Scan Length Research Articles

Size Specific Dose Estimate in Abdominal Computed Tomography by AAPM TG Report-204 and AAPM TG Report-220

Purpose: The AAPM Task Group (TG) reports 204 and 220 presented methods for evaluation of patient dose by announcing the SSDE. The TG reports provide the Size Specific Conversion factors that can be multiplied to CTDIvol to calculate the patient dose in terms of SSDE constructed from Deff (AAPM TG-204) and Dw (AAPM TG-220). Our study presents a comparison of the two TG reports on SSDE for the routine Abdominal Computed Tomography. Materials and Methods: The scan lengths of abdomen were measured from computed tomography (CT) topographic images and cross-section at the mid-slice of the abdomen were measured from tomographic images of 61 adults who had undergone abdominal CT using the GE Advance Workstation (AWS) software. The Deff and Dw was computed according to TG- 204 and TG-220 reports, respectively. Further, we performed the correlation analysis between Deff and BMI, Dw and BMI and SSDE and BMI for both the TG- reports. The Student’s paired t-test was performed to compare the two of SSDE calculation methods. Results: The results confirm that the mean value of SSDE is 13.04 (𝑚𝐺𝑦) and 13.60 (𝑚𝐺𝑦) for AAPM TG-220 and AAPM TG-204, respectively. And a good positive correlation was observed between Deff and BMI, Dw and BMI with r = 0.67 and r = 0.68 respectively. Also, the weak correlation was observed between SSDE and BMI for both the TG - reports. The Student’s paired t-test shows that the two means of SSDE calculation methods are significantly different (𝑝< 0.01) in abdominal computed tomography. Conclusion: We confirm the AAPM TG reports 204/220 using clinical data for SSDE calculation that the mean SSDE values computed from Deff and Dw in abdomenal computed tomography are significantly different and we conclude that the SSDE calculated by Dw method gives a more accurate evaluation of SSDE for the patients undergoing abdominal computed tomography scan then the SSDE calculated by Deff method.

In-situ modification of thermal, microstructural, and mechanical responses by altering scan lengths in laser powder bed fusion additive manufacturing of Ti-6Al-4V

In-situ modification of thermal, microstructural, and mechanical responses by altering scan lengths in laser powder bed fusion additive manufacturing of Ti-6Al-4V

Accuracy, Hemorrhagic Complications and CT Radiation Dose of Emergency External Ventricular Drain (EVD) Placement in Pediatric Patients: A 15-Year Retrospective Analysis.

To assess accuracy, the frequency of hemorrhagic complications and computed tomography (CT) radiation dose parameters in pediatric patients undergoing landmark-guided external ventricular drain (EVD) placement in an emergency setting. Retrospective analysis comprised 36 EVD placements with subsequent CT control scans in 29 patients (aged 0 to 17 years) in our university hospital from 2008 to 2022. The position of the EVD as well as the presence and extension of bleeding were classified according to previously established grading schemes. Dose length product (DLP), volume-weighted CT dose index (CTDIvol) and scan length were extracted from the radiation dose reports and compared to the diagnostic reference values (DRLs) issued by the German Federal Office for Radiation Protection. After the initial EVD placement, optimal positioning of the catheter tip into the ipsilateral frontal horn or third ventricle (Grade I), or a functional positioning in the contralateral lateral ventricle or the non-eloquent cortex (Grade II), was achieved in 28 and 8 cases, respectively. In 32 of 36 procedures, no evidence of hemorrhage was present in the control CT scan. Grade 1 (<1 mL) and Grade 2 (≥1 to 15 mL) bleedings were detected after 3 and 1 placement(s), respectively. For control scans after EVD placements, CTDIvol (median [25%; 75% quartile]) was 39.92 [30.80; 45.55] mGy, DLP yielded 475.50 [375.00; 624.75] mGy*cm and the scan length result was 136 [120; 166] mm. Exceedances of the DRL values were observed in 14.5% for CTDIvol, 12.7% for DLP and 65.6% for the scan length. None of these values was in the range requiring a report to the national authorities. Landmark-based emergency EVD placement in pediatric patients yielded an optimal position in most cases already after the initial insertion. Complications in terms of secondary hemorrhages are rare. CT dose levels associated with the intervention are below the reportable threshold of the national DRLs in Germany.

