Thoracoabdominal-Aortoiliac Multidetector-Row CT Angiography at 80 and 100 kVp: Assessment of Image Quality and Radiation Dose

Automated attenuation-based tube voltage selection for body CTA: Performance evaluation of 192-slice dual-source CT

OBJECTIVE

To assess radiation dose and image quality in body CT-angiography (CTA) with automated attenuation-based tube voltage selection (ATVS) on a 192-slice dual-source CT (DSCT).

METHODS

Forty patients (69.5 ± 9.6 years) who had undergone body CTA with ATVS (ref.kVp 100, ref.mAs 90) using a 2x192-slice CT in single-source mode were retrospectively included. All patients had undergone prior CTA with a 2x128-slice CT and ATVS with identical imaging and contrast media protocols, serving for comparison. Images were reconstructed with iterative reconstruction at similar strength levels. Radiation dose was determined. Image quality was assessed semi-quantitatively (1:excellent, 5:non-diagnostic), aortic attenuation, noise and CNR were determined.

RESULTS

As compared to 128-slice DSCT, 192-slice DSCT selected tube voltages were lower in 30 patients (75 %), higher in 3 (7.5 %), and similar in 7 patients (17.5 %). CTDIvol was lower with 192-slice DSCT (4.7 ± 1.9 mGy vs. 5.8 ± 2.1 mGy; p < 0.001). Subjective image quality, mean aortic attenuation (342 ± 67HU vs. 268 ± 67HU) and CNR (9.8 ± 2.5 vs. 8.2 ± 2.9) were higher with 192-slice DSCT (all p < 0.01), all datasets being diagnostic.

CONCLUSION

Our study suggests that ATVS of 192-slice DSCT for body CTA is associated with an improved image quality and further radiation dose reduction of 19 % compared to 128-slice DSCT.

KEY POINTS

• 192-slice DSCT allows imaging from 70 kVp to 150 kVp at 10 kVp increments. • 192-slice DSCT allows for radiation-dose reduction in body-CTA with ATVS. • Subjective and objective image quality increase compared to 128-slice DSCT.

Review of the Use of Ionizing Radiation in Endovascular Aneurysm Repair

Endovascular repair for aortic aneurysm (EVAR) is rapidly increasing in popularity. The nature of this intervention requires significant exposure to ionizing radiation both during the procedure and for postoperative surveillance, generally in the form of computed tomography. Here the authors review the literature for radiation exposure during EVAR, both for the patient and the physician.

Standard chest CT using combined automated tube potential selection and iterative reconstruction: image quality and radiation dose reduction

OBJECTIVE

To evaluate the image quality and radiation dose reduction of chest computed tomography (CT) using combined automated tube potential selection (ATPS) and iterative reconstruction (IR).

MATERIALS AND METHODS

Image quality and radiation dose were compared between conventional contrast-enhanced chest CT using 120 kVp and filtered back projection (Protocol A) and CT using ATPS and IR (Protocol B) in 43 patients.

RESULTS

The effective radiation dose was 3.6 ± 0.4 mSv for Protocol A and 2.2 ± 0.6 mSv for Protocol B (mean dose reduction, 39.7%). Protocol B showed diagnostic image quality in all patients.

CONCLUSION

ATPS and IR allows for radiation dose reduction while maintaining diagnostic image quality.

Abdominal aortic intimal flap motion characterization in acute aortic dissection: assessed with retrospective ECG-gated thoracoabdominal aorta dual-source CT angiography

Objectives

To evaluate the feasibility of dose-modulated retrospective ECG-gated thoracoabdominal aorta CT angiography (CTA) assessing abdominal aortic intimal flap motion and investigate the motion characteristics of intimal flap in acute aortic dissection (AAD).

Materials and Methods

49 patients who had thoracoabdominal aorta retrospective ECG-gated CTA scan were enrolled. 20 datasets were reconstructed in 5% steps between 0 and 95% of the R-R interval in each case. The aortic intimal flap motion was assessed by measuring the short axis diameters of the true lumen and false lumen 2 cm above of celiac trunk ostium in different R-R intervals. Intimal flap motion and configuration was assessed by two independent observers.

Results

In these 49 patients, 37 had AAD, 7 had intramural hematoma, and 5 had negative result for acute aortic disorder. 620 datasets of 31 patients who showed double lumens in abdominal aorta were enrolled in evaluating intimal flap motion. The maximum and minimum true lumen diameter were 12.2±4.1 mm (range 2.6∼17.4) and 6.7±4.1 mm (range 0∼15.3) respectively. The range of intimal flap motion in all patients was 5.5±2.6 mm (range 1.8∼10.2). The extent of maximum true lumen diameter decreased during a cardiac cycle was 49.5%±23.5% (range 12%∼100%). The maximum motion phase of true lumen diameter was in systolic phase (5%∼40% of R-R interval). Maximum and minimum intimal flap motion was at 15% and 75% of the R-R interval respectively. Intimal flap configuration had correlation with the phase of cardiac cycle.

