Reducing the dose of CT of the paranasal sinuses: potential of an iterative reconstruction algorithm

Comparison of Low-Dose Non-contrast CT in Detecting Anatomical and Surgically Important Variants of Paranasal Sinuses to Standard Dose Non-contrast CT: Experience from a Tertiary Care Hospital in Sub-Himalayan Region of Northern India

Computed tomography (CT) is the gold standard for diagnosing sinusitis and anatomical variations and a guide for paranasal sinus (PNS) surgeries. High doses of radiation lead to increased risk of head and neck malignancies, radiation-induced cataracts, hypothyroidism, and hyperthyroidism. The purpose of this study was to assess the effectiveness of low-dose CT as compared to standard-dose CT in the identification of anatomical variants of paranasal sinus and rhinosinusitis. This was a prospective cross-sectional study consisting of 72 patients who were divided equally into cases (underwent low-dose CT for PNS) and controls (underwent CT for PNS using standard dose protocols). Prevalence of anatomical variants and sinusitis were compared. Image quality was assessed using volume CT dose index (CTDIvol), dose length product (DLP), scan length, and noise. Subjective assessment was done by two radiologists, and scores were given. The comparison and analysis of the quantitative and qualitative variables were done. Anatomical variants were comparable among cases and controls, with post-sellar sphenoid being most common and paradoxical middle turbinate being least common surgically important variant. The difference in mean SD of CTDIvol (mGy), DLP (mGy-cm), effective dose (mSv), globe, and air noise between low and standard doses was statistically significant. A moderate agreement (with kappa 0.50) in cases and substantial agreement (with kappa 0.69) in controls was observed between both observers. Low-dose CT PNS and standard-dose CT PNS are comparable in delineating the paranasal sinus anatomy, with a 3.53× reduction of effective radiation dose to patients.

Evaluation of radiation dose reduction in head CT using the half-dose method

PURPOSE

The present study introduced the half-dose method (HDM), which halves the radiation dose for conventional head computed tomography (CT), for postoperative hydrocephalus and follow-up for craniosynostosis at a children's hospital. This study aimed to evaluate the contribution of selective head CT scanning optimization towards the overall reduction of radiation exposure.

MATERIALS AND METHODS

We retrospectively assessed 1227 and 1352 head CT examinations acquired before and after the introduction of the HDM, respectively, in children aged 0-15 years. The radiation exposure was evaluated using the CT dose index volume (CTDI-vol), dose-length product (DLP), rate of HDM introduction, and effect of reducing in-hospital radiation dose before and after the introduction of the HDM. For an objective evaluation of the image quality, head CT scans acquired with HDM and full-dose method (FDM) were randomly selected, and the image noise standard deviation (SD) was measured for each scan. In addition, some HDM images were randomly selected and independently reviewed by two radiologists.

RESULTS

The HDM was introduced in 27.9% of all head CTs. The mean CTDI-vol of all head CTs was 21.5 ± 6.9 mGy after the introduction, a 14.9% reduction. The mean DLP was 418.4 ± 152.9 mGy.cm after the introduction, a 17.2% reduction. Compared to the FDM images, the noise SD of the HDM ones worsened by almost 0.9; however, none of the images were difficult or impossible to evaluate.

CONCLUSION

The HDM yielded diagnostically acceptable images. In addition, a change in protocol for only two diseases successfully reduced the patients' overall radiation exposure by approximately 15%. Introducing and optimizing the HDM for frequently performed target diseases will be useful in reducing the exposure dose for the hospital's patient population.

Feasibility of low-dose CT protocols for evaluating the sinonasal cavity and reducing radiation exposure in dogs

With the increasing use of radiation therapy for treatment of canine sinonasal neoplasia, there is a need for developing low-dose CT protocols to help minimize radiation exposure. The purpose of this study was to assess the trade-off between image quality and reduced radiation exposure of a low-dose CT technique in the canine sinonasal cavity. In this prospective, experimental study, CT images of the sinonasal cavities from 10 normal Beagles were acquired using high-dose (130 kVp) or low-dose (110 kVp, 80 kVp) protocol. Radiation dose and image quality were compared. Radiation exposure measured by the volume-weighted CT dose index and dose-length product was reduced by 36% at 110 kVp and 74% at 80 kVp respectively, compared to the corresponding values at 130 kVp (P = 0.000). Low-dose protocol resulted in higher image noise and reduced signal-to-noise ratio and contrast-to-noise ratio than 130 kVp in most evaluated regions of interest (P < 0.05). CT numbers of the contrast-enhanced structures were highest at 80 kVp (P = 0.000). Conspicuity of most sinonasal structures was similar for high dose and both lower dose protocols. The results of this study indicate that 80 or 110 kVp can be used for sinonasal CT examinations to reduce radiation exposure to the patient without compromising image quality.