Tangent functional connectomes uncover more unique phenotypic traits

Functional connectomes (FCs) containing pairwise estimations of functional couplings between pairs of brain regions are commonly represented by correlation matrices. As symmetric positive definite matrices, FCs can be transformed via tangent space projections, resulting into tangent-FCs. Tangent-FCs have led to more accurate models predicting brain conditions or aging. Motivated by the fact that tangent-FCs seem to be better biomarkers than FCs, we hypothesized that tangent-FCs have also a higher fingerprint. We explored the effects of six factors: fMRI condition, scan length, parcellation granularity, reference matrix, main-diagonal regularization, and distance metric. Our results showed that identification rates are systematically higher when using tangent-FCs across the "fingerprint gradient" (here including test-retest, monozygotic and dizygotic twins). Highest identification rates were achieved when minimally (0.01) regularizing FCs while performing tangent space projection using Riemann reference matrix and using correlation distance to compare the resulting tangent-FCs. Such configuration was validated in a second dataset (resting-state).

Laser based additive manufacturing of tungsten: Multi-scale thermo-kinetic and thermo-mechanical computational model and experiments

Coupling a multi-scale thermo-kinetic and thermo-mechanical model with critical experiments, the present study investigates the role of process parameters on the resulting densification, cracking behavior, and microstructural evolution in laser-based powder bed fusion (LPBF) of pure tungsten. Thermal management strategies comprising shorter scan length (1 mm) and/or substrate preheating (873 K) were explored to achieve higher densities and mitigate cracks. A finite element (FE) based thermo-kinetic and thermo-mechanical computational model was developed to simulate the process spanning from the melt pool scale to the component level. FE simulations indicated pronounced heat accumulation with reduced scanning lengths. Such increased heat accumulation resulted in melt pools with larger dimensions (width and depth) and more favorable rheological characteristics resulting in printed tungsten parts with higher densities. Using an input laser fluence (ILF) of 28.6 J/mm2 and a shorter scan length of 1 mm, a relative density of maximum 99.2% was achieved, the highest reported value using LPBF in case of pure tungsten. FE simulations indicated nearly 5-fold reduction in thermal gradients and 2-fold reduction in cooling rates associated with the processing conditions corresponding to low degree of cracking (ILFs:28.6 J/mm2 and ILF 15.9 J/mm2 augmented with substrate preheating at 873 K) compared to the processing conditions of high degree of cracking (ILF: 15.9 J/mm2). Further, high ILF samples were characterized by significant extent of in-grain misorientations and low angle boundaries indicating that process induced in-situ restoration mechanisms are operative, thereby potentially aiding in reduction of cracking.

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 Hospitalin 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 meanSD 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.

Thermocycling-guided cracking and deformation control in directed energy deposition

In single-step metal Additive Manufacturing (AM) processes, thermal cycling resulting from inappropriate scanning length and deposition height will eventually cause the cracking and deformation of the deposits, which will significantly damage object performance and intended applications. In this work, a unique altering thermal cycling pathway is proposed to efficiently control the cracking and deformation of AMed CuSi3Mn alloys without either using any auxiliary equipment or adjusting the alloy composition. With the help of the Intrinsic Heat Treatment (IHT) caused by secondary or multiple heating and cooling between the subsequent layers and the previous layers, a crack-free cylindric part fabricated by the Gas Metal Arc assisted Directed Energy Deposition (GMA-DED) based on Surface Tension Transfer (STT) is finally obtained, at the same time, the experimental results were verified by the numerical simulation. This further contributes to a superior deposition strategy to control the crack and deformation behavior on the metal AM.

High-resolution Bragg-edge neutron radiography detects grain morphology in PBF-LB/M IN718

One of the main advantages of metal additive manufacturing (MAM) techniques is their ability to produce components with site-specific microstructural features. Nevertheless, microstructural defects and lack of repeatability are still major concerns in MAM. In this study, a laser powder bed fusion (PBF-LB/M) IN718 material, produced using two different scan length vectors, is investigated using Bragg-edge neutron 2D imaging (BENI) combined with electron backscatter diffraction (EBSD) analysis. BENI is able to detect, on a macroscopic scale, process-induced changes in texture in a large field of view covering the entire sample (20×80 mm2). In addition, high-resolution BENI (HR-BENI), with a pixel size of 12.8 µm, provides a micro-scale examination of the local variations of texture and grain morphology, otherwise undistinguishable using the standard resolution. As such, HR-BENI offers a straightforward and detailed way of screening the integrity of MAM parts at cm-length scales.