Conclusions

Abdominal intimal flap position and configuration varied greatly during a cardiac cycle. Retrospective ECG-gated thoracoabdominal aorta CTA can reflect the actual status of the true lumen and provide more information about true lumen collapse. This information may be helpful to diagnosis and differential diagnosis of dynamic abstraction.

Low-tube-voltage (80 kVp) CT aortography using 320-row volume CT with adaptive iterative reconstruction: lower contrast medium and radiation dose

OBJECTIVES

To evaluate CT aortography at reduced tube voltage and contrast medium dose while maintaining image quality through iterative reconstruction (IR).

METHODS

The Institutional Review Board approved a prospective study of 48 patients who underwent follow-up CT aortography. We performed intra-individual comparisons of arterial phase images using 120 kVp (standard tube voltage) and 80 kVp (low tube voltage). Low-tube-voltage imaging was performed on a 320-detector CT with IR following injection of 40 ml of contrast medium. We assessed aortic attenuation, aortic attenuation gradient, image noise, contrast-to-noise ratio (CNR), volume CT dose index (CTDIvol), and figure of merit (FOM) of image noise and CNR. Two readers assessed images for diagnostic quality, image noise, and artefacts.

RESULTS

The low-tube-voltage protocol showed 23-31% higher mean aortic attenuation and image noise (both P < 0.01) than the standard-tube-voltage protocol, but no significant difference in the CNR and aortic attenuation gradients. The low-tube-voltage protocol showed a 48% reduction in CTDIvol and an 80% increase in FOM of CNR. Subjective diagnostic quality was similar for both protocols, but low-tube-voltage images showed greater image noise (P = 0.01).

CONCLUSIONS

Application of IR to an 80-kVp CT aortography protocol allows radiation dose and contrast medium reduction without affecting image quality.

KEY POINTS

• CT aortography at 80 kVp allows a significant reduction in radiation dose. • Addition of iterative reconstruction reduces image noise and improves image quality. • The injected contrast medium dose can be substantially reduced at 80 kVp. • Aortic enhancement is uniform despite a reduced volume of contrast medium.

Radiation dose optimization and thoracic computed tomography

In the past 3 decades, radiation dose from computed tomography (CT) has contributed to an increase in overall radiation exposure to the population. This increase has caused concerns over harmful effects of radiation dose associated with CT in scientific publications as well as in the lay press. To address these concerns, and reduce radiation dose, several strategies to optimize radiation dose have been developed and assessed, including manual or automatic adjustment of scan parameters. This article describes conventional and contemporary techniques to reduce radiation dose associated with chest CT.

Effect of x-ray tube parameters and iodine concentration on image quality and radiation dose in cerebral pediatric and adult CT angiography: a phantom study

OBJECTIVES

The aim of the present phantom study was to investigate the effect of x-ray tube parameters and iodine concentration on image quality and radiation dose in cerebral computed tomographic (CT) angiographic examinations of pediatric and adult individuals.

MATERIALS AND METHODS

Four physical anthropomorphic phantoms that represent the average individual as neonate, 1-year-old, 5-year-old, and 10-year-old children and the RANDO phantom that simulates the average adult individual were used. Cylindrical vessels were bored along the brain-equivalent plugs of each physical phantom. To simulate the brain vasculature, vessels of 0.6, 1, 2, and 3 mm in diameter were created. These vessels were filled with contrast medium (CM) solutions at different iodine concentrations, that is, 5.6, 4.2, 2.7, and 1.4 mg I/mL. The phantom heads were scanned at 120, 100, and 80 kV. The applied quality reference tube current-time product values ranged from a minimum of 45 to a maximum of 680. The CT acquisitions were performed on a 16-slice CT scanner using the automatic exposure control system. Image quality was evaluated on the basis of image noise and contrast-to-noise ratio (CNR) between the contrast-enhanced iodinated vessels and the unenhanced regions of interest. Dose reduction was calculated as the percentage difference of the CT dose index value at the quality reference tube current-time product and the CT dose index at the mean modulated tube current-time product.

RESULTS

Image noise that was measured using the preset tube current-time product settings varied significantly among the different phantoms (P < 0.0001). Hounsfield unit number of iodinated vessels was linearly related to CM concentration (r² = 0.907) and vessel diameter (r² = 0.918). The Hounsfield unit number of iodinated vessels followed a decreasing trend from the neonate phantom to the adult phantom at all kilovoltage settings. For the same image noise level, a CNR improvement of up to 69% and a dose reduction of up to 61% may be achieved when CT acquisition is performed at 80 kV compared with 120 kV. For the same CNR, a reduction by 25% of the administered CM concentration may be achieved when CT acquisition is performed at 80 kV compared with 120 kV.

CONCLUSIONS

In cerebral CT angiographic studies, appropriate adjustment of the preset tube current-time product settings is required to achieve the same image noise level among participants of different age. Cerebral CT angiography at 80 kV significantly improves CNR and significantly reduces radiation dose. Moreover, at 80 kV, a considerable reduction of the administered amount of the CM may be reached, thus reducing potential risks for contrast-induced nephropathy.

