Nuran Abdullayev

Improvement of Image Quality in Unenhanced Dual-Layer CT of the Head Using Virtual Monoenergetic Images Compared With Polyenergetic Single-Energy CT

Objectives The aims of this study were to compare virtual monoenergetic images and polyenergetic images reconstructed from unenhanced dual-layer detector computed tomography (DLCT) of the head and to determine kiloelectron volt levels that optimize image quality, particularly the gray-white matter contrast, and reduce beam hardening artifacts caused by the skull. Materials and Methods Institutional review board approval was obtained. Forty patients that received DLCT were included in this retrospective study; of these patients, 22 were women and 18 were men. The average age was 61.5 ± 14.3 years. Virtual monoenergetic images were reconstructed from spectral base images at 40 keV to 120 keV. To calculate signal-to-noise ratio and contrast-to-noise ratio, attenuation and standard deviation of supratentorial gray and white matter were measured in virtual monoenergetic and polyenergetic images. Beam hardening artifacts were detected close to the calvarium and in the posterior fossa. Two radiologists rated the assessment of gray-white matter differentiation and of the subcalvarial space, as well as the artifacts caused by the skull and image noise. Student t test and Wilcoxon test were used to determine significance. Results Compared with polyenergetic images, superior signal-to-noise ratio and superior contrast-to-noise ratio of gray and white matter were observed in virtual monoenergetic images at low kiloelectron volt levels (P < 0.0001). Subcalvarial artifacts were significantly lower at 120 keV (P < 0.02). Artifacts measured in the posterior fossa were generally lower at high kiloelectron volt levels; however, no statistical significance was detected. Virtual monoenergetic images were rated superior to polyenergetic images in regard to all 4 criteria (P < 0.0001). The observers reported an optimal radiological assessment of gray-white matter differentiation at 65 keV and optimal assessment of subcalvarial space at 120 keV. Conclusions In comparison to polyenergetic images, virtual monoenergetic images reconstructed from unenhanced DLCT of the head at 65 keV and 120 keV allow to optimize gray-white matter contrast and reduce beam hardening artifacts caused by the skull, respectively.

Metal artifact reduction by dual-layer computed tomography using virtual monoenergetic images

OBJECTIVE The aim of the study was to investigate the performance and diagnostic value of metal artifact reduction in virtual monoenergetic images generated from dual-layer computed tomography (DLCT). METHODS 35 patients that received a DLCT at the University Hospital Cologne and had an orthopedic implant in the examined region were included in this study. For each DLCT virtual monoenergetic images of different energy levels (64keV, 70keV, 105keV, 140keV, 200keV and an optimized photon energy) were reconstructed and analyzed by three blinded observers. Images were analyzed with regard to subjective criteria (extent of artifacts, diagnostic image quality) and objective criteria (width and density of artifacts). RESULTS 21 patients had implants in the spine, 8 in the pelvis and 6 patients in the extremities. Diagnostic image quality improved significantly at high photon energies from a Likert-score of 4.3 (±0.83) to 2.3 (±1.02) and artifacts decreased significantly from a score of 4.3 (±0.66) to 2.6 (±2.57). The average optimized photon energy was 149.2±39.4keV. The density as well as the width of the most pronounced artifacts decreased from-374.6±251.89HU to -12.5±205.84HU and from 14.5±8.74mm to 6.4±10.76mm, respectively. CONCLUSION Using virtual monoenergetic images valuable improvements of diagnostic image quality can be achieved by reduction of artifacts associated with metal implants. As preset for virtual monoenergetic images, 140keV appear to provide optimal artifact reduction. In 20% of the patients, individually optimized keV can lead to a further improvement of image quality compared to 140keV.

