New Frontiers in Oncological Imaging With Computed Tomography: From Morphology to Function

The latest evolutions in Computed Tomography (CT) technology have several applications in oncological imaging. The innovations in hardware and software allow for the optimization of the oncological protocol. Low-kV acquisitions are possible thanks to the new powerful tubes. Iterative reconstruction algorithms and artificial intelligence are helpful for the management of image noise during image reconstruction. Functional information is provided by spectral CT (dual-energy and photon counting CT) and perfusion CT.

A Universal Protocol for Abdominal CT Examinations Performed on a Photon-Counting Detector CT System: A Feasibility Study

OBJECTIVE

The aims of this study were to investigate the feasibility of using a universal abdominal acquisition protocol on a photon-counting detector computed tomography (PCD-CT) system and to compare its performance to that of single-energy (SE) and dual-energy (DE) CT using energy-integrating detectors (EIDs).

METHODS

Iodine inserts of various concentrations and sizes were embedded into different sizes of adult abdominal phantoms. Phantoms were scanned on a research PCD-CT and a clinical EID-CT with SE and DE modes. Virtual monoenergetic images (VMIs) were generated from PCD-CT and DE mode of EID-CT. For each image type and phantom size, contrast-to-noise ratio (CNR) was measured for each iodine insert and the area under the receiver operating characteristic curve (AUC) for iodine detectability was calculated using a channelized Hotelling observer. The optimal energy (in kiloelectrovolt) of VMIs was determined separately as the one with highest CNR and the one with the highest AUC. The PCD-CT VMIs at the optimal energy were then compared with DE VMIs and SE images in terms of CNR and AUC.

RESULTS

Virtual monoenergetic image at 50 keV had both the highest CNR and highest AUC for PCD-CT and DECT. For 1.0 mg I/mL iodine and 35 cm phantom, the CNRs of 50 keV VMIs from PCD-CT (2.01 ± 0.67) and DE (1.96 ± 0.52) were significantly higher (P < 0.001, Wilcoxon signed-rank test) than SE images (1.11 ± 0.35). The AUC of PCD-CT (0.98 ± 0.01) was comparable to SE (0.98 ± 0.01), and both were slightly lower than DE (0.99 ± 0.01, P < 0.01, Wilcoxon signed-rank test). A similar trend was observed for other phantom sizes and iodine concentrations.

CONCLUSIONS

Virtual monoenergetic images at a fixed energy from a universal acquisition protocol on PCD-CT demonstrated higher iodine CNR and comparable iodine detectability than SECT images, and similar performance compared with DE VMIs.

Procedure for optimal implementation of automatic tube potential selection in pediatric CT to reduce radiation dose and improve workflow

It is important to employ radiation dose reduction techniques in pediatric computed tomography (CT) to reduce potential risks of radiation‐induced malignancy. Automatic tube potential (kV) selection tools have been developed and become available on many CT scanners, which select the optimum kV based on the patient size and clinical task to improve the radiation dose efficiency. However, its use in pediatric CT has been mostly empirical, following manufacturer’s default recommendation without solid demonstration for quality improvement. This study aimed to implement an automatic tube potential tool (CAREkV, Siemens Healthcare) into routine pediatric CT practice, using the “Plan‐Do‐Study‐Act” quality improvement process, in place of an existing kV/mAs technique chart. The design of this quality improvement project involved Plan‐Do‐Study‐Act stages. Plan and Do stages identified the criteria for optimal automatic kV selection; a range of phantoms representing typical pediatric groups were scanned on a dual‐source 128‐slice scanner using a fast‐pitch scanning mode. The identified CAREkV settings were implemented into the CT protocol and evaluated after a 6‐month period. In the Study stage, an objective evaluation of the image metrics and radiation dose for two similar patient cohorts using CAREkV and the technique‐chart, respectively, were compared. The kV selected, image quality and radiation dose determined by CAREkV were comparable to those obtained while using the technique‐chart. The CAREkV was successfully implemented into our pediatric abdominopelvic CT practice. By utilizing the “PDSA” process optimal image quality and radiation dose reduction were achieved with an automatic kV selection tool to improve CT workflow.

Assessment of Patient Absorbed Radiation Dose during Hysterosalpingography: A Pilot Study in Southwest Nigeria

BACKGROUND

Hysterosalpingography (HSG) is an indispensable tool for diagnosing infertility in females. The procedure exposes female reproductive organs to ionizing radiation as the genitals are irradiated during the process. Investigating patient absorbed dose during the procedures is essential for effective radiological protection of the patient.

OBJECTIVE

This study aims to investigate the radiation dose received by patient during HSG examination in the study environment in order to enhance optimization of procedures and the associated dose, thereby minimizing radiation risks.

MATERIAL AND METHODS

The prospective pilot study, was conducted in four tertiary healthcare institutions in Southwest Nigeria. Thermoluminescence dosimeter (TLD 100) was used to determine the Entrance Surface Dose (ESD) of 80 patients presented for HSG investigation. The corresponding effective dose, ovary, uterus and urinary bladder doses were evaluated using PCXMC software.

RESULTS

The mean entrance surface doses (ESD) obtained from the four centers were 18.58±6.31 mGy, 15.18±2.27 mGy, 17.44±3.43 mGy and 34.24±11.98 mGy for SW1, SW2, SW3 and SW4 centers, respectively. The corresponding mean of effective doses were 1.54±0.63 mSv, 1.24±0.28 mSv, 1.41±0.30 mSv and 2.53±0.94 mSv for SW1, SW2, SW3 and SW4 centers, respectively. The resulting mean doses to the ovary, urinary bladder and uterus were also presented.

CONCLUSION

The results obtained in general are comparable with international standards. It was, however, recommended that study centers with high doses should conduct dose audit in order to enhance patient safety.

