 patients were reconstructed from 40 to 140 keV and scored by two readers for acute infarct. Sensitivity, specificity, positive, and negative predictive values for infarct detection were compared and a subset of VMI energies were selected. Next, for a separate larger cohort of 100 suspected AIS patients, conventional non-contrast CT (NCT) and selected VMI were scored by two readers for the presence and location of infarct. The same statistics for infarct detection were calculated. Infarct location match was compared per vascular territory. Subgroup analyses were dichotomized by time from last-seen-well to CT imaging. Results: A total of 80–90 keV VMI were marginally more sensitive (36.3–37.3%) than NCT (32.4%; p > 0.680), with marginally higher specificity (92.2–94.4 vs 91.1%; p > 0.509) for infarct detection. Location match was superior for VMI compared with NCT (28.7–27.4 vs 19.5%; p < 0.010). Within 4.5 h from last-seen-well, 80 keV VMI more accurately detected infarct (58.0 vs 54.0%) and localized infarcts (27.1 vs 11.9%; p = 0.004) than NCT, whereas after 4.5 h, 90 keV VMI was more accurate (69.3 vs 66.3%). Conclusion: Non-contrast 80–90 keV VMI best differentiates normal from infarcted brain parenchyma

Non-contrast dual-energy CT virtual ischemia maps accurately estimate ischemic core size in large-vessel occlusive stroke

Dual-energy CT (DECT) material decomposition techniques may better detect edema within cerebral infarcts than conventional non-contrast CT (NCCT). This study compared if Virtual Ischemia Maps (VIM) derived from non-contrast DECT of patients with acute ischemic stroke due to large-vessel occlusion (AIS-LVO) are superior to NCCT for ischemic core estimation, compared against reference-standard DWI-MRI. Only patients whose baseline ischemic core was most likely to remain stable on follow-up MRI were included, defined as those with excellent post-thrombectomy revascularization or no perfusion mismatch. Twenty-four consecutive AIS-LVO patients with baseline non-contrast DECT, CT perfusion (CTP), and DWI-MRI were analyzed. The primary outcome measure was agreement between volumetric manually segmented VIM, NCCT, and automatically segmented CTP estimates of the ischemic core relative to manually segmented DWI volumes. Volume agreement was assessed using Bland–Altman plots and comparison of CT to DWI volume ratios. DWI volumes were better approximated by VIM than NCCT (VIM/DWI ratio 0.68 ± 0.35 vs. NCCT/DWI ratio 0.34 ± 0.35; P < 0.001) or CTP (CTP/DWI ratio 0.45 ± 0.67; P < 0.001), and VIM best correlated with DWI (r VIM = 0.90; r NCCT = 0.75; r CTP = 0.77; P < 0.001). Bland–Altman analyses indicated significantly greater agreement between DWI and VIM than NCCT core volumes (mean bias 0.60 [95%AI 0.39–0.82] vs. 0.20 [95%AI 0.11–0.30]). We conclude that DECT VIM estimates the ischemic core in AIS-LVO patients more accurately than NCCT

MRI-based inter- and intrafraction motion analysis of the pancreatic tail and spleen as preparation for adaptive MRI-guided radiotherapy in neuroblastoma

BACKGROUND: In pediatric radiotherapy treatment planning of abdominal tumors, dose constraints to the pancreatic tail/spleen are applied to reduce late toxicity. In this study, an analysis of inter- and intrafraction motion of the pancreatic tail/spleen is performed to estimate the potential benefits of online MRI-guided radiotherapy (MRgRT). MATERIALS AND METHODS: Ten randomly selected neuroblastoma patients (median age: 3.4 years), irradiated with intensity-modulated arc therapy at our department (prescription dose: 21.6/1.8 Gy), were retrospectively evaluated for inter- and intrafraction motion of the pancreatic tail/spleen. Three follow-up MRIs (T2- and T1-weighted ± gadolinium) were rigidly registered to a planning CT (pCT), on the vertebrae around the target volume. The pancreatic tail/spleen were delineated on all MRIs and pCT. Interfraction motion was defined as a center of gravity change between pCT and T2-weighted images in left-right (LR), anterior-posterior (AP) and cranial-caudal (CC) direction. For intrafraction motion analysis, organ position on T1-weighted ± gadolinium was compared to T2-weighted. The clinical radiation plan was used to estimate the dose received by the pancreatic tail/spleen for each position. RESULTS: The median (IQR) interfraction motion was minimal in LR/AP, and largest in CC direction; pancreatic tail 2.5 mm (8.9), and spleen 0.9 mm (3.9). Intrafraction motion was smaller, but showed a similar motion pattern (pancreatic tail, CC: 0.4 mm (1.6); spleen, CC: 0.9 mm (2.8)). The differences of Dmean associated with inter- and intrafraction motions ranged from - 3.5 to 5.8 Gy for the pancreatic tail and - 1.2 to 3.0 Gy for the spleen. In 6 out of 10 patients, movements of the pancreatic tail and spleen were highlighted as potentially clinically significant because of ≥ 1 Gy dose constraint violation. CONCLUSION: Inter- and intrafraction organ motion results into unexpected constrain violations in 60% of a randomly selected neuroblastoma cohort, supporting further prospective exploration of MRgRT

