Intra-individual consistency of spectral detector CT-enabled iodine quantification of the vascular and renal blood pool.

OBJECTIVES: The objective of this study was to evaluate the intra-individual, longitudinal consistency of iodine measurements regarding the vascular and renal blood pool in patients that underwent repetitive spectral detector computed tomography (SDCT) examinations to evaluate their utility for oncologic imaging. METHODS: Seventy-nine patients with two (n = 53) or three (n = 26) clinically indicated biphasic SDCT scans of the abdomen were retrospectively included. ROI-based measurements of Hounsfield unit (HU) attenuation in conventional images and iodine concentration were performed by an experienced radiologist in the following regions (two ROIs each): abdominal aorta, vena cava inferior, portal vein, and renal cortices. Modified variation coefficients (MVCs) were computed to assess intra-individual longitudinal between the different time points. RESULTS: Variation of HU attenuation and iodine concentration measurements was significantly lower in the venous than in the arterial phase images (attenuation/iodine concentration: arterial - 4.2/- 3.9, venous 0.4/1.0; p ≤ 0.05). Regarding attenuation in conventional images of the arterial phase, the median MVC was - 1.8 (- 20.5-21.3) % within the aorta and - 6.5 (- 44.0-25.0) % within the renal cortex while in the portal venous phase, it was 0.62 (- 11.1-11.7) % and - 1.6 (- 16.2-10.6) %, respectively. Regarding iodine concentration, MVC for arterial phase was - 2.5 (- 22.9-28.4) % within the aorta and - 5.8 (- 55.9-29.6) % within the renal cortex. The referring MVCs of the portal venous phase were - 0.7 (- 17.9-16.9) % and - 2.6 (- 17.6-12.5) %. CONCLUSIONS: Intra-individual iodine quantification of the vascular and cortical renal blood pool at different time points works most accurately in venous phase images whereas measurements conducted in arterial phase images underlay greater variability. KEY POINTS: • There is an intra-individual, physiological variation in iodine map measurements from dual-energy computed tomography. • This variation is smaller in venous phase examinations compared with arterial phase and therefore venous phase images should be preferred to minimize this intra-individual variation. • Care has to be taken, when considering iodine measurements for clinical decision-making, particularly in the context of oncologic initial or follow-up imaging.

Accuracy of iodine density thresholds for the separation of vertebral bone metastases from healthy-appearing trabecular bone in spectral detector computed tomography.

PURPOSE: To evaluate quantitative iodine density mapping (IDM) with spectral detector computed tomography (SDCT) as a quantitative biomarker for separation of vertebral trabecular bone metastases (BM) from healthy-appearing trabecular bone (HTB). MATERIALS AND METHODS: IRB-approved retrospective single-center-study of portal venous SDCT datasets acquired between June 2016 and March 2017. Inclusion of 43 consecutive cancer patients with BM and 40 without. Target lesions and non-affected control vertebrae were defined using follow-up imaging, MRI, and/or bone scintigraphy. ID and standard deviation were determined with ROI measures by two readers in (a) bone metastases, (b) HTB of BM patients and controls, and (c) ID of various vessels. Volumetric bone mineral density (vBMD) of the lumbar spine and age were recorded. Multivariate ROC analyses und Wilcoxon test were used to determine thresholds for separation of BM and HTB. p < 0.05 was considered significant. RESULTS: ID measurements of 40 target lesions and 83 reference measurements of HTB were acquired. Age (p < 0.0001) and vBMD (p < 0.05) affected ID measurements independently in multivariate models. There were significant differences of ID between metastases (n = 43) and HTB ID (n = 124; mean 5.5 ± 0.9 vs. 3.5 ± 0.9; p < 0.0001), however, with considerable overlap. In univariate analysis, increased ID discriminated bone lesions (AUC 0.90) with a maximum combined specificity/sensitivity of 77.5%/90.7% when applying a threshold of 4.5 mg/ml. Multivariate regression models improved significantly when considering vBMD, the noise of ID, and vertebral venous ID (AUC 0.98). CONCLUSION: IDM of SDCT yielded a statistical separation of vertebral bone lesions and HTB. Adjustment for confounders such as age and lumbar vBMD as well as for vertebral venous ID and lesion heterogeneity improved discrimination of trabecular lesions. KEY POINTS: • SDCT iodine density mapping provides the possibility for quantitative analysis of iodine uptake in tissue, which allows to differentiate bone lesions from healthy bone marrow. • Age and vBMD have a significant impact on iodine density measurements. • Iodine density measured in SDCT yielded highest sensitivity and specificity for the statistical differentiation of vertebral trabecular metastases and healthy trabecular bone using an iodine density threshold of 4.5 mg/ml (most performant)-5.0 mg/ml (optimized for specificity).