THE IMPACT OF OBESITY ON ABDOMINAL CT RADIATION DOSE AND IMAGE QUALITY

The aim of this study was to evaluate how iterative reconstruction can compensate for the noise increase in low radiation dose abdominal computed tomography (CT) technique for large size patients and the general impact of obesity on abdominal organ doses and image quality in CT. An anthropomorphic phantom layered with either none or a single layer of 3-cm- thick circumferential animal fat packs to simulate obese patients was imaged using a 128MDCT scanner. Abdominal protocols (n = 12) were applied using automatic tube current modulation (ATCM) with various quality reference mAs (150, 200, 250 and 300). kVs of 100, 120 and 140 were used for each mAs selection. Metal oxide semiconductor field effect transistor dosimeters (MOSFET) measured internal organ dose. All images produced were reconstructed with filtered back projection (FBP) and sinogram affirmed iterative reconstruction (SAFIRE) (3, 4 and 5) and objective noise was measured within three regions of interest at the level of L4-L5. Organ doses varied from 0.12 to 41.9 mGy, the spleen received the highest doses for both phantom sizes. Compared to the phantom simulating average size, the obese phantom was associated with up to twofold increase in delivered mAs, dose length product (DLP) and computed tomography dose index (CTDIvol) for the matched mAs selection (p < 0.05). However, organ dose increased by 50% only. The use of 100 kV resulted in a 40% lower dose (p < 0.05) compared to 120 kV and the associated noise increase was improved by SAFIRE (5) use, which resulted in 60% noise reduction compared to FBP (p < 0.05). When combined with iterative reconstruction, low kV is feasible for obese patients to optimise radiation dose and maintain objective image quality.

Technical Note: Increased photon starvation artifacts at low helical pitch in ultra-low-dose CT

PURPOSE

The aim of this study was to demonstrate that a low helical pitch causes increased photon starvation artifacts at ultra-low-dose CT.

METHODS

A cylindrical water phantom with a diameter of 30 cm was scanned on two different generation CT scanners: a 64-slice scanner (Sensation 64, Siemens Healthcare) and a 192-slice scanner (Somatom Force, Siemens Healthcare) at multiple effective mAs levels (mAs/pitch = 200, 100, 50, 25, and 12). The corresponding CTDI_vol values were 4.1, 2.0, 1.0, 0.5 mGy, on the 64-slice scanner and 3.8, 1.9, 1.0, 0.5 mGy on the 192-slice scanner, for the selected effective mAs values. For each dose setting, the scan was repeated at four helical pitches: 1.2, 0.9, 0.6, and the lowest achievable pitch on each scanner. The tube current was automatically adjusted by the scanner so that the effective mAs, and thus CTDI_vol , were kept the same for different pitches. All CT data sets were reconstructed with a slice thickness of 3mm and a medium smooth kernel. Images acquired at the same dose level but different helical pitches were visually inspected to assess photon starvation artifacts and noise levels.

RESULTS

At the same radiation dose, image noise increased with the decreasing helical pitch. The increase was more severe on the old-generation 64-slice scanner. Photon starvation artifacts were evident at 200 effective mAs on the 64-slice scanner at 80 kV. On the 192-slice scanner there was no visible photon starvation artifacts at both 200 and 50 effective mAs (CTDI_vol  = 4.1 mGy and 1.0 mGy, respectively); nor was there a visible impact from the lower helical pitch. Only when the dose was lowered to be extremely low (~0.26 mGy, achievable at 70 kV), did photon starvation artifacts become evident.

CONCLUSIONS

A low helical pitch may increase image noise and photon starvation artifacts compared to a higher pitch for the same dose level, particularly at ultra-low dose CT.

Computed Tomography Technology-and Dose-in the 21st Century

In the last decade or so, a number of disruptive technological advances have taken place in x-ray computed tomography, making possible new clinical applications. Changes in scanner design have included the use of two x-ray sources and two detectors or the use of large detector arrays that provide 16 cm of longitudinal coverage in one gantry rotation. These advances have allowed images of the entire heart to be acquired in just one heartbeat, lowering the effective dose from cardiac computed tomography from ~15 mSv to <1 mSv. Dual-energy computed tomography is now in widespread clinical use, enabling the assessment of material composition and concentration, as well as a range of new clinical applications. An emerging technology known as photon-counting detector computed tomography directly measures the energies of detected photons and is capable of simultaneously acquiring more than two energy data sets. Photon-counting detector computed tomography also provides advantages such as the ability to reject electronic noise, better iodine contrast-to-noise for a given dose, and spatial resolution as fine as 150 μm. Optimized x-ray tube potential selection has allowed reduction in radiation and contrast doses. Finally, wide adoption of iterative reconstruction and noise-reduction techniques has occurred. In all, body computed tomography doses have fallen dramatically, for example, by over a factor of 3 from the early 1980s. All of these advances increase the medical benefit and decrease the potential radiation risk associated with computed tomography. However, care must be taken to ensure that doses are not lowered to the level at which the clinical task is compromised.

Prospective evaluation of ultra-low-dose contrast-enhanced 100-kV abdominal computed tomography with tin filter: effect on radiation dose reduction and image quality with a third-generation dual-source CT system

OBJECTIVES

To investigate the radiation dose exposure, image quality, and diagnostic performance of enhanced 100-kVp abdominopelvic single-energy CT protocol with tin filter (TF).

METHODS

Ninety-three consecutive patients referred for a single-phase enhanced abdominopelvic CT were prospectively included after informed consent. They underwent in addition to a standard protocol (SP) an acquisition with TF. Both examinations were performed on a third-generation dual-source CT system (DSCT), in single energy, using automatic tube current modulation, identical pitch, and identical level of iterative reconstruction. Radiation metrics were compared. Size-specific dose estimates (SSDE), contrast to noise ratio (CNR), and figure of merit (FOM) were calculated. Diagnostic confidence for the assessment of a predetermined list of abdominal lesions was rated by two independent readers.

RESULTS

The mean dose of the TF protocol was significantly lower (CDTI 1.56 ± 0.43 mGy vs. 8.13 ± 3.32, p < 0.001; SSDE 9.94 ± 3.08 vs. 1.93 ± 0.39, p < 0.001), with an effective dose close to 1 mSv (1.14 mSv ± 0.34; p < 0.001). TF group exhibited non-significant lower liver CNR (2.76 vs. 3.03, p = 0.56) and was more dose efficient (FOM 10.6 vs. 2.49/mSv, p < 0.001) in comparison to SP. The mean diagnostic confidence for visceral, bone, and peritoneal tumors was equivalent between both groups.