Enhancing Radiation Dose Efficiency in Prospective ECG-Triggered Coronary CT Angiography Using Calcium-Scoring CT

Background: This study investigates whether the scan length adjustment of prospectively ECG-triggered coronary CT angiography (CCTA) using calcium-scoring CT (CAS-CT) images can reduce overall radiation doses. Methods: A retrospective analysis was conducted on 182 patients who underwent CAS-CT and prospectively ECG-triggered CCTA using a second-generation Dual-Source CT scanner. CCTA planning was based on CAS-CT images, for which simulated scout view planning was performed for comparison. Effective doses were compared between two scenarios: Scenario 1—CAS-CT-derived CCTA + CAS-CT and Scenario 2—scout-view-derived CCTA without CAS-CT. Dose differences were further analyzed with respect to scan mode and body mass index. Results: Planning CCTA using CAS-CT led to a shorter scan length than planning via scout view (114.3 ± 9.7 mm vs. 133.7 ± 13.2 mm, p &lt; 0.001). The whole-examination effective dose was slightly lower for Scenario 1 (3.2 [1.8–5.3] mSv vs. 3.4 [1.5–5.9] mSv; p &lt; 0.001, n = 182). Notably, Scenario 1 resulted in a significantly lower radiation dose for sequential scans and obese patients. Only high-pitch spiral CCTA showed dose reduction in Scenario 2. Conclusions: Using CAS-CT for planning prospectively ECG-triggered CCTA reduced the overall radiation dose administered compared to scout view planning without CAS-CT, except for high-pitch spiral CCTA, where a slightly opposite effect was observed.

Muon radiography experiments on the subway overburden structure detection

Muon radiography is an innovative and non-destructive technique for internal density structure imaging, based on measuring the attenuation of cosmic-ray muons after they penetrate the target. Due to the strong penetration ability of muons, the detection range of muon radiography can reach the order of hundreds of meters or even kilometers. Using a portable muon detector composed of plastic scintillators and silicon photomultipliers, we performed a short-duration (1 h) flux scanning experiment of the overburden above the platform and tunnel of the Xiaoying West Road subway station under construction. With the observation direction facing up, the detector is placed on the north side of the track and moved eastward from the platform section inside the station to the tunnel section. The scanning length is 264 m and a total of 21 locations are observed. By comparing the observed and predicted values of the muon survival ratio at different locations, the experiment accurately detects the jump in thickness at the interface of the platform section and tunnel section. Furthermore, unknown anomalies caused by randomly placed piles of lightweight bricks and a side passage mouth above the observation locations are detected and confirmed later. This experiment verifies the feasibility of using natural muons to quickly detect abnormal structures of the overburden of tunnel, and shows that muon radiography has broad application prospects in tunnel safety and other similar aspects.

Visualization and comparison of CT dose distribution between axial and helical acquisitions.

It is challenging to assess the accuracy of volume CT Dose Index (CTDIvol ) when the axial scan modes corresponding to a helical scan protocol are not available. An alternative approach was proposed to directly measure using helical acquisitions and relatively small differences (<20%) from CTDIvol were observed. To visually demonstrate the 3D dose distribution for both axial and helical CT acquisitions and quantitively compare and CTDIvol . 3D dose distribution within the standard CTDI phantoms (16 and 32cm diameter) from a single CT projection, Dp (x,y,z) was first generated using Monte Carlo simulation (GEANT4) with 9×108 photons per combination of tube voltage (80-140kV), collimation width (1-8cm), and z-axis location of the central ray of the x-ray beam, with a spatial resolution of 1 mm3 . These dose distributions from one single projection were analytically ensembled to simulate 3D dose volumes DA (x,y,z) and DH (x,y,z) for axial and helical scans, respectively, with different helical pitches (0.3-2) and scan lengths (100-150mm). 2D planar dose distributions were obtained by integrating the inside 100mm of the dose volumes. CTDIvol and were calculated using the planar dose data at corresponding pencil chamber locations and the percentage differences (PD) were reported. High spatial resolution 3D CT dose volumes were generated and visualized. PDs between and CTDIvol had strong dependency on scan length and peripheral chamber locations, with subtle dependency on collimation width and pitch. PDs were mostly within the range of±3% for a scan length of 150mm with four peripheral chamber locations. With a scan length covering the entire phantom length, directly measured from helical scans can serve as an alternative to CTDIvol only if all four peripheral locations were measured.