Carotid CTA: radiation exposure and image quality with the use of attenuation-based, automated kilovolt selection

BACKGROUND AND PURPOSE

CTA is considered the imaging modality of choice in evaluating the supraaortic vessels in many institutions, but radiation exposure remains a matter of concern. The objective of the study was to evaluate a fully automated, attenuation-based kilovolt selection algorithm in carotid CTA in respect to radiation dose and image quality compared with a standard 120-kV protocol.

MATERIALS AND METHODS

Ninety-eight patients were included: 53 examinations (patient age, 66 ± 12 years) were performed by use of automated adaption of tube potential (80-140 kV) on the basis of the attenuation profile of the scout scan (study group), and 45 examinations (patient age, 67 ± 11 years) were performed by use of a standard 120-kV protocol (control group). CT dose index volume and dose-length product were recorded from the examination protocol. Image quality was assessed by ROI measurements and calculations of SNR and contrast-to-noise ratio. Subjective image quality was evaluated by 2 observers with the use of a 4-point scale (3, excellent; 0, not diagnostic).

RESULTS

Subjective image quality was rated as "excellent" or "good" in all examinations (study group, 2.8; control group, 2.8). The algorithm automatically selected 100 kV in 47% and 80 kV in 34%; 120 kV was retained in 19%. An elevation to 140 kV did not occur. Compared with the control group, overall CT dose index volume reduction was 33.7%; overall dose-length product reduction was 31.5%. In the low-kilovolt scans, image noise and mean attenuation of ROIs inside the carotid arteries were significantly higher than in 120-kV scans, resulting in a constant or increased (80-kV group) contrast-to-noise ratio.

CONCLUSIONS

The attenuation-based, kilovolt selection algorithm enables a dose reduction of >30% in carotid artery CTA while maintaining contrast-to-noise ratio and subjective image quality at adequate levels.

CT venography for deep vein thrombosis using a low tube voltage (100 kVp) setting could increase venous enhancement and reduce the amount of administered iodine

Objective

To investigate the validity of the 100 kVp setting in CT venography (CTV) in the diagnosis of deep vein thrombosis (DVT), and to evaluate the feasibility of reducing the amount of administered iodine in this setting.

Materials and Methods

After receiving the contrast medium (CM) of 2.0 mL/kg, 88 patients underwent CTV of the pelvis and lower extremities by using one of four protocols: Group A, 120 kVp setting and 370 mgI/mL CM; group B, 120 kVp and 300 mgI/mL; group C, 100 kVp and 370 mgI/mL; group D, 100 kVp and 300 mgI/mL. The groups were evaluated for venous attenuation, vein-to-muscle contrast-to-noise ratio (CNR_VEIN), DVT-to-vein contrast-to-noise ratio (CNR_DVT), and subjective degree of venous enhancement and image quality.

Results

Venous attenuation and CNR_VEIN were significantly higher in group C (144.3 Hounsfield unit [HU] and 11.9), but there was no significant difference between group A (118.0 HU and 8.2) and D (122.4 HU and 7.9). The attenuation value of DVT was not significantly different among the four groups, and group C had a higher absolute CNR_DVT than the other groups. The overall diagnostic image quality and venous enhancement were significantly higher in group C, but there was no difference between groups A and D.

Conclusion

The 100 kVp setting in CTV substantially help improve venous enhancement and CNR_VEIN. Furthermore, it enables to reduce the amount of administered iodine while maintaining venous attenuation, as compared with the 120 kVp setting.

Radiation dose and image quality at high-pitch CT angiography of the aorta: intraindividual and interindividual comparisons with conventional CT angiography

OBJECTIVE

The objective of our study was to evaluate radiation dose and quantitative image quality parameters at high-pitch CT angiography (CTA) of the aorta compared with conventional CTA.

MATERIALS AND METHODS

We studied the examinations of 110 patients (65 men and 45 women; mean age ± SD, 64 ± 15 years) who had undergone CTA of the entire aorta on a second-generation dual-source CT system; 50 examinations were performed in high-pitch mode. The mean arterial attenuation, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and figure of merit (FOM) were calculated for the high-pitch CTA and conventional CTA groups. Radiation exposures were compared.

RESULTS

All studies were considered of diagnostic quality. At high-pitch CTA, the mean tube voltage and tube current-exposure time product were 118 ± 7 kV (SD) and 197 ± 78 mAs compared with 120 ± 1 kV and 258 ± 78 mAs, respectively, at conventional CTA (p < 0.05). The mean volume CT dose index, dose-length product, and effective dose were 8.1 ± 2.4 mGy, 561.1 ± 178.6 mGy × cm, and 9.6 ± 3.0 mSv at high-pitch CTA and 18.3 ± 7.7 mGy, 1162.6 ± 480.1 mGy × cm, and 19.8 ± 8.2 mSv at conventional CTA (p < 0.001). Attenuation was similar for both protocols, whereas significantly less contrast medium was injected for high-pitch CTA than for standard-pitch CTA (87.3 ± 16 mL vs 97.9 ± 16 mL, respectively; p < 0.01). The SNR and CNR were significantly lower in the high-pitch CTA examinations (p < 0.01), whereas the FOM was nonsignificantly higher. Twenty patients underwent both high-pitch CTA and conventional CTA, with a 45% reduction in radiation dose (p < 0.001).

