Dual-Energy CT-Based Bone Marrow Imaging in Multiple Myeloma: Assessment of Focal Lesions in Relation to Disease Status and MRI Findings.

RATIONALE AND OBJECTIVES: To assess focal multiple myeloma bone lesions via dual-energy CT-based virtual noncalcium (VNCa) bone marrow imaging in relation to the overall hematological disease status and MRI findings. MATERIALS AND METHODS: We retrospectively evaluated 103 focal osteolytic lesions of the axial skeleton in VNCa bone marrow images of 32 patients. Region of interest-based attenuation measurements were correlated with T1w signal intensity and apparent diffusion coefficient (ADC). Results were compared between patients in active and inactive disease. Receiver operating characteristic analysis was performed to determine a cut-off value of VNCa attenuation for differentiation between the two groups. Standard of reference was the overall disease status according to International Myeloma Working Group response criteria. RESULTS: Mean attenuation difference between lesions and background bone marrow was significantly lower in inactive disease (16 HU, SD 30) compared to active disease (35 HU, SD 29). VNCa attenuation measurement allowed for differentiation between active and inactive disease with a sensitivity of 92% and a specificity of 58% at a cut-off value of -21 HU. VNCa attenuation was negatively correlated to T1w signal intensity (Spearman's ρ -0.617, p < 0.001) and positively correlated to ADC (Spearman's ρ 0.521, p < 0.001). CONCLUSION: Quantitative assessment of attenuation of focal osteolytic lesions in VNCa bone marrow images allows differentiation between overall active and inactive disease with higher attenuation signifying an increasing likelihood of active disease. This is supported by a significant positive correlation between the attenuation and the ADC, as well as a corresponding inverse correlation to T1w signal intensity.

Initial Results of a Single-Source Dual-Energy Computed Tomography Technique Using a Split-Filter: Assessment of Image Quality, Radiation Dose, and Accuracy of Dual-Energy Applications in an In Vitro and In Vivo Study.

OBJECTIVE: The aim of this study was to investigate the image quality, radiation dose, and accuracy of virtual noncontrast images and iodine quantification of split-filter dual-energy computed tomography (CT) using a single x-ray source in a phantom and patient study. MATERIALS AND METHODS: In a phantom study, objective image quality and accuracy of iodine quantification were evaluated for the split-filter dual-energy mode using a tin and gold filter. In a patient study, objective image quality and radiation dose were compared in thoracoabdominal CT of 50 patients between the standard single-energy and split-filter dual-energy mode. The radiation dose was estimated by size-specific dose estimate. To evaluate the accuracy of virtual noncontrast imaging, attenuation measurements in the liver, spleen, and muscle were compared between a true noncontrast premonitoring scan and the virtual noncontrast images of the dual-energy scans. Descriptive statistics and the Mann-Whitney U test were used. RESULTS: In the phantom study, differences between the real and measured iodine concentration ranged from 2.2% to 21.4%. In the patient study, the single-energy and dual-energy protocols resulted in similar image noise (7.4 vs 7.1 HU, respectively; P = 0.43) and parenchymal contrast-to-noise ratio (CNR) values for the liver (29.2 vs 28.5, respectively; P = 0.88). However, the vascular CNR value for the single-energy protocol was significantly higher than for the dual-energy protocol (10.0 vs 7.1, respectively; P = 0.006). The difference in the measured attenuation between the true and the virtual noncontrast images ranged from 3.1 to 6.7 HU. The size-specific dose estimate of the dual-energy protocol was, on average, 17% lower than that of the single-energy protocol (11.7 vs 9.7 mGy, respectively; P = 0.008). CONCLUSIONS: Split-filter dual-energy compared with single-energy CT results in similar objective image noise in addition to dual-energy capabilities at 17% lower radiation dose. Because of beam hardening, split-filter dual-energy can lead to decreased CNR values of iodinated structures.

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.

The importance of spectral separation: an assessment of dual-energy spectral separation for quantitative ability and dose efficiency.