Model-based iterative reconstruction in CT of paranasal sinuses in cystic fibrosis

AIM

To assess image quality and dose-reduction efficacy of model-based iterative reconstruction (MBIR) in computed tomography (CT) of the paranasal sinus (CTPNS) compared with adaptive statistical iterative reconstruction (ASIR) in cystic fibrosis (CF) patients.

MATERIALS AND METHODS

Unenhanced CTPNS studies performed in adult CF patients from 2014 to 2020 were included. MBIR and ASIR were used and compared. Two radiologists assessed the CT images blindly and randomly. Quantitative assessment of noise, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) was performed in the maxillary sinus, sphenoid body, temporalis, and background air. Qualitative assessment performed included image sharpness, noise and contrast.

RESULTS

Thirty-seven MBIR and 45 ASIR CT PNS studies were included. MBIR achieved a 74% effective median dose reduction (0.039 mSv) compared with ASIR (0.147 mSv). Measured noise was significantly lower in all regions using MBIR (p<0.001) with superior SNR (p<0.001). MBIR had higher CNR compared to ASIR (4.567 versus 2.03, p<0.001). MBIR images were sharper and less noisy, with equal contrast. Cohen's weighted kappa value was 0.824 for qualitative analysis, indicating good inter-rater agreement. Both methods had 100% diagnostic acceptability.

CONCLUSION

MBIR produces high-quality CTPNS images at a significantly lower dose compared with ASIR. It is the preferred imaging surveillance method in CF patients and may have roles in other patient cohorts.

Comparison of CT image quality between the AIDR 3D and FIRST iterative reconstruction algorithms: an assessment based on phantom measurements and clinical images

Modern CT iterative reconstruction algorithms are transitioning from a statistical-based to model-based approach. However, increasing complexity does not ensure improved image quality for all indications, and thorough characterization of new algorithms is important to understand their potential clinical impacts. This study performs both quantitative and qualitative analyses of image quality to compare Canon's statistical-based Adaptive Iterative Dose Reduction 3D (AIDR 3D) algorithm to its model-based algorithm, Forward-projected model-based Iterative Reconstruction SoluTion(FIRST). A phantom was used to measure the task-specific modulation transfer function (MTF_Task), the noise power spectrum (NPS), and the low-contrast object-specific CNR (CNR_LO) for each algorithm using three dose levels and the convolution algorithm (kernel) appropriate for abdomen, lung, and brain imaging. Additionally, MTF_Taskwas measured at four contrast levels, and CNR_LOwas measured for two object sizes. Lastly, three radiologists participated in a preference study to compare clinical image quality for three study types: non-contrast abdomen, pulmonary embolism (PE), and lung screening. Nine questions related to the appearance of anatomical features or image quality characteristics were scored for twenty exams of each type. The behavior of both algorithms depended strongly on the kernel selected. Phantom measurements suggest that FIRST should be beneficial over AIDR 3D for abdomen imaging, but do not suggest a clear overall benefit to FIRST for lung or brain imaging; metrics suggest performance may be equivalent to or slightly favor AIDR 3D, depending on the size of the object being imaged and whether spatial resolution or low-contrast resolution is more important for the task at hand. Overall, radiologists strongly preferred AIDR 3D for lung screening, slightly preferred AIDR 3D for non-contrast abdomen, and had no preference for PE. FIRST was superior for the reduction of metal artifacts. Radiologist preference may be influenced by changes to noise texture.

Optimization of paranasal sinus CT procedure: Ultra-low dose CT as a roadmap for pre-functional endoscopic sinus surgery

OBJECTIVE

To assess image quality and radiation dose associated with ultra-low dose CT protocol for patients with benign paranasal sinus diseases undergoing functional endoscopic surgery (FESS).

METHODS

We scanned the head portion of Alderson RANDO phantom on a second generation, dual-source, multidetector-row CT scanner (Siemens Definition Flash) using standard-dose and five low-dose protocols. Two radiologists assessed the image quality for each protocol to determine best ultra-low-dose protocols for imaging patients with benign paranasal sinus diseases undergoing FESS. The ultra-low-dose CT protocols were then used for scanning. Thereafter, 40 adult patients (age range 18-54 years, M:F 23:17) were scanned with the four low dose scanning protocols (10 patients per protocol). On both transverse and coronal reformatted CT images, two radiologists assessed visibility of key anatomic landmarks for FESS on a 2-point scale (1 = clear and complete visualization; 2 = suboptimal visualization). Data were analyzed with descriptive statistics and Cohen's kappa coefficient for interobserver agreement.

RESULTS

In phantom study, the lowest dose scan protocol (CTDI_vol 2.1 mGy, 70 kV, 75 mAs) was unacceptable due to poor image quality. For patient studies, both radiologists gave acceptable image quality scores for ultra-low-dose scan protocol with axial scan mode, automatic tube potential selection and tube current modulation (CTDI_vol 2.2 mGy; DLP 22.9 mGy.cm) with up to 60% lower dose compared to prior standard-dose CT (CTDI_vol 5.3 mGy; DLP 73.5 mGy.cm).

