Malte N. Bongers

Single-Source Dual-Energy Computed Tomography Use of Monoenergetic Extrapolation for a Reduction of Metal Artifacts

ObjectivesThe objective of this study was to retrospectively determine the potential of virtual monoenergetic (ME) reconstructions for a reduction of metal artifacts using a new-generation single-source computed tomographic (CT) scanner. Materials and MethodsThe ethics committee of our institution approved this retrospective study with a waiver of the need for informed consent. A total of 50 consecutive patients (29 men and 21 women; mean [SD] age, 51.3 [16.7] years) with metal implants after osteosynthetic fracture treatment who had been examined using a single-source CT scanner (SOMATOM Definition Edge; Siemens Healthcare, Forchheim, Germany; consecutive dual-energy mode with 140 kV/80 kV) were selected. Using commercially available postprocessing software (syngo Dual Energy; Siemens AG), virtual ME data sets with extrapolated energy of 130 keV were generated (medium smooth convolution kernel D30) and compared with standard polyenergetic images reconstructed with a B30 (medium smooth) and a B70 (sharp) kernel. For quantification of the beam hardening artifacts, CT values were measured on circular lines surrounding bone and the osteosynthetic device, and frequency analyses of these values were performed using discrete Fourier transform. A high proportion of low frequencies to the spectrum indicates a high level of metal artifacts. The measurements in all data sets were compared using the Wilcoxon signed rank test. ResultsThe virtual ME images with extrapolated energy of 130 keV showed significantly lower contribution of low frequencies after the Fourier transform compared with any polyenergetic data set reconstructed with D30, B70, and B30 kernels (P < 0.001). ConclusionsSequential single-source dual-energy CT allows an efficient reduction of metal artifacts using high-energy ME extrapolation after osteosynthetic fracture treatment.

Comparison and Combination of Dual-Energy- and Iterative-Based Metal Artefact Reduction on Hip Prosthesis and Dental Implants.

Purpose To compare and combine dual-energy based and iterative metal artefact reduction on hip prosthesis and dental implants in CT. Material and Methods A total of 46 patients (women:50%,mean age:63±15years) with dental implants or hip prostheses (n = 30/20) were included and examined with a second-generation Dual Source Scanner. 120kV equivalent mixed-images were derived from reconstructions of the 100/Sn140kV source images using no metal artefact reduction (NOMAR) and iterative metal artefact reduction (IMAR). We then generated monoenergetic extrapolations at 130keV from source images without IMAR (DEMAR) or from source images with IMAR, (IMAR+DEMAR). The degree of metal artefact was quantified for NOMAR, IMAR, DEMAR and IMAR+DEMAR using a Fourier-based method and subjectively rated on a five point Likert scale by two independent readers. Results In subjects with hip prosthesis, DEMAR and IMAR resulted in significantly reduced artefacts compared to standard reconstructions (33% vs. 56%; for DEMAR and IMAR; respectively, p<0.005), but the degree of artefact reduction was significantly higher for IMAR (all p<0.005). In contrast, in subjects with dental implants only IMAR showed a significant reduction of artefacts whereas DEMAR did not (71%, vs. 8% p<0.01 and p = 0.1; respectively). Furthermore, the combination of IMAR with DEMAR resulted in additionally reduced artefacts (Hip prosthesis: 47%, dental implants 18%; both p<0.0001). Conclusion IMAR allows for significantly higher reduction of metal artefacts caused by hip prostheses and dental implants, compared to a dual energy based method. The combination of DE-source images with IMAR and subsequent monoenergetic extrapolation provides an incremental benefit compared to both single methods.

Dual-Energy CT: Virtual Calcium Subtraction for Assessment of Bone Marrow Involvement of the Spine in Multiple Myeloma