INTRODUCTION: One method to acquire dual-energy (DE) computed tomography (CT) data is to perform CT scans at 2 different x-ray tube voltages, typically 80 and 140 kV, either as 2 separate scans, by means of rapid kV switching, or with the use of 2 x-ray sources as in dual-source CT (DSCT) systems. In DSCT, it is possible to improve spectral separation with tin prefiltration (Sn) of the high-kV beam. Recently, x-ray tube voltages beyond the established range of 80 to 140 kV were commercially introduced, which enable additional voltage combinations for DE acquisitions, such as 80/150 Sn or 90/150 Sn kV. Here, we investigate the DE performance of several x-ray tube voltages and prefilter combinations on 2 DSCT scanners and the impact of the spectra on quantitative analysis and dose efficiency. MATERIALS AND METHODS: Circular phantoms of different sizes (10-40 cm in diameter) equipped with cylindrical inserts containing water and diluted iodine contrast agent (14.5 mg/cm) were scanned using 2 different DSCT systems (SOMATOM Definition Flash and SOMATOM Force; Siemens AG, Forchheim, Germany). Five x-ray tube voltage combinations (80/140 Sn, 100/140 Sn, 80/150 Sn, 90/150 Sn, and 100/150 Sn kV) were investigated, and the results were compared with the previous standard acquisition technique (80/140 kV). As an example, 80/140 Sn kV means that 1 x-ray tube of the DSCT system was operated at 80 kV, whereas the other was operated at 140 kV with additional tin prefiltration (Sn). Dose values in terms of computed tomography dose index (CTDIvol) were kept constant between the different voltage combinations but adjusted with regard to object size according to automatic exposure control recommendations. Reconstructed images were processed using linear blending of the low- and high-kV CT images to combined images, as well as 3-material decomposition techniques to generate virtual noncontrast (VNC) images and iodine images. Contrast and pixel noise were evaluated, as well as DE ratios, which are defined as the CT value at low kV divided by the CT value at high kV. RESULTS: For the 10-, 20-, 30-, and 40-cm phantom, dose values in terms of CTDIvol were 1.2, 2.6, 7.3, and 21.6 mGy, respectively. In the combined images, those obtained with tin filtration showed lower noise values at similar iodine enhancement levels than did images obtained without tin filtration. The largest differences in noise were observed for the larger phantoms, in particular the 40-cm phantom. Dual-energy ratios for iodine increased with decreasing voltages of the low-kV beam and with increasing voltages of the high-kV beam, and they increased when tin prefiltration was added. In case of the 20-cm phantom, DE ratios ranged from 2.0 at 80/140 kV to 3.4 at 80/150 Sn kV. The noise level of the VNC images was strongly correlated with the inverse of the DE ratio. Irrespective of the phantom size, the lowest noise values were measured for 80/150 Sn kV. DISCUSSION: Dual-source CT systems enable DE data to be acquired using a variety of voltage combinations. Combined (or mixed) DE images provide an image impression similar to standard 120 kV images, yet the noise level depends on the DE voltage combination that is selected. Noise in decomposed VNC images is strongly influenced by the DE ratio, and it improves substantially with tin filtration of the high-voltage beam.

Accuracy of contrast-enhanced dual-energy MDCT for the assessment of iodine uptake in renal lesions.

OBJECTIVE: The objective of our study was to assess the accuracy of iodine-related attenuation and iodine quantification as imaging biomarkers of iodine uptake in renal lesions on a single-phase nephrographic image with dual-energy MDCT. MATERIALS AND METHODS: Fifty-nine patients (41 men, 18 women; age range, 28-84 years) with 80 renal lesions underwent contrast-enhanced dual-energy CT during the nephrographic phase of enhancement. Renal lesions were characterized as enhancing or nonenhancing on color-coded iodine overlay maps using iodine-related attenuation (in Hounsfield units) and iodine quantification (in milligrams per milliliter). For iodine-related attenuation the iodine uptake thresholds of 15 and 20 HU were tested; a threshold of 0.5 mg/mL was used for iodine quantification. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of iodine-related attenuation and iodine quantification were calculated from chi-square tests of contingency with histopathology or imaging follow-up as the reference standard. The 95% CIs were calculated from binomial expression. Differences in sensitivity and specificity were assessed by means of McNemar analysis. RESULTS: A significant difference in sensitivity and specificity was found between iodine-related attenuation with the thresholds of 15 HU (sensitivity, 91.4%; specificity, 93.3%; PPV, 91.4%; NPV, 93.3%) and 20 HU (sensitivity, 77.1%; specificity, 100%; PPV, 100%; NPV, 84.9%) (p = 0.008) and between iodine quantification (sensitivity, 100%; specificity, 97.7%; PPV, 97.2%; NPV, 100%) and iodine-related attenuation with a threshold of 20 HU (p = 0.004). No significant difference in sensitivity and specificity was found between iodine quantification and iodine-related attenuation with a threshold of 15 HU. CONCLUSION: Contrast-enhanced dual-energy MDCT with iodine-related attenuation and iodine quantification allows accurate evaluation of iodine uptake in renal lesions on a single-phase nephrographic image.