CONCLUSION

High-pitch CTA of the aorta yields 45-50% reduction of radiation exposure as well as contrast medium savings with maintained vessel attenuation.

Radiation dose reduction in abdominal computed tomography during the late hepatic arterial phase using a model-based iterative reconstruction algorithm: how low can we go?

OBJECTIVE

The aim of this study was to compare the image quality of abdominal computed tomography scans in an anthropomorphic phantom acquired at different radiation dose levels where each raw data set is reconstructed with both a standard convolution filtered back projection (FBP) and a full model-based iterative reconstruction (MBIR) algorithm.

MATERIALS AND METHODS

An anthropomorphic phantom in 3 sizes was used with a custom-built liver insert simulating late hepatic arterial enhancement and containing hypervascular liver lesions of various sizes. Imaging was performed on a 64-section multidetector-row computed tomography scanner (Discovery CT750 HD; GE Healthcare, Waukesha, WI) at 3 different tube voltages for each patient size and 5 incrementally decreasing tube current-time products for each tube voltage. Quantitative analysis consisted of contrast-to-noise ratio calculations and image noise assessment. Qualitative image analysis was performed by 3 independent radiologists rating subjective image quality and lesion conspicuity.

RESULTS

Contrast-to-noise ratio was significantly higher and mean image noise was significantly lower on MBIR images than on FBP images in all patient sizes, at all tube voltage settings, and all radiation dose levels (P < 0.05). Overall image quality and lesion conspicuity were rated higher for MBIR images compared with FBP images at all radiation dose levels. Image quality and lesion conspicuity on 25% to 50% dose MBIR images were rated equal to full-dose FBP images.

CONCLUSION

This phantom study suggests that depending on patient size, clinically acceptable image quality of the liver in the late hepatic arterial phase can be achieved with MBIR at approximately 50% lower radiation dose compared with FBP.

Computed tomographic venography for varicose veins of the lower extremities: prospective comparison of 80-kVp and conventional 120-kVp protocols

OBJECTIVE

To prospectively investigate the feasibility of an 80-kilovolt (peak) (kVp) protocol in computed tomographic venography for varicose veins of the lower extremities by comparison with conventional 120-kVp protocol.

METHODS

Attenuation values and signal-to-noise ratio of iodine contrast medium (CM) were determined in a water phantom for 2 tube voltages (80 kVp and 120 kVp). Among 100 patients, 50 patients were scanned with 120 kVp and 150 effective milliampere second (mAs(eff)), and the other 50 patients were scanned with 80 kVp and 390 mAs(eff) after the administration of 1.7-mL/kg CM (370 mg of iodine per milliliter). The 2 groups were compared for venous attenuation, contrast-to-noise ratio, and subjective degree of venous enhancement, image noise, and overall diagnostic image quality.

RESULTS

In the phantom, the attenuation value and signal-to-noise ratio value for iodine CM at 80 kVp were 63.8% and 33.0% higher, respectively, than those obtained at 120 kVp. The mean attenuation of the measured veins of the lower extremities was 148.3 Hounsfield units (HU) for the 80-kVp protocol and 94.8 HU for the 120-kVp protocol. Contrast-to-noise ratio was also significantly higher with the 80-kVp protocol. The overall diagnostic image quality of the 3-dimensional volume-rendered images was good with both protocols. The subjective score for venous enhancement was higher at the 80-kVp protocol. The mean volume computed tomography dose index of the 80-kVp (5.6 mGy) protocol was 23.3% lower than that of the 120-kVp (7.3 mGy) protocol.

CONCLUSION

The use of the 80-kVp protocol improved overall venous attenuation, especially in perforating vein, and provided similarly high diagnostic image quality with a lower radiation dose when compared to the conventional 120-kVp protocol.

Kilovoltage dependence of the attenuation of a potassium iodide/water solution on CT: presentation of a computer model implementing polychromatic character of the X-ray photon beam

PURPOSE

To describe a program that simulates a computed tomographic scan with the polychromatic aspect of the output of the x-ray tube implemented. This program can be used in the study of the attenuation of different solutions/solutes. These results can subsequently guide the radiologist to obtain a satisfying contrast enhancement at lower tube voltages and eventually lower contrast volumes.

MATERIALS AND METHODS

A Matlab program was written to simulate a computed tomographic scan. The spectrum of the x-ray tube at different kilovoltages was generated with another program (XOP) and used as input. Beam-hardening correction and zero padding were added. The results were validated with attenuation measurements of a corresponding potassium iodide solution in water.

RESULTS

There was a good agreement between the calculated and measured attenuations; the calculated results matched with the measured values and fell within a 5% deviation.

CONCLUSION

It is possible to simulate correctly the attenuation of a potassium iodide in water solution in silico. This can be helpful to determine kilovoltages, administered contrast medium volumes and concentrations to reduce the irradiation of the patients, and obtain equally good contrast enhancement on a basis other than empirical.

