Polychromatic Images Research Articles

Image quality and optimal energy level of spectral CT virtual monochromatic series in atypical osteoblastic metastases in patients with lung cancer

Objective To assess image quality and optimal keV levels of spectral CT virtual monochromatic series in atypical vertebral osteoblastic metastases of lung cancer. Methods Patients with pathologically proven lung cancer who had undergone spectral CT (Discovery CT750 HD, GE) of the chest or abdomen more than twice were analyzed retrospectively. Vertebral osteoblastic metastases were confirmed by follow-up CT examinations, biopsy ,emission CT, PET/CT. The bone lesions were missed due to atypicalappearance or presented with suspicious density at the first exmaination were chosen. A total of twenty two patients with 72 lesions were enrolled. Conventional polychromatic images (140 kVp) and monochromatic images were generated (40 to 140 keV at an interval of 10 keV). The signal to noise ratio(SNR) and contrast to noise ratio (CNR) of the lesions were measured and calculated at all the 12 series images by two radiologists. The two radiologists scored the different series of images independently. Paired sample t test was used to compare SNR and CNR among 40 to 140 keV and 140 kVp images. The inter-observer agreement between the two radiologists was evaluated using Kappa statistics and the difference of different images intrarobserver was compared using Wilcoxon signed rank test. Results The SNR of 140 kVp was 48.03±20.17, and those of 50, 60 70 keV images were 58.52±22.92, 64.07±24.88, 59.54±22.04. SNR of 50, 60, 70 keV images was higher than that of 140 kVp (t values were 13.366,16.278, 18.889,P<0.01), 60 keV images had the highest SNR. The CNR of 140 kVp was 7.64±4.52 and those of 50, 60, 70 and 80 keV images were 7.95±4.99, 8.12±5.08, 8.16±5.05, 7.89±4.81. CNR of 50, 60, 70 and 80 keV images were higher than that of 140 kVp image (t values were 3.519, 5.050, 6.231, 4.413, P<0.01), 60 keV and 70 keV images had the higher CNR than 50 keV and 80 keV. Good interobserver agreement was found for the evaluation of image quality (Kappa =0.864,P<0.05).Moreover, the scores of both the two observes for 60 keV images were higher than 140 kVp images and higher than other monochromatic images. Conclusion Atypical vertebral osteoblastic metastases of lung cancer are more conspicuous in virtual monochromatic images as compared wtih 140 kVp polychromatic images and the optimal energy level was 60 keV, repectively. Key words: Lung neoplasms; Bone neoplasms; Neoplasm metastasis; Tomography, X-ray computed

Spectral CT monochromatic imaging of hepatocellular carcinoma: effect of image fusion on image quality

Objective To assess the effects of image fusion of CT spectral monochromatic imaging on image quality in small hepatocellular carcinoma (HCC). Methods Thirty patients with 40 pathologically proven small HCCs (≤3 cm) underwent upper abdominal plain CT and dual- phase enhanced spectral CT scan were analyzed retrospectively. Conventional 140 kVp polychromatic images (group A) and monochromatic images with energy levels from 40 to 140 keV were reconstructed by using spectral imaging viewer. Monochromatic images with highest CNR(group B) and 70 keV images with lowest noise (group C) were fused to generate fused images (group D) with image fusion software. Objective evaluation of 40 HCCs[contrast-to-noise ratio (CNR) of lesion, image noise in HU] and subjective rating score of 30 patients (image noise score, overall image quality score, and lesion conspicuity score) among the four groups were compared by using One-way ANOVA and Kruskal-Wallis H test. Results CNR (1.3±0.6, 2.1±0.6, 1.5±0.6 and 2.4± 1.3 respectively) and image noise [(20±7), (32±9), (18±3) and (24±6) HU respectively] among group A, B, C and D all had statistical differences(F =5.724 and 13.619, both P values 0.05). Image noise in group D was lower than group B and higher than group C, but showed no difference from group A(all P values >0.05). Image noise scores [(3.5±0.5),(3.3±0.4),(3.6±0.5) and (3.5±0.4) point, respectively] , overall image quality scores [(3.2±0.4),(3.3±0.3), (3.1±0.3)and(3.7±0.4)point respectively] and lesion conspicuity scores [(3.3±0.4),(3.9±0.4), (3.2±0.4)and(3.7±0.4)point, respectively] among the four groups all had statistical differences(Z = 9.581, 37.495 and 43.436, all P values<0.05). Scores of the four groups were all greater than 3 and met the clinical diagnostic level. Group D was higher than group B in image noise score, higher than the other three groups in overall image quality score, higher than group A in lesion conspicuity score (all P values < 0.05). Conclusion Combined use of CT spectral monochromatic imaging and image fusion can improve overall image quality while maintaining or increasing CNR in small HCC. Key words: Liver neoplasms; Tomography, X-ray computed; Comparative study

