CT evaluation of coronary artery stents with iterative image reconstruction: improvements in image quality and potential for radiation dose reduction

Objectives

Comparison of coronary artery stent assessment with cardiac CT angiography (cCTA) using traditional filtered back projection (FBP) and sinogram affirmed iterative reconstruction (SAFIRE), in both full- and half-radiation dose image data.

Methods

Dual-source cCTA studies of 37 implanted stents were reconstructed at full- and half-radiation dose with FBP and SAFIRE. Half-dose data were based on projections from one DSCT detector. In-stent noise, signal-to-noise ratio (SNR), and stent-lumen attenuation increase ratio (SAIR) were measured and image quality graded. Stent volumes were measured to gauge severity of beam hardening artefacts.

Results

Full-dose SAFIRE reconstructions were superior to full-dose FBP vis-à-vis in-stent noise (21.2?±?6.6 vs. 35.7?±?17.5; P?<?0.05), SNR (22.1?±?8.6 vs. 14.3?±?6.7; P?<?0.05), SAIR (19.6?±?17.6 vs. 33.4?±?20.4%; P?<?0.05), and image quality (4.2?±?0.86 vs. 3.5?±?1.0; P?<?0.05). Stent volumes were lower measured with SAFIRE (119.9?±?53.7 vs. 129.8?±?65.0?mm³; P?>?0.05). Comparing half-dose SAFIRE with full-dose FBP, in-stent noise (26.7?±?13.0 vs. 35.7?±?17.5; P?<?0.05) and SNR (18.2?±?6.9 vs. 14.3?±?6.7; P?<?0.05) improved significantly. SAIR (31.6?±?24.3 vs. 33.4?±?20.4%; P?>?0.05), stent volume (129.6?±?57.3 vs. 129.8?±?65.0?mm³; P?>?0.05), and image quality (3.5?±?1.0 vs. 3.7?±?1.1; P?>?0.05) did not differ. Radiation dose decreased from 8.7?±?5.2 to 4.3?±?2.6?mSv.

Conclusions

Iterative reconstruction significantly improves imaging of coronary artery stents by CT compared with FBP, even with half-radiation-dose data.

Key Points

? Computed tomography (CT) is becoming an increasingly important investigation for cardiac problems. ? Iterative CT reconstruction techniques significantly improve coronary artery stent evaluation. ? Iterative reconstruction has the potential to reduce radiation dose requirements. ? Improved stent visualisation detects complications better, further reducing the need for catheterisation.     

Cardiovascular CT angiography in neonates and children: Image quality and potential for radiation dose reduction with iterative image reconstruction techniques

Objectives

To evaluate image quality (IQ) of low-radiation-dose paediatric cardiovascular CT angiography (CTA), comparing iterative reconstruction in image space (IRIS) and sinogram-affirmed iterative reconstruction (SAFIRE) with filtered back-projection (FBP) and estimate the potential for further dose reductions.

Methods

Forty neonates and children underwent low radiation CTA with or without ECG synchronisation. Data were reconstructed with FBP, IRIS and SAFIRE. For ECG-synchronised studies, half-dose image acquisitions were simulated. Signal noise was measured and IQ graded. Effective dose (ED) was estimated.

Results

Mean absolute and relative image noise with IRIS and full-dose SAFIRE was lower than with FBP (P?<?0.001), while SNR and CNR were higher (P?<?0.001). Image noise was also lower and SNR and CNR higher in half-dose SAFIRE studies compared with full-and half-dose FBP studies (P?<?0.001). IQ scores were higher for IRIS, full-dose SAFIRE and half-dose SAFIRE than for full-dose FBP and higher for half-dose SAFIRE than for half-dose FBP (P?<?0.05). Median weight-specific ED was 0.3 mSv without and 1.36 mSv with ECG synchronisation. The estimated ED of half-dose SAFIRE studies was 0.68 mSv.