CONCLUSIONS

Enhanced 100-kVp abdominopelvic CT acquired after spectral shaping with tin filtration can achieve similar diagnostic performance and CNR compared to a standard CT protocol, while reducing the radiation dose by 81%.

KEY POINTS

• 100-kVp spectral filtration enables enhanced abdominal CT with high-dose efficiency. • The radiation dose reaches the 1-mSv range. • Predetermined abdominopelvic lesions can be assessed without impairing on diagnostic confidence.

Automated tube voltage selection in pediatric non-contrast chest CT

BACKGROUND

Modern CT scanners provide automatic dose adjustment systems, which are promising options for reducing radiation dose in pediatric CT scans. Their impact on patient dose, however, has not been investigated sufficiently thus far.

OBJECTIVE

To evaluate automated tube voltage selection (ATVS) in combination with automated tube current modulation (ATCM) in non-contrast pediatric chest CT, with regard to the diagnostic image quality.

MATERIALS AND METHODS

There were 160 non-contrast pediatric chest CT scans (8.7±5.4 years) analyzed retrospectively without and with ATVS. Correlations of volume CT Dose Index (CTDIvol) and effective diameter, with and without ATVS, were compared using Fisher's z-transformation. Image quality was assessed by mean signal-difference-to-noise ratios (SDNR) in the aorta and in the left main bronchus using the independent samples t-test. Two pediatric radiologists and a general radiologist rated overall subjective Image quality. Readers' agreement was assessed using weighted kappa coefficients. A p value <0.05 was considered significant.

RESULTS

CTDIvol correlation with the effective diameter was r = 0.62 without and r = 0.80 with ATVS (CI: -0.04 to -0.60; p = 0.025). Mean SDNR was 10.88 without and 10.03 with ATVS (p = 0.0089). Readers' agreement improved with ATVS (weighted kappa between pediatric radiologists from 0.1 (0.03-0.16) to 0.27 (0.09-0.45) with ATVS; between general and each pediatric radiologist from 0.1 (0.06-0.14) to 0.12 (0.05-0.20), and from 0.22 (0.11-0.34) to 0.36 (0.24-0.49)).

CONCLUSION

ATVS, combined with ATCM, results in a radiation dose reduction for pediatric non-contrast chest CT without a loss of diagnostic image quality and prevents errors in manual tube voltage setting, and thus protecting larger children against an unnecessarily high radiation exposure.

Effect of arm position, presence of medical devices, and off-centering during acquisition of scout image on automatic tube voltage selection and current modulation in pediatric chest CT

PURPOSE

To evaluate the patients' morphologic factors affecting radiation dose in pediatric chest CT.

MATERIALS AND METHODS

From November 2013 to May 2015, 315 pediatric chest CT scans were obtained using a CT scanner, and classified into 5 groups according to the patients' age. For each age group, the chest CT scans were divided into two subgroups. A cut-off value used was the 75th percentile of size-specific dose estimates (SSDE), age-specific diagnostic reference level (DRL): less than the 75th percentile of SSDE (Group A, n = 238) and greater than the 75th percentile of SSDE (Group B, n = 77). All CT scans were performed with the same protocol using automatic tube voltage selection and current modulation techniques. The morphologic factors of the patients including body mass index (BMI), arm angles, presence of medical devices in the scan field, and degree of off-centering within the CT gantry were compared between groups A and B.

RESULTS

Group B showed narrower arm angles on scout and coronal reformatted images, higher frequency of the presence of devices and higher BMI than group A (P < 0.001, P < 0.001; P = 0.018, and P < 0.001, respectively). In multivariate analysis, narrower arm angles, the presence of devices on the scout images and higher BMI were independently associated with higher SSDE (P = 0.001, P = 0.037, and P < 0.001, respectively).

CONCLUSIONS

During acquisition of the scout images, arms-down position and the presence of medical devices were associated with a high radiation dose above age-specific DRLs in pediatric chest CT, regardless of repositioning before the actual scanning. In addition, off-centering had no clinical impact on radiation dose in the routine practice.

Impact of Photon Counting Detector Technology on kV Selection and Diagnostic Workflow in CT

The purpose of this study is to determine the optimal iodine contrast-to-noise ratio (CNR) achievable for different patient sizes using virtual-monoenergetic-images (VMIs) and a universal acquisition protocol on photon-counting-detector CT (PCD-CT), and to compare results to those from single-energy (SE) and dual-source-dual-energy (DSDE) CT. Vials containing 3 concentrations of iodine were placed in torso-shaped water phantoms of 5 sizes and scanned on a 2nd generation DSDE scanner with both SE and DE modes. Tube current was automatically adjusted based on phantom size with CTDIvol ranging from 5.1 to 22.3 mGy. PCD-CT scans were performed at 140 kV, 25 and 75 keV thresholds, with CTDIvol matched to the SE scans. DE VMIs were created and CNR was calculated for SE images and DE VMIs. The optimal kV (SE) or keV (DE VMI) was chosen at the point of highest CNR with no noticeable artifacts. For 10 mgI/cc vials in the 35 cm phantom, the optimal CNR of VMIs on PCD (22.6@50keV) was comparable to that of the best DSDE protocol (23.9@50keV) and was higher than that of the best SE protocol (19.7@80kV). In general, the difference of optimal CNR between PCD and SE increased with phantom size, with PCD 50 keV VMIs having an equivalent CNR (0.6% difference) with that of SE at the 25 cm phantom and 57% higher CNR at the 45 cm phantom. PCD-CT demonstrated comparable iodine CNR of VMIs to that of DSDE across patient sizes. Whereas SE and DSDE CT exams require use of patient-size-specific acquisitions settings, our findings point to the ability of PCD-CT to simplify protocol selection, using a single VMI keV setting (50 keV), acquisition kV (140 kV), and energy thresholds (25 and 75 keV) for all patient sizes, while achieving optimal or near optimal iodine CNR values.

Optimal abdominal CT protocol for obese patients

INTRODUCTION

This study investigated the impact of different protocols on radiation dose and image quality for obese patients undergoing abdominal CT examinations.

