Simon Lennartz

Reduction of artifacts caused by orthopedic hardware in the spine in spectral detector CT examinations using virtual monoenergetic image reconstructions and metal-artifact-reduction algorithms

ObjectiveAim of this study was to assess the artifact reduction in patients with orthopedic hardware in the spine as provided by (1) metal-artifact-reduction algorithms (O-MAR) and (2) virtual monoenergetic images (MonoE) as provided by spectral detector CT (SDCT) compared to conventional iterative reconstruction (CI).MethodsIn all, 28 consecutive patients with orthopedic hardware in the spine who underwent SDCT-examinations were included. CI, O-MAR and MonoE (40–200xa0keV) images were reconstructed. Attenuation (HU) and noise (SD) were measured in order to calculate signal-to-noise ratio (SNR) of paravertebral muscle and spinal canal. Subjective image quality was assessed by two radiologists in terms of image quality and extent of artifact reduction.ResultsO-MAR and high-keV MonoE showed significant decrease of hypodense artifacts in terms of higher attenuation as compared to CI (CI vs O-MAR, 200xa0keV MonoE: −396.5HU vs. –115.2HU, −48.1HU; both pxa0≤xa00.001). Further, artifacts as depicted by noise were reduced in O-MAR and high-keV MonoE as compared to CI in (1) paravertebral muscle and (2) spinal canal—CI vs. O-MAR/200xa0keV: (1) 34.7xa0±xa019.0 HU vs. 26.4xa0±xa014.4 HU, pxa0≤xa00.05/27.4xa0±xa016.1, n.s.; (2) 103.4xa0±xa061.3 HU vs. 72.6xa0±xa062.6 HU/60.9xa0±xa040.1 HU, both pxa0≤xa00.001. Subjectively both O-MAR and high-keV images yielded an artifact reduction in up to 24/28 patients.ConclusionBoth, O-MAR and high-keV MonoE reconstructions as provided by SDCT lead to objective and subjective artifact reduction, thus the combination of O-MAR and MonoE seems promising for further reduction.

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.

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

PURPOSEnTo evaluate calcium suppressed images (CaSupp) in dual-layer detector computed tomography (DLCT) for the detection of bone marrow edema (BME) in vertebral fractures.nnnMATERIALS AND METHODSnThe 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.nnnRESULTSnFifty-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 (chi2u202f<u202f0.0001). No correlation between optimal CaSupp-I and trabecular density was found (pu202f>u202f0.2).nnnCONCLUSIONnCaSupp reconstructed from DLCT enable visualization and detection of BME in traumatic fractured vertebrae with high diagnostic accuracy using CaSupp-I of 70-100.

Dual-layer detector CT of the head: Initial experience in visualization of intracranial hemorrhage and hypodense brain lesions using virtual monoenergetic images

PURPOSEnRetrospective comparison of diagnostic quality of virtual monoenergetic images (VMI) and conventional images (CI) reconstructed from dual-layer detector CT (DLCT) regarding intraparenchymal hemorrhage (IPH) and hypodense parenchymal lesions (HPL) of the brain.nnnMETHODSn58 patients underwent unenhanced DLCT of the head. CI and VMI ranging from 40 to 120u2009keV were reconstructed. Objective image quality was assessed using ROI-based measurements within IPH, HPL, grey matter, white matter and cerebrospinal fluid, from which contrast to noise ratio (CNR) was calculated. Two radiologists assessed IPH, HPL, artifacts and image noise on a 5-point Likert-scale. Statistical significance was determined using Wilcoxon rank sum test.nnnRESULTSnIn comparison to conventional images, CNR of HPL to white matter was significantly increased in VMI at 120u2009keV (pu2009≤u20090.01), whereas at 40u2009keV, CNR to grey matter was enhanced (pu2009≤u20090.0001). Contrary, CNR of IPH to white matter was increased at 40u2009keV (pu2009≤u20090.01), while CNR to grey matter was improved at 120u2009keV (pu2009≤u20090.01). Subjective readings confirmed best delineation of IPH within grey matter at 120u2009keV. Both readers detected four additional hyperdense lesions within white and one within grey matter at 40u2009keV.nnnCONCLUSIONSnVMI obtained with DLCT can improve depiction of hypodense parenchymal lesions and intraparenchymal hemorrhage. The initial data show a great dependency on the type of pathology and on its location: hypodense lesions in white matter and hyperdense lesions in grey matter are better visualized in higher keV reconstructions, while hyperdense lesion in white matter and hypodense lesions in grey matter are better visualized at low keV values.