Automated attenuation-based kilovoltage selection: preliminary observations in patients after endovascular aneurysm repair of the abdominal aorta

OBJECTIVE

The objective of our study was to assess prospectively the impact of automated attenuation-based kilovoltage selection on image quality and radiation dose in patients undergoing body CT angiography (CTA) after endovascular aneurysm repair (EVAR) of the abdominal aorta.

SUBJECTS AND METHODS

Thirty-five patients (five women, 30 men; mean age ± SD, 69 ± 13 years; mean body mass index ± SD, 27.3 ± 4.5 kg/m(2)) underwent 64-MDCT angiography of the thoracoabdominal aorta using a fixed 120-kVp protocol (scan A: 120 mAs [reference]; rotation time, 0.33 second; pitch, 1.2) and, within a median time interval of 224 days, using a protocol with automated kilovoltage selection (scan B: tube voltage, 80-140 kVp). Subjective image quality (5-point scale: 1 [excellent] to 5 [nondiagnostic]) and objective image quality (aortic attenuation at four locations of the aortoiliac system, noise, contrast-to-noise ratio [CNR]) were assessed independently by two blinded radiologists. The volume CT dose index (CTDI(vol)) was compared between scans A and B.

RESULTS

The subjective image quality of scans A and B was similar (median score for both, 1; range, 1-4; p = 0.74), with all datasets being of diagnostic quality. Automated attenuation-based kilovoltage selection led to a reduction to 80 kVp in one patient (2.9%) and 100 kVp in 18 patients (51.4%). Fifteen of 35 patients (42.9%) were scanned at 120 kVp, whereas in one patient (2.9%) the kilovoltage setting increased to 140 kVp. Image noise (scan A vs scan B: mean ± SD, 12.8 ± 2.3 vs 13.7 ± 2.9 HU, respectively) was significantly (p < 0.05) higher in scan B than in scan A, whereas CNR was similar among scans (A vs B: mean ± SD, 15.7 ± 7.0 vs 16.9 ± 9.7; p = 0.43). The CTDI(vol) was significantly lower in scan B (mean ± SD, 8.9 ± 2.9 mGy; scan A, 10.6 ± 1.5 mGy; average reduction, 16%; p = 0.002) despite a higher tube current-exposure time product (B vs A: mean ± SD, 152 ± 27 vs 141 ± 29 mAs; p = 0.01).

CONCLUSION

In patients undergoing follow-up after EVAR of the abdominal aorta, body CTA using automated attenuation-based kilovoltage selection yields similar subjective image quality and CNR at a significantly reduced dose compared with a protocol that uses 120 kVp.

Cerebral computed tomography angiography using a low tube voltage (80 kVp) and a moderate concentration of iodine contrast material: a quantitative and qualitative comparison with conventional computed tomography angiography

OBJECTIVE

To investigate the feasibility of an 80-kVp protocol using a moderate concentration contrast material (MC-CM) for cerebral computed tomography angiography by comparison with a conventional 120-kVp protocol using a high concentration contrast material (HC-CM).

MATERIALS AND METHODS

Attenuation values and signal-to-noise ratios (SNRs) were determined in a head phantom for 2 tube voltages (80 and 120 kVp) and 2 different iodine concentration contrast materials (HC-CM and MC-CM). Among 90 consecutive patients, 45 patients were scanned with 120 kVp and 150 mAs(eff) after administration of 70 mL of HC-CM (370 mg iodine [mgI]/mL), whereas the other 45 patients were scanned with 80 kVp and 370 mAs(eff) after administration of 70 mL of MC-CM (300 mgI/mL). The Hounsfield units (HU) of the internal carotid artery T junction, SNR, contrast-to-noise ratio (CNR), subjective degree of arterial enhancement, image noise, sharpness of the cerebral arterial boundary, and overall diagnostic image quality were compared between the 2 groups.

RESULTS

The mean attenuation of the internal carotid artery T junction, SNR, and CNR was significantly higher in the 80 kVp with MC-CM group (379.2, 33.7, and 31.1 HU, respectively) than in the 120 kVp with HC-CM group (282.2, 31.1, and 27.2 HU, respectively). The 80-kVp protocol resulted in significantly higher score in arterial enhancement, sharpness of the cerebral arteries, and overall diagnostic image quality. The effective dose of 80 kVp (0.7 mSv) was 22.2% lower than that of 120 kVp (0.9 mSv).

CONCLUSIONS

The use of 80 kVp with MC-CM improved arterial enhancement, SNR, and CNR and provided superior quality images using a smaller amount of iodine and a lower radiation dose than the conventional protocol of 120 kVp with HC-CM.

"Sweet spot" for endoleak detection: optimizing contrast to noise using low keV reconstructions from fast-switch kVp dual-energy CT

OBJECTIVE

To assess endoleak detection and conspicuity using low-kiloelectron volt (keV) monochromatic reconstructions of single-source (fast-switch kilovolt [peak]) dual-energy data sets.

METHODS

With approval of the institutional review board, multiphasic dual-energy computed tomographic (CT) scans for aortic endograft surveillance were retrospectively reviewed for 39 patients. Two abdominal radiologists each performed 2 separate reading sessions, at 55-keV and standard 75-keV reconstruction, respectively. The readers tabulated endoleak presence, conspicuity on 1-to-5 scale, and type overall and in arterial and venous phases. Originally, dictated reports in medical records were used as criterion standard.

