Chest X-ray Dose Equivalent Low-dose CT with Tin Filtration: Potential Role for the Assessment of Pectus Excavatum.

RATIONALE AND OBJECTIVES: To determine the value of chest CT with tin filtration applying a dose equivalent to chest x-ray for the assessment of the Haller index for evaluation of pectus excavatum. MATERIALS AND METHODS: Two hundred seventy-two patients from a prospective single center study were included and underwent a clinical standard dose chest CT (effective dose 1.8 ± 0.7 mSv) followed by a low-dose CT (0.13 ± 0.01 mSv) in the same session. Two blinded readers independently evaluated all data sets. Image quality for bony chest wall assessment was noted. Radiologists further assessed (a) transverse thoracic diameter, (b) anteroposterior thoracic diameter, and calculated (c) Haller index by dividing transverse diameter by anteroposterior diameter. The agreement of both readers in standard dose and low-dose CT was assessed using Lin's concordance correlation coefficient (pc). RESULTS: Subjective image quality was lower for low dose compared to standard dose CT images by both readers (p < 0.001). In total, 99% (n = 540) of low-dose CT scans were rated as diagnostic for bony chest wall assessment by both readers. There was a high agreement for assessment of transverse diameter, anteroposterior diameter and Haller index comparing both readers in standard dose and low-dose CT with pc values indicating substantial agreement (i.e., 0.95> and ≤0.99) in 12/18 (67%) and almost perfect agreement (i.e., >0.99) in 6/18 (33%). CONCLUSION: Our study suggests that low-dose CT with tin filtration applying a radiation dose equivalent to a plain chest X-ray is excellent for assessing the Haller index.

Coronary risk assessment at X-ray dose equivalent ungated chest CT: Results of a multi-reader study.

OBJECTIVES: To determine the value of ultra-low dose chest CT with tin filtration for ordinal coronary artery calcium (CAC) risk scoring. METHODS: 50 patients were prospectively included and underwent clinical standard dose chest CT (1.8±0.7mSv) and ultra-low dose CT (0.13±0.01mSv). Four radiologists estimated presence and extent of CAC. RESULTS: Weighted kappa values for CAC were 0.76-0.97 in standard dose and 0.75-0.95 in ultra-low dose CT (p<0.001). Good to excellent agreement was observed for CAC ordinal risk assessment, with readers reporting identical risk in 81% of cases. CONCLUSION: CAC risk can be qualitatively assessed from X-ray dose equivalent ungated chest CT.

Diagnostic accuracy of chest X-ray dose-equivalent CT for assessing calcified atherosclerotic burden of the thoracic aorta.

OBJECTIVE: To determine the value of ultralow-dose chest CT for estimating the calcified atherosclerotic burden of the thoracic aorta using tin-filter CT and compare its diagnostic accuracy with chest direct radiography. METHODS: A total of 106 patients from a prospective, IRB-approved single-centre study were included and underwent standard dose chest CT (1.7 ± 0.7 mSv) by clinical indication followed by ultralow-dose CT with 100 kV and spectral shaping by a tin filter (0.13 ± 0.01 mSv) to achieve chest X-ray equivalent dose in the same session. Two independent radiologists reviewed the CT images, rated image quality and estimated presence and extent of calcification of aortic valve, ascending aorta and aortic arch. Conventional radiographs were also reviewed for presence of aortic calcifications. RESULTS: The sensitivity of ultralow-dose CT for the detection of calcifications of the aortic valve, ascending aorta and aortic arch was 93.5, 96.2 and 96.2%, respectively, compared with standard dose CT. The sensitivity for the detection of thoracic aortic calcification was significantly lower on chest X-ray (52.3%) compared with ultralow-dose CT (p < 0.001). CONCLUSION: A reliable estimation of calcified atherosclerotic burden of the thoracic aorta can be achieved with modern tin-filter CT at dose values comparable to chest direct radiography. Advances in knowledge: Our findings suggest that ultralow-dose CT is an excellent tool for assessing the calcified atherosclerotic burden of the thoracic aorta with higher diagnostic accuracy than conventional chest radiography and importantly without the additional cost of increased radiation dose.

