Single-portal-phase low-tube-voltage dual-energy CT for short-term follow-up of acute pancreatitis: evaluation of CT severity index,interobserver agreement and radiation dose

Objectives

To intra-individually compare single-portal-phase low-tube-voltage (100-kVp) computed tomography (CT) with 120-kVp images for short-term follow-up assessment of CT severity index (CTSI) of acute pancreatitis, interobserver agreement and radiation dose.

Methods

We retrospectively analysed 66 patients with acute pancreatitis who underwent initial dual-contrast-phase CT (unenhanced, arterial, portal phase) at admission and short-term (mean interval 11.4 days) follow-up dual-contrast-phase dual-energy CT. The 100-kVp and linearly blended images representing 120-kVp acquisition follow-up CT images were independently evaluated by three radiologists using a modified CTSI assessing pancreatic inflammation, necrosis and extrapancreatic complications. Scores were compared with paired t test and interobserver agreement was evaluated using intraclass correlation coefficients (ICC).

Results

Mean CTSI scores on unenhanced, portal- and dual-contrast-phase images were 4.9, 6.1 and 6.2 (120 kVp) and 5.0, 6.0 and 6.1 (100 kVp), respectively. Contrast-enhanced series showed a higher CTSI compared to unenhanced images (P?P?>?0.7). CTSI scores were comparable for 100-kVp and 120-kVp images (P?>?0.05). Interobserver agreement was substantial for all evaluated series and subcategories (ICC 0.67–0.93). DLP of single-portal-phase 100-kVp images was reduced by 41 % compared to 120-kVp images (363.8 versus 615.9 mGy cm).

Conclusions

Low-tube-voltage single-phase 100-kVp CT provides sufficient information for follow-up evaluation of acute pancreatitis and significantly reduces radiation exposure.

Key Points

? Single-portal-phase CT provides sufficient evaluation for follow-up of acute pancreatitis. ? Follow-up CT does not benefit from unenhanced or arterial-phase acquisition. ? CT severity index scores are equal for dual-contrast-phase 100-/120-kVp acquisition (P?>?0.05). ? 100-kVp single-portal-phase follow-up CT of acute pancreatitis significantly reduces radiation exposure.     

Low contrast media volume in pre-TAVI CT examinations

Purpose

To evaluate image quality using reduced contrast media (CM) volume in pre-TAVI assessment.

Methods

Forty-seven consecutive patients referred for pre-TAVI examination were evaluated. Patients were divided into two groups: group 1 BMI?<?28 kg/m² (n?=?29); and group 2 BMI?>?28 kg/m² (n?=?18). Patients received a combined scan protocol: retrospective ECG-gated helical CTA of the aortic root (80kVp) followed by a high-pitch spiral CTA (group 1: 70 kV; group 2: 80 kVp) from aortic arch to femoral arteries. All patients received one bolus of CM (300 mgI/ml): group 1: volume?=?40 ml; flow rate?=?3 ml/s, group 2: volume?=?53 ml; flow rate?=?4 ml/s. Attenuation values (HU) and contrast-to-noise ratio (CNR) were measured at the levels of the aortic root (helical) and peripheral arteries (high-pitch). Diagnostic image quality was considered sufficient at attenuation values > 250HU and CNR > 10.

Results

Diagnostic image quality for TAVI measurements was obtained in 46 patients. Mean attenuation values and CNR (HU?±?SD) at the aortic root (helical) were: group 1: 381?±?65HU and 13?±?8; group 2: 442?±?68HU and 10?±?5. At the peripheral arteries (high-pitch), mean values were: group 1: 430?±?117HU and 11?±?6; group 2: 389?±?102HU and 13?±?6.

Conclusion

CM volume can be substantially reduced using low kVp protocols, while maintaining sufficient image quality for the evaluation of aortic root and peripheral access sites.

Key points

? Image quality could be maintained using low kVp scan protocols. ? Low kVp protocols reduce contrast media volume by 34–67 %. ? Less contrast media volume lowers the risk of contrast-induced nephropathy.