CONCLUSIONS

Ultra-low-dose CT protocol provides sufficient image quality for scanning patients undergoing functional endoscopic surgery for benign paranasal sinus diseases.

Image optimization and reduction of radiation dose in CT of the paranasal sinuses

INTRODUCTION

Due to use of ionization radiation in the computed tomography (CT), optimal parameters should be used to reduce the risk of incidence of secondary cancers in patients who are constantly exposed to x-rays. To reduce the dose delivered to patients in each scan, CT technologists can change the image acquisition parameters. However, this reduces image quality. The present study aimed to optimize and reduce radiation dose in a CT of the paranasal sinuses while minimizing deterioration of image quality.

METHODS

In this study patients were divided in two groups: Group A was scanned axially and coronally using default parameters, while Group B was scanned axially and coronally using new parameters. Common CT dose descriptors including weighted computed tomography dose index (CTDIw), volumetric CTDI (CTDIvol), dose length product (DLP), effective dose (ED) and image noise were measured for each group. The patients' organ doses were estimated using the ImPACT CT patient Dosimetry Calculator. The tube voltage, tube current, pitch, rotation time, and other parameters were then reduced and optimized. After reconstruction and analysis, all of the images were of good diagnostic quality in both groups Results: Using the new parameters, good agreement was found between the direct and reconstructed images. The CT parameters were reduced by the following proportions: kVp-16.6%, mA-75%, rotation time-20%, and mAs-80%. However, these reductions did not obscure any anatomical landmarks. These parameters reduced the CTDIw, CTDIvol and DLP by 88.2%, 91.3%, and 91.3% respectively.

CONCLUSION

The results suggest that the use of a Bone algorithm reduces the total amount of radiation used during CT of the sinuses. We recommend using these parameters in children, in the evaluation of facial trauma, and in emergency CT of the paranasal sinuses.

LOW-DOSE COMPUTED TOMOGRAPHY OF THE PARANASAL SINUSES: PERFORMANCE OF TWO DIFFERENT ITERATIVE RECONSTRUCTION ALGORITHMS

To evaluate the performance of two iterative reconstruction algorithms in low-dose paranasal sinus computed tomography (CT). Sinus CT scans were reconstructed using Adaptive Iterative Dose Reduction 3D (AIDR 3D, n = 36 patients) or Sinogram Affirmed Iterative Reconstruction (SAFIRE, n = 32 patients). Reconstructed images were evaluated regarding subjective image quality, depiction of anatomic landmarks and noise (HU). Dose-length product (DLP), calculated effective dose (ED) and CT dose index (CTDIvol) were documented for each scan. Images were not significantly different in subjective image quality (p = 0.09) and conspicuity of anatomic landmarks (p = 0.28). Noise was significantly lower in images reconstructed with AIDR 3D (p = 0.012). DLP, ED and CTDIvol were significantly lower in the SAFIRE datasets (each p < 0.001). The results indicate that iterative reconstruction, independent of the manufacturer, enables for imaging the paranasal sinuses with an ED below 0.1 mSv while ensuring diagnostic image quality.

Wide-detector CT combined iterative reconstruction in pediatric low-dose scan of the paranasal sinus

BACKGROUND

Computed tomography (CT) is considered a standard modality for imaging the paranasal sinus (PS), but increasingly radiation dose is of concern, especially in children.

OBJECTIVE

This study aims to investigate the feasibility of using a 320-detector CT scanner with a 16 cm wide-detector combined with iterative reconstruction (IR) algorithm to further reduce radiation dose when scanning the PS.

METHODS

A total of 90 children who underwent CT of the PS were randomly allocated into three groups namely, (1) the experimental group using low-dose wide-detector scan (n = 30, 9±4 years); (2) low-dose helical group (n = 30, 9±4 years); and (3) pediatric conventional group (n = 30, 8±4 years). Statistical software SPSS 19.0 was used for one-way ANOVA analysis of the general data (age, BMI), image quality, and radiation dose. Multiple comparisons of data without homogeneity of variance were analyzed by Bonferroni test and Tamhane's test.

RESULTS

All patients underwent successful CT examinations. No significant differences in the general data and image quality evaluation were detected between three groups (all P values > 0.05). CTDIvol and DLP were 2.87 mGy and 32.58 mGy·cm in the experimental group, 4.92 mGy and 70.84 mGy·cm in the low-dose helical group, and 9.95 mGy and 131.83 mGy·cm in the conventional group, respectively, which were significantly different among these three groups as indicated by multiple comparisons (all P values < 0.05). In the experimental group, the effective radiation dose was 0.07 mSv, which was reduced by 76% and 56% comparing to the conventional group and the low-dose helical group, respectively.