Dual-Energy Computed Tomography Virtual Monoenergetic Imaging of Lung Cancer: Assessment of Optimal Energy Levels.

OBJECTIVE: The aim of the study was to evaluate objective and subjective image qualities of virtual monoenergetic imaging (VMI) in dual-source dual-energy computed tomography (DECT) and optimal kiloelectron-volt (keV) levels for lung cancer. METHODS: Fifty-nine lung cancer patients underwent chest DECT. Images were reconstructed as VMI series at energy levels of 40, 60, 80, and 100 keV and standard linear blending (M_0.3) for comparison. Objective and subjective image qualities were assessed. RESULTS: Lesion contrast peaked in 40-keV VMI reconstructions (2.5 ± 2.9) and 60 keV (1.9 ± 3.0), which was superior to M_0.3 (0.5 ± 2.7) for both comparisons (P < 0.001). Compared with M_0.3, subjective ratings were highest for 60-keV VMI series regarding general image quality (4.48 vs 4.52; P = 0.74) and increased for lesion demarcation (4.07 vs 4.84; P < 0.001), superior to all other VMI series (P < 0.001). Image sharpness was similar between both series. Image noise was rated superior in the 80-keV and M_0.3 series, followed by 60 keV. CONCLUSIONS: Virtual monoenergetic imaging reconstructions at 60-keV provided the best combination of subjective and objective image qualities in DECT of lung cancer.

Assessment of an Advanced Monoenergetic Reconstruction Technique in Dual-Energy Computed Tomography of Head and Neck Cancer.

OBJECTIVES: To define optimal keV settings for advanced monoenergetic (Mono+) dual-energy computed tomography (DECT) in patients with head and neck squamous cell carcinoma (SCC). METHODS: DECT data of 44 patients (34 men, mean age 55.5 ± 16.0 years) with histopathologically confirmed SCC were reconstructed as 40, 55, 70 keV Mono + and M_0.3 (30 % 80 kV) linearly blended series. Attenuation of tumour, sternocleidomastoid muscle, internal jugular vein, submandibular gland, and noise were measured. Three radiologists with >3 years of experience subjectively assessed image quality, lesion delineation, image sharpness, and noise. RESULTS: The highest lesion attenuation was shown for 40 keV series (248.1 ± 94.1 HU), followed by 55 keV (150.2 ± 55.5 HU; P = 0.001). Contrast-to-noise ratio (CNR) at 40 keV (19.09 ± 13.84) was significantly superior to all other reconstructions (55 keV, 10.25 ± 9.11; 70 keV, 7.68 ± 6.31; M_0.3, 5.49 ± 3.28; all P < 0.005). Subjective image quality was highest for 55 keV images (4.53; κ = 0.38, P = 0.003), followed by 40 keV (4.14; κ = 0.43, P < 0.001) and 70 keV reconstructions (4.06; κ = 0.32, P = 0.005), all superior (P < 0.004) to linear blending M_0.3 (3.81; κ = 0.280, P = 0.056). CONCLUSIONS: Mono + DECT at low keV levels significantly improves CNR and subjective image quality in patients with head and neck SCC, as tumour CNR peaks at 40 keV, and 55 keV images are preferred by observers. KEY POINTS: • Mono + DECT combines increased contrast with reduced image noise, unlike linearly blended images. • Mono + DECT imaging allows for superior CNR and subjective image quality. • Head and neck tumour contrast-to-noise ratio peaks at 40 keV. • 55 keV images are preferred over all other series by observers.

Dual-energy CT-based phantomless in vivo three-dimensional bone mineral density assessment of the lumbar spine.