     

Novel connecting tube for saline chaser in contrast-enhanced CT: the effect of spiral flow of saline on contrast enhancement

Objective

To evaluate the effect of a newly developed connecting tube, which generates a spiral flow of saline, on aortic and hepatic contrast enhancement during hepatic-arterial phase (HAP) and portal venous phase (PVP) computed tomography (CT).

Methods

Eighty patients were randomly assigned to one of two protocols: with a new or a conventional tube. The contrast material (600 mgI/kg) was delivered over 30 s; this was followed by the administration of 25 ml saline solution delivered at the same injection rate as the contrast material. Unenhanced and contrast-enhanced CT images of the upper abdomen were obtained. We calculated the changes in the CT number (?HU) for the aorta during HAP and PVP, and for the liver during PVP. We compared ?HU between protocols.

Results

The mean ?HU for the abdominal aorta during HAP was significantly higher with the new tube protocol than with the conventional tube protocol (322?±?53 vs. 290?±?53, P?<?0.01). There were no significant differences in the mean ?HU for the abdominal aorta and liver during PVP between the two protocols (P?>?0.05).

Conclusion

The new connecting tube increased the effect of a saline chaser and significantly improved aortic enhancement during HAP.

Key Points

? Optimal administration of intravenous contrast material is essential for optimal CT quality. ? A new connecting tube can generate spiral flow, which improves intravenous administration. ? The new connecting tube improved aortic contrast enhancement during the hepatic-arterial phase. ? The new connecting tube increased the effect of a saline chaser.     

Clinical evaluation of automatic tube voltage selection in chest CT angiography

Objective

To evaluate the clinical impact of automatic tube voltage selection on chest CT angiography (CTA).

Methods

Ninety-three patients were prospectively evaluated with a CT protocol aimed at comparing two successive CTAs acquired under similar technical conditions except for the kV selection: (1) the initial CTA was systematically obtained at 120 kVp and 90 ref mAs; (2) the follow-up CTA was obtained with an automatic selection of the kilovoltage (Care KV; Siemens Healthcare) for optimised CTA.

Results

At follow-up, 90 patients (97 %) underwent CTA with reduced tube voltage, 100 kV (n?=?26; 28 %) and 80 kV (n?=?64; 69 %), resulting in a significant dose-length-product reduction (follow-up: 87.27; initial: 141.88 mGy.cm; P?<?0.0001; mean dose reduction: 38.5 %) and a significant increase in the CNR at follow-up (follow-up: 11.5?±?3.5 HU; initial: 10.9?±?3.7 HU; P?=?0.03). The increase in objective image noise at follow-up (follow-up: 23.2?±?6.7 HU vs. 17.8?±?5.1 HU; P?<?0.0001) did not alter the diagnostic value of images.

Conclusion

Automatic tube voltage selection reduced the radiation dose delivered during chest CT angiograms by 38.5 % while improving the contrast-to-noise ratio of the examinations.

Key Points

? As low a dose as possible must be used for CT angiography. ? Automatic tube voltage selection permits reduced patient exposure. ? Lowering the kVp enables increased intravascular attenuation. ? Automatic tube voltage selection does not compromise the overall image quality.     

C-arm CT during hepatic arteriography tumour-to-liver contrast: intraindividual comparison of three different contrast media application protocols

Objective

To compare tumour-to-liver contrast (TLC) of C-arm CT during hepatic arteriography (CACTHA) acquired using three protocols in patients with HCC.

Methods

This prospective study was IRB approved and informed consent was obtained from each patient. Twenty-nine patients (mean age, 68?±?7 years; 27 men) with 55 HCCs (mean diameter, 2.6?±?1.5 cm) underwent three different CACTHA protocols in random order before chemoembolisation. Contrast medium (100 mg iodine/ml) was injected into the common hepatic artery (flow rate 4 ml/s). The imaging delay for the start of the CACTHA examination was 4 s (protocol A), 8 s (protocol B) and 12 s (protocol C) (total amount of injected contrast medium: 48 ml, 64 ml, 80 ml). TLC was measured by placing regions of interest (ROIs) in the HCC and liver parenchyma. Mixed model ANOVAs and Bonferroni corrected post hoc tests were used for statistical analysis.

Results

Mean values for TLC were 132?±?3.3 HU, 186?±?5.8 HU and 168?±?2.8 HU for protocols A, B and C. Protocol B provided significantly higher TLC than protocols A and C (p?<?0.001).