Conclusions

IR improves image noise, SNR, CNR and subjective IQ compared with FBP in low-radiation-dose paediatric CTA and allows further dose reductions without compromising diagnostic IQ.

Key Points

? Iterative reconstruction techniques significantly improve non-invasive cardiovascular CT in children. ? Using half traditional radiation dose image quality is higher with iterative reconstruction. ? Iterative reconstruction techniques may allow further radiation reductions in paediatric cardiovascular CT.     

Image quality of ultra-low radiation exposure coronary CT angiography with an effective dose <0.1 mSv using high-pitch spiral acquisition and raw data-based iterative reconstruction

Objectives

We evaluated the potential of prospectively ECG-triggered high-pitch spiral acquisition with low tube voltage and current in combination with iterative reconstruction to achieve coronary CT angiography with sufficient image quality at an effective dose below 0.1 mSv.

Methods

Contrast-enhanced coronary dual source CT angiography (2?×?128?×?0.6 mm, 80 kV, 50 mAs) in prospectively ECG-triggered high-pitch spiral acquisition mode was performed in 21 consecutive individuals (body weight <100 kg, heart rate ≤60/min). Images were reconstructed with raw data-based filtered back projection (FBP) and iterative reconstruction (IR). Image quality was assessed on a 4-point scale (1 = no artefacts, 4 = unevaluable).

Results

Mean effective dose was 0.06?±?0.01 mSv. Image noise was significantly reduced in IR (128.9?±?46.6 vs. 158.2?±?44.7 HU). The mean image quality score was lower for IR (1.9?±?1.1 vs. 2.2?±?1.0, P?<?0.0001). Of 292 coronary segments, 55 in FBP and 40 in IR (P?=?0.12) were graded “unevaluable”. In patients with a body weight ≤75 kg, both in FBP and in IR, the rates of fully evaluable segments were significantly higher in comparison to patients >75 kg.

Conclusions

Coronary CT angiography with an estimated effective dose <0.1 mSv may provide sufficient image quality in selected patients through the combination of high-pitch spiral acquisition and raw data-based iterative reconstruction.

Key Points

? Coronary CT angiography with an estimated effective dose <0.1 mSv is possible. ? Combination of high-pitch spiral acquisition with iterative reconstruction achieves sufficient image quality. ? Diagnostic accuracy remains to be assessed in future trials.     

Percutaneous lung biopsies: performance of an optical CT-based navigation system with a low-dose protocol

Objectives

To compare patients’ radiation exposure, technical feasibility, imaging quality and complication rate of percutaneous lung biopsies (PLBs) performed with a low-dose (LD) CT protocol under guidance of an optical navigation system.

Methods

Fifty-two consecutive patients with suspected malignant lung lesions were enrolled and randomised into group 1 (PLBs under the guidance of the navigation system) and group 2 (PLBs under the guidance navigation system with an LD protocol). Patients’ demographics, lesion features, procedure-related variables and CT image quality for group 2 were recorded and compared.

Results

Technical success was 100 % in both groups. The radiation dose to patients’ chest was significantly lower in group 2 than in group 1 (group 1: mean TDLP 206?±?59 mGy·cm, ~ 3.5?±?1.0 mSv; group 2: 54.2?±?46.2 mGy·cm, ~ 0.92?±?0.78 mSv; P?<?0.0001). The PNX rate was 12 % in group 1 and 11.1 % in group 2. The haemoptysis rate was 8.0 % in group 1 and 3.7 % in group 2. CT image quality obtained in group 2 was always rated as adequate and as excellent in 15 cases (56.0 %).

Conclusions

An optical navigation system with LD CT protocol is useful for performing lung biopsies with decreased patient radiation exposure.

Key Points

? Navigation systems are useful tools in percutaneous imaging-guided procedures. ? For lung biopsies, low-dose (LD) CT protocols may be used. ? Combining LD protocols with optical CT navigation results in significantly reduced radiation exposure.     

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.     

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.     