PURPOSE: To evaluate the feasibility of phantomless in vivo dual-energy computed tomography (CT)-based three-dimensional (3D) bone mineral density (BMD) assessment in comparison with dual x-ray absorptiometry (DXA). MATERIALS AND METHODS: This retrospective study was approved by the institutional review board, and the requirement to obtain informed consent was waived. Data from clinically indicated dual-energy CT and DXA examinations within 2 months, comprising the lumbar spine of 40 patients, were included. By using automated dedicated postprocessing dual-energy CT software, the trabecular bone of lumbar vertebrae L1-L4 were analyzed and segmented. A mixed-effects model was used to assess the correlations between BMD values derived from dual-energy CT and DXA. RESULTS: One hundred sixty lumbar vertebrae were analyzed in 40 patients (mean age, 57.1 years; range, 24-85 years), 21 male (mean age, 54.3 years; range, 24-85 years) and 19 female (mean age, 58.5 years; range, 31-80 years). Mean BMD of L1-L4 determined with DXA was 0.995 g/cm(2), and 18 patients (45%) showed an osteoporotic BMD (T score less than -2.5) of at least two vertebrae. Mean dual-energy CT-based BMD of L1-L4 was 0.254 g/cm(3). Bland-Altman analysis with mixed effects demonstrated a lack of correlation between dual-energy CT-based and DXA-based BMD values, with a mean difference of 0.7441 and 95% limits of agreement of 0.7441 ± 0.4080. CONCLUSION: Dedicated postprocessing of dual-energy CT data allows for phantomless in vivo BMD assessment of the trabecular bone of lumbar vertebrae and enables freely rotatable color-coded 3D visualization of intravertebral BMD distribution.

Estimation and comparison of effective dose (E) in standard chest CT by organ dose measurements and dose-length-product methods and assessment of the influence of CT tube potential (energy dependency) on effective dose in a dual-source CT.

PURPOSE: To determine effective dose (E) during standard chest CT using an organ dose-based and a dose-length-product-based (DLP) approach for four different scan protocols including high-pitch and dual-energy in a dual-source CT scanner of the second generation. MATERIALS AND METHODS: Organ doses were measured with thermo luminescence dosimeters (TLD) in an anthropomorphic male adult phantom. Further, DLP-based dose estimates were performed by using the standard 0.014mSv/mGycm conversion coefficient k. Examinations were performed on a dual-source CT system (Somatom Definition Flash, Siemens). Four scan protocols were investigated: (1) single-source 120kV, (2) single-source 100kV, (3) high-pitch 120kV, and (4) dual-energy with 100/Sn140kV with equivalent CTDIvol and no automated tube current modulation. E was then determined following recommendations of ICRP publication 103 and 60 and specific k values were derived. RESULTS: DLP-based estimates differed by 4.5-16.56% and 5.2-15.8% relatively to ICRP 60 and 103, respectively. The derived k factors calculated from TLD measurements were 0.0148, 0.015, 0.0166, and 0.0148 for protocol 1, 2, 3 and 4, respectively. Effective dose estimations by ICRP 103 and 60 for single-energy and dual-energy protocols show a difference of less than 0.04mSv. CONCLUSION: Estimates of E based on DLP work equally well for single-energy, high-pitch and dual-energy CT examinations. The tube potential definitely affects effective dose in a substantial way. Effective dose estimations by ICRP 103 and 60 for both single-energy and dual-energy examinations differ not more than 0.04mSv.

Dual energy CT for the assessment of reperfused chronic infarction - a feasibility study in a porcine model.