Dual energy CT: how well can pseudo-monochromatic imaging reduce metal artifacts?

Dual Energy CT (DECT) provides so-called monoenergetic images based on a linear combination of the original polychromatic images. At certain patient-specific energy levels, corresponding to certain patient- and slice-dependent linear combination weights, e.g., E = 160 keV corresponds to α = 1.57, a significant reduction of metal artifacts may be observed. The authors aimed at analyzing the method for its artifact reduction capabilities to identify its limitations. The results are compared with raw data-based processing. Clinical DECT uses a simplified version of monochromatic imaging by linearly combining the low and the high kV images and by assigning an energy to that linear combination. Those pseudo-monochromatic images can be used by radiologists to obtain images with reduced metal artifacts. The authors analyzed the underlying physics and carried out a series expansion of the polychromatic attenuation equations. The resulting nonlinear terms are responsible for the artifacts, but they are not linearly related between the low and the high kV scan: A linear combination of both images cannot eliminate the nonlinearities, it can only reduce their impact. Scattered radiation yields additional noncanceling nonlinearities. This method is compared to raw data-based artifact correction methods. To quantify the artifact reduction potential of pseudo-monochromatic images, they simulated the FORBILD abdomen phantom with metal implants, and they assessed patient data sets of a clinical dual source CT system (100, 140 kV Sn) containing artifacts induced by a highly concentrated contrast agent bolus and by metal. In each case, they manually selected an optimal α and compared it to a raw data-based material decomposition in case of simulation, to raw data-based material decomposition of inconsistent rays in case of the patient data set containing contrast agent, and to the frequency split normalized metal artifact reduction in case of the metal implant. For each case, the contrast-to-noise ratio (CNR) was assessed. In the simulation, the pseudo-monochromatic images yielded acceptable artifact reduction results. However, the CNR in the artifact-reduced images was more than 60% lower than in the original polychromatic images. In contrast, the raw data-based material decomposition did not significantly reduce the CNR in the virtual monochromatic images. Regarding the patient data with beam hardening artifacts and with metal artifacts from small implants the pseudo-monochromatic method was able to reduce the artifacts, again with the downside of a significant CNR reduction. More intense metal artifacts, e.g., as those caused by an artificial hip joint, could not be suppressed. Pseudo-monochromatic imaging is able to reduce beam hardening, scatter, and metal artifacts in some cases but it cannot remove them. In all cases, the CNR is significantly reduced, thereby rendering the method questionable, unless special post processing algorithms are implemented to restore the high CNR from the original images (e.g., by using a frequency split technique). Raw data-based dual energy decomposition methods should be preferred, in particular, because the CNR penalty is almost negligible.

Feasibility of Improved Attenuation Correction for SPECT Reconstruction in the Presence of Dense Materials Using Dual-Energy Virtual Monochromatic CT: A Phantom Study

