CT pulmonary angiography using organ dose modulation with an iterative reconstruction algorithm and 3D Smart mA in different body mass indices: image quality and radiation dose

Reduction of radiation dose and contrast medium volume in computed tomography pulmonary angiography: adaptation of dual-energy computed tomography (CT) protocols to the body mass index

AIM

To evaluate the image quality and diagnostic value of a body mass index (BMI)-based dual-energy computed tomography (CT) protocol in computed tomography pulmonary angiography (CTPA) for reduction of radiation dose and contrast medium (CM) volume.

MATERIALS AND METHODS

Patients suspected of having pulmonary embolism were prospectively included and randomly assigned to one of three protocols: Protocol A (a standard protocol, 100 kV/140 mAs/50 mL iodinated CM), B (a conventional dual-energy protocol, 80-140 kV switching/automatic tube current/weight-dependent CM volume) and C (a BMI-based dual-energy protocol, 80-140 kV switching/BMI-based tube current/weight-dependent CM volume, BMI-based CM injection rate). Subjective and objective image analysis were performed by two radiologists independently. Diagnostic accuracy of pulmonary embolism were evaluated. Inter-group comparison was performed.

RESULTS

Ninety patients (mean age 54.1 ± 13.3 years, 57 men) were included, with 30 patients in each group. The CT values, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) of the pulmonary arteries in group C were significantly higher than those in group B (358.2 ± 50.5 vs 324.9 ± 57.2, p=0.047, 17.8 ± 3.2 vs 15.3 ± 2.9, p=0.010, 19.2 ± 4.1 vs 15.7 ± 3.8, p=0.014). The dose length product (DLP) and CM volume were significantly reduced in groups B and C (A vs B vs C, DLP, 287.9 ± 34.0 vs 177.2 ± 39.2 vs 183.8 ± 23.1 mGy·cm), p<0.001, CM, 50.0 ± 0.0 vs 22.1 ± 3.0 vs 23.2 ± 4.0 ml, p<0.001). There were no significant differences in diagnostic accuracy or subjective image quality among the three groups.

CONCLUSION

The BMI-based dual-energy CT protocol can reduce radiation exposure and iodine burden compared to routine CTPA without affecting the image quality and diagnostic accuracy in patients with a BMI under 30 kg/m2.

Reducing contrast medium dose with low photon energy images in renal dual-energy spectral CT angiography and adaptive statistical iterative reconstruction (ASIR)

OBJECTIVE

To evaluate the value of using low energy (keV) images in renal dual-energy spectral CT angiography (CTA) and adaptive statistical iterative reconstruction (ASIR) to reduce contrast medium dose.

METHODS

40 patients with renal CTA on a Discovery CT750HD were randomly divided into two groups: 20 cases (Group A) with 600 mgI kg^-1 and 20 cases (Group B) with 300 mgI kg^-1. The scan protocol for both groups was: dual-energy mode with mA selection for noise index of 10 HU, pitch 1.375:1, rotating speed 0.6 s/r. Images were reconstructed at 0.625 mm thickness with 40%ASIR, Group A used the conventional 70keV monochromatic images, and Group B used monochromatic images from 40 to 70 keV at 5 keV interval for analysis. The CT values and standard deviation (SD) values of the renal artery and erector spine in the plain and arterial phases were measured with the erector spine SD value representing image noise. The enhancement degree of the renal artery (ΔCT = CT(arterial) -CT(plain)), signal-to-noise ratio (SNR=CT_renal-artery/SD_renal-artery) and contrast-to-noise ratio (CNR=(CT_renal-artery-CT_{erector spine})/SD_{erector-spine}) were calculated. The single factor analysis of variance was used to analyze the difference of ΔCT, SNR and CNR among image groups with p < 0.05 being statistically significant. The subjective image scores of the groups were assessed blindly by two experienced physicians using a 5-point system and the score consistency was compared by the κ test.