BACKGROUND: Detection of myocardial infarction has been the focus of considerable research over the past few decades. Recently developed dual source computed tomography (DSCT) scanners with dual energy mode have been used to detect myocardial infarction, but the studies on this topic are few. PURPOSE: To evaluate the feasibility and performance of dual energy CT (DECT) during arterial phase in coronary CT angiography for the detection of chronic infarction compared with late enhancement MRI (LE-MRI) and histopathology in a porcine model of reperfused myocardial infarction. MATERIAL AND METHODS: Myocardial infarctions were induced by 30 min occlusion of the proximal left anterior descending coronary artery in eight minipigs. DECT, post-contrast LE-MRI and histopathology were performed 60 days after infarct induction. The CT scan was performed in dual energy mode using a dedicated protocol. Myocardial iodine distribution was superimposed as color maps on grey scale multiplanar reformats of the heart. Two radiologists in consensus interpreted all imaging studies for presence of gadolinium uptake at LE-MRI reduced iodine content at DECT and hypoenhanced areas in the initial 100 kV coronary CT angiography images that were acquired during the DECT-acquisition. Results were compared with histopathology. RESULTS: Based on evaluable segments, DECT showed a sensitivity and specificity of 0.72 and 0.88; LE-MRI showed a sensitivity and specificity of 0.78 and 0.92; and the 100 kV data-set of the DECT scan showed a sensitivity and specificity of 0.60 and 0.93, respectively, for the detection of histological proved ischemia. CONCLUSION: DECT during arterial phase coronary CT angiography, which is ordinarily used for coronary artery evaluation, is feasible for the detection of a chronic reperfused myocardial infarction.

Dual energy CT pulmonary blood volume assessment in acute pulmonary embolism - correlation with D-dimer level, right heart strain and clinical outcome.

OBJECTIVE: To investigate the role of perfusion defect (PD) size on dual energy CT pulmonary blood volume assessment as predictor of right heart strain and patient outcome and its correlation with d-dimer levels in acute pulmonary embolism (PE). METHODS: 53 patients with acute PE who underwent DECT pulmonary angiography were retrospectively analyzed. Pulmonary PD size caused by PE was measured on DE iodine maps and quantified absolutely (VolPD) and relatively to the total lung volume (RelPD). Signs of right heart strain (RHS) on CT were determined. Information on d-dimer levels and readmission for recurrent onset of PE and death was collected. RESULTS: D-dimer level was mildly (r = 0.43-0.47) correlated with PD size. Patients with RHS had significantly higher VolPD (215 vs. 73 ml) and RelPD (9.9 vs. 2.9%) than patients without RHS (p < 0.003). There were 2 deaths and 1 readmission due of PE in 18 patients with >5% RelPD, while no such events were found for patients with <5% RelPD. CONCLUSION: Pulmonary blood volume on DECT in acute PE correlates with RHS and appears to be a predictor of patient outcome in this pilot study.

Dual-energy CT for the assessment of chronic myocardial infarction in patients with chronic coronary artery disease: comparison with 3-T MRI.

OBJECTIVE: The purpose of this article is to compare the performance of dual-energy CT with that of 3-T MRI with late enhancement for the detection of chronic myocardial infarction during first-pass coronary CT angiography (CTA). SUBJECTS AND METHODS: Thirty-six patients underwent coronary CTA for the assessment of coronary bypass graft patency on a first-generation dual-source CT scanner in dual-energy mode. Gray-scale images (100 kV, 140 kV, and blended virtual 120 kV) were assessed for areas of hypodense myocardium during the arterial phase. In addition, a color-coded map of myocardial iodine distribution was calculated from the dual-energy data for perfusion analysis. Dual-energy CT data were compared with data from 3-T MRI with late enhancement, which served as the reference standard for scar detection using the American Heart Association's 17-segment model of the left ventricle. RESULTS: One hundred one (17%) of 612 myocardial segments in 22 (61%) of 36 patients showed late enhancement on MRI. Although myocardial iodine mapping was prone to artifacts, mostly arising from sternal wires (70% sensitivity), 100-kV gray-scale images showed the highest sensitivity (80%) for the detection of myocardial scar. Blended virtual 120-kV images with lower noise and higher resolution had the best diagnostic accuracy (77% sensitivity, 97% specificity, 85% positive predictive value, 96% negative predictive value, and 94% accuracy). CONCLUSION: Detection of chronic myocardial infarction on color-coded iodine distribution analysis with first-generation dual-energy CT is impeded by thoracic metallic devices. This group of patients benefits more from adequate blending of high- and low-kilovoltage gray-scale images. Further technical improvements are desirable to lower artifact burden and improve sensitivity on myocardial iodine distribution mapping.