Changes in Microstructure and Mechanical Properties of 17-4PH Stainless Steel according to the Application of Laser Rotation in the Powder Bed Fusion(PBF) Process

17-4 precipitation hardened stainless steel (17-4PH SS) has been reported to have excellent mechanical properties and excellent corrosion resistance, and is one of the materials used and studied with the powder bed fusion (PBF) method. Powder bed fusion (PBF) is a new manufacturing technology that has recently attracted attention in automotive, aerospace and other industries because of its ability to produce complex geometries for high-strength and lightweight applications. In the PBF process, each layer has a different laser scan length resulting from the application of laser rotation. The laser rotation could affect the laser scan length, which causes a difference in the peak temperature and cooling rate of the deposited layer, resulting in microstructure changes. This work aims to investigate how varying the laser scan pattern in the PBF process affects the microstructure and mechanical properties of 17-4PH SS. A decrease in cooling rate was observed after applying laser scan rotation, resulting in a higher austenite phase fraction. It was confirmed that a transformation induced plasticity (TRIP) phenomenon affects mechanical characteristics. These results could be suggested for fabricating thin wall shaped such as tire blow mold parts in the powder bed fusion process using the 17-4PH SS.

Arrhythmogenicity of anti-tachycardia pacing in patients with implantable cardioverter defibrillator

BackgroundAnti-tachycardia pacing therapy (ATP) has shown comparable efficacy to shock therapy in ventricular tachycardia (VT) termination with better quality of life. However, some ATPs may lead to VT acceleration or degeneration to ventricular fibrillation (VF), which will result in more ICD shocks. The aim of this study was to investigate the predictors of VT acceleration by ATP therapy in a real-life patient cohort.ResultsWe retrospectively reviewed 448 monomorphic VT episodes that required ATP therapy in 60 patients with structural heart diseases implanted with ICD or CRTD. The clinical data of the patients and the episodes’ details were evaluated. We found that patients with a higher ejection fraction (EF) were more likely to be cardioverted by ATP therapy (P: 0.024). VT acceleration was more frequent in patients with lower EF (mean 31.24 ± 4.08) compared with the non-accelerated patients with higher EF (mean 37.00 ± 9.4, P: 0.016). The percentage of accelerated episodes was 8.5%. VT episodes with a mean cycle length (CL) < 310 ms are more likely to accelerate (sensitivity 76.3%, specificity 67.7%, PPV value 45%, NPV 86%, and AUC 0.790). There was a statistically significant difference in the accelerated VT episodes as compared to non-accelerated episodes regarding the number of ATP bursts (mean 3.66 ± 2.22 vs. 1.76 ± 1.35, P: < 0.001), ramp (23.7% vs. 4.2%, P: < 0.001), scanning (55.3% vs. 31.3%, P: 0.003) and burst adaptive cycle length (mean 83.55 ± 2.92 vs. 84.64 ± 2.61, P: 0.016). In a multivariate analysis, the VT CL, number of ATP bursts and ramp pacing predicted VT acceleration by ATP therapy.ConclusionsVentricular tachycardia in patients with low LV EF and fast VTs with a CL less than 310 ms were more likely to accelerate with ATP therapy. The number of ATP bursts and the use of ramp had a significant effect on VT acceleration. To avoid VT acceleration by ATP therapy, ramp pacing better be avoided, especially in fast VTs, and lesser number of bursts should be delivered.