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

The original version of this article, published on 03 May 2018, unfortunately contained a mistake. The following correction has therefore been made in the original.

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

OBJECTIVES: This 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). METHODS: Twenty-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. RESULTS: In 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). CONCLUSIONS: MAR 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.

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 Student's 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.

Diffusion-weighted Imaging Allows for Downgrading MR BI-RADS 4 Lesions in Contrast-enhanced MRI of the Breast to Avoid Unnecessary Biopsy.

PURPOSE: Diffusion-weighted imaging with the calculation of an apparent diffusion coefficient (ADC) has been proposed as a quantitative biomarker on contrast-enhanced MRI (CE-MRI) of the breast. There is a need to approve a generalizable ADC cutoff. The purpose of this study was to evaluate whether a predefined ADC cutoff allows downgrading of BI-RADS 4 lesions on CE-MRI, avoiding unnecessary biopsies. EXPERIMENTAL DESIGN: This was a retrospective, multicentric, cross-sectional study. Data from five centers were pooled on the individual lesion level. Eligible patients had a BI-RADS 4 rating on CE-MRI. For each center, two breast radiologists evaluated the images. Data on lesion morphology (mass, non-mass), size, and ADC were collected. Histology was the standard of reference. A previously suggested ADC cutoff (≥1.5 × 10-3 mm2/second) was applied. A negative likelihood ratio of 0.1 or lower was considered as a rule-out criterion for breast cancer. Diagnostic performance indices were calculated by ROC analysis. RESULTS: There were 657 female patients (mean age, 42; SD, 14.1) with 696 BI-RADS 4 lesions included. Disease prevalence was 59.5% (414/696). The area under the ROC curve was 0.784. Applying the investigated ADC cutoff, sensitivity was 96.6% (400/414). The potential reduction of unnecessary biopsies was 32.6% (92/282). CONCLUSIONS: An ADC cutoff of ≥1.5 × 10-3 mm2/second allows downgrading of lesions classified as BI-RADS 4 on breast CE-MRI. One-third of unnecessary biopsies could thus be avoided.

Differentiation of Clot Composition Using Conventional and Dual-Energy Computed Tomography.

BACKGROUND AND PURPOSE: In unenhanced computed tomography (CT) of acute ischemic stroke, the density of occluding clots is associated with the content of red blood cells and successful recanalization with stent thrombectomy. However, no CT marker for fibrin content is established. In order to improve clot diagnostics, we conducted an in vitro study to investigate thrombus composition of histologically defined ovine blood clots with unenhanced and contrast-enhanced CT using spectral detector CT (SDCT). METHODS: Ovine blood clot types containing defined amounts of red blood cells (RBC; pure fibrin clots: RBC 0% ± 0, fibrin 100% ± 0), mixed clots (RBC 35.1% ± 4.11, fibrin 79.2% ± 5.6) and red clots (RBC 99.05% ± 1.14, fibrin 0.95% ± 1.14) were scanned in a SDCT (IQon®, Philips, Amsterdam, The Netherlands) (a) in a tube containing saline, (b) 5 min and (c) 3 days after exposure to a 1:50 dilution of iohexol (Accupaque-350®, GE-Healthcare, Boston, MA, USA). The attenuation of the clots was measured in Hounsfield units (HU) in conventional CT datasets as well as virtual noncontrast reconstructions (VNC) of nonenhanced and contrast-enhanced SDCT in a blinded and randomized fashion. Statistical analysis was conducted with ANOVA, Spearman's correlation, linear and multivariable regression models. RESULTS: In unenhanced scans, clots differed in density with linear interrelation (fibrin 23.6 ± 1.1, mixed 34.9 ± 1.6, red 46.7 ± 1.6, mean HU ± SD). The blood clots did not show any overlap of density in the native scans and VNC at different time points (p < 0.0001 for each setting and clot type). However, they could not be differentiated after initial contrast exposure (fibrin 108.5 ± 7.8, mixed 105.3 ± 3.5, red 104.8 ± 3.8, mean HU ± SD). After prolonged exposure, the fibrin rich clots showed a significant increase of density due to further uptake of contrast medium (fibrin 163.6 ± 3.6, mixed 138.3 ± 4.1, red 109.6 ± 5.4, mean HU ± SD). In multivariable models, native CT density and contrast enhancement were independent variables associated with thrombus type (p < 0.01 each). CONCLUSION: The fibrin content in blood clots is strongly associated with contrast uptake. As previously shown, the density of the clot formations in native CT scans is dependent on the RBC. Our data show that CT density and relative enhancement of clots are independent determinants of clot composition. Using both variables in the CT workup of acute ischemic stroke has the potential to have a decisive impact on patient stratification for treatment.