Conclusion

TLC was significantly higher using an imaging delay of 8 s compared with a delay of 4 or 12 s.

Key Points

? C-arm cone-beam CT (CACT) angiography offers additional information during hepatic intervention. ? CACT hepatic arteriography tumour-to-liver contrast is highest with an 8-s delay. ? An 8-s delay is recommended for early arterial phase CACTHA for hepatocelullar carcinoma.     

Comparison of image quality between 70 kVp and 80 kVp: application to paediatric cardiac CT

Purpose

To evaluate noise level and contrast-to-noise ratio (CNR) with various kVp-mAs pairs producing the same computed tomography dose index (CTDI) value. The 80 kVp and new 70-kVp settings were compared.

Materials and methods

The noise was measured in 10 ovoid water phantoms with different diameters from 10 cm to 28 cm. Contrast was obtained from CTs of iodine-filled tubes. Spiral acquisition protocols at 70 kVp and 80 kVp, with the same CTDI, were applied. In the clinical study, two matched groups, each of 21 paediatric patients, underwent 70-kVp or 80-kVp ECG-gated iodinated-enhanced sequential CT.

Results

Noise was significantly higher with 70 kVp than 80-kVp settings for all phantom sizes. Estimated CNR with phantoms was higher at 70 kVp than 80 kVp, and the difference decreased from 17 % to 3 % as phantom size increased. The mean CNR in paediatric patients was 15.2 at 70 kVp and 14.3 at 80 kVp (ns). The CNR difference was significantly larger in the small-child subgroup.

Conclusion

Noise level is slightly higher at the 70-kVp than the 80-kVp setting, but the CNR is higher, particularly for small children. Therefore, 70 kVp may be appropriate for contrast-enhanced CT examinations and 80 kVp for non-enhanced CT in small children.

Key Points

? 70-kVp settings provide a slightly higher noise level compared to 80-kVp settings. ? The CNR is higher with 70-kVp than with 80-kVp settings. ? Without contrast, 80-kVp settings may be preferable over 70-kVp settings.     

Determination of optimal intravenous contrast agent iodine dose for the detection of liver metastasis at 80-kVp CT

Objectives

To determine the optimal iodine mass (IM) to achieve a 50-HU increase in hepatic attenuation for the detection of liver metastasis based on total body weight (TBW) or body surface area (BSA) at 80-kVp computed tomography (CT) imaging of the liver.

Methods

One-hundred and fifty patients who underwent contrast-enhanced CT at 80-kVp were randomised into three groups: 0.5 gI/kg, 0.4 gI/kg and 0.3 gI/kg. Portal venous phase images were evaluated for hepatic parenchymal enhancement (?HU) and visualisation of liver metastasis. Iodine mass per BSA (gI/m²) calculated in individual patients were evaluated.

Results

Mean ?HU for the 0.5 gI/kg group (84.2 HU) was higher than in the 0.4 gI/kg (66.1 HU) and 0.3 gI/kg (53.7 HU) groups (P?<?0.001). Linear correlation equations between ?HU and IM per TBW or BSA are ?HU?=?7.0?+?153.0?×?IM/TBW (r?=?0.73, P?<?0.001) and ?HU?=?11.4?+?4.0?×?IM/BSA (r?=?0.75, P?<?0.001), respectively. The three groups were comparable for the visualisation of hepatic metastases.

Conclusions

The iodine mass to achieve a 50-HU increase in hepatic attenuation at 80-kVp CT was estimated to be 0.28 gI/kg of body weight or 9.6 gI/m² of body surface area.

Key Points

? Hepatic enhancement is expressed as ?HU?=?7.0?+?153.0?×?IM [g]/TBW [kg]. ? Hepatic enhancement is expressed as ?HU?=?11.4?+?4.0?×?IM [g]/BSA [m ² ]. ? Essential iodine dose at 80-kVp CT was 0.28 gI/kg or 9.6 gI/m ² .     