Investigating CT head diagnostic reference levels based on indication-based protocols – a single site study

IntroductionThis study aimed to provide clinically-relevant insights into establishing CT DRLs based on indication-based protocols in Ireland, focusing on CT head examinations performed at a neurology centre of excellence hospital. MethodsDose data were collected retrospectively. Typical values for six CT head indication-based protocols were established using a sample size of 50 patients for each protocol. Typical values for each protocol were set as the median of the distribution curve. Dose distributions for each protocol were calculated and compared using non-parametric median test (k-samples) to ascertain significant dose differences between the typical values. ResultsMost typical values pairings showed significant differences (p < 0.001) except between stroke/non-vascular brain, stroke/acute brain, and acute brain/non-vascular brain pairings. This was expected due to similar scan parameters. The typical value for stroke (3-phases angiogram) was 52% lower than the typical value for stroke. Dose levels of the male populations recorded were higher than female populations for all protocols. Statistical comparison showed significant differences for dose quantities and/or scan length between both genders in five protocols. ConclusionProposed values for DLP were up to 63% and 69% lower than the EU and Irish national DRLs respectively. Establishment of CT stroke DRLs should be based on the scan performed instead of number of scan acquisitions. Lastly, gender-based CT DRLs for specific protocols within the head region require further investigation. Implications for practiceWith increasing CT examinations worldwide, radiation dose optimisation is key. The value of indication based DRLs is to enhance the required patient protection so image quality can be maintained, however with relevant DRLs for varying protocols. Establishment of CT typical values and site specific DRLs for procedures beyond the national DRLs can drive dose optimisation locally.

Probability of induced cancers related to computed tomography examinations

Computed tomography (CT) is considered as one of the most used radiation imaging modalities, and CT procedures are increasing continuously all over the world, hence leading to considerable rise in cancers and radiation related diseases risk. This study was conducted in three general hospitals in Saudi Arabia, to analyze the associated radiation cancer risk from CT procedures. The collected data included the head chest, abdomen, abdomen pelvis (AP) and chest abdomen pelvis (CAP) procedures along with exposure parameter data (DLP and scan length). The risk of cancer was estimated by multiplying the effective dose with the risk coefficients obtained from ICRP 103. The mean DLP values were higher for females (647.5 ± 323.37 mGy cm) compared to male patients (587.7 ± 338.36 mGy cm), with no statistically significant differences (p = 0.497). The overall effective doses were 1.7 ± 0.53, 3.89 ± 1.22, 6.6 ± 4.23, 5.76 ± 3.28 and 10.75 ± 5.48 mSv for the head, chest, abdomen, abdomen pelvis (AP), and chest abdomen pelvis (CAP) procedures, respectively. The risk of cancer per procedure from head, chest, abdomen, AP and CAP procedures were found to be 6.96 × 10−5, 1.59 × 10−4, 2.71 × 10−4, 2.36 × 10−4, and 4.41 × 10−4, respectively. The effective doses and therefore the probability of cancer values were found to be within the range of other studies in the literature. However, dose optimization is always required, for the purpose of minimize the dose and cancer risk. Moreover, there is a clear need to improve awareness among radiology workers of unessential risks from suboptimal techniques in addition to applying the new imaging protocols in accordance with excellent practice around the world.

Interpretation of bimodal interference in and optimized operational modal analysis for long-range continuously scanning laser Doppler vibrometer measurements with a beam under white noise excitation

This paper explains the phenomenon of a dominant frequency in the spectrum of a raw response measured by a long-range continuously scanning laser Doppler vibrometer (LCSLDV) system being symmetrically shifted into two sharp peaks. This phenomenon is referred to as bimodal interference in this work, which gradually becomes obvious when the scanning length is greater than 0.5 m. Bimodal interference is significant because it makes natural frequencies unable to be estimated in LCSLDV measurements and this paper analyzes its nature. Natural frequencies and mode shapes of a structure under white noise excitation can be estimated by analysis of its responses measured by the LCSLDV system. The effect of bimodal interference has been ignored in previous LCSLDV and continuously scanning laser Doppler vibrometer (CLSDV) measurement studies, but its appearance makes the value of the dominant frequency not to be accurately identified. By deducing mathematical interpretation of bimodal interference with analysis of incidence and reflection of a continuously scanning laser beam in a tiny time interval and comparing experimental results with 21 groups of different conditions, it is concluded that bimodal interference is caused by signal coupling between the scanning frequency of the mirror and the vibration frequency of the measured structure. There is a positive correlation between the scanning frequency and the magnitude of the symmetric frequency shifts centered at the dominant frequency generated by bimodal interference. In experimental results of LCSLDV measurements with a distance of 60 m, the frequency shift ratio compared to the dominant frequency can be reduced to 0.06% when the scanning frequency is lower than 0.01 Hz. In this case, bimodal interference is not noticeable in the spectrum. The experiment was carried out on a cantilever beam machined based on a prescribed design. Modal parameters of the cantilever beam estimated by white noise excitation were successfully estimated by the LCSLDV system with a distance of 60 m. The maximum difference between the first four natural frequencies of the cantilever beam from the finite element model and the LCSLDV system was 2.97% and the minimum difference was 1.1%.