OBJECTIVE. Dual-energy CT (DECT) enables subtraction of calcium, facilitating the visualization of bone marrow (BM) in the axial skeleton. The purpose of this study was to assess whether DECT BM images have the potential to improve the detection of multifocal and diffuse BM infiltration in multiple myeloma (MM) in comparison with regular CT with MRI as the reference standard. SUBJECTS AND METHODS. This study included 32 consecutive patients who had known MM or presented with monoclonal gammopathy of unknown significance and underwent DECT and MRI of the axial skeleton. The degrees (none, n = 14; moderate, n = 10; and high, n = 8) and patterns (diffuse, n = 10 or multifocal, n = 8) of infiltration were assessed on MR images. Attenuation in BM and CT images in known uninvolved and involved areas was measured. Cutoff values of attenuation in BM images for infiltration in lytic and nonlytic lesions were established by ROC analysis. At least 120 days later, sensitivity and specificity for reading CT images alone and when using additional BM images were evaluated. RESULTS. ROC analysis revealed larger AUC in BM images than in CT images; cutoff values for marrow invasion in BM images were 4 and -3 HU in lytic and nonlytic lesions, respectively. In the blinded reading session, BM images improved the sensitivity for the detection of diffuse infiltration from 0 to as much as 75% for cases with high-grade infiltration. In multifocal patterns, BM images did not significantly change the detection rate. CONCLUSION. BM images have the potential to improve the sensitivity for detection of diffuse BM involvement in comparison with regular CT.

Impact of iterative metal artifact reduction on diagnostic image quality in patients with dental hardware

Background Metal artifacts often impair diagnostic accuracy in computed tomography (CT) imaging. Therefore, effective and workflow implemented metal artifact reduction algorithms are crucial to gain higher diagnostic image quality in patients with metallic hardware. Purpose To assess the clinical performance of a novel iterative metal artifact reduction (iMAR) algorithm for CT in patients with dental fillings. Material and Methods Thirty consecutive patients scheduled for CT imaging and dental fillings were included in the analysis. All patients underwent CT imaging using a second generation dual-source CT scanner (120 kV single-energy; 100/Sn140 kV in dual-energy, 219 mAs, gantry rotation time 0.28–1/s, collimation 0.6 mm) as part of their clinical work-up. Post-processing included standard kernel (B49) and an iterative MAR algorithm. Image quality and diagnostic value were assessed qualitatively (Likert scale) and quantitatively (HU ± SD) by two reviewers independently. Results All 30 patients were included in the analysis, with equal reconstruction times for iMAR and standard reconstruction (17 s ± 0.5 vs. 19 s ± 0.5; P > 0.05). Visual image quality was significantly higher for iMAR as compared with standard reconstruction (3.8 ± 0.5 vs. 2.6 ± 0.5; P < 0.0001, respectively) and showed improved evaluation of adjacent anatomical structures. Similarly, HU-based measurements of degree of artifacts were significantly lower in the iMAR reconstructions as compared with the standard reconstruction (0.9 ± 1.6 vs. –20 ± 47; P < 0.05, respectively). Conclusion The tested iterative, raw-data based reconstruction MAR algorithm allows for a significant reduction of metal artifacts and improved evaluation of adjacent anatomical structures in the head and neck area in patients with dental hardware.

Effect of Noise-Optimized Monoenergetic Postprocessing on Diagnostic Accuracy for Detecting Incidental Pulmonary Embolism in Portal-Venous Phase Dual-Energy Computed Tomography.

Objectives The aim of this study was to evaluate the diagnostic accuracy of virtual monoenergetic images (MEI+) at low kiloelectronvolt levels for the detection of incidental pulmonary embolism (PE) in oncological follow-up portal-venous phase dual-energy (DE-CTpv) staging. Materials and Methods Twenty-six patients with incidental PE in DE-CTpv staging, which was confirmed by computed tomography pulmonary angiography (CTPA), were included in this study. In addition, 26 matched control patients who were negative for PE in both DE-CTpv and CTPA were included. All examinations were performed on a third-generation DE-CT system in single-energy (CTPA) and dual-energy mode (DE-CTpv). Subsequently, 2 series of MEI+ data sets were reconstructed at 40 and 55 keV from the DE-CTpv data and compared with CTPA and the linearly blended CTpv images. Diagnostic accuracy and diagnostic confidence were calculated and compared for MEI+ reconstructions and for CTpv images regarding the detection of PE with CTPA as standard of reference. Results In 3 patients, PE was only detectable in CTPA and in the 40-kV and 55-kV MEI+ reconstructions but not in CTpv images. Diagnostic accuracy increased significantly for both MEI+ series (40 keV; area under the curve [AUC], 0.928; 95% confidence interval [CI], 0.879–0.978; 55 keV; AUC, 0.960; 95% CI, 0.922–0.998) as compared with CTpv (AUC, 0.814; 95% CI, 0.741–0.887; P ⩽ 0.004). Diagnostic confidence was rated highest in CTPA (median, 5; range, 3–5) followed by 55-keV MEI+ and 40-keV MEI+ (median, 5; range, 2–5 and median, 5; range, 2–5, respectively) and was lowest for CTpv (median, 4; range, 1–5), with significant differences to CTPA and MEI+ reconstructions (P ⩽ 0.001). Conclusions Monoenergetic image reconstructions from DE-CT data sets at low kiloelectronvolt levels improve diagnostic accuracy for the detection of incidental PE in oncological follow-up DE-CTpv staging, with the highest subjective diagnostic confidence in MEI+ at 55 keV.