Objective: Computed tomography (CT)-based attenuation correction (CTAC) offers the clear benefit of reliable reconstruction of single-photon emission computed tomography (SPECT) images through its ability to achieve object-specific attenuation maps, but artifacts from dense materials often deteriorate CTAC performance. Therefore, we investigate the feasibility of CTAC in the presence of dense materials using dual-energy virtual monochromatic CT data. Methods: A sodium pertechnetate-filled cylindrical uniform phantom, with a pair of undiluted iodine syringes attached, is scanned with a dual-source CT scanner to obtain both single-energy (120 kVp) polychromatic and dual-energy (80 kVp/140 kVp with tin filtering) virtual monochromatic CT images. The single-energy and the dual-energy CT images are then converted to attenuation maps at 141 keV. SPECT images are reconstructed from 99mTc emission data of the phantom using each single-energy and dual-energy attenuation map and incorporating CTAC procedure. A region-of-in- terest analysis is performed to quantitatively compare the attenuation maps between the single-energy and the dual-energy techniques, each at an iodine-free position and a position adjacent to the iodine solutions. Results: At the iodine-free position, the phantom provides a uniform distribution of attenuation maps in both the single-energy and the dual-energy techniques. In the presence of adjacent iodine solutions, however, severe artifacts appeare in the single-energy CT images. These artifacts make attenuation values fluctuate, resulting in erroneous pixel values in the CTAC SPECT images. In contrast, dual-energy CT strongly suppresses the artifacts and hence improves the uniformity of the attenuation maps and the resultant SPECT images. Conclusions: Dual-energy CT with virtual monochromatic reconstruction has the potential to substantially reduce artifacts arising from dense materials. It has the potential to improve the accuracy of attenuation maps and the resultant CTAC SPECT images.

First experience with single-source, dual-energy CCTA for monochromatic stent imaging.

Single-source, dual-energy coronary computed tomography angiography (CCTA) with monochromatic image reconstruction allows significant noise reduction. The aim of the study was to evaluate the impact of monochromatic CCTA image reconstruction on coronary stent imaging, as the latter is known to be affected by artefacts from highly attenuating strut material resulting in artificial luminal narrowing. Twenty-one patients with 62 stents underwent invasive coronary angiography and single-source, dual-energy CCTA after stent implantation. Standard polychromatic images as well as eight monochromatic series (50, 60, 70, 80, 90, 100, 120, and 140 keV) were reconstructed for each CCTA. Signal and noise were measured within the stent lumen and in the aortic root. Mean in-stent luminal diameter was assessed in all CCTA reconstructions and compared with quantitative invasive coronary angiography (QCA). Luminal attenuation was higher in the stent than in the aortic root throughout all monochromatic reconstructions (P < 0.001). An increase in monochromatic energy was associated with a decrease in luminal attenuation values (P < 0.001). The mean in-stent luminal diameter underestimation by monochromatic CCTA compared with QCA was 90% at low monochromatic energy (50 keV) and improved to 37% at high monochromatic (140 keV) reconstruction while stent diameter was underestimated by 39% with standard CCTA. Monochromatic CCTA can be used reliably in patients with coronary stents. However, reconstructions with energies below 80 keV are not recommended as the blooming artefacts are most pronounced at such low energies, resulting in up to 90% stent diameter underestimation.

PAINTER: a spatiospectral image reconstruction algorithm for optical interferometry.

Astronomical optical interferometers sample the Fourier transform of the intensity distribution of a source at the observation wavelength. Because of rapid perturbations caused by atmospheric turbulence, the phases of the complex Fourier samples (visibilities) cannot be directly exploited. Consequently, specific image reconstruction methods have been devised in the last few decades. Modern polychromatic optical interferometric instruments are now paving the way to multiwavelength imaging. This paper is devoted to the derivation of a spatiospectral (3D) image reconstruction algorithm, coined Polychromatic opticAl INTErferometric Reconstruction software (PAINTER). The algorithm relies on an iterative process, which alternates estimation of polychromatic images and complex visibilities. The complex visibilities are not only estimated from squared moduli and closure phases, but also differential phases, which helps to better constrain the polychromatic reconstruction. Simulations on synthetic data illustrate the efficiency of the algorithm and, in particular, the relevance of injecting a differential phases model in the reconstruction.

Abdominal CT: An intra-individual comparison between virtual monochromatic spectral and polychromatic 120-kVp images obtained during the same examination