Improved depiction of atherosclerotic carotid artery stenosis in virtual monoenergetic reconstructions of venous phase dual-layer computed tomography in comparison to polyenergetic reconstructions

OBJECTIVESnTo compare virtual monoenergetic images (VMI) reconstructed from venous phase Dual-Layer CT (DLCT) with polyenergetic images (PI) of DLCT-Angiography (DLCT-A) regarding vessel contrast and image quality especially in sight to atherosclerotic carotid artery stenosis.nnnMETHODS & MATERIALSn25 DLCT-A and 55 venous phase DLCT were analyzed in this retrospective study. For objective analysis PI and VMI (40-120u202fkeV) were assessed comparing attenuation, standard deviation, signal-/contrast- to noise ratios (SNR, CNR) in the common carotid artery (CCA), vertebral artery, sternocleidomastoid muscle and air. For subjective analysis, vessel contrast, delineation of the superficial temporal artery, depiction of calcified plaque as well as vessel patency within the atherosclerotic stenosis of the internal carotid artery were rated and the extent of the calcified plaque and remaining vessel lumen were measured in venous phase DLCT.nnnRESULTSnIn venous phase DLCT, attenuation, SNR and CNR in the CCA increased with lower keV. Attenuation, SNR and CNR at 40u202fkeV in the CCA were comparable to PI of DLCT-A (all: pu202f>u202f0.05). Subjective image contrast, assessment of vessel patency within a stenosis as well as delineation of the superficial temporal artery were rated superior at 40-60u202fkeV in comparison to PI of venous phase DLCT (all: pu202f≤u202f0.05). Slightly more blooming of the atherosclerotic plaque was found in VMI at 40-60u202fkeV. There was no difference of NASCET-criteria of carotid stenosis between VMI at different keV-levels and PI (pu202f=u202f1.0).nnnCONCLUSIONnVMI at 40u202fkeV reconstructed from venous phase DLCT yield an image quality equal to CT-Angiography, especially regarding vessel contrast. Perception and assessment of the carotid artery within an atherosclerotic stenosis are not impaired at low keV.

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

OBJECTIVESnImage 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).nnnMETHODSn38 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 40-200u202fkeV (10u202fkeV 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).nnnRESULTSnThe hypo- and hyperattenuating artifacts showed an increase and decrease of HU-values in VMIhigh (CI/VMI200u202fkeV: -218.7/-174.4 HU, pu202f=u202f0.1; and 309.8/119.2, pu202f≤u202f0.05, respectively). Artifacts in the fat, as depicted by image noise did also decrease in VMIhigh (CI/VMI200u202fkeV: 23.9/16.4, pu202f≤u202f0.05). Qualitatively, hyperdense artifacts were decreased significantly in VMI ≥100u202fkeV (e.g. CI/VMI200u202fkeV: 2(1-3)/3(1-5), pu202f≤u202f0.05). Artifact reduction resulted in improved assessment of the soft palate and cheeks (e.g. CI/VMI200u202fkeV: 2(1-4)/3(1-5) and 2(1-5)/3(1-5), pu202f≤u202f0.05). Overall interrater agreement was good (ICCu202f=u202f0.77).nnnCONCLUSIONSnVirtual monoenergetic images from SDCT reduce metal artifacts from dental implants and improve diagnostic assessment of surrounding soft tissue.