RESULTS

Original dictations identified 19 endoleaks (9 abdominal and 10 thoracic), 13 of which were type II. The blinded readers (R1 and R2) exhibited good to very good intraobserver and interobserver agreement. Endoleak detection was higher at 55 keV than at 75 keV (sensitivity, 100% (95% confidence interval [CI], 82.4%-100.0%) and 84.2% (95% CI, 60.4-96.6%) at 55 keV vs 79% (95% CI, 54.4-94.0%) and 68.4% (95% CI, 43.5%-87.4%) at 75 keV in venous phase). Further, endoleak conspicuity ratings (where original dictation showed positive leak) were higher at 55 keV than at 75 keV, which was a significant difference for R2 in the overall ratings (P = 0.03) and for both readers in the venous phase ratings (R1, P = 0.01; R2, P = 0.004). There was no difference in endoleak type characterization between the kiloelectron volt levels.

CONCLUSION

Sensitivity for endoleak detection and overall endoleak conspicuity ratings were both higher at 55 keV than 75 keV, favoring the inclusion of a lower-energy monochromatic reconstruction for endoleak surveillance protocols with dual-energy computed tomography.

Advances in diagnostic radiology

Recent advances in diagnostic radiology are discussed on the basis of current publications in Investigative Radiology. Publications in the journal during 2009 and 2010 are reviewed, evaluating developments by modality and anatomic region. Technological advances continue to play a major role in the evolution and clinical practice of diagnostic radiology, and as such constitute a major publication focus. In the past 2 years, this includes advances in both magnetic resonance and computed tomography (in particular, the advent of dual energy computed tomography). An additional major focus of publications concerns contrast media, and in particular continuing research involving nephrogenic systemic fibrosis, its etiology, and differentiation of the gadolinium chelates on the basis of in vivo stability.

Dose reduction in abdominal computed tomography: intraindividual comparison of image quality of full-dose standard and half-dose iterative reconstructions with dual-source computed tomography

OBJECTIVES

We sought to evaluate the image quality of iterative reconstruction in image space (IRIS) in half-dose (HD) datasets compared with full-dose (FD) and HD filtered back projection (FBP) reconstruction in abdominal computed tomography (CT).

MATERIALS AND METHODS

To acquire data with FD and HD simultaneously, contrast-enhanced abdominal CT was performed with a dual-source CT system, both tubes operating at 120 kV, 100 ref.mAs, and pitch 0.8. Three different image datasets were reconstructed from the raw data: Standard FD images applying FBP which served as reference, HD images applying FBP and HD images applying IRIS. For the HD data sets, only data from 1 tube detector-system was used. Quantitative image quality analysis was performed by measuring image noise in tissue and air. Qualitative image quality was evaluated according to the European Guidelines on Quality criteria for CT. Additional assessment of artifacts, lesion conspicuity, and edge sharpness was performed.

RESULTS

: Image noise in soft tissue was substantially decreased in HD-IRIS (-3.4 HU, -22%) and increased in HD-FBP (+6.2 HU, +39%) images when compared with the reference (mean noise, 15.9 HU). No significant differences between the FD-FBP and HD-IRIS images were found for the visually sharp anatomic reproduction, overall diagnostic acceptability (P = 0.923), lesion conspicuity (P = 0.592), and edge sharpness (P = 0.589), while HD-FBP was rated inferior. Streak artifacts and beam hardening was significantly more prominent in HD-FBP while HD-IRIS images exhibited a slightly different noise pattern.

CONCLUSIONS

Direct intrapatient comparison of standard FD body protocols and HD-IRIS reconstruction suggest that the latest iterative reconstruction algorithms allow for approximately 50% dose reduction without deterioration of the high image quality necessary for confident diagnosis.

Raw data-based iterative reconstruction in body CTA: evaluation of radiation dose saving potential

OBJECTIVE

To evaluate prospectively, in patients undergoing body CTA, the radiation dose saving potential of raw data-based iterative reconstruction as compared to filtered back projection (FBP).

METHODS

Twenty-five patients underwent thoraco-abdominal CTA with 128-slice dual-source CT, operating both tubes at 120 kV. Full-dose (FD) images were reconstructed with FBP and were compared to half-dose (HD) images with FBP and HD-images with sinogram-affirmed iterative reconstruction (SAFIRE), both reconstructed using data from only one tube-detector-system. Image quality and sharpness of the aortic contour were assessed. Vessel attenuation and noise were measured, contrast-to-noise-ratio was calculated.

RESULTS

Noise as image quality deteriorating artefact occurred in 24/25 (96%) HD-FBP but not in FD-FBP and HD-raw data-based iterative reconstruction datasets (p < 0.001). Other artefacts occurred with similar prevalence among the datasets. Sharpness of the aortic contour was higher for FD-FBP and HD-raw data-based iterative reconstruction as compared to HD-FBP (p < 0.001). Aortoiliac attenuation was similar among all datasets (p > 0.05). Lowest noise was found for HD-raw data-based iterative reconstruction (7.23HU), being 9.4% lower than that in FD-FBP (7.98HU, p < 0.05) and 30.8% lower than in HD-FBP images (10.44HU, p < 0.001). Contrast-to-noise-ratio was lower in HD-FBP (p < 0.001) and higher in HD-raw data-based iterative reconstruction (p < 0.001) as compared to FD-FBP.