Detection of Cardioembolic Sources With Nongated Cardiac Computed Tomography Angiography in Acute Stroke: Results From the ENCLOSE Study

BACKGROUND: Identifying cardioembolic sources in patients with acute ischemic stroke is important for the choice of secondary prevention strategies. We prospectively investigated the yield of admission (spectral) nongated cardiac computed tomography angiography (CTA) to detect cardioembolic sources in stroke. METHODS: Participants of the ENCLOSE study (Improved Prediction of Recurrent Stroke and Detection of Small Volume Stroke) with transient ischemic attack or acute ischemic stroke with assessable nongated head-to-heart CTA at the University Medical Center Utrecht were included between June 2017 and March 2022. The presence of cardiac thrombus on cardiac CTA was based on a Likert scale and dichotomized into certainly or probably absent versus possibly, probably, or certainly present. The diagnostic certainty of cardiac thrombus was evaluated again on spectral computed tomography reconstructions. The likelihood of a cardioembolic source was determined post hoc by an expert panel in patients with cardiac thrombus on CTA. Parametric and nonparametric tests were used to compare the outcome groups. RESULTS: Forty four (12%) of 370 included patients had a cardiac thrombus on admission CTA: 35 (9%) in the left atrial appendage and 14 (4%) in the left ventricle. Patients with cardiac thrombus had more severe strokes (median National Institutes of Health Stroke Scale score, 10 versus 4; P=0.006), had higher clot burden (median clot burden score, 9 versus 10; P=0.004), and underwent endovascular treatment more often (43% versus 20%; P<0.001) than patients without cardiac thrombus. Left atrial appendage thrombus was present in 28% and 6% of the patients with and without atrial fibrillation, respectively ( P<0.001). The diagnostic certainty for left atrial appendage thrombus was higher for spectral iodine maps compared with the conventional CTA ( P<0.001). The presence of cardiac thrombus on CTA increased the likelihood of a cardioembolic source according to the expert panel ( P<0.001). CONCLUSIONS: Extending the stroke CTA to cover the heart increases the chance of detecting cardiac thrombi and helps to identify cardioembolic sources in the acute stage of ischemic stroke with more certainty. Spectral iodine maps provide additional value for detecting left atrial appendage thrombus. REGISTRATION: URL: https://www. CLINICALTRIALS: gov; Unique identifier: NCT04019483