Cerebral bone subtraction CT angiography using 80 kVp and sinogram-affirmed iterative reconstruction: contrast medium and radiation dose reduction with improvement of image quality

Introduction

The purpose of this study was to evaluate the feasibility of a contrast medium (CM), radiation dose reduction protocol for cerebral bone-subtraction CT angiography (BSCTA) using 80-kVp and sinogram-affirmed iterative reconstruction (SAFIRE).

Methods

Seventy-five patients who had undergone BSCTA under the 120- (n = 37) or the 80-kVp protocol (n = 38) were included. CM was 370 mgI/kg for the 120-kVp and 296 mgI/kg for the 80-kVp protocol; the 120- and the 80-kVp images were reconstructed with filtered back-projection (FBP) and SAFIRE, respectively. We compared effective dose (ED), CT attenuation, image noise, and contrast-to-noise ratio (CNR) of two protocols. We also scored arterial contrast, sharpness, depiction of small arteries, visibility near skull base/clip, and overall image quality on a four-point scale.

Results

ED was 62% lower at 80- than 120-kVp (0.59 ± 0.06 vs 1.56 ± 0.13 mSv, p < 0.01). CT attenuation of the internal carotid artery (ICA) and middle cerebral artery (MCA) was significantly higher on 80- than 120-kVp (ICA: 557.4 ± 105.7 vs 370.0 ± 59.3 Hounsfield units (HU), p < 0.01; MCA: 551.9 ± 107.9 vs 364.6 ± 62.2 HU, p < 0.01). The CNR was also significantly higher on 80- than 120-kVp (ICA: 46.2 ± 10.2 vs 36.9 ± 7.6, p < 0.01; MCA: 45.7 ± 10.0 vs 35.7 ± 9.0, p < 0.01). Visibility near skull base and clip was not significantly different (p = 0.45). The other subjective scores were higher with the 80- than the 120-kVp protocol (p < 0.05).

Conclusion

The 80-kVp acquisition with SAFIRE yields better image quality for BSCTA and substantial reduction in the radiation and CM dose compared to the 120-kVp with FBP protocol.

     

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 (CTDI_vol), 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 CTDI_vol 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.     

Low contrast dose protocol involving a 100 kVp tube voltage for hypervascular hepatocellular carcinoma in patients with renal dysfunction

Purpose

To evaluate the feasibility of a 20 % reduced contrast dose hepatic arterial phase (HAP) CT for hypervascular hepatocellular carcinoma (HCC) with 100 kVp.

Materials and methods

The study included 97 patients with hypervascular HCC who underwent dynamic CT, including HAP scanning. The 54 patients had an estimated glomerular filtration rate (eGFR) of ≥60 were scanned with our conventional 120 kVp protocol. The other 43 patients (eGFR < 60) underwent scans using a tube voltage of 100 kVp and a 20 % reduced contrast dose. We compared the estimated effective dose, image noise, tumor-liver contrast (TLC), and contrast-to-noise ratio (CNR) in the hepatic arterial phase between the two groups using the Student’s t test.

Results

Estimated effective dose and image noise were not significantly different between these groups (p = 0.67 and p = 0.20, respectively). The TLC and CNR were significantly higher for the 100 kVp protocol than for the 120 kVp protocol (52.2 HU ± 17.4 vs 40.8 HU ± 18.6, p < 0.01 and 6.8 ± 2.6 vs 5.5 ± 2.4, p = 0.01, respectively).

Conclusion

For hepatic arterial phase CT of hypervascular HCC, 100 kVp scan allows a 20 % reduction in the contrast dose without reduction in image quality compared with a standard 120 kVp CT protocol.

     

Contrast agent bolus tracking with a fixed threshold or a manual fast start for coronary CT angiography

Objectives

Comparison of bolus tracking with a fixed threshold versus a manual fast start for coronary CT angiography.

Methods

We retrospectively analysed 320-row coronary CT angiography of 50 patients with suspected or known coronary artery disease. Twenty-five examinations were initiated by a bolus tracking method (group 1), 25 examinations with a manual fast surestart (group 2).