CONCLUSION

Intra-individual comparisons of image quality of body CTA suggest that raw data-based iterative reconstruction allows for dose reduction >50% while maintaining image quality. Key Points • Raw data-based iterative reconstruction reduces image noise and improves image quality as compared to filtered back projection • At a similar radiation dose, raw data-based iterative reconstruction improves the sharpness of vessel contours • In body CTA a dose reduction of >50% might be possible when using raw data-based iterative reconstructions, while image quality can be maintained.

A review of patient dose and optimisation methods in adult and paediatric CT scanning

An increasing number of publications and international reports on computed tomography (CT) have addressed important issues on optimised imaging practice and patient dose. This is partially due to recent technological developments as well as to the striking rise in the number of CT scans being requested. CT imaging has extended its role to newer applications, such as cardiac CT, CT colonography, angiography and urology. The proportion of paediatric patients undergoing CT scans has also increased. The published scientific literature was reviewed to collect information regarding effective dose levels during the most common CT examinations in adults and paediatrics. Large dose variations were observed (up to 32-fold) with some individual sites exceeding the recommended dose reference levels, indicating a large potential to reduce dose. Current estimates on radiation-related cancer risks are alarming. CT doses account for about 70% of collective dose in the UK and are amongst the highest in diagnostic radiology, however the majority of physicians underestimate the risk, demonstrating a decreased level of awareness. Exposure parameters are not always adjusted appropriately to the clinical question or to patient size, especially for children. Dose reduction techniques, such as tube-current modulation, low-tube voltage protocols, prospective echocardiography-triggered coronary angiography and iterative reconstruction algorithms can substantially decrease doses. An overview of optimisation studies is provided. The justification principle is discussed along with tools that assist clinicians in the decision-making process. There is the potential to eliminate clinically non-indicated CT scans by replacing them with alternative examinations especially for children or patients receiving multiple CT scans.

Dual-energy, standard and low-kVp contrast-enhanced CT-cholangiography: a comparative analysis of image quality and radiation exposure

OBJECTIVE

Quantitative image quality assessment in terms of image noise (IN), contrast-to-noise ratio (CNR), and signal-to-noise ratio (SNR) in relation to required radiation dose (RD) for dual-energy (DE), standard and low-kVp contrast-enhanced computed-tomography (CT) cholangiography.

MATERIALS AND METHODS

For each of 22 DECT-cholangiography examinations, 3 image datasets were analyzed as independent single-source CT-acquisitions at different tube potential, i.e. 80 kVp, 120 kVp-equivalent (linear blended dataset M0.3: 30% 80 kVp, 70% 140 kVp), and 140 kVp. Analysis comprised determination of IN, CNR and SNR in regions of interest (ROI) placed in liver parenchyma and contrasted bile ducts. IN was evaluated as mean standard deviation of 3 ROI placed within liver parenchyma (segments 6/7, 5/8, 2/3); CNR was assessed as bile duct-to-liver parenchyma ratio, and SNR as bile duct-to-image noise ratio. RD in terms of CT dose index (CTDI(vol)), dose-length product (DLP) and effective dose (ED) has been determined for each of the datasets, and compared to console prediction and scan summary values. Using phantom measurements of CTDI(vol), a method for separating comprehensive RD values of DE-acquisitions into the original RD contribution of each tube (80 kVp/140 kVp) has been developed, enabling comparison of all 3 datasets as if independently acquired using single-source "single-energy" technique.

RESULTS

Highest IN was detected for 80 kVp- (38.6 ± 5.1HU), lowest for 120 kVp-equivalent linear blended M0.3-datasets (23.1 ± 3.4HU) with significant differences between all datasets (P<0.001). Highest SNR and CNR were measured for M0.3- (SNR: 14.8 ± 4.1; CNR: 11.6 ± 3.8) and 80 kVp-datasets (SNR: 13.8 ± 4.8; CNR: 11.2 ± 4.5); lowest for 140 kVp-datasets (SNR: 9.5 ± 2.5; CNR: 7.1 ± 2.3) with significant differences between M0.3- and 140 kVp-datasets as well as between 80 kVp- and 140 kVp-datasets (both P<0.001 for both CNR, SNR). CTDI(vol), DLP and ED were reduced by 50% for low-kilovoltage acquisitions (CTDI(vol): 5.5 ± 1.4 mGy; DLP: 127.8 ± 40.1 mGy cm; ED: 1.9 ± 0.6 mSv) compared to comprehensive DE-acquisitions (CTDI(vol): 11.0 ± 2.3 mGy; DLP: 253.8 ± 67.5 mGy cm; ED: 3.8 ± 1.0 mSv, tube contribution: 80 kVp: 44.5%; 140 kVp: 55.5%), and by 20% compared to conventional acquisitions at 120 kVp (CTDI(vol): 6.71 mGy; DLP: 153.5 ± 16.9 mGy cm; ED: 2.3 ± 0.3 mSv).