METHODS

Five abdominal/pelvis CT protocols employed across three scanners from a single manufacturer in a single centre used a variety of parameters (kV: 100/120, reference mAs: 150/190/218/250/300, image reconstruction: filtered back projection (FBP)/iterative (IR)). The routine protocol employed 300 reference mAs and 120 kV. Data sets resulting from obese patient examinations (n = 42) were assessed for image quality using visual grading analysis by three experienced radiologists. Objective assessment (noise, signal/contrast-noise ratios) and radiation dose was compared to determine optimal protocols for prospective testing on a further sample of patients (n = 47) for scanners using FBP and IR techniques.

RESULTS

Compared to the routine protocol, mean radiation dose was reduced by 60% when using 100 kV and SAFIRE technique strength 3 (p = 0.001). Reduction of up to 30% in radiation dose was noted for the FBP protocol: 120 kV and 190 reference mAs (p = 0.008). Subjective and objective image quality for both protocols were comparable to that of the routine protocol (p > 0.05). An overall improvement in image quality with increasing strength of SAFIRE was noted. Upon clinical implementation of the optimal dose protocols, local radiology consensus deemed image quality to be acceptable for the participating obese patient cohort.

CONCLUSION

Radiation dose for obese patients can be optimised whilst maintaining image quality. Where iterative reconstruction is available relatively low kV and quality reference mAs are also viable for imaging obese patients at 30-60% lower radiation doses.

Diagnostic efficacy of single-pass abdominal multidetector-row CT: prospective evaluation of a low dose protocol

OBJECTIVE

To evaluate the diagnostic efficacy of single-pass contrast-enhanced multidetector CT (CE-MDCT) performed with a low-radiation high-contrast (LR-HC) dose protocol in selected patients with non-traumatic acute bowel disease.

METHODS

65 (32 males, 33 females; aged 20-67 years) consecutive patients with non-traumatic acute bowel disease underwent single-pass CE-MDCT performed 70-100 s after i.v. bolus injection of a non-ionic iodinated contrast medium (CM) (370 mgI ml^-1). In 46 (70%) patients with a clinical and/or ultrasonographic suspicion of inflammatory bowel disease, up to 1.2-1.4 l of a 7% polyethylene-glycol solution was orally administered 45-60 mins prior to the CT examination. Patients were then divided into two groups according to age: Group A (20-44 years; n = 34) and Group B (45-70 years; n = 31). Noise index (NI) and CM dose were selected as follows: Group A (NI = 15; 2.5 ml kg^-1) and Group B (NI = 12.5; 2 ml kg^-1). All patients of Group A underwent thyroid functional tests at 4-6 weeks. Final diagnoses were obtained by open (n = 12) or laparoscopic surgery (n = 4), endoscopy w/without biopsy (n = 24) and clinical (n = 19) and/or instrumental (ultrasonography) (n = 6) follow-up at 11 ± 4 months (range 6-18 mo.). Statistical analysis was performed by χ² and Student's t-test for categorical and continuous variables, respectively.

RESULTS

Sensitivity and specificity were 91.3 vs 95.4% (p = 0.905) and 90.9 vs 88.8% (p = 0.998) with an overall diagnostic accuracy of 91.1 vs 93.5% (p = 0.756), whereas the radiation (in millisievert) and CM dose (in millilitre) were 7.5 ± 2.8 mSv and 155 ± 30 ml for Group A and 14.1 ± 5.3 mSv and 130 ± 24 ml for Group B (p < 0.001), respectively. No patients of Group A showed laboratory signs of thyrotoxicosis at follow-up.

CONCLUSION

The LR-HC has proved to be a safe and a dose-effective protocol in the evaluation of selected young patients with non-traumatic acute bowel disease. Advances in knowledge: (1) As reaching the highest diagnostic benefit to risk ratio (AHARA) appears to be the current principle of MDCT imaging, an increased amount of iodinated CM (0.7-0.9 gI ml^-1) can be safely administered to young patients (<40 years) with normal thyroid and renal function to compensate for the lower image quality resulting from low-dose CT protocols performed with the standard filter back-projection algorithm. Such an approach will result in a significant reduction of the radiation dose, which could be otherwise achieved only using iterative reconstruction algorithms combined with either low tube voltage and/or low tube current protocols. (2) An optimal scan delay (T_delay) for a venous phase caudocranial acquisition can be calculated by the following formula: T_delay = CI + 25 - T_SD, where CI is the duration of the contrast injection, 25 is the average of the sum of abdominal aortic and peak hepatic arrival times and T_SD is the scan duration. With such an approach, the radiation exposure resulting from bolus tracking, albeit performed with low-dose scans, can be spared in patients with normal transit times.

Increased Computed Tomography Dose Due to Miscentering With Use of Automated Tube Voltage Selection: Phantom and Patient Study

The purpose of the article is to determine if miscentering affected dose with use of automated tube voltage selection software. An anthropomorphic phantom was imaged at different table heights (centered in the computed tomography [CT] gantry, and -6, -3, +3, and +5.7cm relative to the centered position). Topogram magnification, tube voltage selection, and dose were assessed. Effect of table height on dose also was assessed retrospectively in human subjects (n = 50). When the CT table was positioned closer to the x-ray source, subjects appeared up to 33% magnified in topogram images. When subjects appeared magnified in topogram images, automated software selected higher tube potentials and tube currents that were based on the magnified size of the subject rather than the subject׳s true size. Table height strongly correlated with CT dose index (r = 0.98, P < 0.05) and dose length product (r = 0.98, P < 0.05) in the phantom study. Transverse dimension in the topogram highly correlated with dose in human subjects (r = 0.75-0.87, P <0.05). Miscentering results in increased dose due to topogram magnification with automated voltage selection software.

Balancing Radiation and Contrast Media Dose in Single-Pass Abdominal Multidetector CT: Prospective Evaluation of Image Quality

RATIONALE AND OBJECTIVES

As both contrast and radiation dose affect the quality of CT images, a constant image quality in abdominal contrast-enhanced multidetector computed tomography (CE-MDCT) could be obtained balancing radiation and contrast media dose according to the age of the patients.