ObjectivesTo compare quantitative and subjective image quality between virtual monochromatic spectral (VMS) and conventional polychromatic 120-kVp imaging performed during the same abdominal computed tomography (CT) examination. Materials and methodsOur institutional review board approved this prospective study; each participant provided written informed consent. 51 patients underwent sequential fast kVp-switching dual-energy (80/140kVp, volume CT dose index: 12.7mGy) and single-energy (120-kVp, 12.7mGy) abdominal enhanced CT over an 8cm scan length with a random acquisition order and a 4.3-s interval. VMS images with filtered back projection (VMS-FBP) and adaptive statistical iterative reconstruction (so-called hybrid IR) (VMS-ASIR) (at 70keV), as well as 120-kVp images with FBP (120-kVp-FBP) and ASIR (120-kVp-ASIR), were generated from dual-energy and single-energy CT data, respectively. The objective image noises, signal-to-noise ratios and contrast-to-noise ratios of the liver, kidney, pancreas, spleen, portal vein and aorta, and the lesion-to-liver and lesion-to-kidney contrast-to-noise ratios were measured. Two radiologists independently and blindly assessed the subjective image quality. The results were analyzed using the paired t-test, Wilcoxon signed rank sum test and mixed-effects model with Bonferroni correction. ResultsVMS-ASIR images were superior to 120-kVp-FBP, 120-kVp-ASIR and VMS-FBP images for all the quantitative assessments and the subjective overall image quality (all P<0.001), while VMS-FBP images were superior to 120-kVp-FBP and 120-kVp-ASIR images (all P<0.004). ConclusionsVMS images at 70keV have a higher image quality than 120-kVp images, regardless of the application of hybrid IR. Hybrid IR can further improve the image quality of VMS imaging.

Spectral CT imaging in patients with Budd-Chiari syndrome: investigation of image quality.

To assess the image quality of monochromatic imaging from spectral CT in patients with Budd-Chiari syndrome (BCS), fifty patients with BCS underwent spectral CT to generate conventional 140 kVp polychromatic images (group A) and monochromatic images, with energy levels from 40 to 80, 40 + 70, and 50 + 70 keV fusion images (group B) during the portal venous phase (PVP) and the hepatic venous phase (HVP). Two-sample t tests compared vessel-to-liver contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) for the portal vein (PV), hepatic vein (HV), inferior vena cava. Readers' subjective evaluations of the image quality were recorded. The highest SNR values in group B were distributed at 50 keV; the highest CNR values in group B were distributed at 40 keV. The higher CNR values and SNR values were obtained though PVP of PV (SNR 18.39 ± 6.13 vs. 10.56 ± 3.31, CNR 7.81 ± 3.40 vs. 3.58 ± 1.31) and HVP of HV (3.89 ± 2.08 vs. 1.27 ± 1.55) in the group B; the lower image noise for group B was at 70 keV and 50 + 70 keV (15.54 ± 8.39 vs. 18.40 ± 4.97, P = 0.0004 and 18.97 ± 7.61 vs. 18.40 ± 4.97, P = 0.0691); the results show that the 50 + 70 keV fusion image quality was better than that in group A. Monochromatic energy levels of 40-70, 40 + 70, and 50 + 70 keV fusion image can increase vascular contrast and that will be helpful for the diagnosis of BCS, we select the 50 + 70 keV fusion image to acquire the best BCS images.

Comparison of gastric vascular anatomy by monochromatic and polychromatic dual-energy spectral computed tomography imaging

To evaluate the use of monochromatic and polychromatic dual-energy spectral computed tomography (CT) imaging for preoperative assessment of gastric vascular anatomy. Patients with suspected gastric cancer underwent spectral CT to generate conventional 140 kVp polychromatic and monochromatic images with energy levels ranging from 40 to 140 keV during the late arterial and portal venous phases. Optimal monochromatic images were selected according to the contrast-to-noise ratio (CNR) for the gastric artery. Image quality was subjectively assessed. Display rates of the arteries were recorded. The study included 64 patients. Monochromatic images at 53 ± 3 keV provided the optimum CNR. At this energy level, subjective image scores were significantly higher for monochromatic images than polychromatic images. There were no significant differences in the display rates of arteries between polychromatic and optimal monochromatic images. Monochromatic images obtained with spectral CT can improve the visualization of gastric arteries.