RESULTS

Contrast medium dose in the 300 mgI kg^-1 group was reduced by 50% compared with the 600 mgI kg^-1 group, while radiation dose was similar between the two groups. The subjective scores were 4.00 ± 0.65, 4.50 ± 0.60 and 3.70 ± 0.80 for images at 70 keV (600 mgI kg^-1 group), 40 keV (300 mgI kg^-1 group) and 45 keV (300 mgI kg^-1 group), respectively with good consistency between the two reviewers (p > 0.05). The 40 keV images in the 300 mgI kg^-1 group had similar ΔCT (469.77 ± 86.95 HU vs 398.54 ± 73.68 HU) and CNR (15.52 ± 3.32 vs 18.78 ± 6.71) values as the 70 keV images in the 600 mgI kg^-1) group but higher SNR values (30.19 ± 4.41 vs 16.91 ± 11.12, p < 0,05).

CONCLUSION

Contrast dose may be reduced by 50% while maintaining image quality by using lower energy images combined with ASIR in renal dual-energy CTA.

ADVANCES IN KNOWLEDGE

Combined with ASIR and energy spectrum, can reduce the amount of contrast dose in renal CTA.

Cardiac magnetic resonance in arrhythmogenic cardiomyopathies

Over the past few years, the approach to the 'arrhythmic patient' has profoundly changed. An early clinical presentation of arrhythmia is often accompanied by non-specific symptoms and followed by inconclusive electrocardiographic findings. In this scenario, cardiac magnetic resonance (CMR) has been established as a clinical tool of fundamental importance for a correct prognostic stratification of the arrhythmic patient. This technique provides a high-spatial-resolution tomographic evaluation of the heart, which allows studying accurately the ventricular volumes, identifying even segmental kinetic anomalies and properly detecting diffuse or focal tissue alterations through an excellent tissue characterization, while depicting different patterns of fibrosis distribution, myocardial edema or fatty substitution. Through these capabilities, CMR has a pivotal role for the adequate management of the arrhythmic patient, allowing the identification of those phenotypic manifestations characteristic of structural heart diseases. Therefore, CMR provides valuable information to reclassify the patient within the wide spectrum of potentially arrhythmogenic heart diseases, the definition of which remains the major determinants for both an adequate treatment and a poor prognosis. The purpose of this review study was to focus on the role of CMR in the evaluation of the main cardiac clinical entities associated with arrhythmogenic phenomena and to present a brief debate on the main pathophysiological mechanisms involved in the arrhythmogenesis process.

Individualization of computed tomography protocols for suspected pulmonary embolism: a national investigation of routines

Objective

Given the extensive use of computed tomography (CT) in radiation-sensitive patients such as pregnant and pediatric patients, and considering the importance of tailoring CT protocols to patient characteristics for both the radiation dose and image quality, this study was performed to investigate the extent to which individualization of CT protocols is practiced across Norway.

Methods

This cross-sectional study involved collection of CT protocols and administration of a mini-questionnaire to obtain additional information about how CT examinations are individualized. All public hospitals performing CT to detect pulmonary embolism were invited, and 41% participated.

Results

Tailoring a standard protocol to different patient groups was more common than using dedicated protocols. Most of the available radiation dose-reduction approaches were used. However, implementation of these strategies was not systematic. Children and pregnant patients were examined without using dedicated CT protocols or by using protocol adjustments focusing on radiation dose reduction in 30% and 39% of the hospitals, respectively.

Conclusion

Practice optimization is needed, especially the development of dedicated CT protocols or guidelines that tailor the existing protocol to pediatric and pregnant patients. Practice might benefit from a more systematic approach to individualization of CT examinations, such as inserting tailoring instructions into CT protocols.

Dual-energy CT: theoretical principles and clinical applications

The physical principles of dual-energy computed tomography (DECT) are as old as computed tomography (CT) itself. To understand the strengths and the limits of this technology, a brief overview of theoretical basis of DECT will be provided. Specific attention will be focused on the interaction of X-rays with matter, on the principles of attenuation of X-rays in CT toward the intrinsic limits of conventional CT, on the material decomposition algorithms (two- and three-basis-material decomposition algorithms) and on effective Rho-Z methods. The progresses in material decomposition algorithms, in computational power of computers and in CT hardware, lead to the development of different technological solutions for DECT in clinical practice. The clinical applications of DECT are briefly reviewed in relation to the specific algorithms.