Image quality assessment of ultra low-dose chest CT using sinogram-affirmed iterative reconstruction

Objectives

To assess the image quality of ultra-low-dose computed tomography (ULDCT) using sinogram-affirmed iterative reconstruction (SAFIRE) compared to reduced dose CT (RDCT).

Methods

Eighty-one consecutive patients underwent non-enhanced ULDCT using 80 kVp and 30 mAs and contrast-enhanced RDCT using automated tube potential selection and tube current modulation. CT images were reconstructed with SAFIRE. Image noise and subjective image quality of normal structures and various pulmonary lesions were assessed.

Results

The mean effective doses were 0.29?±?0.03 and 2.88?±?1.11 mSv for ULDCT and RDCT, respectively. ULDCT had significantly higher noise (p?<?0.001). Image quality of five normal structures was diagnostic in 91.1 % of ULDCT and 100 % of RDCT. With ULDCT, the frequencies of non-diagnostic image quality were 2.0 (1/50), 4.6 (13/280), 25.5 (14/55), and 40.0 (8/20)% for BMIs of?<?20, 20–25, 25–30, and >30. In the assessment of pulmonary lesions, non-diagnostic image quality was observed for 11.2 % of all lesions, 60.9 % of decreased attenuation (significantly more frequent for upper lung lesions), and 23.5 % of ground-glass nodules.

Conclusion

ULDCT generates diagnostic images in patients with a BMI ≤25, but is of limited use for lesions with decreased attenuation, ground-glass nodules, or those located in the upper lobe.

Key Points

? Iterative reconstruction enables ultra-low-dose CT (ULDCT) with very low radiation doses. ? Image quality of ULDCT depends on the patient body mass index (BMI). ? Selection of kVp and mAs depends on both BMI and lesion type. ? Diagnosis of pulmonary emphysema or ground-glass nodules requires higher radiation doses.     

Prospective randomised comparison of diagnostic confidence and image quality with normal-dose and low-dose CT pulmonary angiography at various body weights

Objectives

To find a threshold body weight (BW) below 100 kg above which computed tomography pulmonary angiography (CTPA) using reduced radiation and a reduced contrast material (CM) dose provides significantly impaired quality and diagnostic confidence compared with standard-dose CTPA.

Methods

In this prospectively randomised study of 501 patients with suspected pulmonary embolism and BW <100 kg, 246 were allocated into the low-dose group (80 kVp, 75 ml CM) and 255 into the normal-dose group (100 kVp, 100 ml CM). Contrast-to-noise ratio (CNR) in the pulmonary trunk was calculated. Two blinded chest radiologists independently evaluated subjective image quality and diagnostic confidence. Data were compared between the normal-dose and low-dose groups in five BW subgroups.

Results

Vessel attenuation did not differ between the normal-dose and low-dose groups within each BW subgroup (P?=?1.0). The CNR was higher with the normal-dose compared with the low-dose protocol (P?<?0.006) in all BW subgroups except for the 90-99 kg subgroup (P?=?0.812). Subjective image quality and diagnostic confidence did not differ between CT protocols in all subgroups (P between 0.960 and 1.0).

Conclusions

Subjective image quality and diagnostic confidence with 80 kVp CTPA is not different from normal-dose protocol in any BW group up to 100 kg.

Key Points

? 80 kVp CTPA is safe in patients weighing <100 kg ? Reduced radiation and iodine dose still provide high vessel attenuation ? Image quality and diagnostic confidence with low-dose CTPA is good ? Diagnostic confidence does not deteriorate in obese patients weighing <100 kg     

A prospective feasibility study of sub-millisievert abdominopelvic CT using iterative reconstruction in Crohn’s disease

Objective

Iterative reconstruction (IR) allows diagnostic CT imaging with less radiation exposure than filtered back projection (FBP). We studied an IR low-dose CT abdomen/pelvis (LDCTAP) protocol, designed to image at an effective dose (ED) approximating 1 mSv in patients with Crohn’s disease (CD).

