Technical Note: Quality assessment of virtual monochromatic spectral images on a dual energy CT scanner

Establishing the effect of computed tomography reconstruction kernels on the measure of bone mineral density in opportunistic osteoporosis screening

Opportunistic computed tomography (CT) scans, which can assess relevant bones of interest, offer a potential solution for identifying osteoporotic individuals. However, it has been well documented that image protocol parameters, such as reconstruction kernel, impact the quantitative analysis of volumetric bone mineral density (vBMD) from CT scans. The purpose of this study was to investigate the impact that CT reconstruction kernels have on quantitative results for vBMD from clinical CT scans using phantom and internal calibration. 45 clinical CT scans were reconstructed using the standard kernel and seven alternative kernels: soft, chest, detail, edge, bone, bone plus and lung [GE HealthCare]. Two methods of image calibration, internal and phantom, were used to calibrate the scans. The total hip and fourth lumbar vertebra (L4) were extracted from the scans via deep learning segmentation. Integral vBMD was calculated based on both calibration techniques from CT scans reconstructed with the eight kernels. Linear regression and Bland-Altman analyses were used to determine the coefficient of determination [Formula: see text] and to quantify the agreement between the different kernels. Differences between the reconstruction kernels were determined using paired t tests, and mean differences from the standard were computed. Using internal calibration, the smoothest kernel (soft) yielded a mean difference of -0.95 mg/cc (-0.33%) compared to the reference standard at the L4 vertebra and 2.07 mg/cc (0.51%) at the left femur. The sharpest kernel (lung) yielded a mean difference of 25.36 mg/cc (9.63%) at the L4 vertebra and -25.10 mg/cc (-5.98%) at the left femur. Alternatively, using phantom calibration soft yielded higher mean differences than internal calibration at both locations, with mean differences of 1.21 mg/cc (0.42%) at the L4 vertebra and 2.53 mg/cc (0.65%) at the left femur. The most error-prone results stemmed from the use of the lung kernel, as this kernel displayed a mean difference of -21.90 mg/cc (-7.38%) and -17.24 mg/cc (-4.34%) at the L4 vertebra and femur, respectively. These results indicate when performing opportunistic CT analysis, errors due to interchanging smoothing kernels soft, chest and detail are negligible, but that interchanging between sharpening kernels (lung, bone, bone plus, edge) results in large errors that can significantly impact vBMD measures for osteoporosis screening and diagnosis.

Application of Computed Tomography Angiography in Preoperative Diagnosis of Coarctation of Aorta and Evaluation of Aortic Dilatation in Infants

OBJECTIVE

To evaluate the occurrence of aortic dilatation and its associated predictors with coarctation of the aorta (CoA) in infants using multi-slice computed tomography (MSCT).

METHODS

The clinical data of 47 infantile patients with CoA diagnosed by MSCT and 28 infantile patients with simple ventricular septal defect were analyzed retrospectively. Aortic diameters were measured at six different levels, and aortic sizes were compared by z score. The coarctation site-diaphragm ratio was used to describe the degree of narrowing. Relevant clinical data were collated and analyzed.

RESULTS

The dilation rate and z score of the ascending aorta in the severe CoA group were significantly higher than those in the mild CoA group (11 [52.38%] vs. 21 [80.77%], P=0.038 and 2.00 ± 0.48 vs. 2.36 ± 0.43, P=0.010). Pearson's correlation analysis found that the z score of the ascending aorta was negatively correlated with the coarctation site-diaphragm ratio value (r=-0.410, P=0.004). A logistic retrospective analysis found that an increased degree of coarctation was an independent predictor of aortic dilatation (adjusted odds ratio 0.002; 95% confidence interval 0.00-0.819; P=0.043). The z score of the ascending aorta in the severe CoA group was significantly higher than that in the ventricular septal defect group (P<0.05).

CONCLUSION

Most infants with CoA can also have significant dilatation of the ascending aorta, and the degree of this dilatation is related to the degree of coarctation. Assessment of aortic diameter and related malformations by MSCT can predict the risk of aortic dilatation in infants with CoA.

Effects of convolution filter with beam hardening correction on computed tomography image quality

PURPOSE

To quantify the effects of convolution filters (FC) with beam hardening correction (BHC) compared to FC without BHC on the computed tomography (CT) image quality.

METHODS

This study was conducted on a Canon® Aquilion Lightning scanner. The exposure protocol includes acquisitions at 120 and 100 kVp. Sixteen FCs (8 with and 8 without BHC) were investigated using a Catphan®504 phantom. Uniformity, slice thickness, spatial resolution, Hounsfield unit and noise were analysed using the SPICE-CT ImageJ plugin and the noise power spectrum was analysed using the Imquest software.

RESULTS

It was observed that the BHC did not significantly influence the uniformity, slice thickness, noise and noise power spectrum. Comparisons of 10% MTF between FC01 and FC11 showed relative differences of -29% and -5% at 120 and 100 kVp, respectively, while those between FC09 and FC19 were -55% and -25%. The Hounsfield unit of the Catphan's region of highest electron density was reduced by -7.29% at 120 kVp for FC with BHC. In both cases (FC with and without BHC), the noise values agreed with CT operating manual. At 120 kVp, FC11 and FC09 presented the maximum and minimum noise values, respectively.