Results

Mean attenuation values in the ascending aorta were 519?±?111 Hounsfield units (HU) in group 1 and 476?±?65 HU in group 2 (p?=?0.10). Assessable vessel lengths were 171?±?44 mm vs 172?±?29 mm for the right coronary artery (p?=?0.91), 11?±?4 mm vs 12?±?4 mm for the left main (p?=?0.9), 163?±?28 mm vs 151?±?26 mm for the left anterior descending coronary artery (p?=?0.11) and 125?±?41 mm vs 110?±?37 mm for the left circumflex coronary artery (p?=?0.18). Image quality for all coronary arteries was not significantly different between the groups (p?>?0.41). The attenuation ratio between the left and right ventricle was 2.8?±?0.7 vs 3.6?±?1.0 (p?=?0.003). Significantly less contrast agent was used in group 2 (64?±?6 ml vs 80?±?0 ml; p?<?0.001).

Conclusions

Bolus tracking with a fixed threshold and with a manual fast start are both suitable methods; the fast start allowed a reduction of contrast agent volumes.

Key Points

? Fixed threshold bolus tracking is suitable for coronary 320-row CT angiography ? Manual fast start bolus tracking can reduce contrast agent volumes ? Manual fast start and fixed threshold initiation achieve good image quality ? Fixed threshold bolus tracking achieves a more reliable contrast bolus position     

Combining automated attenuation-based tube voltage selection and iterative reconstruction: a liver phantom study

Objectives

To determine the value of combined automated attenuation-based tube-potential selection and iterative reconstructions (IRs) for optimising computed tomography (CT) imaging of hypodense liver lesions.

Methods

A liver phantom containing hypodense lesions was imaged by CT with and without automated attenuation-based tube-potential selection (80, 100 and 120 kVp). Acquisitions were reconstructed with filtered back projection (FBP) and sinogram-affirmed IR. Image noise and contrast-to-noise ratio (CNR) were measured. Two readers marked lesion localisation and rated confidence, sharpness, noise and image quality on a five-point scale (1 = worst, 5 = best).

Results

Image noise was lower (31–52 %) and CNR higher (43–102 %) on IR than on FBP images at all tube voltages. On 100-kVp and 80-kVp IR images, confidence and sharpness were higher than on 120-kVp FBP images. Scores for image quality score and noise as well as sensitivity for 100-kVp IR were similar or higher than for 120-kVp FBP and lower for 80-kVp IR. Radiation dose was reduced by 26 % at 100 kVp and 56 % at 80 kVp.

Conclusions

Compared with 120-kVp FBP images, the combination of automated attenuation-based tube-potential selection at 100 kVp and IR provides higher image quality and improved sensitivity for detecting hypodense liver lesions in vitro at a dose reduced by 26 %.

Key Points

? Combining automated tube voltage selection/iterative CT reconstruction improves image quality. ? Attenuation values remain stable on IR compared with FBP images. ? Lesion detection was highest on 100-kVp IR images.     

Low-dose CT of the lung: potential value of iterative reconstructions

Objectives

To prospectively assess the impact of sinogram-affirmed iterative reconstruction (SAFIRE) on image quality of nonenhanced low-dose lung CT as compared to filtered back projection (FBP).

Methods

Nonenhanced low-dose chest CT (tube current-time product: 30?mAs) was performed on 30 patients at 100?kVp and on 30 patients at 80?kVp. Images were reconstructed with FBP and SAFIRE. Two blinded, independent readers measured image noise; two readers assessed image quality of normal anatomic lung structures on a five-point scale. Radiation dose parameters were recorded.

Results

Image noise in datasets reconstructed with FBP (57.4?±?15.9) was significantly higher than with SAFIRE (31.7?±?9.8, P?<?0.001). Image quality was significantly superior with SAFIRE than with FBP (P?<?0.01), without significant difference between FBP at 100?kVp and SAFIRE at 80?kVp (P?=?0.68). Diagnostic image quality was present with FBP in 96% of images at 100?kVp and 88% at 80?kVp, and with SAFIRE in 100% at 100?kVp and 98% at 80?kVp. There were significantly more datasets with diagnostic image quality with SAFIRE than with FBP (P?<?0.01). Mean CTDI_vol and effective doses were 1.5?±?0.7?mGy·cm and 0.7?±?0.2?mSv at 100?kVp, and 1.4?±?2.8?mGy·cm and 0.5?±?0.2?mSv at 80?kVp (P?<?0.001, both).

