Accuracy of the raw-data-based effective atomic numbers and monochromatic CT numbers for contrast medium with a dual-energy CT technique

Variation in Hounsfield unit calculated using dual-energy computed tomography: comparison of dual-layer, dual-source, and fast kilovoltage switching technique

The purpose of the study is to investigate the variation in Hounsfield unit (HU) values calculated using dual-energy computed tomography (DECT) scanners. A tissue characterization phantom inserting 16 reference materials were scanned three times using DECT scanners [dual-layer CT (DLCT), dual-source CT (DSCT), and fast kilovoltage switching CT (FKSCT)] changing scanning conditions. The single-energy CT images (120 or 140 kVp), and virtual monochromatic images at 70 keV (VMI70) and 140 keV (VMI140) were reconstructed, and the HU values of each reference material were measured. The difference in HU values was larger when the phantom was scanned using the half dose with wrapping with rubber (strong beam-hardening effect) compared with the full dose without the rubber (reference condition), and the difference was larger as the electron density increased. For SECT, the difference in HU values against the reference condition measured by the DSCT (3.2 ± 5.0 HU) was significantly smaller (p < 0.05) than that using DLCT with 120 kVp (22.4 ± 23.8 HU), DLCT with 140 kVp (11.4 ± 12.8 HU), and FKSCT (13.4 ± 14.3 HU). The respective difference in HU values in the VMI70 and VMI140 measured using the DSCT (10.8 ± 17.1 and 3.5 ± 4.1 HU) and FKSCT (11.5 ± 21.8 and 5.5 ± 10.4 HU) were significantly smaller than those measured using the DLCT120 (23.1 ± 27.5 and 12.4 ± 9.4 HU) and DLCT140 (22.3 ± 28.6 and 13.1 ± 11.4 HU). The HU values and the susceptibility to beam-hardening effects varied widely depending on the DECT scanners.

Dual-Energy Computed Tomography For Differentiation Between Osteoblastic Metastases and Bone Islands

Objective

The objective of our study was to evaluate the utility of Rho/Z on dual-energy computed tomography (DECT) for the differentiation of osteoblastic metastases (OBMs) from bone islands (BIs).

Methods

DECT images of 110 patients with malignancies were collected. The effective atomic number (Z), electron density (Rho), dual energy index (DEI), and regular CT (rCT) values were measured by two observers. Independent-sample t-test was used to compare these values between OBMs and BIs. The diagnostic performance was assessed by receiver operating characteristic (ROC) analysis and the cutoff values were evaluated according to ROC curves.

Results

A total of 205 OBMs and 120 BIs were included. The mean values of Z, Rho, DEI, and rCT of OBMs were significantly lower than those of BIs, whereas the standard deviation values were higher than those of BIs (all p ≤ 0.05). ROC analysis showed that 11.86 was the optimal cutoff value for Z, rendering an area under the ROC curve (AUC) of 0.91, with a sensitivity of 91.2% and a specificity of 82.5%.

Conclusion

DECT can provide quantitative values of Z, Rho, and DEI and has good performance in differentiating between OBMs and BIs.

Significance of the spectral correction of photon counting detector response in material classification from spectral x-ray CT

Purpose: Photon counting imaging detectors (PCD) has paved the way for spectral x-ray computed tomography (spectral CT), which simultaneously measures a sample's linear attenuation coefficient (LAC) at multiple energies. However, cadmium telluride (CdTe)-based PCDs working under high flux suffer from detector effects, such as charge sharing and photon pileup. These effects result in the severe spectral distortions of the measured spectra and significant deviation of the extracted LACs from the reference attenuation curve. We analyze the influence of the spectral distortion correction on material classification performance. Approach: We employ a spectral correction algorithm to reduce the primary spectral distortions. We use a method for material classification that measures system-independent material properties, such as electron density, ρ e , and effective atomic number, Z eff . These parameters are extracted from the LACs using attenuation decomposition and are independent of the scanner specification. The classification performance with the raw and corrected data is tested on different numbers of energy bins and projections and different radiation dose levels. We use experimental data with a broad range of materials in the range of 6 ≤ Z eff ≤ 15 , acquired with a custom laboratory instrument for spectral CT. Results: We show that using the spectral correction leads to an accuracy increase of 1.6 and 3.8 times in estimating ρ e and Z eff , respectively, when the image reconstruction is performed from only 12 projections and the 15 energy bins approach is used. Conclusions: The correction algorithm accurately reconstructs the measured attenuation curve and thus gives better classification performance.