Development of an optical coherence tomographic surface profiling system with a wide scanning area based on telecentric F–θ imaging optics

This study was conducted to develop an in situ tomographic profiling system that can detect surface defects over a wide area by applying a telecentric F–θ scanning optical system, with an effective measurement width of 200 mm, to a spectral domain optical coherence tomography (SD-OCT) system. A telecentric F–θ scanning optical system with an effective scanning length of up to 210 mm was designed. A focal depth up to 32 mm without loss of resolution was predicted when the entrance pupil diameter (EPD) was set to 4.0 mm. The obtained three-dimensional tomographic images of tire treads and scientific calculators confirmed the possibility of surface profiling for areas with a width of up to 200 mm and depth over 7 mm. Combining a large-area telecentric lens with an SD-OCT system made it possible to perform deep 3D profiling simultaneously with a large-area surface inspection. The developed surface tomographic profiling system can adjust the size of the EPD to achieve a resolution of less than 50 µm. It can thus provide axial and lateral resolutions equivalent to those of a conventional OCT system as well as a wide effective measurement area.

Estimation of cancer risks due to chest radiotherapy treatment planning computed tomography (CT) simulations.

The objective of our study was to determine organ doses to estimate the lifetime attributable risk (LAR) of cancer incidence related to chest tomography simulations for Radiotherapy Treatment Planning (RTTP) using patient-specific information. Patient data were used to calculate organ doses and effective dose. The effective dose (E) was calculated by two methods. First, to calculate effective dose in a standard phantom, the collected dosimetric parameters were used with the ImPACT CT Patient Dosimetry Calculator and E was calculated by applying related correction factors. Second, using the scanner-derived Dose Length Product, LARs were computed using the US National Academy of Sciences (BEIR VII) model for age- and sex-specific risks at each exposure. DLP, CTDIvol, and scan length were 507 ± 143mGy.cm, 11 ± 4mGy, and 47 ± 7cm, respectively. The effective dose was 10 ± 3mSv using ImPACT patient dosimetry calculator software and 9 ± 2mSv using the scanner-derived Dose Length Product. The LAR of cancer incidence for all cancers, all solid cancers and leukemia were 65 ± 29, 62 ± 27, 7 ± 2 cases per 100,000 individuals, respectively. Radiation exposure from the usage of CT for radiotherapy treatment planning (RTTP) causes non-negligible increases in lifetime attributable risk. The results of this study can be used as a guide by physicians to implement strategies based on the As Low As Reasonably Achievable (ALARA) principle that lead to a reduction dose without sacrificing diagnostic information.

P003 A dedicated short MRI protocol for assessing synovitis: evaluating patient acceptability and rheumatologist perceptions