CONCLUSION

In CT procedures that quantitatively evaluate the bone or calcium Hounsfield unit, FC with BHC should be avoided due to its effects on Hounsfield units, in special at higher voltage, such as 120 kVp.

Evaluation of the aorta in infants with simple or complex coarctation of the aorta using CT angiography

Objective

To assess aortic dilatation and determine its related factors in infants with coarctation of the aorta (CoA) by using computed tomography angiography (CTA).

Methods

The clinical data of 55 infantile patients with CoA diagnosed by CTA were analyzed retrospectively. Aortic diameters were measured at six different levels and standardized as Z scores based on the square root of body surface area. The results of simple and complex CoA were compared. Univariate and multivariate logistic regression were used to analyze the effects of sex, age, hypertension, degree of coarctation, CoA type, bicuspid aortic valve (BAV), and other factors related to aortic dilatation.

Results

In total, 52 infant patients with CoA were analyzed, including 22 cases of simple CoA and 30 cases of complex CoA. The ascending aorta of the infants in the simple CoA group and the complex CoA group were dilated to different degrees, but the difference was not statistically significant (50.00% vs. 73.33%, P = 0.084, and 2.05 ± 0.40 vs. 2.22 ± 0.43 P = 0.143). The infants in the complex CoA group had more aortic arch hypoplasia than those in the simple CoA group (33.33% vs. 9.09%, P = 0.042). Compared to the ventricular septal defect (VSD) group, the Z score of the ascending aorta in the CoA group was significantly higher than that in the VSD group (P = 0.023 and P = 0.000). A logistic retrospective analysis found that an increased degree of coarctation (CDR value) was an independent predictor of ascending aortic dilatation (adjusted OR = 0.002; P = 0.034).

Conclusion

Infants with simple or complex CoA are at risk of ascending aortic dilatation, and the factors of ascending aortic dilatation depend on the degree of coarctation. The risk of aortic dilatation in infants with CoA can be identified by CTA.

Non-Invasive characterisation of renal stones using dual energy CT: A method to differentiate calcium stones

BACKGROUND

Non-invasive DECT based characterization of renal stones using their effective atomic number (Zeff) and the electron density (ρe) in patients.

AIM

This paper aims to develop a method for in-vivo characterization of renal stone. Differentiation of renal stones in-vivo especially sub types of calcium stones have very important advantage for better judgement of treatment modality.

MATERIALS AND METHODS

50 extracted renal stones were scanned ex-vivo using dual energy CT scanner. A method was developed to characterize these renal stones using effective atomic number and electron density obtained from dual energy CT data. The method and formulation developed in ex-vivo experiments was applied in in-vivo study of 50 randomly selected patients of renal stones who underwent dual energy CT scan.

RESULTS

The developed method was able to characterize Calcium Oxalate Monohydrate (COM) and the combination of COM and Calcium Oxalate Dihydrate (COD) stones non-invasively in patients with a sensitivity of 81% and 83%respectively. The method was also capable of differentiating Uric, Cystine and mixed stones with the sensitivity of 100, 100 and 85.71% respectively.

CONCLUSION

The developed dual energy CT based method was capable of differentiating sub types of calcium stones which is not differentiable on single energy or dual energy CT images.

The effect of tube focal spot size and acquisition mode on task-based image quality performance of a GE revolution HD dual energy CT scanner

PURPOSE

To assess the task-based performance of images obtained under different focal spot size and acquisition mode on a dual-energy CT scanner.

METHODS

Axial CT image series of the Catphan phantom were obtained using a tube focus at different sizes. Acquisitions were performed in standard single-energy, high resolution (HR) and dual-energy modes. Images were reconstructed using conventional and high definition (HD) kernels. Task-based transfer function at the 50% level (TTF_50%) for teflon, delrin, low density polyethylene (LDPE) and acrylic, as well as image noise and noise texture, were assessed across all focal spots and acquisition modes using Noise Power Spectrum (NPS) analysis. A non-prewhitening mathematical observer model was used to calculate detectability index (d_NPW^').

RESULTS

TTF_50% degraded with increasing focal spot size. TTF_50% ranged from 0.67 mm^-1 for teflon to 0.25 mm^-1 for acrylic. For standard kernel, image noise and NPS-determined average spatial frequency were 8.3 HU and 0.29 mm^-1, respectively in single-energy, 12.0 HU and 0.37 mm^-1 in HR, and 7.9 HU and 0.26 mm^-1 in dual-energy mode. For standard kernel, d_NPW^' was 61 in single-energy and HR mode and reduced to 56 in dual-energy mode.

CONCLUSIONS

The task-based image quality assessment metrics have shown that spatial resolution is higher for higher image contrast materials and detectability is higher in the standard single-energy mode compared to HR and dual-energy mode. The results of the current study provide CT operators the required knowledge to characterize their CT system towards the optimization of its clinical performance.