Dual-source CT coronary angiography: effectiveness of radiation dose reduction with lower tube voltage

A Systematic Review of Double Low-dose CT Pulmonary Angiography in Pulmonary Embolism

BACKGROUND

The aim of this study is to perform a systematic review of the feasibility and clinical application of double low-dose CT pulmonary angiography (CTPA) in the diagnosis of patients with suspected pulmonary embolism.

DISCUSSION

A total of 13 studies were found to meet selection criteria reporting both low radiation dose (70 or 80 kVp versus 100 or 120 kVp) and low contrast medium dose CTPA protocols. Lowdose CTPA resulted in radiation dose reduction from 29.6% to 87.5% in 12 studies (range: 0.4 to 23.5 mSv), while in one study, radiation dose was increased in the dual-energy CT group when compared to the standard 120 kVp group. CTPA with use of low contrast medium volume (range: 20 to 75 ml) was compared to standard CTPA (range: 50 to 101 ml) in 12 studies with reduction between 25 and 67%, while in the remaining study, low iodine concentration was used with 23% dose reduction achieved. Quantitative assessment of image quality (in terms of signal-to-noise ratio and contrast-to-noise ratio) showed that low-dose CTPA was associated with higher, lower and no change in image quality in 3, 3 and 6 studies, respectively when compared to the standard CTPA protocol. The subjective assessment indicated similar image quality in 11 studies between low-dose and standard CTPA groups, and improved image quality in 1 study with low-dose CTPA.

CONCLUSION

This review shows that double low-dose CTPA is feasible in the diagnosis of pulmonary embolism with significant reductions in both radiation and contrast medium doses, without compromising diagnostic image quality.

Quantitative assessment on coronary computed tomography angiography (CCTA) image quality: comparisons between genders and different tube voltage settings

BACKGROUND

This study was carried out to quantify and compare the quantitative image quality of coronary computed tomography angiography (CCTA) between genders as well as between different tube voltages scan protocols.

METHODS

Fifty-five cases of CCTA were collected retrospectively and all images including reformatted axial images at systolic and diastolic phases as well as images with curved multi planar reformation (cMPR) were obtained. Quantitative image quality including signal intensity, image noise, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of right coronary artery (RCA), left anterior descending artery (LAD), left circumflex artery (LCx) and left main artery (LM) were quantified using Analyze 12.0 software.

RESULTS

Six hundred and fifty-seven coronary arteries were evaluated. There were no significant differences in any quantitative image quality parameters between genders. 100 kilovoltage peak (kVp) scanning protocol produced images with significantly higher signal intensity compared to 120 kVp scanning protocol (P<0.001) in all coronary arteries in all types of images. Higher SNR was also observed in 100 kVp scan protocol in all coronary arteries except in LCx where 120 kVp showed better SNR than 100 kVp.

CONCLUSIONS

There were no significant differences in image quality of CCTA between genders and different tube voltages. Lower tube voltage (100 kVp) scanning protocol is recommended in clinical practice to reduce the radiation dose to patient.

Double-low protocol for hepatic dynamic CT scan: Effect of low tube voltage and low-dose iodine contrast agent on image quality

The radiation-induced carcinogenesis from computed tomography (CT) and iodine contrast agent induced nephropathy has attracted international attention. The reduction of the radiation dose and iodine intake in CT scan is always a direction for researchers to strive. The purpose of this study was to evaluate the feasibility of a "double-low" (i.e., low tube voltage and low-dose iodine contrast agent) scanning protocol for dynamic hepatic CT with the adaptive statistical iterative reconstruction (ASIR) in patients with a body mass index (BMI) of 18.5 to 27.9 kg/m.A total of 128 consecutive patients with a BMI between 18.5 and 27.9 kg/m were randomly assigned into 3 groups according to tube voltage, iodine contrast agent, and reconstruction algorithms. Group A (the "double-low" protocol): 100 kVp tube voltage with 40% ASIR, iodixanol at 270 mg I/mL, group B: 120 kVp tube voltage with filtered back projection (FBP), iodixanol at 270 mg I/ mL, and group C: 120 kVp tube voltage with FBP, ioversol at 350 mg I/ mL.The volume CT dose index (CTDIvol) and effective dose (ED) in group A were lower than those in group B and C (all P < 0.01). The iodine intake in group A was decreased by approximately 26.5% than group C, whereas no statistical difference was observed between group A and B (P > 0.05). There was no significant difference of the CT values between group A and C (P > 0.05), which both showed higher CT values than that in group B (P < 0.001). However, no statistic difference was observed in the contrast-to-noise ratio (CNR), the signal-to-noise ratio (SNR), and image-quality scores among the 3 groups (all P > 0.05). Near-perfect consistency of the evaluation for group A, B, and C (Kenall's W = 0.921, 0.874, and 0.949, respectively) was obtained by the 4 readers with respect to the overall image quality.These results suggested that the "double-low" protocol with ASIR algorithm for multi-phase hepatic CT scan can dramatically decrease radiation dose and iodine intake with adequate image quality in patients with BMI of 18.5 to 27.9 kg/m.