MATERIALS AND METHODS

Seventy-two (38 Men; 34 women; aged 20-83 years) patients underwent a single-pass abdominal CE-MDCT. Patients were divided into three different age groups: A (20-44 years); B (45-65 years); and C (>65 years). For each group, a different noise index (NI) and contrast media dose (370 mgI/mL) was selected as follows: A (NI, 15; 2.5 mL/kg), B (NI, 12.5; 2 mL/kg), and C (NI, 10; 1.5 mL/kg). Radiation exposure was reported as dose-length product (DLP) in mGy × cm. For quantitative analysis, signal-to-noise (SNR) and contrast-to-noise (CNR) ratios were calculated for both the liver (L) and the abdominal aorta (A). Statistical analysis was performed with a one-way analysis of variance. Standard imaging criteria were used for qualitative analysis.

RESULTS

Although peak hepatic enhancement was 152 ± 16, 128 ± 12, and 101 ± 14 Hounsfield units (P < .001) for groups A, B, and C, respectively, no significant differences were observed in the corresponding SNRL with 9.2 ± 1.4, 9.1 ± 1.2, and 9.2 ± 3. Radiation (mGy × cm) and contrast media dose (mL) administered were 476 ± 147 and 155 ± 27 for group A, 926 ± 291 and 130 ± 16 for group B, and 1981 ± 451 and 106 ± 15 for group C, respectively (P < .001). None of the studies was graded as poor or inadequate by both readers, and the prevalence-adjusted bias-adjusted kappa ranged between 0.48 and 0.93 for all but one criteria.

CONCLUSIONS

A constant image quality in CE-MDCT can be obtained balancing radiation and contrast media dose administered to patients of different age.

Effect of Automated Attenuation-based Tube Voltage Selection on Radiation Dose at CT: An Observational Study on a Global Scale

PURPOSE

To evaluate the effect of automated tube voltage selection (ATVS) on radiation dose at computed tomography (CT) worldwide encompassing all body regions and types of CT examinations.

MATERIALS AND METHODS

No patient information was accessed; therefore, institutional review board approval was not sought. Data from 86 centers across the world were analyzed. All CT interactions were automatically collected and transmitted to the CT vendor during two 6-week periods immediately before and 2 weeks after implementation of ATVS. A total of 164 323 unique CT studies were analyzed. Studies were categorized by body region and type of examination. Tube voltage and volume CT dose index (CTDIvol) were compared between examinations performed with ATVS and those performed before ATVS implementation. Descriptive statistical methods and multilevel linear regression models were used for analysis.

RESULTS

Across all types of CT examinations and body regions, CTDIvol was 14.7% lower in examinations performed with ATVS (n = 30 313) than in those performed before ATVS implementation (n = 79 275). Relative reductions in mean CTDIvol were most notable for temporal bone CT (-56.1%), peripheral runoff CT angiography (-48.6%), CT of the paranasal sinus (-39.6%), cerebral or carotid CT angiography (-36.4%), coronary CT angiography (-25.1%), and head CT (-23.9%). An increase in mean CTDIvol was observed for renal stone protocols (26.2%) and thoracic or lumbar spine examinations (6.6%). In the multilevel model with fixed effects ATVS and examination type, and the interaction of these variables and the random effect country, a significant influence on CTDIvol for all fixed efects was revealed (ATVS, P = .0031; examination type, P < .0001; interaction term, P < .0001).

CONCLUSION

ATVS significantly reduces radiation dose across most, but not all, body regions and types of CT examinations.

Paediatric CT protocol optimisation: a design of experiments to support the modelling and optimisation process

In the last decade, several studies have emphasised the need to understand and optimise the computed tomography (CT) procedures in order to reduce the radiation dose applied to paediatric patients. To evaluate the influence of the technical parameters on the radiation dose and the image quality, a statistical model has been developed using the design of experiments (DOE) method that has been successfully used in various fields (industry, biology and finance) applied to CT procedures for the abdomen of paediatric patients. A Box-Behnken DOE was used in this study. Three mathematical models (contrast-to-noise ratio, noise and CTDI vol) depending on three factors (tube current, tube voltage and level of iterative reconstruction) were developed and validated. They will serve as a basis for the development of a CT protocol optimisation model.

Automated Tube Potential Selection as a Method of Dose Reduction for CT of the Neck: First Clinical Results

OBJECTIVE

The objective of our study was to investigate whether the use of a software-based automated tube potential selection (ATPS) CT neck protocol can result in radiation dose reduction as compared with a set 120-kV protocol without a statistically significant reduction in image quality.

MATERIALS AND METHODS

Three hundred sixty-four patients (median age, 52 years) underwent CT of the neck. Group 1 (n = 320) underwent CT with ATPS with 80, 100, or 120 kV. Group 2 (n = 44) was examined with the standard CT protocol at 120 kV. Attenuation, image background noise, signal-to-noise ratio (SNR), dose-length product (DLP), volume CT dose index (CTDIvol), body mass index (BMI [weight in kilograms divided by the square of height in meters]), and subjective image quality (5-point Likert scale, two readers in consensus) were analyzed.

RESULTS

A tube potential of 100 kV was selected in 279 patients, 120 kV in 40 patients, and 80 kV in one patient of the ATPS group. A significant correlation was found for selected tube potential and BMI (80 kV, BMI = 20.4; 100 kV, mean BMI = 24.2; 120 kV, BMI = 28.6; r = 0.28, p < 0.01). The average radiation dose was significantly lower with ATPS activated than with the standard protocol (mean DLP, 259 vs 350 mGy × cm, respectively). Background noise did not differ between groups 1 and 2 at the levels of the mandibular angle and the upper mediastinum; however, attenuation and SNR increased significantly with lower tube potential settings. Subjective image quality did not suffer (mean image quality score: ATPS protocol vs standard protocol, 4.56 vs 4.61, respectively; p > 0.05) with good interobserver agreement (κ > 0.56).

CONCLUSION

ATPS allows significant dose savings for CT of the neck compared with a standard protocol that uses a fixed 120-kV setting without a statistically significant reduction in image quality.

Paediatric CT dose: a multicentre audit of subspecialty practice in Australia and New Zealand

OBJECTIVES

To evaluate paediatric CT dosimetry in Australia and New Zealand and calculate size-specific dose estimates (SSDEs) for chest and abdominal examinations.