Methods

Forty patients, mean age 37?±?13.4 years (range 17–69), with CD underwent two synchronous CT protocols (conventional-dose (CDCTAP) and LDCTAP). CDCTAP and LDCTAP images were compared for diagnostic acceptability, yield, image quality and ED (in millisieverts). The optimal level of IR for LDCTAP was also studied.

Results

LDCTAP yielded a mean ED of 1.3?±?0.8 mSv compared with 4.7?±?2.9 mSv for CDCTAP, reducing ED by 73.7?±?3.3 % (mean dose reduction, 3.5?±?2.1 mSv; P?<?0.001) and dose length product by 73.6?±?2.6 % (P?<?0.001). Sub-millisievert (0.84 mSv) imaging was performed for patients with a body mass index (BMI) less than 25 (i.e. 63 % of our cohort). LDCTAP resulted in increased image noise and reduced diagnostic acceptability compared with CDCTAP despite use of IR, but detection of extra-luminal complications was comparable.

Conclusion

Patients with suspected active CD can be adequately imaged using LDCTAP, yielding comparable information regarding extent, activity and complications of CD compared with CDCTAP, but with 74 % less dose. LDCTAP at doses equivalent to that of two abdominal radiographs represents a feasible alternative to CDCTAP.

Key points

? Radiation dose is a concern when imaging patients with Crohn’s disease. ? New techniques allow low-dose abdominopelvic CT with acceptable image quality. ? Using hybrid iterative reconstruction, its diagnostic yield compares well with that of conventional CT. ? Sub-millisievert CT of patients with Crohn’s disease appears technically and clinically feasible.     

High-pitch computed tomography pulmonary angiography with iterative reconstruction at 80 kVp and 20 mL contrast agent volume

Objectives

To evaluate the image quality, radiation dose and diagnostic accuracy of 80kVp, high-pitch CT pulmonary angiography (CTPA) with iterative reconstruction using 20 ml of contrast agent.

Methods

One hundred patients with suspected pulmonary embolism (PE) were randomly divided into two groups (n?=?50 each; group A, 100 kVp, 1.2 pitch, 60 ml of contrast medium and filtered back projection algorithm; group B, 80 kVp, 2.2 pitch, 20 ml of contrast medium and sinogram affirmed iterative reconstruction). Image quality, diagnostic accuracy and radiation dose were evaluated and compared.

Results

Mean CT numbers of pulmonary arteries in group B were higher than those in group A (all P?P?P?=?0.807). The interobserver agreement was excellent (k?=?0.836). There was no significant difference in diagnostic accuracy between the two groups (P?>?0.05). Compared with group A, radiation dose of group B was reduced by 50.3 % (P?Conclusions High-pitch CTPA at 80 kVp can obtain sufficient image quality in normal-weight individuals with 20 ml of contrast agent and half the radiation dose of a conventional CTPA protocol.

Key Points

? CTPA is feasible at 80 kVp using only 20 ml of contrast agent. ? High-pitch CTPA at 80 kVp has an effective dose under 1 mSv. ? This CTPA protocol can obtain sufficient image quality in normal-weight individuals.     

Coronary CT angiography: image quality, diagnostic accuracy, and potential for radiation dose reduction using a novel iterative image reconstruction technique��comparison with traditional filtered back projection

Objectives

To compare image noise, image quality and diagnostic accuracy of coronary CT angiography (cCTA) using a novel iterative reconstruction algorithm versus traditional filtered back projection (FBP) and to estimate the potential for radiation dose savings.

Methods

Sixty five consecutive patients (48 men; 59.3?±?7.7?years) prospectively underwent cCTA and coronary catheter angiography (CCA). Full radiation dose data, using all projections, were reconstructed with FBP. To simulate image acquisition at half the radiation dose, 50% of the projections were discarded from the raw data. The resulting half-dose data were reconstructed with sinogram-affirmed iterative reconstruction (SAFIRE). Full-dose FBP and half-dose iterative reconstructions were compared with regard to image noise and image quality, and their respective accuracy for stenosis detection was compared against CCA.