Metabolic crosstalk between fatty pancreas and fatty liver: effects on local inflammation and insulin secretion

Aims/hypothesisObesity-linked ectopic fat accumulation is associated with the development of type 2 diabetes. Whether pancreatic and liver steatosis impairs insulin secretion is controversial. We examined the crosstalk of human pancreatic fat cells with islets and the role of diabetogenic factors, i.e. palmitate and fetuin-A, a hepatokine released from fatty liver.MethodsHuman pancreatic resections were immunohistochemically stained for insulin, glucagon, somatostatin and the macrophage/monocyte marker CD68. Pancreatic adipocytes were identified by Oil Red O and adiponectin staining. Primary pancreatic pre-adipocytes and differentiated adipocytes were co-cultured with human islets isolated from organ donors and the metabolic crosstalk between fatty liver and fatty pancreas was mimicked by the addition of palmitate and fetuin-A. Insulin secretion was evaluated by ELISA and RIA. Cytokine expression and secretion were assessed by RT-PCR and multiplex assay, respectively. Subcellular distribution of proteins was examined by confocal microscopy and protein phosphorylation by western blotting.ResultsIn human pancreatic parenchyma, highly differentiated adipocytes were detected in the proximity of islets with normal architecture and hormone distribution. Infiltration of adipocytes was associated with an increased number of CD68-positive cells within islets. In isolated primary pancreatic pre-adipocytes and differentiated adipocytes, palmitate and fetuin-A induced IL6, CXCL8 and CCL2 mRNA expression. Cytokine production was toll-like receptor 4 (TLR4)-dependent and further accentuated in pre-adipocytes when co-cultured with islets. In islets, IL6 and CXCL8 mRNA levels were also increased by fetuin-A and palmitate. Only in macrophages within the isolated islets, palmitate and fetuin-A stimulated the production of the cytotoxic cytokine IL-1β. Palmitate, but not fetuin-A, exerted pro-apoptotic effects in islet cells. Instead, fetuin-A impaired glucose-induced insulin secretion in a TLR4-independent, but c-Jun N-terminal kinase- and Ca2+-dependent, manner.Conclusions/interpretationThese results provide the first evidence that fetuin-A-mediated metabolic crosstalk of fatty liver with islets may contribute to obesity-linked glucose blindness of beta cells, while fatty pancreas may exacerbate local inflammation.

Clinical applications for dual energy CT versus dynamic contrast enhanced CT in oncology

Both Dual Energy CT (DECT) and Volume Perfusion CT (VPCT) have gained interest in recent years with several studies providing evidence of benefits for both in a variety of oncological settings. These technologies open a new spectrum of diagnostic opportunities aiming at an improved detection and characterization of suspected tumor lesions, early evaluation of therapy response and generally more accurate treatment monitoring. Here, we review and discuss current advances, beneficial aspects and potential shortcomings of both imaging modalities with regard to their clinical use in oncology.

Intra- and interindividual variability of fatty acid unsaturation in six different human adipose tissue compartments assessed by 1H-MRS in vivo at 3 T

It is generally accepted that the amount and distribution of adipose tissue (AT) in the human body play an important role in the pathogenesis of metabolic diseases. In addition, metabolic effects of released saturated fatty acids (FAs) in blood are known to be more critical than those of unsaturated FAs. However, little is known about the variability in unsaturation of FAs in various AT compartments. The aim of this prospective study was the assessment of mono‐ and polyunsaturated FAs in various AT compartments by localized 1H‐MRS in order to obtain insight into the intra‐ and interindividual variability. Associations of FA unsaturation with intrahepatic lipids (IHLs), insulin sensitivity and related AT volumes were analyzed.