Abstract Background/Aims Magnetic resonance imaging (MRI) plays an increasingly important role in diagnosing and monitoring patients with inflammatory arthropathies due to its ability to detect early, sometimes subclinical, inflammatory changes, including synovitis. It is a sensitive, accurate and relatively non-operator dependent modality. However, it is typically perceived as expensive and time-consuming, and is used infrequently for evaluation of synovitis in clinical care. MRI is thought to be generally well-tolerated by patients, however, there is a paucity of research on patient experience of MRI, particularly in rheumatology where patients may have complex and/or chronic pain. To improve the acceptability, cost-effectiveness and overall utility of MRI for clinicians and patients, we introduced a short synovitis MRI protocol (MRI-SSP) for rapid assessment of synovitis in the hands and feet. Here, we evaluated the acceptability of MRI-SSP to patients and the perceived utility of the protocol for rheumatologists. Methods Different structured questionnaires were designed for patients and rheumatologists which contained qualitative (free-text) and quantitative (five-point Likert-scale) questions. All patients undergoing MRI-SSP of the hand or wrist at University College London Hospital (UCLH) between 01/02/22 to 01/07/22 were prospectively invited to participate and completed the questionnaire via telephone within four weeks of their scan. All rheumatologists at our centre were invited to respond to an online questionnaire. Likert scores were analysed quantitatively and thematic analysis was performed on free-text comments. Results Patient experience - 30 patients agreed to participate (mean age 48 years, range 21-74; 87% female). Average patient Numerical Pain Rating Scale score was 5.1/10 (range 1-10). We found that: 90% found the scan length acceptable; 90% had no or mild side-effects from intravenous contrast; 40% had no pain during the scan; 57% had no anxiety during the scan; 97% found the scan acceptable overall; 97% would be happy to have the scan again; scan length and comfort were important for patients; good radiographer communication helped to alleviate patient anxiety. Rheumatologist perception - 10 rheumatologists responded. Of these, 40% perform ultrasound to assess for synovitis in clinic. We found that: 90% strongly agreed that the MRI-SSP report was helpful in answering clinical questions; 90% strongly agreed that the MRI-SSP influenced clinical decision making; there was a mixed response regarding which modality rheumatologists preferred for assessing synovitis (40% no preference, 30% MRI, 30% ultrasound) and this was independent of which rheumatologists performed ultrasound in clinic. Conclusion Overall, patients found MRI-SSP to be an acceptable investigation, and rheumatologists felt it helpful in clinical decision-making. Important factors affecting patient acceptability were scan length and comfort. In general, our results suggest that dedicated short MRI scanning protocols have the potential to improve the acceptability and accessibility of MRI for rheumatology patients. Disclosure N. Thorley: None. L. Dwyer-Hemmings: None. S. Singh: None. T.J.P. Bray: None. L. Bida: None. M.A. Hall-Craggs: None.

Feasibility of size-specific organ-dose estimates based on water equivalent diameter for common head CT examinations: a Monte Carlo study

Computed tomography dose index (CTDI) is an unreliable dose estimate outside of the standard CTDI phantom diameters (16 and 32 cm). Size-specific dose estimate (SSDE) for head computed tomography (CT) examination was studied in the American Association of Physicists in Medicine Report 293 to provide SSDE coefficient factors based on water equivalent diameter as size metrics. However, it is limited to one protocol and for a fully irradiated organ. This study aimed to evaluate the dependency of normalized organ dose (ND) on water equivalent diameter as a size metric in three common protocols: routine head, paranasal sinus, and temporal bone. CTDIw measurements were performed for outlined protocols in the Siemens Emotion 16-slice-configuration scanner. Geant4 Application for Tomographic Emission Monte Carlo simulation platform, coupled with ten GSF patient models, was used to estimate organ doses. CT scanner system was modeled. Helical CT scans were simulated using constructor scan parameters and calculated scan lengths of each patient model. Organ doses provided by simulations were normalized to CTDIvol. The water equivalent diameters (D w) of patient models were obtained via relationships between D w and both effective diameter for a sample of patients’ data.NDs received by fully, partially, and non-directly irradiated organs were then reported as a function of D w. For fully irradiated organs, brain (R 2 > 0.92), eyes (R 2 > 0.88), and eye lens (R 2 > 0.89) correlate well with D w. For the rest of the results, a poor correlation was observed. For partially irradiated organs, the exception was scalp (R 2 = 0.93) in temporal bone CT. For non-directly irradiated organs, the exception was thyroid (R 2 > 0.90) and lungs (R 2 > 0.91) in routine head CT. ND correlates well in routine head CT than other protocols. For the most part, no relationship seems to exist between R 2 and scan percentage coverage. The results have revealed additional factors that may influence the ND and D w relationship, which explains the need for more studies in the future to investigate the effect of scan conditions and organ anatomy variation.