Results

Compared with full-dose FBP, half-dose iterative reconstructions showed significantly (p?=?0.001 ?C p?=?0.025) lower image noise and slightly higher image quality. Iterative reconstruction improved the accuracy of stenosis detection compared with FBP (per-patient: accuracy 96.9% vs. 93.8%, sensitivity 100% vs. 100%, specificity 94.6% vs. 89.2%, NPV 100% vs. 100%, PPV 93.3% vs. 87.5%).

Conclusions

Iterative reconstruction significantly reduces image noise without loss of diagnostic information and holds the potential for substantial radiation dose reduction from cCTA.     

Effect of hybrid iterative reconstruction technique on quantitative and qualitative image analysis at 256-slice prospective gating cardiac CT

Objectives

To evaluate the effect of hybrid iterative reconstruction on qualitative and quantitative parameters at 256-slice cardiac CT.

Methods

Prospective cardiac CT images from 20 patients were analysed. Paired image sets were created using 3 reconstructions, i.e. filtered back projection (FBP) and moderate- and high-level iterative reconstructions. Quantitative parameters including CT-attenuation, noise, and contrast-to-noise ratio (CNR) were determined in both proximal- and distal coronary segments. Image quality was graded on a 4-point scale.

Results

Coronary CT attenuation values were similar for FBP, moderate- and high-level iterative reconstruction at 293?±?74-, 290?±?75-, and 283?±?78 Hounsfield units (HU), respectively. CNR was significantly higher with moderate- and high-level iterative reconstructions (10.9?±?3.5 and 18.4?±?6.2, respectively) than FBP (8.2?±?2.5) as was the visual grading of proximal vessels. Visualisation of distal vessels was better with high-level iterative reconstruction than FBP. The mean number of assessable segments among 289 segments was 245, 260, and 267 for FBP, moderate- and high-level iterative reconstruction, respectively; the difference between FBP and high-level iterative reconstruction was significant. Interobserver agreement was significantly higher for moderate- and high-level iterative reconstruction than FBP.

Conclusions

Cardiac CT using hybrid iterative reconstruction yields higher CNR and better image quality than FBP.

Key Points

? Cardiac CT helps clinicians to assess patients with coronary artery disease ? Hybrid iterative reconstruction provides improved cardiac CT image quality ? Hybrid iterative reconstruction improves the number of assessable coronary segments ? Hybrid iterative reconstruction improves interobserver agreement on cardiac CT     

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.     

Prospectively ECG-triggered high-pitch spiral acquisition for coronary CT angiography using dual source CT: technique and initial experience

Objective

We evaluated radiation exposure and image quality of a new coronary CT angiography protocol, high-pitch spiral acquisition, using dual source CT (DSCT).

Material and methods

Coronary CTA was performed in 25 consecutive patients with a stable heart rate of 60 bpm or less after premedication, using 2?×?128 0.6-mm sections, 38.4-mm collimation width and 0.28-s rotation time. Tube settings were 100 kV/320 mAs and 120 kV/400 mAs for patients below and above 100-kg weight, respectively. Data acquisition was prospectively ECG-triggered at 60% of the R–R interval using a pitch of 3.2 (3.4 for the last 10 patients). Images were reconstructed with 75-ms temporal resolution, 0.6-mm slice thickness and 0.3-mm increment. Image quality was evaluated using a four-point scale (1 = excellent, 4 = unevaluable).

Results

Mean range of data acquisition was 113?±?22 mm, mean duration was 268?±?23 ms. Of 363 coronary artery segments, 327 had an image quality score of 1, and only 2 segments were rated as “unevaluable”. Mean dose–length product (DLP) was 71?±?23 mGy cm, mean effective dose was 1.0?±?0.3 mSv (range 0.78–2.1 mSv). For 21 patients with a body weight below 100 kg, mean DLP was 63?±?5 mGy cm (0.88?±?0.07 mSv; range 0.78–0.97 mSv).