Dual-energy CT and CT perfusion for improved CT stroke imaging

CT is often used as the modality of choice for the diagnosis of patients with suspicion of stroke. CT imaging allows visualization of occluded blood vessels and identification of location and volume of the infarction. Current CT technological innovations are aimed at increasing the diagnostic image quality, increasing the predictive value and quantitative accuracy of CT, and reducing the radiation dose. Modern CT techniques include CT perfusion (CTP) for infarct assessment and dual-energy CT (DECT) for improved tissue characterization. The goal of this thesis was to improve the diagnostic performance for infarct detection using novel DECT and improve CTP analysis with DECT and high-resolution CTP. In part one of this thesis, we showed that dual-layer detector CT, using a 120 kVp tube potential, can be routinely used in daily clinical practice to provide additional information without increasing radiation dose when compared with a conventional single-layer detector CT scanner. We also found that the image quality of conventional CT images acquired on a dual-layer CT scanner is similar to its counterpart on a conventional CT scanner for medium-sized phantoms, and slightly lower for (very) large phantoms at lower tube voltages. Next, we found that non-contrast DECT virtual monochromatic images (VMI) significantly improves the image quality of non-contrast brain CTs compared with conventional CT. In part two, we found that non-contrast head VMI at 80–90 keV more accurately detected and localized infarcts compared with conventional CT. Next, we found that virtual ischemia maps from non-contrast brain CT were more accurate than conventional CT in approximating infarct core volumes and the infarct location. This suggests that DECT more accurately differentiates between infarcted and healthy tissue than conventional CT. In addition, the added value of dual-energy VMI CTP scans to the quality of the perfusion maps was shown. We found that the image quality and visual quality of 50 keV CT perfusion maps is superior to that of conventional 80 and 120 kVp images. In part three, we found that increasing the acquisition interval may introduce a bias in the perfusion parameters, but this bias can be corrected by calibration of the perfusion maps and therefore still allow distinction between healthy and infarcted tissue. Infarct volumes can likewise be influenced by the acquisition interval, but visual inspection indicated minor differences in infarct volumes between acquisition intervals. For a commercial block-circulant singular value decomposition (bSVD) perfusion analysis package acquisition intervals up to 4 seconds could be achieved, and for a non-commercial bSVD and a non-linear regression model-based method intervals up to 5 seconds. We also shown the ability of thin-slice CTP to detect small-volume infarctions by noise reduction using two bilateral filters. We found that perfusion values are estimated more accurately and with higher contrast using guided bilateral filtering compared with time-intensity profile similarity (TIPS) bilateral filtering on thin-slice CTP. While the detection of small-volume infarctions remains difficult, infarcts could be detected with higher sensitivity and significantly higher diagnostic certainty and improved image quality using guided bilateral filtering than with the current state-of-the-art TIPS filter

Dual-energy CT and CT perfusion for improved CT stroke imaging

CT is often used as the modality of choice for the diagnosis of patients with suspicion of stroke. CT imaging allows visualization of occluded blood vessels and identification of location and volume of the infarction. Current CT technological innovations are aimed at increasing the diagnostic image quality, increasing the predictive value and quantitative accuracy of CT, and reducing the radiation dose. Modern CT techniques include CT perfusion (CTP) for infarct assessment and dual-energy CT (DECT) for improved tissue characterization. The goal of this thesis was to improve the diagnostic performance for infarct detection using novel DECT and improve CTP analysis with DECT and high-resolution CTP. In part one of this thesis, we showed that dual-layer detector CT, using a 120 kVp tube potential, can be routinely used in daily clinical practice to provide additional information without increasing radiation dose when compared with a conventional single-layer detector CT scanner. We also found that the image quality of conventional CT images acquired on a dual-layer CT scanner is similar to its counterpart on a conventional CT scanner for medium-sized phantoms, and slightly lower for (very) large phantoms at lower tube voltages. Next, we found that non-contrast DECT virtual monochromatic images (VMI) significantly improves the image quality of non-contrast brain CTs compared with conventional CT. In part two, we found that non-contrast head VMI at 80–90 keV more accurately detected and localized infarcts compared with conventional CT. Next, we found that virtual ischemia maps from non-contrast brain CT were more accurate than conventional CT in approximating infarct core volumes and the infarct location. This suggests that DECT more accurately differentiates between infarcted and healthy tissue than conventional CT. In addition, the added value of dual-energy VMI CTP scans to the quality of the perfusion maps was shown. We found that the image quality and visual quality of 50 keV CT perfusion maps is superior to that of conventional 80 and 120 kVp images. In part three, we found that increasing the acquisition interval may introduce a bias in the perfusion parameters, but this bias can be corrected by calibration of the perfusion maps and therefore still allow distinction between healthy and infarcted tissue. Infarct volumes can likewise be influenced by the acquisition interval, but visual inspection indicated minor differences in infarct volumes between acquisition intervals. For a commercial block-circulant singular value decomposition (bSVD) perfusion analysis package acquisition intervals up to 4 seconds could be achieved, and for a non-commercial bSVD and a non-linear regression model-based method intervals up to 5 seconds. We also shown the ability of thin-slice CTP to detect small-volume infarctions by noise reduction using two bilateral filters. We found that perfusion values are estimated more accurately and with higher contrast using guided bilateral filtering compared with time-intensity profile similarity (TIPS) bilateral filtering on thin-slice CTP. While the detection of small-volume infarctions remains difficult, infarcts could be detected with higher sensitivity and significantly higher diagnostic certainty and improved image quality using guided bilateral filtering than with the current state-of-the-art TIPS filter