Spectral CT Imaging of Laryngeal and Hypopharyngeal Squamous Cell Carcinoma: Evaluation of Image Quality and Status of Lymph Nodes

PurposeThe purpose of this study was to evaluate image quality and status of lymph nodes in laryngeal and hypopharyngeal squamous cell carcinoma (SCC) patients using spectral CT imaging.Materials and MethodsThirty-eight patients with laryngeal and hypopharyngeal SCCs were scanned with spectral CT mode in venous phase. The conventional 140-kVp polychromatic images and one hundred and one sets of monochromatic images were generated ranging from 40 keV to 140 keV. The mean optimal keV was calculated on the monochromatic images. The image quality of the mean optimal keV monochromatic images and polychromatic images was compared with two different methods including a quantitative analysis method and a qualitative analysis method. The HU curve slope (λHU) in the target lymph nodes and the primary lesion was calculated respectively. The ratio of λHU was studied between metastatic and non-metastatic lymph nodes group.ResultsA total of 38 primary lesions were included. The mean optimal keV was obtained at 55±1.77 keV on the monochromatic images. The image quality evaluated by two different methods including a quantitative analysis method and a qualitative analysis method was obviously increased on monochromatic images than polychromatic images (p<0.05). The ratio of λHU between metastatic and non-metastatic lymph nodes was significantly different in the venous phase images (p<0.05).ConclusionThe monochromatic images obtained with spectral CT can be used to improve the image quality of laryngeal and hypopharyngeal SCC and the N-staging accuracy. The quantitative ratio of λHU may be helpful for differentiating between metastatic and non-metastatic cervical lymph nodes.

Spectral CT Demonstration of the Superior Mesenteric Artery: Comparison of Monochromatic and Polychromatic Imaging

To investigate the performance of spectral computed tomography (CT) in depiction of the superior mesenteric artery (SMA) compared to conventional polychromatic CT. This prospective study had institutional review board approval, and written informed consent was obtained. Fifty patients underwent spectral CT examination using gemstone spectral imaging with a single-tube, fast dual-tube voltage-switching technique. Spectrum analysis was used to select the monochromatic images that provide the optimal contrast-to-noise ratio (CNR) for SMA angiography. The CNR for SMA at the selected monochromatic level was compared with that from the conventional polychromatic images. Image quality and visibility of the branch order of SMA were also assessed and compared. The monochromatic images at 50 keV (mean 50.09 ± 1.98) provided the optimal CNR for SMA angiography. At this energy level, the monochromatic images had higher (20.8 vs 9.2) CNR than the polychromatic images, and the image quality was superior to conventional polychromatic images (P < .05). Fourth to fifth (mean 4.3) and third to fourth (mean 3.5) order branches of SMA were demonstrated at monochromatic and polychromatic images, respectively. Gemstone spectral imaging with monochromatic images at 50 keV by spectral CT could improve the CTA image quality and demonstrate more branch order in depiction of normal SMA compared to conventional polychromatic imaging.

Quantitative Iodine-Based Material Decomposition Images with Spectral CT Imaging for Differentiating Prostatic Carcinoma from Benign Prostatic Hyperplasia

To investigate the value of iodine-based material decomposition images produced via spectral computed tomography (CT) in differentiating prostate cancer (PCa) from benign prostate hyperplasia (BPH). Fifty-six male patients underwent CT examination with spectral imaging during arterial phase (AP), venous phase (VP), and parenchymal phase (PP) of enhancement. Iodine concentrations of lesions were measured and normalized to that of the obturator internus muscle. Lesion CT values at 75keV (corresponding to the energy of polychromatic images at 120 kVp) were measured and also normalized; their differences between AP and VP, VP and PP, and PP and AP were also obtained. The two-sample t-test was performed for comparisons. A receiver operating characteristic curve was generated to establish the threshold for normalized iodine concentration (NIC). Fifty-two peripheral lesions were found, which were confirmed by biopsy as 28 cases of PCa and 24 BPHs. The NICs of prostate cancers significantly differed from those of the BPHs: 2.38±1.72 compared with 1.21±0.72 in AP, respectively, and 2.67±0.61 compared with 2.27±0.77 in VP. Receiver operating characteristic analysis indicated that an NIC of 1.24 in the AP provided a sensitivity of 88% and a specificity of 71% for differentiating PCa from BPH. Spectral CT imaging enabled quantitative depiction of contrast medium uptake in prostatic lesions and improved sensitivity and specificity for differentiating PCa from BPH.

