Analysis of effective and organ dose estimation in CT when using mA modulation : a single scanner pilot study

Effective dose (ED) estimation in CT examinations can be obtained by combining dose length product (DLP) with published ED per DLP coefficients or performed using software. These methods do not account for tube current (mA) modulation which is influenced by patient size. Aim To compare different methods of organ and ED estimation to measured values when using mA modulation in CT chest, abdomen and pelvis examinations. Method Organ doses from CT of the chest, abdomen and pelvis were measured using digital dosimeters and a dosimetry phantom. ED was calculated. Six methods of estimating ED accounting for mA modulation were performed using ImPACT CTDosimetry and Dose Length Product to ED coefficients. Corrections for the phantom mass were applied resulting in 12 estimation methods. Estimated organ doses from ImPACT CTDosimtery were compared to measured values. Results Calculated EDs were; chest 12.35 mSv (±1.48 mSv); abdomen 8.74 mSv (±1.36 mSv) and pelvis 4.68 mSv (±0.75 mSv). There was over estimation in all three anatomical regions. Correcting for phantom mass improved agreement between measured and estimated ED. Organ doses showed overestimation of dose inside the scan range and underestimation outside the scan range. Conclusion Reasonable estimation of effective dose for CT of the chest and abdomen can be obtained using ImPACT CTDosimetry software or k-coefficients. Further work is required to improve the accuracy of ED estimation from CT of the pelvis. Accuracy of organ dose estimation has been shown to depend on the inclusion or exclusion of the organ from the scan range

Application of Dual-Energy Computed Tomography to the Evalution of Coronary Atherosclerotic Plaque

Atherosclerotic coronary artery disease is responsible for around 50 of cardiovascular deaths in USA. Early detection and characterization of coronary artery atherosclerotic plaque could help prevent cardiac events. Computed tomography (CT) is an excellent modality for imaging calcifications and has higher spatial resolution than other common non-invasive modalities (e.g MRI), making it more suitable for coronary plaque detection. However, attenuation-based classification of non-calcified plaques as fibrous or lipid is difficult with conventional CT, which relies on a single x-ray energy. Dual-energy CT (DECT) may provide additional attenuation data for the identification and discrimination of plaque components. The purpose of this research was to evaluate the feasibility of DECT imaging for coronary plaque characterization and further, to explore the limits of CT for non-invasive plaque analysis. DECT techniques were applied to plaque classification using a clinical CT system. Saline perfused coronary arteries from autopsies were scanned at 80 and 140 kVp, prior to and during injection of iodinated contrast. Plaque attenuation was measured from CT images and matched to histology. Measurements were compared to assess differences among plaque types. Although calcified and non-calcified plaques could be identified and differentiated with DECT, further characterization of non-calcified plaques was not possible. The results also demonstrated that calcified plaque and iodine could be discriminated. The limits of x-ray based non-calcified plaque discrimination were assessed using microCT, a pre-clinical x-ray based high spatial resolution modality. Phantoms and tissues of different composition were scanned using different tube voltages (i.e., different energies) and resulting attenuation values were compared. Better vessel wall visualization and increase in tissue contrast resolution was observed with decrease in x-ray energy. Feasibility of calcium quantification from contrast-enhanced scans by creating virtual n