Assessment of an advanced image-based technique to calculate virtual monoenergetic computed tomographic images from a dual-energy examination to improve contrast-to-noise ratio in examinations using iodinated contrast media.

INTRODUCTION: Following the trend of low-radiation dose computed tomographic (CT) imaging, concerns regarding the detectability of low-contrast lesions have been growing. The goal of this research was to evaluate whether a new image-based algorithm (Mono+) for virtual monoenergetic imaging with a dual-energy CT scanner can improve the contrast-to-noise ratio (CNR) and conspicuity of these low-contrast objects when using iodinated contrast media. MATERIALS AND METHODS: Four circular phantoms of different diameter (10-40 cm) with an iodine insert at the center were scanned at a fixed radiation dose with different single- (80, 100, 120 kV) and dual-energy protocols (80/140 kV, 80/140 Sn kV, 100/140 Sn kV) using a dual-source CT system. In addition, an anthropomorphic abdominal phantom with different low-contrast lesions was scanned with the settings previously mentioned but also at only a half and a quarter of the initial dose. Dual-energy data were processed, and virtual monoenergetic images (range, 40-190 keV) were generated. Beside the established technique, a newly developed prototype algorithm to calculate monoenergetic images (Mono+) was used. To avoid noise increase at lower calculated energies, which is a known drawback of virtual monoenergetic images at low kilo electron-volt, a regional spatial frequency-based recombination of the high signal at lower energies and the superior noise properties at medium energies is performed to optimize CNR in case of Mono+ images. The CNR and low-contrast detectability were evaluated. RESULTS: For all phantom sizes, the Mono+ technique provided increasing iodine CNR with decreasing kilo electron-volt, with the optimum CNR obtained at the lowest energy level of 40 keV. For all investigated phantom sizes, CNR of Mono+ images at low kilo electron-volt was superior to the CNR in single-energy images at an equivalent radiation dose and even higher than the CNR obtained with 80-kV protocols. In case of the anthropomorphic phantom, low-contrast detectability in monoenergetic images was, for all settings, similar to the circular phantoms, best for the voltage combination 80/140 Sn kV, irrespective of the dose level. For all dual-energy voltage combinations, the Mono+ algorithm led to superior results compared with single-energy imaging. DISCUSSION: With regard to optimized iodine CNR, it is more efficient to perform dual-energy scans and compute virtual monoenergetic images at 40 keV using the Mono+ technique than to perform low kilovolt scans. Given the improved CNR, the Mono+ algorithm could be very useful in improving both detection and differential diagnosis of abdominal lesions, specifically low-contrast lesions, as well as in other anatomical regions where improved iodine CNR is beneficial.

Optimization of dual-energy xenon-computed tomography for quantitative assessment of regional pulmonary ventilation.