Towards Personalised Contrast Injection: Artificial-Intelligence-Derived Body Composition and Liver Enhancement in Computed Tomography

In contrast-enhanced computed tomography, total body weight adapted contrast injection protocols have proven successful in achieving a homogeneous enhancement of vascular structures and liver parenchyma. However, because solid organs have greater perfusion than adipose tissue, the lean body weight (fat-free mass) rather than the total body weight is theorised to cause even more homogeneous enhancement. We included 102 consecutive patients who underwent a multiphase abdominal computed tomography between March 2016 and October 2019. Patients received contrast media (300 mgI/mL) according to bodyweight categories. Using regions of interest, we measured the Hounsfield unit (HU) increase in liver attenuation from unenhanced to contrast-enhanced computed tomography. Furthermore, subjective image quality was graded using a four-point Likert scale. An artificial intelligence algorithm automatically segmented and determined the body compositions and calculated the percentages of lean body weight. The hepatic enhancements were adjusted for iodine dose and iodine dose per total body weight, as well as percentage lean body weight. The associations between enhancement and total body weight, body mass index, and lean body weight were analysed using linear regression. Patients had a median age of 68 years (IQR: 58–74), a total body weight of 81 kg (IQR: 73–90), a body mass index of 26 kg/m² (SD: ±4.2), and a lean body weight percentage of 50% (IQR: 36–55). Mean liver enhancements in the portal venous phase were 61 ± 12 HU (≤70 kg), 53 ± 10 HU (70–90 kg), and 53 ± 7 HU (≥90 kg). The majority (93%) of scans were rated as good or excellent. Regression analysis showed significant correlations between liver enhancement corrected for injected total iodine and total body weight (r = 0.53; p < 0.001) and between liver enhancement corrected for lean body weight and the percentage of lean body weight (r = 0.73; p < 0.001). Most benefits from personalising iodine injection using %LBW additive to total body weight would be achieved in patients under 90 kg. Liver enhancement is more strongly associated with the percentage of lean body weight than with the total body weight or body mass index. The observed variation in liver enhancement might be reduced by a personalised injection based on the artificial-intelligence-determined percentage of lean body weight.

Synthesized effective atomic numbers for commercially available dual-energy CT

Purpose

The objective of this study was to assess synthesized effective atomic number (Z_eff) values with a new developed tissue characteristic phantom and contrast material of varying iodine concentrations using single-source fast kilovoltage switching dual-energy CT (DECT) scanner.

Methods

A newly developed multi energy tissue characterisation CT phantom and an acrylic phantom with various iodine concentrations of were scanned using single-source fast kilovoltage switching DECT (GE-DECT) scanner. The difference between the measured and theoretical values of Z_eff were evaluated. Additionally, the difference and coefficient of variation (CV) values of the theoretical and measured values were compared with values obtained with the Canon-DECT scanner that was analysed in our previous study.

Results

The average Z_eff difference in the Multi-energy phantom was within 4.5%. The average difference of the theoretical and measured Z_eff values for the acrylic phantom with variation of iodine concentration was within 3.3%. Compared to the results for the single-source Canon-DECT scanner used in our previous study, the average difference and CV of the theoretical and measured Z_eff values obtained with the GE-DECT scanner were markedly smaller.

Conclusions

The accuracy of the synthesized Z_eff values with GE-DECT had a good agreement with the theoretical Z_eff values for the Multi-Energy phantom. The GE-DECT could reduce the noise and the accuracy of the Z_eff values than that with Canon-DECT for the varying iodine concentrations of contrast medium.

Advances in knowledge

The accuracy and precision of the Z_eff values of the contrast medium with the GE-DECT could be sufficient with human equivalent materials.

Metal artifact reduction techniques for single energy CT and dual-energy CT with various metal materials

Objective:

The aim of the current study is to evaluate the effectiveness of reduction metal artifacts using kV-CT image with the single-energy based metal artefact reduction (SEMAR) technique by single-energy reconstruction, monochromatic CT and rED reconstructed by dual-energy reconstruction.