Metal artifacts reduction using monochromatic images from spectral CT: Evaluation of pedicle screws in patients with scoliosis

PurposeTo evaluate the effectiveness of spectral CT in reducing metal artifacts caused by pedicle screws in patients with scoliosis. Materials and methodsInstitutional review committee approval and written informed consents from patients were obtained. 18 scoliotic patients with a total of 228 pedicle screws who underwent spectral CT imaging were included in this study. Monochromatic image sets with and without the additional metal artifacts reduction software (MARS) correction were generated with photon energy at 65keV and from 70 to 140keV with 10keV interval using the 80kVp and 140kVp projection sets. Polychromatic images corresponded to the conventional 140kVp imaging were also generated from the same scan data as a control group. Both objective evaluation (screw width and quantitative artifacts index measurements) and subjective evaluation (depiction of pedicle screws, surrounding structures and their relationship) were performed. ResultsImage quality of monochromatic images in the range from 110 to 140keV (0.97±0.28) was rated superior to the conventional polychromatic images (2.53±0.54) and also better than monochromatic images with lower energy. Images of energy above 100keV also give accurate measurement of the width of screws and relatively low artifacts index. The form of screws was slightly distorted in MARS reconstruction. ConclusionsCompared to conventional polychromatic images, monochromatic images acquired from dual-energy CT provided superior image quality with much reduced metal artifacts of pedicle screws in patients with scoliosis. Optimal energy range was found between 110 and 140keV.

Gemstone Spectral Imaging Dual-energy Computed Tomography: A Novel Technique to Determine Urinary Stone Composition

To assess the capability of determining the chemical composition of urinary stones using dual-energy spectral computed tomography (CT). A total of 116 urinary stones with a known chemical composition determined by infrared spectroscopy were scanned using both gemstone spectral imaging and conventional polychromatic imaging (at 120 kVp) invitro. The CT numbers of each stone were recorded from the 11 sets of monochromatic images (40-140 keV, 10-keV interval) and 120-kVp polychromatic images. The differences between the CT numbers obtained in the 12 sets were compared among the stone groups. The 116 urinary stones were classified into 7 groups: uric acid (n= 16), cystine (n= 10), brushite (n= 17), weddellite (n= 14), whewellite (n= 24), carbapatite (n= 12), and struvite (n= 23). The paired CT numbers (at 120 kVp and 50 keV, respectively) of each stone group were as follows: uric acid, 469.11 ± 69.83 and 474.06 ± 40.55 Hounsfield units (HU); cystine, 564.81 ± 97.71 and 839.58 ± 92.14 HU; brushite, 1830.94 ± 59.19 and 2787.41 ± 306.07 HU; weddellite, 1438.09 ± 191.12 and 2100.79 ± 202.32 HU; whewellite, 1493.48 ± 259.90 and 2321.39 ± 367.23 HU; carbapatite, 1784.58 ± 106.42 and 2513.86 ± 189.09 HU; and struvite, 833.037 ± 9.91 and 1123.24 ± 267.70 HU. The differences in the CT numbers at 120 kVp and 50 keV among the groups were statistically significant by binary comparison (P<.05), except for those at 120 kVp between uric acid and cystine (P= .121), whewellite and weddellite (P= .280), and brushite and carbapatite (P= .419). Gemstone spectral imaging dual-energy CT provides a novel method to better characterize pure urinary stones using the CT numbers at 50 keV.

Gastric Cancer Staging with Dual Energy Spectral CT Imaging

PurposeTo evaluate the clinical utility of dual energy spectral CT (DEsCT) in staging and characterizing gastric cancers.Materials and Methods96 patients suspected of gastric cancers underwent dual-phasic scans (arterial phase (AP) and portal venous phase (PP)) with DEsCT mode. Three types of images were reconstructed for analysis: conventional polychromatic images, material-decomposition images, and monochromatic image sets with photon energies from 40 to 140 keV. The polychromatic and monochromatic images were compared in TNM staging. The iodine concentrations in the lesions and lymph nodes were measured on the iodine-based material-decomposition images. These values were further normalized against that in aorta and the normalized iodine concentration (nIC) values were statistically compared. Results were correlated with pathological findings.ResultsThe overall accuracies for T, N and M staging were (81.2%, 80.0%, and 98.9%) and (73.9%, 75.0%, and 98.9%) determined with the monochromatic images and the conventional kVp images, respectively. The improvement of the accuracy in N-staging using the keV images was statistically significant (p<0.05). The nIC values between the differentiated and undifferentiated carcinoma and between metastatic and non-metastatic lymph nodes were significantly different both in AP (p = 0.02, respectively) and PP (p = 0.01, respectively). Among metastatic lymph nodes, nIC of the signet-ring cell carcinoma were significantly different from the adenocarcinoma (p = 0.02) and mucinous adenocarcinoma (p = 0.01) in PP.ConclusionThe monochromatic images obtained with DEsCT may be used to improve the N-staging accuracy. Quantitative iodine concentration measurements may be helpful for differentiating between differentiated and undifferentiated gastric carcinoma, and between metastatic and non-metastatic lymph nodes.