CONCLUSIONS

The 320-detector CT scanner equipped with the wide-detector combined with IR can further reduce radiation dose, while maintaining good image quality comparing to the low-dose helical or pediatric modes.

Application value of iterative reconstruction with CTA to intractable headache patients

Application value of iterative reconstruction with computed tomographic angiography (CTA) in the patients with intractable headache was investigated. One hundred and eighty patients with headache, who were admitted and treated in Cangzhou Central Hospital, were selected to undergo CTA scan. The patients were divided into group A, B and C according to different scanning conditions and data reconstruction techniques. In group A, the scanning parameters were 120 kV and 300 mA, and filtered back projection (FBP) algorithm was used for data reconstruction. In group B, the scan parameters were 100 kV and automatic milliamperes. Further, adaptive iterative dose reduction via three-dimensional processing (AIDR-3D) was used for data reconstruction. In group C, the scan parameters were 80 kV with automatic milliamperes, and AIDR-3D technique was utilized for data reconstruction. The CT value, noise, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), subjective assessment score of image quality and radiation dose of the three groups of images were compared. There were significant differences in CT values, standard deviation (SD) values, SNRs and CNRs of different vessel segments and muscles among the three groups (P<0.05). The image assessment scores at the levels of the atlas and C7 vertebra as well as those of the brain parenchyma in the three groups had notable differences (P<0.05). However, they showed no differences at the level of the C4 vertebra (P>0.05). Further, significant differences were observed in volume computed tomography dose index (CTDI_vol), dose-length product (DLP) and effective dose (ED) (P<0.05). In conclusion, for patients with intractable headache, the image quality of the CTA scan using AIDR-3D reconstruction method showed better results over FBP reconstruction method. Further, best results were observed when the scan parameters were 100 kV, automatic milliamperes and the data reconstruction was performed by AIDR-3D.

Low-Dose Noncontrast Examination of the Paranasal Sinuses Using Volumetric Computed Tomography

OBJECTIVES

The objective of this study was to evaluate image quality of low dose in noncontrast paranasal sinus computed tomography (CT) using single volumetric 320-row multidetector CT technique.

METHODS

The low-dose protocol including tube voltage of 135 kV and tube current of 5 mAs was chosen based on results of the present phantom study. Forty-six patients were assigned to control group with factory standard settings (120 kVp, 75 mAs), and 46 patients were assigned to study group and underwent noncontrast CT of paranasal sinus with low-dose protocol using single volumetric 320-row multidetector CT device. Objective and subjective image qualities were performed.

RESULTS

Effective radiation dose calculated for control group scans was 0.45 (SD, 0.39) mSv. It was 0.038 (SD, 0.004) mSv for study group scans. The effective radiation dose of study group was statistically significant lower than control group (P < 0.001).

CONCLUSIONS

Noncontrast paranasal sinus CT imaging can be performed at very low radiation exposure maintaining high image quality with 135 kVp and 5 mAs.

Comparing subjective and objective image quality at two different radiation exposure ranges of the paranasal sinus CT examinations using a volumetric 320-row detector CT system

OBJECTIVES

To evaluate image quality of protocol including 135 kVp, 5 mAs and 80 kVp, 5 mAs in the paranasal sinus CT examinations using single volumetric 320-row multidetector CT technique.

METHODS

From September to December 2016, both of our control group including 135 kVp and 5 mAs and our study group including 80 kVp and 5 mAs paranasal CT protocols were simultaneously performed on 40 patients using single volumetric 320-row multidetector CT device. Image quality for bony structures, air-filled structures and soft tissues were independently assessed for each group by three blinded observers using a 3-point grading scale (0 = not diagnostic, 1 = partially diagnostic, 2 = diagnostic). Objective image quality was also performed by region of interests were placed on axial soft tissue reconstructions in both eye bulbs, retrobulbar fat and maxillary sinuses to obtain different values for aqueous tissue, soft tissue and air, respectively. Effective dose was calculated from the dose-length product.

RESULTS

The effective radiation dose which calculated for the control group scans was 0.037 ± 0.003 mSv. But, it was 0.0099 ± 0.001 mSv for the study group scans. The effective radiation dose of study group was statistically significant lower than control group (p < 0.001). Despite significant lowering of the radiation doses, image qualities were sufficient for evaluating all the bony structures, air-filled structures and soft tissues except for eye muscle, retrobulbar fat and eye bulb.

CONCLUSIONS

Our results present that our protocols for study and control group provide significant dose reduction without the loss of diagnostic image quality for paranasal sinus CT. Paranasal sinus CT imaging can be performed at very low radiation exposure maintaining high image quality using a single volume 320-row detector CT device using 135 kVp and 5 mAs.