OBJECTIVE: Dual-energy x-ray computed tomography (DECT) offers visualization of the airways and quantitation of regional pulmonary ventilation using a single breath of inhaled xenon gas. In this study, we sought to optimize scanning protocols for DECT xenon gas ventilation imaging of the airways and lung parenchyma and to characterize the quantitative nature of the developed protocols through a series of test-object and animal studies. MATERIALS AND METHODS: The Institutional Animal Care and Use Committee approved all animal studies reported here. A range of xenon/oxygen gas mixtures (0%, 20%, 25%, 33%, 50%, 66%, 100%; balance oxygen) were scanned in syringes and balloon test-objects to optimize the delivered gas mixture for assessment of regional ventilation while allowing for the development of improved 3-material decomposition calibration parameters. In addition, to alleviate gravitational effects on xenon gas distribution, we replaced a portion of the oxygen in the xenon/oxygen gas mixture with helium and compared gas distributions in a rapid-prototyped human central-airway test-object. Additional syringe tests were performed to determine if the introduction of helium had any effect on xenon quantitation. Xenon gas mixtures were delivered to anesthetized swine to assess airway and lung parenchymal opacification while evaluating various DECT scan acquisition settings. RESULTS: Attenuation curves for xenon were obtained from the syringe test-objects and were used to develop improved 3-material decomposition parameters (Hounsfield unit enhancement per percentage xenon: within the chest phantom, 2.25 at 80 kVp, 1.7 at 100 kVp, and 0.76 at 140 kVp with tin filtration; in open air, 2.5 at 80 kVp, 1.95 at 100 kVp, and 0.81 at 140 kVp with tin filtration). The addition of helium improved the distribution of xenon gas to the gravitationally nondependent portion of the airway tree test-object, while not affecting the quantitation of xenon in the 3-material decomposition DECT. The mixture 40% Xe/40% He/20% O2 provided good signal-to-noise ratio (SNR), greater than the Rose criterion (SNR > 5), while avoiding gravitational effects of similar concentrations of xenon in a 60% O2 mixture. Compared with 100/140 Sn kVp, 80/140 Sn kVp (Sn = tin filtered) provided improved SNR in a swine with an equivalent thoracic transverse density to a human subject with a body mass index of 33 kg/m. Airways were brighter in the 80/140 Sn kVp scan (80/140 Sn, 31.6%; 100/140 Sn, 25.1%) with considerably lower noise (80/140 Sn, coefficient of variation of 0.140; 100/140 Sn, coefficient of variation of 0.216). CONCLUSION: To provide a truly quantitative measure of regional lung function with xenon-DECT, the basic protocols and parameter calibrations need to be better understood and quantified. It is critically important to understand the fundamentals of new techniques to allow for proper implementation and interpretation of their results before widespread usage. With the use of an in-house derived xenon calibration curve for 3-material decomposition rather than the scanner supplied calibration and a xenon/helium/oxygen mixture, we demonstrate highly accurate quantitation of xenon gas volumes and avoid gravitational effects on gas distribution. This study provides a foundation for other researchers to use and test these methods with the goal of clinical translation.

Estimation and comparison of effective dose (E) in standard chest CT by organ dose measurements and dose-length-product methods and assessment of the influence of CT tube potential (energy dependency) on effective dose in a dual-source CT.

PURPOSE: To determine effective dose (E) during standard chest CT using an organ dose-based and a dose-length-product-based (DLP) approach for four different scan protocols including high-pitch and dual-energy in a dual-source CT scanner of the second generation. MATERIALS AND METHODS: Organ doses were measured with thermo luminescence dosimeters (TLD) in an anthropomorphic male adult phantom. Further, DLP-based dose estimates were performed by using the standard 0.014mSv/mGycm conversion coefficient k. Examinations were performed on a dual-source CT system (Somatom Definition Flash, Siemens). Four scan protocols were investigated: (1) single-source 120kV, (2) single-source 100kV, (3) high-pitch 120kV, and (4) dual-energy with 100/Sn140kV with equivalent CTDIvol and no automated tube current modulation. E was then determined following recommendations of ICRP publication 103 and 60 and specific k values were derived. RESULTS: DLP-based estimates differed by 4.5-16.56% and 5.2-15.8% relatively to ICRP 60 and 103, respectively. The derived k factors calculated from TLD measurements were 0.0148, 0.015, 0.0166, and 0.0148 for protocol 1, 2, 3 and 4, respectively. Effective dose estimations by ICRP 103 and 60 for single-energy and dual-energy protocols show a difference of less than 0.04mSv. CONCLUSION: Estimates of E based on DLP work equally well for single-energy, high-pitch and dual-energy CT examinations. The tube potential definitely affects effective dose in a substantial way. Effective dose estimations by ICRP 103 and 60 for both single-energy and dual-energy examinations differ not more than 0.04mSv.

Dual-energy CT for assessment of the severity of acute pulmonary embolism: pulmonary perfusion defect score compared with CT angiographic obstruction score and right ventricular/left ventricular diameter ratio.