Dual-source CT coronary angiographic evaluation of coronary artery fistulas

The aim of the present study was to retrospectively evaluate the incidence and morphological features of coronary artery fistulas (CAFs) detected by dual-source computed tomography coronary angiography (DS-CTCA). Between January 2011 and January 2013, 19,584 consecutive patients that had undergone electrocardiogram-triggering DS-CTCA were retrospectively reviewed. Image reconstructions were performed and image quality was evaluated. The medical information of the patients with CAF was reviewed from the medical records. Among the 19,584 patients, 66 patients were diagnosed with CAFs by CTCA, including 60 patients with coronary pulmonary artery fistulas (CPAFs) and six with coronary left ventricular fistulas. Therefore, the incidence of CAFs was 0.34%. Image quality was considered to be excellent in 61 patients and moderate in five cases. CPAFs were identified as small and tortuous vessels in 24 patients and dilated vessels close to the surface of the pulmonary artery (PA) in 36 patients. The coronary left ventricular fistulas were identified as dilated vessels that were draining into the posterior wall of the left ventricle. Among the 66 patients, 54 patients had one traceable fistula and the remaining 12 patients were shown to have two fistula vessels. The average diameter of the detected fistulas, measured with CTCA, was 3.1±1.9 mm. A high-density flow jet of contrast agent shunting from the fistula into the low density PA was observed in 46 patients with CPAF. The results indicate that DS-CTCA is a reliable noninvasive tool that allows the accurate delineation of CAFs.

Experimental estimates of peak skin dose and its relationship to the CT dose index using the CTDI head phantom

A straightforward method is presented to estimate peak skin doses (PSDs) delivered by computed tomography (CT) scanners. The measured PSD values are related to the well-known volume CT dose index (CTDI(vol)), displayed on the console of CT scanners. PSD measurement estimates were obtained, in four CT units, by placing radiochromic film on the surface of a CTDI head phantom. Six different X-ray tube currents including the maximum allowed value were used to irradiate the phantom. PSD and CTDI(vol) were independently measured and later related to the CTDI(vol) value displayed on the console. A scanner-specific relationship was found between the measured PSD and the associated CTDI(vol) displayed on the console. The measured PSD values varied between 27 and 136 mGy among all scanners when the routine head scan parameters were used. The results of this work allow relating the widely used CTDI(vol) to an actual radiation dose delivered to the skin of a patient.

Chest circumference as a predictive parameter of computed tomography coronary angiography radiation doses from dual-source computed tomography

OBJECTIVE

Our aim in this study was to determine the relationship between chest circumference and the radiation doses received by breast tissues during Dual-Source Computed Tomography (DSCT) cardiac scans.

MATERIALS AND METHODS

Routine cardiac DSCT examinations with similar exposure lengths were applied to 30 female patients. The scanogram image, multi-slice helical scan x-ray tube voltage and anode-cathode current were adjusted automatically according to attenuation for each patient during the scanogram acquisition. The standard protocol was otherwise applied to all patients. The 30 patients had an average weight of 67.8±15.3 kg, and the average length of the scanned region was 278.0±11.6 mm. Radiation doses were calculated from the dose-length product (DLP) and the computed tomography dose index (CTDI) scanner data values. The correlations between radiation dose and chest circumference were investigated. The level of significance was set at p<0.05.

RESULTS

For routine cardiac DSCT scans, the average values were as follows: total DLP: 715.54±317.01 mGycm, CTDIvol: 40.79±19.41 mGy, and effective dose (ED): 17.89±7.93 mSv. The chest circumference of patients correlates well with their radiation exposure (p<0.01).

CONCLUSION

The distribution of different tissues throughout the human body may vary among races and genders. Because of this, many researchers use body mass index (BMI) to set image quality and predict the radiation dose distribution from general computed tomography (CT) examinations. Additional anthropomorphic phantom studies should be conducted to determine more accurate conversion factors and, hence, better ED predictions.