Conclusions

Use of SAFIRE in low-dose lung CT reduces noise, improves image quality, and renders more studies diagnostic as compared to FBP.

Key Points

? Low-dose computed tomography is an important thoracic investigation tool. ? Radiation dose can be less than 1?mSv with iterative reconstructions. ? Iterative reconstructions render more low-dose lung CTs diagnostic compared to conventional reconstructions.     

Tube potential can be lowered to 80 kVp in test bolus phase of CT coronary angiography (CTCA) and CT pulmonary angiography (CTPA) to save dose without compromising diagnostic quality

Objectives

The purpose of this study was to determine whether performing the test bolus (TB) of computed tomography coronary angiography (CTCA) and computed tomography pulmonary angiography (CTPA) at 80 kVp reduces dose without compromising diagnostic quality.

Methods

An 80 kVp TB protocol for CTCA and CTPA was retrospectively compared to standard TB protocol (non-obese: 100 kVp, obese: 120 kVp). CT angiogram parameters were unchanged between cohorts. Thirty-seven consecutive 80 kVp TB CTCA images were compared to 53 standard CTCA images. Fifty consecutive CTPAs from each protocol were analysed. Diagnostic quality of the CT angiogram was assessed by: mean attenuation, signal-to-noise ratio (SNR) in the ascending aorta (AA) in CTCA and in the main pulmonary artery (MPA) in CTPA, diagnostic rate, and number of repeated monitoring scans. Mean effective dose was estimated using the dose-length product.

Results

Mean TB effective doses were significantly lower (P?Conclusions Routinely performing TB at 80 kVp, regardless of body habitus, in CTCA and CTPA results in a small but significant dose reduction, without compromising CT angiogram diagnostic quality.

Key Points

? CT coronary angiography is performed to exclude the presence of significant coronary atherosclerosis. ? CT pulmonary angiography is performed to diagnose pulmonary thromboembolism. ? This retrospective study showed dose reduction by performing test bolus at 80 kVp. ? Diagnosis can be made with reduced exposure to ionising radiation.     

Preliminary report on virtual monochromatic spectral imaging with fast kVp switching dual energy head CT: comparable image quality to that of 120-kVp CT without increasing the radiation dose

Purpose

This study aimed to evaluate whether the image quality of virtual monochromatic spectral imaging with fast kVp switching dual-energy CT (DECT) can be comparable to that of 120-kVp single-energy CT (SECT) without increasing the radiation dose.

Materials and methods

We retrospectively identified 15 postoperative patients who had undergone both DECT and 120-kVp SECT within a short period of time for follow-up after brain surgery. Simulated 65 keV monochromatic images were reconstructed from DECT data. Subjective image noise, gray–white matter contrast, and overall image quality were rated using a four-point scale. Quantitative measurement of noise, contrast-to-noise ratio (CNR), and posterior fossa beam-hardening artifact were also performed. The figure of merit (FOM), calculated as CNR²/CTDI_vol, was used to quantify image quality improvement per exposure risk.

Results

The mean CTDI_vol was 70.2 ± 0.3 mGy for DECT, which was 11 % lower than SECT (78.9 ± 2.1 mGy). All images were graded above clinically acceptable. Quantitative and qualitative measures for simulated 65-keV images were comparable with SECT images, except for increase in subjective noise. FOM was significantly greater for simulated 65-keV images (P = .03).

Conclusion

Our results indicate that virtual monochromatic imaging possibly provides comparable image quality to that afforded by 120-kVp SECT without increasing the dose in routine head CT.     

An optimised patient-specific approach to administration of contrast agent for CT pulmonary angiography

Objectives

To investigate pulmonary vasculature opacification during CTPA using an optimised patient-specific protocol for administering contrast agent.

Methods

CTPA was performed on 200 patients with suspected PE. Patients were assigned to two protocol groups: protocol A, fixed 80 ml contrast agent; protocol B used a patient-specific approach. The mean cross-sectional opacification profile of 8 central and 11 peripheral pulmonary arteries and veins was measured and the arteriovenous contrast ratio (AVCR) calculated. Protocols were compared using Mann–Whitney U non-parametric statistics. Jack-knife alternative free-response receiver-operating characteristic (JAFROC) analyses assessed diagnostic efficacy. Interobserver variations were investigated using kappa methods.