METHODS

Eight hospitals provided data from 12 CT systems for 1462 CTs in children aged 0-15. Imaging data were recorded for eight examinations: head (trauma, shunt), temporal bone, paranasal sinuses, chest (mass) and chest HRCT (high-resolution CT), and abdomen/pelvis (mass/inflammation). Dose data for cranial examinations were categorised by age and SSDEs by lateral dimension. Diagnostic reference ranges (DRRs) were defined by the 25th and 75th percentiles. Centralised image quality assessment was not undertaken.

RESULTS

DRRs for 201 abdominopelvic SSDEs were: 2.8-4.7, 3.6-11.5, 8.5-15.0, 7.6-15, and 10.6-16.2 for the <15 cm, 15-19 cm, 20-24 cm, 25-29 cm and >30 cm groups, respectively. For 147 chest examinations using these body width categories, SSDE DRRs were 2.0-4.4, 3.3-7.9, 4.0-9.4, 4.5-12, and 6.5-12. Kilovoltage peak (kVp), but not AEC or IR, was associated with SSDE (parameter estimate [standard error]: 0.12 (0.03); p < 0.0001).

CONCLUSIONS

Australian and New Zealand paediatric CT DRRs and abdominal SSDEs are comparable to international data. SSDEs for chest examinations are proposed. Dose variations could be reduced by adjusting kVp.

KEY POINTS

• SSDEs can be calculated for all patients, CT systems, and practices • Kilovoltage peak (kVp) has the greatest association with dose in similar-sized patients • Paediatric DRRs for CT are now available for use internationally.

Pediatric Computed Tomography Dose Optimization Strategies: A Literature Review

INTRODUCTION

Computed tomography (CT) dose optimization is an important issue in radiography because CT is the largest contributor to medical radiation dose and its use is increasing. However, CT dose optimization for pediatric patients could be more challenging than their adult counterparts. The purpose of this literature review was to identify and discuss the current pediatric CT dose saving techniques. Optimized pediatric protocols were also proposed.

METHODS

A comprehensive literature search was conducted using the Medline, ProQuest Health and Medical Complete, PubMed, ScienceDirect, Scopus, Springer Link, and Web of Science databases and the keywords CT, pediatric, optimization, protocol, and radiation dose to identify articles focusing on pediatric CT dose optimization strategies published between 2004 and 2014.

RESULTS AND SUMMARY

Seventy-seven articles were identified in the literature search. Strategies for optimizing a range of scan parameters and technical considerations including tube voltage and current, iterative reconstruction, diagnostic reference levels, bowtie filters, scout view, pitch, scan collimation and time, overscanning, and overbeaming for pediatric patients with different ages and body sizes and compositions were discussed. An example of optimized pediatric protocols specific to age and body size for the 64-slice CT scanners was devised. It is expected that this example could provide medical radiation technologists, radiologists, and medical physicists with ideas to optimize their pediatric protocols.

Observer Performance in the Detection and Classification of Malignant Hepatic Nodules and Masses with CT Image-Space Denoising and Iterative Reconstruction

PURPOSE

To determine if lower-dose computed tomographic (CT) scans obtained with adaptive image-based noise reduction (adaptive nonlocal means [ANLM]) or iterative reconstruction (sinogram-affirmed iterative reconstruction [SAFIRE]) result in reduced observer performance in the detection of malignant hepatic nodules and masses compared with routine-dose scans obtained with filtered back projection (FBP).

MATERIALS AND METHODS

This study was approved by the institutional review board and was compliant with HIPAA. Informed consent was obtained from patients for the retrospective use of medical records for research purposes. CT projection data from 33 abdominal and 27 liver or pancreas CT examinations were collected (median volume CT dose index, 13.8 and 24.0 mGy, respectively). Hepatic malignancy was defined by progression or regression or with histopathologic findings. Lower-dose data were created by using a validated noise insertion method (10.4 mGy for abdominal CT and 14.6 mGy for liver or pancreas CT) and images reconstructed with FBP, ANLM, and SAFIRE. Four readers evaluated routine-dose FBP images and all lower-dose images, circumscribing liver lesions and selecting diagnosis. The jackknife free-response receiver operating characteristic figure of merit (FOM) was calculated on a per-malignant nodule or per-mass basis. Noninferiority was defined by the lower limit of the 95% confidence interval (CI) of the difference between lower-dose and routine-dose FOMs being less than -0.10.

RESULTS

Twenty-nine patients had 62 malignant hepatic nodules and masses. Estimated FOM differences between lower-dose FBP and lower-dose ANLM versus routine-dose FBP were noninferior (difference: -0.041 [95% CI: -0.090, 0.009] and -0.003 [95% CI: -0.052, 0.047], respectively). In patients with dedicated liver scans, lower-dose ANLM images were noninferior (difference: +0.015 [95% CI: -0.077, 0.106]), whereas lower-dose FBP images were not (difference -0.049 [95% CI: -0.140, 0.043]). In 37 patients with SAFIRE reconstructions, the three lower-dose alternatives were found to be noninferior to the routine-dose FBP.

CONCLUSION

At moderate levels of dose reduction, lower-dose FBP images without ANLM or SAFIRE were noninferior to routine-dose images for abdominal CT but not for liver or pancreas CT.

Estimation of effective dose during hystrosalpingography procedures in certain hospitals in Sudan

The aims of this study were to measure the patients' entrance surface air kerma doses (ESAK), effective doses and to compare practices between different hospitals in Sudan. ESAK were measured for patient using calibrated thermo luminance dosimeters (TLDs, GR200A). Effective doses were estimated using National radiological Protection Board (NRPB) software. This study was conducted in five radiological departments: Two Teaching Hospitals (A and D), two private hospitals (B and C) and one University Hospital (E). The mean ESAK was 20.1mGy, 28.9mGy, 13.6mGy, 17.5mGy, 35.7mGy for hospitals A, B, C, D, and E, respectively. The mean effective dose was 2.4mSv, 3.5mSv, 1.6mSv, 2.1mSv and 4.3mSv in the same order. The study showed wide variations in the ESDs with three of the hospitals having values above the internationally reported values.