Comparison of virtual monoenergetic and polyenergetic images reconstructed from dual-layer detector CT angiography of the head and neck

ObjectivesTo compare the image quality of virtual monoenergetic images and polyenergetic images reconstructed from dual-layer detector CT angiography (DLCTA).MethodsThirty patients who underwent DLCTA of the head and neck were retrospectively identified and polyenergetic as well as virtual monoenergetic images (40 to 120 keV) were reconstructed. Signals (± SD) of the cervical and cerebral vessels as well as lateral pterygoid muscle and the air surrounding the head were measured to calculate the CNR and SNR. In addition, subjective image quality was assessed using a 5-point Likert scale. Students t-test and Wilcoxon test were used to determine statistical significance.ResultsCompared to polyenergetic images, although noise increased with lower keV, CNR (p < 0.02) and SNR (p > 0.05) of the cervical, petrous and intracranial vessels were improved in virtual monoenergetic images at 40 keV and virtual monoenergetic images at 45 keV were also rated superior regarding vascular contrast, assessment of arteries close to the skull base and small arterial branches (p < 0.0001 each).ConclusionsCompared to polyenergetic images, virtual monoenergetic images reconstructed from DLCTA at low keV ranging from 40 to 45 keV improve the objective and subjective image quality of extra- and intracranial vessels and facilitate assessment of vessels close to the skull base and of small arterial branches.Key points• Virtual monoenergetic images greatly improve attenuation, while noise only slightly increases.• Virtual monoenergetic images show superior contrast-to-noise ratios compared to polyenergetic images.• Virtual monoenergetic images significantly improve image quality at low keV.

CT metal artifacts in patients with total hip replacements: for artifact reduction monoenergetic reconstructions and post-processing algorithms are both efficient but not similar

ObjectivesThis study compares metal artifact (MA) reduction in imaging of total hip replacements (THR) using virtual monoenergetic images (VMI), for MA-reduction-specialized reconstructions (MAR) and conventional CT images (CI) from detector-based dual-energy computed tomography (SDCT).MethodsTwenty-seven SDCT-datasets of patients carrying THR were included. CI, MAR and VMI with different energy-levels (60–200 keV) were reconstructed from the same scans. MA width was measured. Attenuation (HU), noise (SD) and contrast-to-noise ratio (CNR) were determined in: extinction artifact, adjacent bone, muscle and bladder. Two radiologists assessed MA-reduction and image quality visually.ResultsIn comparison to CI, VMI (200 keV) and MAR showed a strong artifact reduction (MA width: CI 29.9±6.8 mm, VMI 17.6±13.6 mm, p<0.001; MAR 16.5±14.9 mm, p<0.001; MA density: CI -412.1±204.5 HU, VMI -279.7±283.7 HU; p<0.01; MAR -116.74±105.6 HU, p<0.001). In strong artifacts reduction was superior by MAR. In moderate artifacts VMI was more effective. MAR showed best noise reduction and CNR in bladder and muscle (p<0.05), whereas VMI were superior for depiction of bone (p<0.05). Visual assessment confirmed that VMI and MAR improve artifact reduction and image quality (p<0.001).ConclusionsMAR and VMI (200 keV) yielded significant MA reduction. Each showed distinct advantages both regarding effectiveness of artifact reduction, MAR regarding assessment of soft tissue and VMI regarding assessment of bone.Key Points• Spectral-detector computed tomography improves assessment of total hip replacements and surrounding tissue.• Virtual monoenergetic images and MAR reduce metal artifacts and enhance image quality.• Evaluation of bone, muscle and pelvic organs can be improved by SDCT.

Carotid Artery Stenosis Contralateral to Intracranial Large Vessel Occlusion: An Independent Predictor of Unfavorable Clinical Outcome after Mechanical Thrombectomy

Background: Clinical outcome in patients undergoing mechanical thrombectomy (MT) due to intracranial large vessel occlusion (LVO) in the anterior circulation is influenced by several factors. The impact of a concomitant extracranial carotid artery stenosis (CCAS) contralateral to the intracranial lesion remains unclear. Methods: Retrospective analysis of 392 consecutive patients treated with MT due to intracranial LVO in the anterior circulation in two comprehensive stroke centers between 2014 and 2017. Clinical (including demographics and NIHSS), imaging (including angiographic evaluation of CCAS via NASCET criteria), and procedural data were evaluated. Primary endpoint was an unfavorable clinical outcome defined as modified Rankin Scale 3–6 at 90 days. Results: In 27/392 patients (7%) pre-interventional imaging exhibited a CCAS (>50%) contralateral to the intracranial lesion compared to 365 patients without relevant stenosis. Median baseline NIHSS, procedural timings, and reperfusion success did not differ between groups. Median volume of the final infarct core was larger in CCAS patients (176 cm3, IQR 32-213 vs. 11 cm3, 1-65; p < 0.001). At 90 days, unfavorable outcome was documented in 25/27 CCAS patients (93%) vs. 211/326 (65%; p = 0.003) with a mortality of 63 vs. 19% (p = 0.001), respectively. Presence of CCAS was associated with an unfavorable outcome at 90 days independent of age and baseline NIHSS in multivariate logistic regression (OR 2.2, CI 1.1-4.7; p < 0.05). Conclusion: For patients undergoing MT due to intracranial vessel occlusion in the anterior circulation, the presence of a contralateral CCAS >50% is a predictor of unfavorable clinical outcome at 90 days.