Improving the Quality of Cerebral Perfusion Maps With Monoenergetic Dual-Energy Computed Tomography Reconstructions

OBJECTIVE: We compared 40- to 70-keV virtual monoenergetic to conventional computed tomography (CT) perfusion reconstructions with respect to quality of perfusion maps. METHODS: Conventional CT perfusion (CTP) images were acquired at 80 kVp in 25 patients, and 40- to 70-keV images were acquired with a dual-layer CT at 120 kVp in 25 patients. First, time-attenuation-curve contrast-to-noise ratio was assessed. Second, the perfusion maps of both groups were qualitatively analyzed by observers. Last, the monoenergetic reconstruction with the highest quality was compared with the clinical standard 80-kVp CTP acquisitions. RESULTS: Contrast-to-noise ratio was significantly better for 40 to 60 keV as compared with 70 keV and conventional images (P < 0.001). Visually, the difference between the blood volume maps among reconstructions was minimal. The 50-keV perfusion maps had the highest quality compared with the other monoenergetic and conventional maps (P < 0.002). CONCLUSIONS: The quality of 50-keV CTP images is superior to the quality of conventional 80- and 120-kVp images

Fully automated quantification method (FQM) of coronary calcium in an anthropomorphic phantom

Objective: Coronary artery calcium (CAC) score is a strong predictor for future adverse cardiovascular events. Anthropomorphic phantoms are often used for CAC studies on computed tomography (CT) to allow for evaluation or variation of scanning or reconstruction parameters within or across scanners against a reference standard. This often results in large number of datasets. Manual assessment of these large datasets is time consuming and cumbersome. Therefore, this study aimed to develop and validate a fully automated, open-source quantification method (FQM) for coronary calcium in a standardized phantom. Materials and Methods: A standard, commercially available anthropomorphic thorax phantom was used with an insert containing nine calcifications with different sizes and densities. To simulate two different patient sizes, an extension ring was used. Image data were acquired with four state-of-the-art CT systems using routine CAC scoring acquisition protocols. For interscan variability, each acquisition was repeated five times with small translations and/or rotations. Vendor-specific CAC scores (Agatston, volume, and mass) were calculated as reference scores using vendor-specific software. Both the international standard CAC quantification methods as well as vendor-specific adjustments were implemented in FQM. Reference and FQM scores were compared using Bland-Altman analysis, intraclass correlation coefficients, risk reclassifications, and Cohen’s kappa. Also, robustness of FQM was assessed using varied acquisitions and reconstruction settings and validation on a dynamic phantom. Further, image quality metrics were implemented: noise power spectrum, task transfer function, and contrast- and signal-to-noise ratio among others. Results were validated using imQuest software. Results: Three parameters in CAC scoring methods varied among the different vendor-specific software packages: the Hounsfield unit (HU) threshold, the minimum area used to designate a group of voxels as calcium, and the usage of isotropic voxels for the volume score. The FQM was in high agreement with vendor-specific scores and ICC’s (median [95% CI]) were excellent (1.000 [0.999-1.000] to 1.000 [1.000-1.000]). An excellent interplatform reliability of κ = 0.969 and κ = 0.973 was found. TTF results gave a maximum deviation of 3.8% and NPS results were comparable to imQuest. Conclusions: We developed a fully automated, open-source, robust method to quantify CAC on CT scans in a commercially available phantom. Also, the automated algorithm contains image quality assessment for fast comparison of differences in acquisition and reconstruction parameters.</p

Computed Tomography Perfusion Data for Acute Ischemic Stroke Evaluation Using Rapid Software : Pitfalls of Automated Postprocessing

Computed tomography perfusion (CTP) is increasingly used to determine treatment eligibility for acute ischemic stroke patients. Automated postprocessing of raw CTP data is routinely used, but it can fail. In reviewing 176 consecutive acute ischemic stroke patients, failures occurred in 20 patients (11%) during automated postprocessing by the RAPID software. Failures were caused by motion (n = 11, 73%), streak artifacts (n = 2, 13%), and poor contrast bolus arrival (n = 2, 13%). Stroke physicians should review CTP results with care before they are being integrated in their decision-making process