Emerging techniques for dose optimization in abdominal CT

Recent advances in computed tomographic (CT) scanning technique such as automated tube current modulation (ATCM), optimized x-ray tube voltage, and better use of iterative image reconstruction have allowed maintenance of good CT image quality with reduced radiation dose. ATCM varies the tube current during scanning to account for differences in patient attenuation, ensuring a more homogeneous image quality, although selection of the appropriate image quality parameter is essential for achieving optimal dose reduction. Reducing the x-ray tube voltage is best suited for evaluating iodinated structures, since the effective energy of the x-ray beam will be closer to the k-edge of iodine, resulting in a higher attenuation for the iodine. The optimal kilovoltage for a CT study should be chosen on the basis of imaging task and patient habitus. The aim of iterative image reconstruction is to identify factors that contribute to noise on CT images with use of statistical models of noise (statistical iterative reconstruction) and selective removal of noise to improve image quality. The degree of noise suppression achieved with statistical iterative reconstruction can be customized to minimize the effect of altered image quality on CT images. Unlike with statistical iterative reconstruction, model-based iterative reconstruction algorithms model both the statistical noise and the physical acquisition process, allowing CT to be performed with further reduction in radiation dose without an increase in image noise or loss of spatial resolution. Understanding these recently developed scanning techniques is essential for optimization of imaging protocols designed to achieve the desired image quality with a reduced dose.

Advanced modelled iterative reconstruction for abdominal CT: qualitative and quantitative evaluation

AIM

To determine qualitative and quantitative image-quality parameters in abdominal imaging using advanced modelled iterative reconstruction (ADMIRE) with third-generation dual-source 192 section CT.

MATERIALS AND METHODS

Forty patients undergoing abdominal portal-venous CT at different tube voltage levels (90, 100, 110, and 120 kVp, n = 10 each) and 10 consecutive patients undergoing abdominal non-enhanced low-dose CT (100 kVp, 60 mAs) using a third-generation dual-source 192 section CT machine in the single-source mode were included. Images were reconstructed with filtered back projection (FBP) and ADMIRE (strength levels 1-5). Two blinded, independent readers subjectively determined image noise, artefacts, visibility of small structures, and image contrast, and measured attenuation in the liver, spleen, kidney, muscle, fat, and urinary bladder, and objective image noise.

RESULTS

Subjective noise was significantly lower and image contrast significantly higher for each increasing ADMIRE strength level and also for ADMIRE 1 compared to FBP (all, p < 0.001). No significant differences were found for artefact and visibility ratings among image sets (all, p > 0.05). Attenuation was similar across tube voltage-image datasets in all anatomical regions (all, p > 0.05). Objective noise was significantly lower for each increasing ADMIRE strength level, and for ADMIRE 1 compared to FBP (all, p < 0.001, maximal reduction 53%). Independent predictors of noise were tube voltage (p < 0.05) and current (p < 0.001), diameter (p < 0.05), and reconstruction algorithm (p<0.001); the amount of noise reduction was related only to the reconstruction algorithm (p < 0.001).

CONCLUSION

Abdominal CT using ADMIRE results in an improved image quality with lower image noise as compared with FBP, while the attenuation of various anatomical regions remains constant among reconstruction algorithms.

Chest-abdomen-pelvis CT for staging in cancer patients: dose effectiveness and image quality using automated attenuation-based tube potential selection

Background

Evaluation of automated attenuation-based tube potential selection and its impact on image quality and radiation dose in CT (computed tomography) examinations for cancer staging.

Methods

A total of 110 (59 men, 51 women) patients underwent chest-abdomen-pelvis CT examinations; 55 using a fixed tube potential of 120 kV/current of 210 Reference mAs (using CareDose4D), and 55 using automated attenuation-based tube potential selection (CAREkV) also using a current of 210 Reference mAs.

This evaluation was performed as a single-centre, observer-blinded retrospective analysis. Image quality was assessed by two readers in consensus. Attenuation, image noise, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) were measured or calculated for objective image evaluation. For the evaluation of radiation exposure, dose-length-product (DLP) values were compared and Size-specific dose estimates (SSDE) values were calculated.

Results

Diagnostic image quality was obtained from all patients. The median DLP (703.5 mGy · cm, range 390–2203 mGy · cm) was 7.9% lower when using the algorithm compared with the standard 120 kV protocol (median 756 mGy · cm, range 345–2267 mGy · cm). A reduction in potential to 100 kV occurred in 32 cases; therefore, these patients received significantly lower radiation exposure compared with the 120 kV protocol.

Conclusion

Automated attenuation-based tube potential selection produces good diagnostic image quality in chest-abdomen-pelvis CT and reduces the patient’s overall radiation dose by 7.9% compared to the standard 120 kV protocol.

Reduced radiation dose and improved image quality at cardiovascular CT angiography by automated attenuation-based tube voltage selection: intra-individual comparison

OBJECTIVES

To evaluate the effect of automated tube voltage selection on radiation dose and image quality at cardiovascular CT angiography (CTA).

METHODS

We retrospectively analysed paired studies in 72 patients (41 male, 60.5 ± 16.5 years), who had undergone CTA acquisitions of the heart or aorta both before and after the implementation of an automated x-ray tube voltage selection algorithm (ATVS). All other parameters were kept identical between the two acquisitions. Subjective image quality (IQ) was rated and objective IQ was measured by image noise, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and figure of merit (FOM). Image quality parameters and effective dose were compared between acquisitions.

RESULTS

Overall subjective image quality improved with the percentage of cases scored as adequate or higher increasing from 79 % to 92 % after implementation of ATVS (P = 0.03). SNR (14.1 ± 5.9, 15.7 ± 6.1, P = 0.009), CNR (11.6 ± 5.3, 13.2 ± 5.6, P = 0.011), and FOM (19.9 ± 23.3, 43.8 ± 51.1, P < 0.001) were significantly higher after implementation of ATVS. Mean image noise (24.1 ± 8.4 HU, 22.7 ± 7.1 HU, P = 0.048) and mean effective dose (10.6 ± 5.9 mSv, 8.8 ± 5.0 mSv, P = 0.003) were significantly lower after implementation of ATVS.

CONCLUSIONS

Automated tube voltage selection can operator-independently optimize cardiovascular CTA image acquisition parameters with improved image quality at reduced dose.

KEY POINTS

• Automatic tube voltage selection optimizes tube voltage for each individual patient. • In this population, overall radiation dose decreased while image quality improved. • This tool may become valuable for improving dose/quality ratio.