Bone marrow edema in traumatic vertebral compression fractures: Diagnostic accuracy of dual-layer detector CT using calcium suppressed images

PURPOSE To evaluate calcium suppressed images (CaSupp) in dual-layer detector computed tomography (DLCT) for the detection of bone marrow edema (BME) in vertebral fractures. MATERIALS AND METHODS The retrospective study was approved by the institutional review board. 34 patients with synchronous DLCT and MRI, who were diagnosed with one or more acute vertebral fractures, were included. MRI were systematically analyzed as reference standard. Two blinded and independent readers evaluated CaSupp for vertebral BME. Additionally, both readers determined the optimal calcium suppression indices (CaSupp-I) for visualization of BME in consensus and correlated the CaSupp-I with parallel measurement of trabecular density as surrogate parameter for bone mineral density. ROI-based measurements of the contrast-to-noise ratios (CNR) were also conducted. Interrater agreement was determined by kappa-statistics. CNR were analyzed using Wilcoxon signed rank test. RESULTS Fifty-seven acute fractured vertebrae out of 383 vertebrae (14.9%) were found. CaSupp yielded an average sensitivity of 87% and specificity of 99%, a positive predictive value of 95%, a negative predictive value of 98% and an accuracy of 97% for the detection of fracture-associated edema. Interrater agreement was excellent (kappa 0.91). Increase in CNR of BME correlated with increasing CaSupp-I. Edema adjacent to the cortical endplates was better visualized using CaSupp-I of 70 and 80, while extensive edema was better visualized using a CaSupp-I of 90 and 100 (chi2 < 0.0001). No correlation between optimal CaSupp-I and trabecular density was found (p > 0.2). CONCLUSION CaSupp reconstructed from DLCT enable visualization and detection of BME in traumatic fractured vertebrae with high diagnostic accuracy using CaSupp-I of 70-100.

Artifact reduction from dental implants using virtual monoenergetic reconstructions from novel spectral detector CT

OBJECTIVES Image quality in head and neck imaging is often severely hampered by artifacts arising from dental implants. This study evaluates metal artifact (MA) reduction using virtual monoenergetic images (VMI) compared to conventional CT images (CI) from spectral-detector computed tomography (SDCT). METHODS 38 consecutive patients with dental implants were included in this retrospective study. All examinations were performed using a SDCT (IQon, Philips, Best, The Netherlands). Images were reconstructed as conventional images (CI) and as VMI in a range of 40-200 keV (10 keV increment). Quantitative image analysis was performed ROI-based by measurement of attenuation (HU) and standard deviation in most pronounced hypo- and hyperdense artifact, fat and soft tissue with presence of artifacts. Qualitatively, extent of artifact reduction, assessment of soft palate and cheeks were rated on 5-point Likert-scales by two radiologists. Statistical data evaluation included ANOVA and Wilcoxon-test with correction for multiple comparisons; interrater-agreement was determined by intraclass-correlation coefficient (ICC). RESULTS The hypo- and hyperattenuating artifacts showed an increase and decrease of HU-values in VMIhigh (CI/VMI200 keV: -218.7/-174.4 HU, p = 0.1; and 309.8/119.2, p ≤ 0.05, respectively). Artifacts in the fat, as depicted by image noise did also decrease in VMIhigh (CI/VMI200 keV: 23.9/16.4, p ≤ 0.05). Qualitatively, hyperdense artifacts were decreased significantly in VMI ≥100 keV (e.g. CI/VMI200 keV: 2(1-3)/3(1-5), p ≤ 0.05). Artifact reduction resulted in improved assessment of the soft palate and cheeks (e.g. CI/VMI200 keV: 2(1-4)/3(1-5) and 2(1-5)/3(1-5), p ≤ 0.05). Overall interrater agreement was good (ICC = 0.77). CONCLUSIONS Virtual monoenergetic images from SDCT reduce metal artifacts from dental implants and improve diagnostic assessment of surrounding soft tissue.