Improving image quality with model-based iterative reconstruction algorithm for chest CT in children with reduced contrast concentration

OBJECTIVE

To evaluate model-based iterative reconstruction (MBIR) in improving the image quality of chest CT in children with reduced concentration contrast medium (CM).

METHODS

Fifty-six children (median age of 4 years) who received low-dose enhanced chest CT were enrolled as the study group and compared with the control group of 56 children. Both groups used the automatic tube current modulation to achieve age-based noise index values of 11-15 HU. The study group used 100 kVp and reduced CM concentration of 270 mgI/ml, and the images in this group were reconstructed with 50% adaptive statistical iterative reconstruction (ASIR) and MBIR. The control group used 120 kV and standard CM of 320 mgI/ml, and the images in this group were reconstructed with ASIR only. Subjective image quality and objective image quality of the three image sets were evaluated. The subjective quality included overall image noise, enhancement degree, lesion (including mediastinum mass, pulmonary space-occupying lesions, and parenchymal infiltrative lesions) conspicuity, and beam-hardening artifacts. The objective quality included the measurement of noise in the left ventricle and back muscle to calculate signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of ventricle.

RESULTS

There was no difference in radiation dose between the study (CTDIvol of 1.79 ± 1.45 mGy) and control (1.68 ± 0.92 mGy) groups (p = 0.65). However, the study group used 19.7% lower CM dose than the control group (5.84 ± 2.69 vs. 7.27 ± 3.80 gI), and the enhancement in all images met the diagnostic requirements. MBIR reduced image noise by 58.6% and increased SNR and CNR by 143.6% and 165.7%, respectively, compared to ASIR images in the control group. The two ASIR image sets had similar image quality.

CONCLUSION

MBIR improved the image quality of low-radiation-dose chest CT in children at 19.3% reduced CM dose.

Assessment of radiation dose and iodine load reduction in head-neck CT angiography using two scan protocols with wide-detector

OBJECTIVE

To compare image quality, radiation dose, and iodine intake of head-neck CT angiography (CTA) acquired by wide-detector with the gemstone spectral imaging (GSI) combination with low iodine intake or routine scan protocol.

METHODS

Three hundred patients who had head-neck CTA were enrolled and divided into three groups according to their BMI values: group A (18.5 kg/m2 ≦ BMI <24.9 kg/m2), group B (24.9 kg/m2 ≦ BMI <29.9 kg/m2) and group C (29.9 kg/m2 ≦ BMI ≦ 34.9 kg/m2) with 100 patients in each group. Patients in each group were randomly divided into two subgroups (n = 50) namely, A1, A2, B1, B2, C1 and C2. The patients in subgroups A1, B1 and C1 underwent GSI with low iodine intake (270 mgI/ml, 50 ml) and combined with the ASiR-V algorithm. Other patients underwent three dimensional (3D) smart mA modulation with routine iodine intake (350 mgI/ml, 60 ml). Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of all images were calculated after angiography. Images were then subjectively assessed using a 5-point scale. CT dose index of volume and dose-length product (DLP) was converted to the effective dose (ED) and then compared.

RESULTS

The mean CT values, SNR, CNR and subjective image quality in subgroups A2, B2 and C2 are significantly lower than in subgroups A1, B1, and C1 (P < 0.01), respectively. The ED values in subgroup A1, B1, and C1 are 55.18%, 61.89%, and 69.64% lower than those in A2, B2, and C2, respectively (P < 0.01). The total iodine intakes in subgroups A1, B1, and C1 are 35.72% lower than those in subgroups A2, B2, and C2.

CONCLUSIONS

The gemstone spectral imaging with monochromatic images at 53-57 keV combined with ASiR-V algorithm allows significant reduction in iodine load and radiation dose in head-neck CT angiography than those yielded in routine scan protocol. It also enhances signal intensity of head-neck CTA and maintains image quality.