Conclusion

Prospectively ECG-triggered high-pitch spiral CT acquisition provides high and stable image quality at very low radiation dose.     

Subtracted 3D CT angiography for the evaluation of intracranial aneurysms in 256-slice multidetector CT: usefulness of the 80-kVp plus compact contrast medium bolus protocol

Objectives

To evaluate the usefulness of an 80-kVp and compact contrast material protocol for arterial phase subtracted cerebral 3D-CTA using 256-slice multidetector CT.

Methods

Thirty-two patients underwent CT with 100 kVp and received a contrast dose of 370 mgI/kg body weight over 15 s (protocol A). Thirty-three patients underwent CT with 100 kVp and received a contrast dose of 296 mgI/kg body weight over 10 s (protocol B). Thirty-three other patients underwent CT with 80 kVp and received a contrast medium dose of 296 mgI/kg body weight over 10 s (protocol C). We compared the arterial attenuation and contrast noise ratio (CNR) of each protocol. Two independent readers assessed overall image quality.

Results

Arterial attenuation was significantly higher under protocols A (418.6?±?71.1 HU) and C (442.7?±?79.3 HU) than under protocol B (355.8?±?107.2 HU; P?<?0.05). The CNR of protocol C (26.1?±?6.1) was higher than that of protocol A (20.7?±?8.4; P?<?0.05). The overall image quality of protocol A was higher than that of protocol C (P?<?0.01).

Conclusion

The 80-kVp plus compact contrast protocol is well suited to arterial phase subtracted cerebral 3D-CTA without confounding venous enhancement.

Key Points

? Subtracted 3D CT angiography is useful in the evaluation of intracranial aneurysms. ? A compact contrast material protocol increased arterial attenuation without venous contamination. ? Low-kVp CT compensated for the decreased amount of contrast medium. ? An 80-kVp CT with a compact enhancement bolus provides good intracranial 3D-CT angiography.     

Clinical impact of an adaptive statistical iterative reconstruction algorithm for detection of hypervascular liver tumours using a low tube voltage, high tube current MDCT technique

Objectives

To investigate the impact of an adaptive statistical iterative reconstruction (ASiR) algorithm on diagnostic accuracy and confidence for the diagnosis of hypervascular liver tumours, as well as the reader’s perception of image quality, using a low tube voltage (80 kVp), high tube current computed tomography (CT) technique.

Methods

Forty patients (29 men, 11 women) with 65 hypervascular liver tumours underwent dual energy CT. The 80 kV set of the dual energy acquisition was reconstructed with standard filtered backprojection (FBP) and ASiR at different blending levels. Lesion contrast-to-noise ratio (CNR), reader’s confidence for lesion detection and characterisation, and reader’s evaluation of image quality were recorded.

Results

ASiR yielded significantly higher CNR values compared with FBP (P?<?0.0001 for all comparisons). Reader’s perception of lesion conspicuity and confidence in the diagnosis of malignancy were also higher with 60 % and 80 % ASiR, compared with FBP (P?=?0.01 and?<?0.001, respectively). Compared with FBP, ASiR yielded nearly significantly lower specificity for lesion detection and a substantial decrease in the reader’s perception of image quality.

Conclusions

Compared with the standard FBP algorithm, ASiR significantly improves conspicuity of hypervascular liver lesions. This improvement may come at the cost of decreased specificity and reader’s perception of image quality.

Key Points

? Adaptive statistical iterative reconstruction algorithms (ASiRs) offer increasing potential in multidetector CT. ? An ASiR algorithm significantly improves conspicuity of hypervascular liver lesions at MDCT. ? Improved lesion conspicuity translates into increased reader’s confidence for diagnosis of malignancy. ? False positive findings may increase with ASiR, leading to potentially lower specificity.     