Results

A number of pulmonary arteries demonstrated increases in opacification (P?<?0.03) for protocol B compared to A, whilst opacification in the heart and veins was reduced in protocol B (P?=?0.05). Increased AVCR in protocol B compared with A was observed at all anatomic locations (P?<?0.0002). Increased JAFROC (P?<?0.0002) and kappa variation were observed with protocol B (κ?=?0.78) compared to A (κ?=?0.25). Mean contrast volume was reduced in protocol B (33?±?9 ml) compared to A (80?±?1 ml).

Conclusions

Significant improvements in visualisation of the pulmonary vasculature can be achieved with a low volume of contrast agent using injection timing based on a patient-specific contrast formula.

Key points

? Optimal opacification of the pulmonary arteries is essential for CT pulmonary angiography. ? Matching timing with vessel dynamics significantly improves vessel opacification. ? This leads to increased arterial opacification and reduced venous opacification. ? This can also lead to a reduced volume of contrast agent.     

Image noise-based dose adaptation in dynamic volume CT of the heart: dose and image quality optimisation in comparison with BMI-based dose adaptation

Objectives

To compare the image quality and radiation dose using image-noise (IN)-based determination of X-ray tube settings compared with a body mass index (BMI)-based protocol during CT coronary angiography (CTCA).

Methods

Two hundred consecutive patients referred for CTCA to our institution were divided into two groups: BMI-based, 100 patients had CTCA with the X-ray tube current adjusted to the patient’s BMI while maintaining a fixed tube potential of 120 kV; IN-based, 100 patients underwent imaging with the X-ray tube current and voltage adjusted to the IN measured within the mid-left ventricle on a pre-acquisition trans-axial image. Two independent cardiac radiologists performed blinded image quality assessment with quantification of the IN and signal-to-noise ratio (SNR) from the mid-LV and qualitative assessment using a three-point score. Radiation dose (CTDI and DLP) was recorded from the console.

Results

Results showed: IN (HU): BMI-based, 30.1?±?9.9; IN-based, 33.1?±?6.7; 32 % variation reduction (P?=?0.001); SNR: BMI-based, 18.6?±?7.1; IN-based, 15.4?±?3.7; 48 % variation reduction (P?<?0.0001). Visual scores: BMI-based, 2.3?±?0.6; IN-based, 2.2?±?0.5 (P?=?0.54). Radiation dose: CTDI (mGy), BMI-based, 22.68?±?8.9; IN-based, 17.16?±?7.6; 24.3 % reduction (P?<?0.001); DLP (mGy.cm), BMI-based, 309.3?±?127.5; IN-based, 230.6?±?105.5; 25.4 % reduction (P?<?0.001).

Conclusions

Image-noise-based stratification of X-ray tube parameters for CTCA results in 32 % improvement in image quality and 25 % reduction in radiation dose compared with a BMI-based protocol.

Key Points

? Image quality and radiation dose are closely related in CT coronary angiography. ? So too are the image quality, radiation dose and body mass index (BMI). ? An image-noise-based CTCA protocol reduces the radiation dose by 25 %. ? It improves inter-patient image homogeneity by 32 %.     

Low tube voltage and low contrast material volume cerebral CT angiography

Objectives

To evaluate the image quality, radiation dose and diagnostic accuracy of low kVp and low contrast material volume cerebral CT angiography (CTA) in intracranial aneurysm detection.

Methods

One hundred twenty patients were randomly divided into three groups (n?=?40 for each): Group A, 70 ml iodinated contrast agent/120 kVp; group B, 30 ml/100 kVp; group C, 30 ml/80 kVp. The CT numbers, noise, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were measured in the internal carotid artery (ICA) and middle cerebral artery (MCA). Subjective image quality was evaluated. For patients undergoing DSA, diagnostic accuracy of CTA was calculated with DSA as reference standard and compared.