CONCLUSIONS

Despite higher IN, low-kilovoltage CT-cholangiography reveals no significant difference with respect to CNR and SNR when compared to linear blended images yielded by DECT. Compared to DECT or conventional CT at 120 kVp, contrast-enhanced low-kVp CT cholangiography potentially allows reduction of patient dose by up to 50% or 20%, respectively. Therefore, CT-cholangiography at 80 kVp should be considered as an alternative to DECT-cholangiography whenever DECT is unavailable, or if increased image quality of DECT regarding quantitative bile duct evaluation is not needed for diagnosis.

State of the art low-dose CT angiography of the body

This review summarizes current evidence based on pertinent literature on low-dose computed tomography angiography (CTA) of the body. Various strategies for optimizing CTA protocols with the aim to lower the radiation dose while maintaining the diagnostic accuracy of the examination are summarized. To date, various publications have demonstrated that CTA of the body can be performed at a low radiation dose while providing high quality information. Nevertheless, a number of questions still need to be answered, including the optimal combination of tube voltage and tube current settings, as well as the appropriate protocol parameters in relation to the body physiognomy and the specific body region imaged.

Nonlinear three-dimensional noise filter with low-dose CT angiography: effect on the detection of small high-contrast objects in a phantom model

PURPOSE

To study the effect of a nonlinear noise filter on the detection of simulated endoleaks in a phantom with 80- and 100-kVp multidetector computed tomographic (CT) angiography.

MATERIALS AND METHODS

An aortic aneurysm phantom, including iodinated endoleaks, was constructed. Multidetector CT angiography with use of 80-, 100-, and 120-kVp tube voltages was performed for simulated intermediate-sized and large patients (estimated body weights, 72-85 kg and 118-142 kg, respectively). Images obtained with 80 and 100 kVp were postprocessed by using a nonlinear noise filter. CT images containing 1152 endoleaks and images with no endoleaks were randomized and independently analyzed by three radiologists blinded to the location of the endoleaks. Diagnostic confidence and image quality were rated by using subjective scales. Analysis of variance was used for statistical assessment.

RESULTS

In simulated intermediate-sized patients, energy reduction from 120 to 100 kVp and from100 to 80 kVp did not decrease image quality when images with reduced kilovoltage were filtered (P = .2692 and P > .99, respectively). Readers detected more endoleaks on the filtered 100-kVp images than on the nonfiltered images in simulated large patients (83 vs 75 lesions, P = .041). The number of detected endoleaks and the confidence rate were similar at 100 kVp with a filter and at 120 kVp in simulated large patients (P = .339 and P = .211, respectively).

CONCLUSION

In a phantom, the nonlinear noise filter can prevent decreased image quality with use of 80- and 100-kVp abdominal multidetector CT angiography at a wide range of simulated body weights and may facilitate a better detection rate of endoleaks in heavy patients.

Reducing abdominal CT radiation dose with adaptive statistical iterative reconstruction technique

PURPOSE

To assess radiation dose reduction for abdominal computed tomography (CT) examinations with adaptive statistical iterative reconstruction (ASIR) technique.

MATERIALS AND METHODS

With institutional review board approval, retrospective review of weight adapted abdominal CT exams were performed in 156 consecutive patients with ASIR and in 66 patients with filtered back projection (FBP) on a 64-slice MDCT. Patients were categorized into 3 groups of <60 kg (n = 42), 61 to 90 kg (n = 100), and >or=91 kg (n = 80) for weight-based adjustment of automatic exposure control technique. Remaining scan parameters were held constant at 1.375:1 pitch, 120 kVp, 55 mm table feed per rotation, 5 mm section thickness. Two radiologists reviewed all CT examinations for image noise and diagnostic acceptability. CT dose index volume, and dose length product were recorded. Image noise and transverse abdominal diameter were measured in all patients. Data were analyzed using analysis of variance.

RESULTS

ASIR allowed for an overall average decrease of 25.1% in CT dose index volume compared with the FBP technique (ASIR, 11.9 +/- 3.6 mGy; FBP, 15.9 +/- 4.3 mGy) (P < 0.0001). In each of the 3 weight categories, CT examinations reconstructed with ASIR technique were associated with significantly lower radiation dose compared with FBP technique (P < 0.0001). There was also significantly less objective image noise with ASIR (6.9 +/- 2.2) than with FBP (9.5 +/- 2.0) (P < 0.0001). For the subjective analysis, all ASIR and FBP reconstructed abdominal CTs had optimal or less noise. However, 9% of FBP and 3.8% of ASIR reconstructed CT examinations were diagnostically unacceptable because of the presence of artifacts. Use of ASIR reconstruction kernel results in a blotchy pixilated appearance in 39% of CT sans which however, was mild and did not affect the diagnostic acceptability of images. The critical reproduction of visually sharp anatomic structures was preserved in all but one ASIR 40% reconstructed CT examination.

CONCLUSION

ASIR technique allows radiation dose reduction for abdominal CT examinations whereas improving image noise compared with the FBP technique.