Impact of iterative reconstruction on image quality and radiation dose in multidetector CT of large body size adults

Objective

To compare image quality and radiation dose using Adaptive Statistical Iterative Reconstruction (ASiR) and Filtered Back Projection (FBP) in patients weighing ≥91?kg.

Methods

In this Institution Review Board-approved retrospective study, single-phase contrast-enhanced abdominopelvic CT examinations of 100 adults weighing ≥91?kg (mean body weight: 107.6?±?17.4?kg range: 91–181.9?kg) with (1) ASiR and (2) FBP were reviewed by two readers in a blinded fashion for subjective measures of image quality (using a subjective standardized numerical scale and objective noise) and for radiation exposure. Imaging parameters and radiation dose results of the two techniques were compared within weight and BMI sub-categories.

Results

All examinations were found to be of adequate quality. Both subjective (mean?=?1.4?±?0.5 vs. 1.6?±?0.6, P?P?P?Conclusion In obese individuals, abdominal CT images reconstructed using ASiR provide diagnostic images with reduced image noise at lower radiation dose.

Key Points

? CT images in obese adults are noisy, even with high radiation dose. ? Newer iterative reconstruction techniques have theoretical advantages in obese patients. ? Adaptive statistical iterative reconstruction should reduce image noise and radiation dose. ? This has been proven in abdominopelvic CT images of obese patients.     

Feasibility of myocardial perfusion imaging with half the radiation dose using ordered-subset expectation maximization with resolution recovery software

Objective

This study sought to assess the feasibility of performing myocardial perfusion imaging (MPI) with half the technetium activity using ordered-subset expectation maximization with resolution recovery (OSEM-RR), an iterative reconstruction software developed to improve count statistics and acquisition time.

Methods

Two hundred eighteen patients referred for MPI were randomly allocated to undergo stress-rest or rest-stress protocols with standard full-dose (FD) injections of technetium (Tc)-99m sestamibi or half-dose (HD) injections and OSEM-RR processing. Dose activities were adjusted individually by weight. The groups were compared for image quality and clinical results.

Results

The groups were similar for mean patient age, weight, and body mass index, sex distribution, pre-test probability of CAD and CAD prevalence. Mean Tc-99m activities for the low-dose and high-dose stages were as follows: FD group: 429?±?85?MBq and 1132?±?200?MBq; HD group: 263?±?129?MBq and 629?±?85?MBq (P?<?.0001 for both). Mean effective dose per study was 13.6?±?1.4?mSv in the FD group and 7.7?±?1.0?mSv in the HD group (P?<?.001). Over all image quality was good-to-excellent in 98% and 95% of the groups, respectively. However, when we analyzed the low-dose stage separately, image quality was slightly worse in the HD than the FD, though still within the good-to excellent range.

Conclusions

MPI with nearly half the radiation dose is feasible with good image quality.     

Optimisation of low-dose CT with adaptive statistical iterative reconstruction in total body examination

Purpose

The aim of this study was to assess the feasibility of low-dose computed tomography (CT) with the adaptive statistical iterative reconstruction (ASIR) algorithm in whole-body imaging with low tube voltage and current.

Materials and methods

Twenty-three patients underwent whole-body CT with 40% of ASIR and parameters modulated according to body mass index (BMI). All had previously undergone conventional-dose CT with 100% filtered back projection (FBP). Two radiologists jointly assessed image quality (sharpness, noise, artefacts) and diagnostic quality blinded to the scanning technique. The effective dose and image quality obtained with the ASIR protocol were compared with those obtained with the FBP algorithm.

Results

The mean effective dose achieved with ASIR was 15.6±5 mSv versus 21.8±5.3 mSv with the FBP protocol (p<0.0001). Image quality was good in all low-dose CT scans, and diagnostic quality was comparable with or superior to that of conventional-dose CT.

Conclusions

Low-dose CT with the ASIR algorithm is feasible and ensures significant reduction in effective dose.     

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.