Accuracy of Non-Enhanced CT in Detecting Early Ischemic Edema Using Frequency Selective Non-Linear Blending.

Purpose Ischemic brain edema is subtle and hard to detect by computed tomography within the first hours of stroke onset. We hypothesize that non-enhanced CT (NECT) post-processing with frequency-selective non-linear blending (“best contrast”/BC) increases its accuracy in detecting edema and irreversible tissue damage (infarction). Methods We retrospectively analyzed the NECT scans of 76 consecutive patients with ischemic stroke (exclusively middle cerebral artery territory—MCA) before and after post-processing with BC both at baseline before reperfusion therapy and at follow-up (5.73±12.74 days after stroke onset) using the Alberta Stroke Program Early CT Score (ASPECTS). We assessed the differences in ASPECTS between unprocessed and post-processed images and calculated sensitivity, specificity, and predictive values of baseline NECT using follow-up CT serving as reference standard for brain infarction. Results NECT detected brain tissue hypoattenuation in 35 of 76 patients (46.1%). This number increased to 71 patients (93.4%) after post-processing with BC. Follow-up NECT confirmed brain infarctions in 65 patients (85.5%; p = 0.012). Post-processing increased the sensitivity of NECT for brain infarction from 35/65 (54%) to 65/65 (100%), decreased its specificity from 11/11 (100%) to 7/11 (64%), its positive predictive value (PPV) from 35/35 (100%) to 65/69 (94%) and increased its accuracy 46/76 (61%) to 72/76 (95%). Conclusions This post-hoc analysis suggests that post-processing of NECT with BC may increase its sensitivity for ischemic brain damage significantly.

Improved Delineation of Pulmonary Embolism and Venous Thrombosis Through Frequency Selective Nonlinear Blending in Computed Tomography

Objective The aim of this study was to test the hypothesis that a novel frequency selective nonlinear blending (NLB) algorithm increases the delineation of pulmonary embolism and venous thrombosis in portal-venous phase whole-body staging computed tomography (CT). Materials and Methods A cohort of 67 patients with incidental pulmonary embolism and/or venous thrombosis in contrast-enhanced oncological staging CT were retrospectively selected. Computed tomography data sets were acquired 65 to 90 seconds after intravenous iodine contrast administration using state-of-the-art multi-detector CT scanners. A novel frequency selective NLB postprocessing technique was applied to reconstructed standard CT images. Two readers determined the most suitable settings to increase the delineation of pulmonary embolism and venous thrombosis. Outcome measure included region of interest and contrast-to-noise ratio (CNR) analyses, image noise, overall image quality, subjective delineation, as well as number and size of emboli and thrombi. Statistical testing included quantitative comparisons of Hounsfield units of thrombus and vessel, image noise and related CNR values and subjective image analyses of image noise, image quality and thrombus delineation, number and size in standard, and NLB images. Results Using frequency selective NLB settings with a center of 100 HU, delta of 40 HU, and a slope of 5, CNR values of pulmonary embolism (StandardCNR, 10 [6, 16]; NLBCNR, 22 [15, 30]; P < 0.001) and venous thrombosis (StandardCNR, 8 [5, 15]; NLBCNR, 12 [7, 19]; P = 0.0007) increased. Mean vascular enhancement using NLB was significantly higher than in standard images for pulmonary arteries (Standard, 138 [118, 191] HU; NLB, 269 [176, 329] HU; P < 0.0001) and veins (Standard, 120 [103, 162] HU; NLB, 169 [132, 217] HU; P < 0.0001), respectively. Image noise was not significantly different between standard and NLB images (P = 0.64-0.88). There was substantial to almost perfect interrater agreement as well as a significant increase of overall image quality (P < 0.004) and subjective delineation of the thrombotic material (P < 0.0001) in both subgroups. Nonlinear blending images revealed 8 additional segmental and 13 subsegmental emboli. Thrombus sizes were not significantly different, but subjective accuracy of the measurement could be significantly increased using NLB (P = 0.03). Conclusions Postprocessing of standard whole-body staging CT images with frequency selective NLB improves image quality and the delineation of pulmonary embolism and venous thrombosis.