OBJECTIVE: The purpose of this study was to prospectively evaluate the usefulness of scoring perfusion defects on perfusion images at dual-energy CT for assessment of the severity of pulmonary embolism. SUBJECTS AND METHODS: Thirty patients (13 men, 17 women; mean age, 55 +/- 15 [SD] years; range, 26-81 years) with pulmonary thromboembolism underwent dual-source CT at two voltages (140 and 80 kV). The weighted average image of two acquisitions was used for CT angiograms, and a color-coded iodine image was used for perfusion images. Two thoracic radiologists with 15 and 6 years of clinical experience independently assigned perfusion defect scores to perfusion images and both a CT angiographic (CTA) obstruction score and right ventricular-to-left ventricular (RV/LV) diameter ratio to CT angiograms. The CTA obstruction score was based on the Qanadli method. The perfusion defect score was defined as Sigma (n . d) / 40 x 100, where n is the number of segments and d is the degree of perfusion from 0 to 2. Correlations between perfusion defect score, CTA obstruction score, and RV/LV diameter ratio were evaluated. Agreement between perfusion defect score and CTA score was assessed per patient and per segment. Interobserver agreement regarding perfusion defect and CTA obstruction scores was analyzed. RESULTS: Perfusion defect and CTA obstruction scores had good correlation with RV/LV diameter ratio (r = 0.69, r = 0.66; all p < 0.001). Per patient, correlation between perfusion defect score and CTA obstruction score also was good (reader 1, r = 0.87; reader 2, r = 0.85; all p < 0.001). Per segment, moderate agreement was found between perfusion defect score and CTA obstruction score (reader 1, kappa = 0.56; reader 2, kappa = 0.51; all p < 0.05). Both readers were in strong agreement on perfusion defect score and CTA obstruction score. CONCLUSION: The proposed perfusion defect score had good correlation with RV/LV diameter ratio and CTA obstruction score. Therefore, acquisition of perfusion images at dual-energy CT may be helpful for assessing the severity of acute pulmonary embolism.

Technical principles of dual source CT.

During the past years, multi-detector row CT (MDCT) has evolved into clinical practice with a rapid increase of the number of detector slices. Today's 64 slice CT systems allow whole-body examinations with sub-millimeter resolution in short scan times. As an alternative to adding even more detector slices, we describe the system concept and design of a CT scanner with two X-ray tubes and two detectors (mounted on a CT gantry with a mechanical offset of 90 degrees) that has the potential to overcome limitations of conventional MDCT systems, such as temporal resolution for cardiac imaging. A dual source CT (DSCT) scanner provides temporal resolution equivalent to a quarter of the gantry rotation time, independent of the patient's heart rate (83 ms at 0.33 s rotation time). In addition to the benefits for cardiac scanning, it allows to go beyond conventional CT imaging by obtaining dual energy information if the two tubes are operated at different voltages. Furthermore, we discuss how both acquisition systems can be used to add the power reserve of two X-ray tubes for long scan ranges and obese patients. Finally, future advances of DSCT are highlighted.

First performance evaluation of a dual-source CT (DSCT) system.

We present a performance evaluation of a recently introduced dual-source computed tomography (DSCT) system equipped with two X-ray tubes and two corresponding detectors, mounted onto the rotating gantry with an angular offset of 90 degrees . We introduce the system concept and derive its consequences and potential benefits for electrocardiograph [corrected] (ECG)-controlled cardiac CT and for general radiology applications. We evaluate both temporal and spatial resolution by means of phantom scans. We present first patient scans to illustrate the performance of DSCT for ECG-gated cardiac imaging, and we demonstrate first results using a dual-energy acquisition mode. Using ECG-gated single-segment reconstruction, the DSCT system provides 83 ms temporal resolution independent of the patient's heart rate for coronary CT angiography (CTA) and evaluation of basic functional parameters. With dual-segment reconstruction, the mean temporal resolution is 60 ms (minimum temporal resolution 42 ms) for advanced functional evaluation. The z-flying focal spot technique implemented in the evaluated DSCT system allows 0.4 mm cylinders to be resolved at all heart rates. First clinical experience shows a considerably increased robustness for the imaging of patients with high heart rates. As a potential application of the dual-energy acquisition mode, the automatic separation of bones and iodine-filled vessels is demonstrated.