Selecting optimal monochromatic level with spectral CT imaging for improving imaging quality in hepatic venography

Objective To investigate the effect of spectral CT monochromatic images for improving imaging quality in hepatic venography. Methods Thirty patients underwent spectral CT examination on a GE Discovery CT 750 HD scanner.During portal phase,1.25 mm slice thickness polychromatic images and optimal monochromatic images were obtained,and volume rendering and maximum intensity projection were created to show the hepatic veins respectively.The overall imaging quality was evaluated on a five-point scale by two radiologists.Inter-observer agreement in subjective image quality grading was assessed byKappastatistics.Paired-sample t test were used to compare hepatic vein attenuation,hepatic parenchyma attenuation,CT value difference between the hepatic vein and the liver parenchyma,image noise,vein-to-liver contrast-to-noise ratio (CNR),the image quality score of hepatic venography between the two image data sets. Results The monochromatic images at 50 ke V were found to demonstrate the best CNR for hepatic vein.The hepatic vein attenuation[ (329±47) HU],hepatic parenchyma attenuation[ (178±33) HU],CT value difference between the hepatic vein and the liver parenchyma[ (151±33) HU],image noise (17.33±4.18),CNR (9.13±2.65),the image quality score (4.2±0.6) of optimal monochromatic images were significantly higher than those of polychromatic images[ (149±18) HU],[ (107±14) HU],[ (43±11) HU],12.55±3.02,3.53±1.03,3.1±0.8 (t values were 24.79,13.95,18.85,9.07,13.25 and 12.04,respectively,P<0.01).In the comparison of image quality,Kappa value was 0.81 with optimal monochromatic images and 0.69 with polychromatic images. Conclusion Monochromatic images of spectral CT could improve CNR for displaying hepatic vein and improve the image quality compared to the conventional polychromatic images. Key words: Hepatic vein; Tomography,X-ray computed; Comparative study

Spectral Optimization of Chest CT Angiography with Reduced Iodine Load: Experience in 80 Patients Evaluated with Dual-Source, Dual-Energy CT

To determine the energy levels that provide optimal imaging of thoracic circulation at dual-energy computed tomographic (CT) angiography with reduced iodine load in comparison with a standard technique. The institutional review board approved the study with waiver of patient consent. Eighty patients underwent a dual-source, dual-energy CT examination after administration of low-concentration contrast material (170 mg of iodine per milliliter), and eight series of images were reconstructed, including the original polychromatic images at 80 and 140 kV and six series of virtual monochromatic spectral images at 50, 60, 70, 80, 90, and 100 keV. For each vascular compartment, the energy level that provided optimal evaluation on virtual monochromatic spectral images was determined, and these series were compared with the polychromatic dual-energy images and with standard chest CT images that were used as controls. Comparisons between groups were performed by using the paired Student t test for continuous variables and the McNemar test for categorical variables. Comparisons between dual-energy and standard CT images were performed by using the unpaired Student t test for continuous variables and the χ(2) test for categorical variables. For the aorta, pulmonary arteries, and veins, the reconstruction at 60 keV provided adequate attenuation without marked beam-hardening artifacts in 90% of patients, with the highest contrast-to-noise and signal-to-noise ratios, the lowest level of subjective noise, and no significant differences with images at 80 kV (mean energy, 54 keV). For the superior vena cava and brachiocephalic veins, the reconstructions at 100 keV enabled artifact-free analysis of the perivascular anatomic zone without a significant difference with images at 140 kV (mean energy, 92 keV). Compared with standard CT images acquired after administration of a 35% iodinated contrast agent, there was a statistically significant reduction in the frequency of artifacts around systemic veins at 100 keV (P < .001) and similar overall image quality for central vessels at 60 keV (P > .05). An optimal analysis of thoracic circulation can be achieved on virtual monochromatic spectral images at 60 keV and 100 keV and on the original polychromatic images at 80 kV and 140 kV. http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.12120195/-/DC1.