Results

CT numbers of ICA and MCA were higher in groups B and C than in group A (P?<?0.01). SNR and CNR in groups A and B were higher than in group C (both P?<?0.05). There was no difference in subjective image quality among the three groups (P?=?0.939). Diagnostic accuracy for aneurysm detection among these groups had no statistical difference (P?=?1.00). Compared with group A, the radiation dose of groups B and C was decreased by 45 % and 74 %.

Conclusion

Cerebral CTA at 100 or 80 kVp using 30 ml contrast agent can obtain diagnostic image quality with a low radiation dose while maintaining the same diagnostic accuracy for aneurysm detection.

Key Points

? Cerebral CTA is feasible using 100/80 kVp and 30 ml contrast agent. ? This approach obtains diagnostic image quality with 45–74 % radiation dose reduction. ? Diagnostic accuracy for intracranial aneurysm detection seems not to be compromised.     

Feasibility of prospectively ECG-triggered high-pitch coronary CT angiography with 30 mL iodinated contrast agent at 70 kVp: initial experience

Objectives

To evaluate the feasibility, image quality and radiation dose of prospectively ECG-triggered high-pitch coronary CT angiography (CCTA) with 30 mL contrast agent at 70 kVp.

Methods

Fifty-eight patients with suspected coronary artery disease, a body mass index (BMI) of less than 25 kg/m², sinus rhythm and a heart rate (HR) of less than 70 beats per minute (bpm) were prospectively enrolled in this study. Thirty mL of 370 mg I/mL iodinated contrast agent was administrated at a flow rate of 5 mL/s. All patients underwent prospectively ECG-triggered high-pitch CCTA on a second-generation dual-source CT system at 70 kVp using automated tube current modulation.

Results

Fifty-six patients (96.6 %) had diagnostic CCTA images and two patients (3.4 %) had one vessel with poor image quality each rated as non-diagnostic. No significant effects of HR, HR variability and BMI on CCTA image quality were observed (all P?>?0.05). Effective dose was 0.17?±?0.02 mSv and the size-specific dose estimate was 1.03?±?0.13 mGy.

Conclusion

Prospectively ECG-triggered high-pitch CCTA at 70 kVp with 30 mL of contrast agent can provide diagnostic image quality at a radiation dose of less than 0.2 mSv in patients with a BMI of less than 25 kg/m² and an HR of less than 70 bpm.

Key points

? Prospectively ECG-triggered high-pitch CCTA at 70 kVp/30 mL contrast agent is feasible. ? Diagnostic image quality can be obtained at a radiation dose of less than 0.2 mSv. ? This protocol is suitable for normal-weight patients with slow heart rate.     

Computed tomography angiography of carotid and coronary artery via a single-bolus injection protocol: a feasibility study using 320-row multidetector CT

Objectives

To investigate the feasibility of using a single-dose injection protocol in CT angiography (CTA) of the carotid and coronary artery with 320-row multidetector CT.

Methods

A total of 82 consecutive patients with suspected carotid artery disease underwent an original CTA protocol aiming at capturing the extra-cranial carotid arteries and coronary arteries simultaneously using 320-row MDCT. The image quality, attenuation, and CNRs of the carotid and coronary arteries were assessed. The lag time (between two separated volumetric acquisitions) was compared between patients with and without cardiac venous opacification (CVO). The contrast medium volume and radiation dose were recorded.

Results

The image quality was 99.4 % diagnostic in carotid and 86.9 % in coronary artery segments. The mean attenuation of carotid and coronary arteries ranged from 462.2 Hu to 533.7 Hu, 415.9 Hu to 454.7 Hu respectively. The mean CNR of the carotid and coronary artery ranged from 15.8 to 18.9 and 17.7 to 20.4 respectively. The lag time in patients with and without CVO was 5.75?±?1.64 s vs. 4.21?±?1.14 s (p?<?0.05). The mean radiation dose was 6.6?±?4.1 mSv.The mean contrast media volume was 71.9?±?9.1 ml.

Conclusions

The carotid and coronary artery can be imaged simultaneously via our original single-dose injection CTA protocol using 320-row CT with adequate image quality.

Key Points

? Carotid and coronary 320-row CTA can be achieved in a single-dose injection. ? Longer coverage was achieved with two or more volumes using 320-row CT. ? The single-dose protocol allows a reduced contrast agent dose of about 72 ml.