Topogram-based automated selection of the tube potential and current in thoraco-abdominal trauma CT - a comparison to fixed kV with mAs modulation alone

OBJECTIVE

To investigate the impact of automated attenuation-based tube potential selection on image quality and exposure parameters in polytrauma patients undergoing contrast-enhanced thoraco-abdominal CT.

METHODS

One hundred patients were examined on a 16-slice device at 120 kV with 190 ref.mAs and automated mA modulation only. Another 100 patients underwent 128-slice CT with automated mA modulation and topogram-based automated tube potential selection (autokV) at 100, 120 or 140 kV. Volume CT dose index (CTDI(vol)), dose-length product (DLP), body diameters, noise, signal-to-noise ratio (SNR) and subjective image quality were compared.

RESULTS

In the autokV group, 100 kV was automatically selected in 82 patients, 120 kV in 12 patients and 140 kV in 6 patients. Patient diameters increased with higher kV settings. The median CTDI(vol) (8.3 vs. 12.4 mGy; -33%) and DLP (594 vs. 909 mGy cm; -35%) in the entire autokV group were significantly lower than in the group with fixed 120 kV (p < 0.05 for both). Image quality remained at a constantly high level at any selected kV level.

CONCLUSION

Topogram-based automated selection of the tube potential allows for significant dose savings in thoraco-abdominal trauma CT while image quality remains at a constantly high level.

KEY POINTS

• Automated kV selection in thoraco-abdominal trauma CT results in significant dose savings • Most patients benefit from a 100-kV protocol with relevant DLP reduction • Constantly good image quality is ensured • Image quality benefits from higher kV when arms are positioned downward.

Automatic selection of tube potential for radiation dose reduction in vascular and contrast-enhanced abdominopelvic CT

OBJECTIVE

The purpose of this study is to assess the ability of a novel automatic tube potential selection tool to reduce radiation dose while maintaining diagnostic quality in CT angiography (CTA) and contrast-enhanced abdominopelvic CT.

MATERIALS AND METHODS

One hundred one CTA examinations and 90 contrastenhanced abdominopelvic examinations were performed using an automatic tube potential selection tool on a 128-MDCT scanner. Two vascular radiologists and two abdominal radiologists evaluated the image quality for sharpness, noise, artifact, and diagnostic confidence. In a subset of patients who had undergone prior studies (CTA, 28 patients; abdominopelvic CT, 25 patients), a side-by-side comparison was performed by a separate radiologist. Dose reduction and iodine contrast-to-noise ratio resulting from use of the tool were calculated.

RESULTS

For CTA, 80 or 100 kV was selected for 73% of the scans, with a mean dose reduction of 36% relative to the reference 120-kV protocol. For abdominopelvic CT examinations, 80 or 100 kV was used for 55% of the scans, with a mean dose reduction of 25%. Overall dose reduction relative to the reference 120-kV protocol was 25% and 13% for CTA and abdominopelvic CT scans, respectively. Over 98% of scans had acceptable sharpness, noise texture, artifact, and diagnostic confidence for both readers and diagnostic tasks; 94-100% of scans had acceptable noise. Iodine contrast-to-noise ratio was significantly higher than (p < 0.001) or similar to (p = 0.11) that of prior scans, and equivalent quality was achieved despite the dose reduction.

CONCLUSION

Automatic tube potential selection provides an efficient and quantitativeway to guide the selection of the optimal tube potential for CTA and abdominopelvic CT examinations.

Attenuation-based automatic kilovolt (kV)-selection in computed tomography of the chest: effects on radiation exposure and image quality

OBJECTIVES

To evaluate an automated attenuation-based kV-selection in computed tomography of the chest in respect to radiation dose and image quality, compared to a standard 120 kV protocol.

MATERIALS AND METHODS

104 patients were examined using a 128-slice scanner. Fifty examinations (58 ± 15 years, study group) were performed using the automated adaption of tube potential (100-140 kV), based on the attenuation profile of the scout scan, 54 examinations (62 ± 14 years, control group) with fixed 120 kV. Estimated CT dose index (CTDI) of the software-proposed setting was compared with a 120 kV protocol. After the scan CTDI volume (CTDIvol) and dose length product (DLP) were recorded. Image quality was assessed by region of interest (ROI) measurements, subjective image quality by two observers with a 4-point scale (3--excellent, 0--not diagnostic).

RESULTS

The algorithm selected 100 kV in 78% and 120 kV in 22%. Overall CTDIvol reduction was 26.6% (34% in 100 kV) overall DLP reduction was 22.8% (32.1% in 100 kV) (all p<0.001). Subjective image quality was excellent in both groups.

CONCLUSION

The attenuation based kV-selection algorithm enables relevant dose reduction (~27%) in chest-CT while keeping image quality parameters at high levels.

Perspective on radiation risk in CT imaging

Awareness of and communication about issues related to radiation dose are beneficial for patients, clinicians, and radiology departments. Initiating and facilitating discussions of the net benefit of CT by enlisting comparisons to more familiar activities, or by conveying that the anticipated radiation dose to an exam is similar to or much less than annual background levels help resolve the concerns of many patients and providers. While radiation risk estimates at the low doses associated with CT contain considerable uncertainty, we choose to err on the side of safety by assuming a small risk exists, even though the risk at these dose levels may be zero. Thus, radiologists should individualize CT scans according to patient size and diagnostic task to ensure that maximum benefit and minimum risk is achieved. However, because the magnitude of net benefit is driven by the potential benefit of a positive exam, radiation dose should not be reduced if doing so may compromise making an accurate diagnosis. The benefits and risks of CT are also highly individualized, and require consideration of many factors by patients, clinicians, and radiologists. Radiologists can assist clinicians and patients with understanding many of these factors, including test performance, potential patient benefit, and estimates of potential risk.

CT enterography of Crohn's disease

CT enterography (CTE) is a technique using neutral oral contrast, intravenous contrast and thin cut, multiplanar CT acquisitions to optimize small bowel imaging. One of the primary indications for CTE is the detection and evaluation of Crohn's disease. This article summarizes the advantages/disadvantages, scanning technique, imaging findings, performance and pitfalls of CTE for the evaluation of Crohn's disease.