Methods:

Seven different metal materials (brass, aluminum, copper, stainless, steel, lead and titanium) were placed inside the water-based PMMA phantom. After DECT-based scan, the artefact index (AI) were evaluated with the kV-CT images with and without SEMAR by single-energy reconstruction, and raw-data based electron density (rED), monochromatic CT images by dual-energy reconstruction. Moreover, the AI with evaluated with rED and the converted ED images from the kV-CT and monochromatic CT images.

Results:

The minimum average value of the AI with all-metal inserts was approximately 80 keV. The AI without SEMAR was larger than that with SEMAR for the 80 kV and 135 kV CT images. In the comparison of the AI for the rED and ED images that were converted from 80 kV and 135 kV CT images with and without SEMAR, the monochromatic CT images of the PMMA phantom with inserted metal materials at 80 keV revealed that the kV-CT with SEMAR reduced the metal artefact substantially.

Conclusion:

The converted ED from the kV-CT and monochromatic CT images could be useful for a comparison of the AI using the same contrast scale. The kV-CT image with SEMAR by single-energy reconstruction was found to substantially reduce metal artefact.

Advances in knowledge:

The effectiveness of reduction of metal artifacts using single-energy based metal artefact reduction (SEMAR) technique and dual-energy CT (DECT) was evaluated the electron density conversion techniques.

Automatic spectral imaging protocol and iterative reconstruction for radiation dose reduction in typical hepatic hemangioma computed tomography with reduced iodine load: a preliminary study

OBJECTIVE

To evaluate the effect of automatic spectral imaging protocol selection (ASIS) and adaptive statistical iterative reconstruction (ASiR) technique in the reduction of radiation and contrast medium dose in typical hepatic hemangioma (HH) dual energy spectral CT (DEsCT).

METHODS

62 patients with suspected HH were randomly divided into two groups equally: Group A, conventional 120-kVp CT with standard iodine load; Group B, DEsCT with ASIS technique and reduced iodine load, two sets of monochromatic spectral images were reconstructed: 69 keV level with 30% ASiR (Group B₁) and 52 keV level with 50% ASiR (Group B₂). The radiation and total iodine dose, quantitative analysis (standard deviation value, contrast-to-noise and contrast enhancement ratio) and qualitative analysis were evaluated.

RESULTS

No difference was observed in the standard deviation values, subjective image noise, and the diagnostic acceptability score among the three groups (p > 0.05). Contrast to noise [Group B₂  vs A, B₁ in arterial phase (AP): 19.51 ± 6.29 vs 15.77 ± 5.93, 11.46 ± 2.84; Group B₂  vs A, B₁ in portal venous phase (PVP): 9.96 ± 2.18 vs 8.19 ± 3.04, 6.01 ± 1.82], contrast enhancement ratio (Group B₂  vs A, B₁ in AP: 6.88 ± 2.01 vs 5.47 ± 2.01, 4.15 ± 1.28; Group B₂  vs A, B₁ in PVP: 5.58 ± 1.02 vs 4.54 ± 1.13, 3.49 ± 0.83), and the lesion conspicuity score (Group B₂  vs A, B₁ in AP: 3.93 ± 0.26 vs 3.45 ± 0.51, 3.10 ± 0.49; Group B₂  vs A, B₁ in PVP: 3.90 ± 0.31 vs 3.48 ± 0.57, 3.14 ± 0.44) for Group B₂ were higher than those in Group A and B₁ (p < 0.05). Compared to Group A, the radiation dose and total iodine dose in Group B were reduced by 30 and 41%, respectively (radiation dose in Group B vs A: 5.53 ± 1.59 vs 7.91± 2.71 mSv; iodine dose in Group B vs A: 18.85 ± 2.88 vs 31.78±3.89 ml; p < 0.05).

CONCLUSION

DEsCT with ASIS and ASiR technique can reduce the radiation dose without image quality degradation as compared to the conventional 120-kVp CT. The monochromatic spectral images at 52 keV level with 50% ASiR allows the reduction in total iodine dose without deteriorating diagnostic performance. Advances in knowledge: ASIS combined with ASiR technique, by using monochromatic spectral images at 52 keV level, represents a feasible imaging protocol to reduce the radiation and total iodine dose in assessment of typical HH.