Order of Treatment Matters in Ischemic Stroke: Mechanical Thrombectomy First, Then Carotid Artery Stenting for Tandem Lesions of the Anterior Circulation

Background: One endovascular treatment option of acute ischemic stroke due to tandem occlusion (TO) comprises intracranial thrombectomy and acute extracranial carotid artery stenting (CAS). In this setting, the order of treatment may impact the clinical outcome in this stroke subtype. Methods: Retrospective analysis was performed on data prospectively collected in 4 international stroke centers between 2013 and 2017. One hundred sixty-five patients with anterior TO were treated by endovascular therapy. Clinical and procedural data were evaluated. Favorable clinical outcome was defined as modified Rankin Scale (mRS) ≤2 at 90 days. Propensity score matching was performed for different treatment strategies. Results: Patients’ mean age was 65 ± 11 years and 118 were male (69%). The median admission National Institutes of Health Stroke Scale was 15 (interquartile range 8). In 59% of the patients (n = 101), the antegrade strategy (first stenting, then thrombectomy) was performed, in 41% (n = 70) retrograde treatment (first thrombectomy, then stenting). Successful reperfusion (mTICI ≥2b) was achieved in 128 patients (75%). Fifty-nine patients (39%) showed a favorable clinical outcome after 90 days. After propensity score matching, data of 100 patients could be analyzed. Analysis revealed that the retrograde strategy yielded a significantly higher rate of successful reperfusion compared to the antegrade strategy (92 vs. 56%; p < 0.001). The rate of favorable clinical outcome after 90 days (mRS ≤2) was consistently higher (44 vs. 30%; p < 0.05) in the retrograde strategy group. Conclusion: Mechanical thrombectomy prior to acute CAS in TO is a predictive factor for favorable clinical outcome at 90 days.

Effects of Contrast Enhancement on In-Body Calibrated Phantomless Bone Mineral Density Measurements in Computed Tomography

We aimed to test the potential of phantomless volumetric bone mineral density (PLvBMD) measurements for the determination of volumetric bone mineral density (vBMD) in routine contrast-enhanced computed tomography (CECT). We evaluated 56 tri-phasic abdominal computed tomography scans, including an unenhanced scan as well as defined CECT scans in the arterial and portalvenous phase. PLvBMD analysis was performed by 4 radiologists using an FDA-approved tool for phantomless evaluation of bone density (IntelliSpace, Philips, The Netherlands). Mean vBMD of the first 3 lumbar vertebrae in each contrast phase was determined and interobserver variance of vBMD independent of contrast phase was analyzed using intraclass correlation, Bland-Altman plots, and Students t test. CECT scans were associated with a significantly higher PLvBMD compared with unenhanced scans (unenhanced computed tomography: 97.8 mg/cc; arterial CECT: 106.3 mg/cc, portalvenous CECT: 106.3 mg/cc). Overall, there was no significant difference of PLvBMD between data acquisition in arterial and portalvenous phases (increase of 8.6% each, standard deviation ratio 37.7%-38.3%). In Bland-Altman analysis, there was no evidence of a relevant reader-related bias or an increase in standard deviation of PLvBMD measurements in contrast-enhanced scans compared with unenhanced scans. The following conversion formulas for unenhanced PLvBMD were determined: unenhancedPLvBMD=0.89×arterialPLvBMD+3,74mg/cc(r2 = 0.94) and unenhancedPLvBMD=0.88×venousPLvBMD+4,56mg/cc(r2 = 0.93). Compared with the results of phantom-based quantitative computed tomography measurements reported in the literature, the PLvBMD changes associated with contrast enhancement were relatively moderate with an increase of 8.6% in average. The time-point of the contrast-enhanced PLvBMD measurements after injection of contrast media did not appear to affect the results. With the adjustment formulas provided in this study, the method can improve osteoporosis screening through detection of reduced bone mass of the vertebrae in routinely conducted CECT.