이중에너지 전산화단층촬영술을 이용한 요오드 정량화: 측정 변이에 관한 인자 탐색, 측정 변이의 범위 계산 및 임상적 검증

학위논문 (박사)-- 서울대학교 대학원 : 의과대학 의학과, 2019. 2. 구진모.서론: 이 연구는 이중에너지 전산화단층촬영술을(CT) 통한 요오드 정량화에 이중에너지 CT 스캐너, 영상 획득 파라미터, 그리고 액체 성상이 미치는 영향을 분석하고, 측정 변이의 범위(measurement variability)를 계산 및 임상적으로 검증하고자 하였다. 방법: Part I과 II에서는 종격동 팬텀을 스캔하고, 요오드 밀도를(iodine density) 측정하여, 이중에너지 CT 스캐너와 영상 획득 파라미터, 액체 성상의 영향을 linear-mixed effect model로 분석하였다. 요오드 밀도의 측정 변이 범위 또한 계산하였다. Part III에서는 요오드 정량화의 변이 범위를 통해 얻은 참조영증강 기준값의(cutoff) 임상적 유용성을 가슴샘종과 가슴샘 낭종으로 수술적 치료를 받은 환자-대조군 연구를 통해 후향적으로 검증하였다. 결과: Part I에서 요오드 밀도의 절대오차는 이중에너지 CT 스캐너 또는 액체 성상에 영향을 받지 않았다(P>0.05). 요오드 참값이 0 mg/ml인 경우, 변이 범위는 -0.6 mg/ml에서 0.4 mg/ml였으며, 따라서 참조영증강의 기준값은 0.4 mg/ml로 정의하였다. Part II에서 관전압과(P<0.001) 관전류(P<0.05교호작용 변수에 따라 P 값에 차이가 있음)는 요오드 정량값에 유의한 영향이 있었으나, 그 영향의 크기, 즉, 회귀계수의 절대값은 매우 작았다. 요오드를 희석한 용매의 성상 역시 유의한 영향이 있었으며(P=0.007), 물과 아미노산 용액 간의 최소제곱평균의 차는 ≥5 mg/ml의 농도를 갖는 튜브에 대해서는 0.1에서 0.3 mg/ml였으며, ≤1 mg/ml의 농도를 갖는 튜브에서는 -0.4에서 -0.1 mg/ml였다. 변수 중 스펙트럴 레벨은 측정에 영향을 미치지 않았다 (P=0.647). Part III에서 참조영증강 기준값은(0.4 mg/ml) 환자-대조군 연구에서 가슴샘종과 가슴샘 낭종을 구분하는데 있어 민감도 100%, 특이도 85.7%, 정확도 90.9%, 양성 예측률 80.0%, 음성 예측률 100%를 보였다. 결론: 요오드 밀도는 이종에너지 CT 촬영기계에 영향을 받지 않는 측정값이다. 요오드 밀도는 CT 획득 변수에 유의한 영향을 받으나, 진단적 CT의 범위 내에서 그 영향의 정도는 미미하다. 참조영증강 요오드 밀도 기준값은(0.4 mg/ml) 가슴샘종과 가슴샘 낭종을 정확하게 구분할 수 있는 유용한 파라미터이다.Purpose: To analyze the effect of dual-energy computed tomography (DECT) scanners, acquisition parameters, and fluid characteristics on iodine quantification and to calculate and validate the measurement variability range induced by those variables. Methods: In Part I and II, experimental studies were performed using four mediastinal iodine phantoms. Phantoms were scanned with three different DECT scanners from major vendors using various acquisition parameters and their effects on the measurement of iodine density (IoD) were investigated using linear mixed-effect models. Measurement variability range of IoD was also calculated. In Part III, diagnostic usefulness of the true enhancement cutoff was retrospectively validated in patients who underwent surgical resections for thymic cysts and thymic epithelial tumors. Results: In Part I, absolute error of IoD was not significantly affected by the DECT systems and kind of solvents (P>0.05). Measurement variability range was from -0.6 to 0.4 mg/ml for the true iodine concentration 0 mg/ml. In Part II, tube voltage (P<0.001) and tube current-time product (P<0.05, depending on the interaction terms) had statistically significant effects on IoD. However, the magnitude of their effects was minimal in the range of diagnostic CT scans. Solvents also had significant effects on IoD (P=0.007). Specifically, the difference of least squares means between water and amino acid solution ranged from 0.1 to 0.3 for tubes with iodine concentrations ≥5 mg/ml and from -0.4 to -0.1 mg/ml for tubes with iodine concentrations ≤1 mg/ml. Spectral level was not an affecting factor (P=0.647). In Part III, the true enhancement cutoff for IoD, which was 0.4 mg/ml, exhibited diagnostic sensitivity, specificity, accuracy, positive predictive value, and negative predictive value of 100%, 85.7%, 90.9%, 80.0%, and 100%, respectively, for the differentiation of thymic epithelial tumors from thymic cysts. Conclusions: IoD measurement is robust to the DECT scanners from different vendors. IoD is significantly affected by the acquisition parameters, but the magnitude of effects are minimal in the range of diagnostic CT scans. The true enhancement cutoff of 0.4 mg/ml is an accurate parameter for the differentiation of thymic epithelial tumors from thymic cysts.Abstract i Contents iv List of tables and figures v List of Abbreviations vi Introduction 1 Part I. Materials and Methods 4 Part I. Results 14 Part II. Materials and Methods 30 Part II. Results 36 Part III. Materials and Methods 45 Part III. Results 51 Discussion 54 References 65 Abstract in Korean 74Docto