Improving the Image Quality in Computed Tomographic Pulmonary Angiography With Dual-Energy Subtraction

The objectives of this study were to assess quantitative and subjective image quality in computed tomographic pulmonary angiography using dual-energy subtraction methods compared with those of the monochromatic images using optimal contrast-to-noise ratios and those of the routine polychromatic images and to select the best dual-energy subtraction method. A total of 1 routine polychromatic image, 3 sets of dual-energy subtraction images (DESIs), and 2 sets of monochromatic images with different optimal contrast-to-noise ratios from 30 patients were obtained. The signal intensity and noise were measured; signal-to-noise ratio and contrast-to-noise ratio (CNR) were calculated. The global subjective image quality was subjectively assessed. The DESI 3 got the highest CNR and the DESI 1 got the second highest CNR. The DESI 1 got the highest global subjective image quality score. The 3 subtraction image sets got the highest score in visualization of the pulmonary artery branches. Computed tomographic pulmonary angiography with dual-energy subtraction technique is feasible. The DESI 1 afforded the best balance between the quantitative analysis and the subjective evaluation.

First experience with monochromatic coronary computed tomography angiography from a 64-slice CT scanner with Gemstone Spectral Imaging (GSI)

BackgroundNew technology combining dual-energy CT with the latest gemstone detectors for spectral imaging (GSI) can be used to synthesize monochromatic images that mimic images as if different monochromatic x-ray sources were used. ObjectiveThe aim of the study was to evaluate the optimal combination of monochromatic image energy and adaptive statistical iterative reconstruction (ASiR) for monochromatic reconstruction of coronary CT angiography (CTA) images with the use of GSI. MethodsTwenty consecutive patients underwent coronary CTA on a GSI capable 64-slice CT scanner (Discovery CT 750 High Definition, GE Healthcare). In 7 sets of monochromatic images (60, 65, 70, 75, 80, 90, and 110 keV; each with increasing contributions of ASiR, ie, 0%, 20%, 40%, 60%, and 80%; n = 35 reconstructions per patient), signal-to-noise (aortic root) and contrast-to-noise (left main artery) ratios were assessed. Signal-to-noise ratio, contrast-to-noise ratio, and image quality (graded on a 5-point Likert scale) were assessed in all above monochromatic reconstructions and compared with the respective standard (conventional polychromatic) image. ResultsCompared with conventional polychromatic images, reconstructions with 60 keV and 80% ASiR showed the highest improvement in contrast-to-noise (144%; P < 0.001) and signal-to-noise ratio (173%; P < 0.001). Image quality reached a plateau at 65–75 keV with 40%–60% ASiR blending, yielding a maximal image quality score improvement of 50% compared with conventional imaging (P < 0.001). ConclusionIn coronary CTA with low radiation technique (mean radiation dose, 1.8 ± 0.7 mSv), GSI with monochromatic reconstructions (65–75 keV) and ASiR (40%–60%) offers significant noise reduction and image quality improvement.

Spectral CT in the demonstration of the gastrocolic ligament: a comparison study

To investigate the performance of spectral CT in the depiction of the gastrocolic ligament (GCL) compared to conventional polychromatic CT. Gemstone spectral CT and conventionally polychromatic CT examinations were randomly allocated to be performed on 62 consecutive patients. A total of 11 groups of monochromatic images were generated on energy levels ranging from 40 to 140keV at an interval of 10keV. A five-score classification system was used to evaluate the performances of CT images in the demonstration of GCL. The inter-observer agreement between two radiologists in their evaluation of the GCL by each method was evaluated using kappa statistics. There were statistically significant differences between the spectral CT and polychromatic CT in their abilities to highlight the GCL (observer 1: χ(2)=18.310, P<0.001; observer 2: χ(2)=19.780, P<0.001). The distinct display (score≥3) rates of the GCL by integrated monochromatic images were higher than that of polychromatic images (P<0.001). The best energy level for displaying the GCL by spectral CT was 50-70keV. The kappa value for the image scores on the integrated keV images between the two radiologists was higher than that for polychromatic CT images (P<0.01). Spectral CT can improve the visualisation of the GCL compared to polychromatic CT.