Yan E. Zhao

Monoenergetic Imaging of Dual-energy CT Reduces Artifacts from Implanted Metal Orthopedic Devices in Patients with Factures

RATIONALE AND OBJECTIVES The purpose of this study was to optimize photon energy setting to reduce metal artifact of computed tomography (CT) images from implanted metal orthopedic devices in patients with fractures with monoenergetic imaging of dual-energy CT. MATERIALS AND METHODS This study included 47 patients with factures who underwent metal orthopedic device implanting. After dual-energy CT scan, monoenergetic software was used to postprocess with the following six photon energies: 40 kiloelectron-voltage (keV), 70 keV, 100 keV, 130 keV, 160 keV, and 190 keV. Two radiologists evaluated and rated the reformatted images with six different photon energies and average weighted 120 kVp images according to 4-score scale. The Wilcoxon rank-sum test was used to compare image quality scores for total, internal, and external metal orthopedic devices. Interreader agreement for image quality scoring was calculated. RESULTS Monoenergetic imaging of dual-energy CT improved the quality of CT images in the fracture patients with metal orthopedic devices compared to the average weighted 120 kVp images for the total, external, and internal metal orthopedic devices (all P values < .01). Optimal keV setting with the lowest metal artifact was 130 keV for total, internal, and external metal orthopedic devices. Good interreader agreement was found for the evaluation of image quality for total, internal, and external metal orthopedic devices. CONCLUSIONS Monoenergetic imaging of dual-energy CT improves quality of CT images in patients with metal orthopedic devices after fracture. Reformatted images at 130 keV have the optimal quality for total, internal, and external metal orthopedic devices.

Dual-Energy CT Angiography in the Evaluation of Intracranial Aneurysms: Image Quality, Radiation Dose, and Comparison With 3D Rotational Digital Subtraction Angiography

OBJECTIVE The purpose of this study was to evaluate the image quality, radiation dose, and diagnostic accuracy of dual-energy CT angiography (CTA) compared with 3D rotational digital subtraction angiography (DSA) in the detection of intracranial aneurysms. SUBJECTS AND METHODS Forty-six patients with clinically suspected intracranial aneurysms underwent dual-source dual-energy CTA and 3D DSA. For the analysis of the image quality and radiation dose of dual-energy CTA, 46 patients who underwent digital subtraction CTA were recruited as a control group. The image quality of dual-energy CTA and digital subtraction CTA was rated on a 4-point scale as excellent, good, moderate, or poor. The radiation dose of CTA was recorded according to patient protocol. Aneurysm detection with dual-energy CTA compared with 3D DSA was analyzed on a per-patient and on a peraneurysm basis. Sensitivity, specificity, and positive and negative predictive values for aneurysm presence were determined. The mean maximum diameter and dome and neck dimensions of aneurysms were measured on dual-energy CTA and 3D DSA images. Correlation analysis between the two techniques was performed. RESULTS There was no statistical difference between the image quality of dual-energy CTA and that of digital subtraction CTA (p>0.05). Patients undergoing dual-energy CTA received a smaller radiation dose (volume CT dose index, 20.6+/-0.1 mGy [mean+/-SD]; dose-length product, 398.6+/-19.0 mGy x cm) than those undergoing digital subtraction CTA (volume CT dose index, 50.4+/-3.4 mGy; dose-length product, 1,095.6+/-114.2 mGyxcm) (p<0.05). Three-dimensional DSA showed no aneurysm in 11 patients and 40 aneurysms in 35 patients. The mean maximum diameter of the aneurysms was 6+/-3 mm; the dome measurement, 5+/-3 mm; and the neck dimension, 3+/-2 mm. With dual-energy CTA, 38 aneurysms in 34 patients were correctly detected, and two aneurysms in two patients were missed. With DSA as the standard of reference, the sensitivity, specificity, and positive and negative predictive values of dual-energy CTA in the detection of intracranial aneurysm were 97.1%, 100%, 100%, and 91.7% on a per-patient basis and 95.0%, 100%, 100%, and 99.7% on a per-aneurysm basis. Dual-energy CTA had sensitivities of 93.8%, 100%, and 80.0% and specificities of 100%, 100%, and 100% in the detection of aneurysms larger than 5 mm, those measuring 3.1-5 mm, and aneurysms 3 mm or smaller. At dual-energy CTA, the mean maximum diameter and dome and neck dimensions were 6+/-3 mm, 5+/-3 mm, and 3+/-2 mm. Excellent correlation was found between DSA and dual-energy CTA findings with respect to mean maximum diameter and dome and neck dimensions (r=0.969, 0.957, and 0.870; p = 0.000). CONCLUSION On the basis of the findings in the small series of patients evaluated, contrast-enhanced dual-energy CTA had diagnostic image quality at a lower radiation dose than digital subtraction CTA and high diagnostic accuracy compared with 3D DSA in the detection of intracranial aneurysms.

Dual-Energy CT of the Lung

OBJECTIVE The introduction of dual-energy CT (DECT) has ushered in the ability of material differentiation and tissue characterization beyond the traditional CT attenuation scale. This quality has been exploited for visualizing and quantifying the specific tissue content using radiographic contrast agents, such as iodine-based contrast media or inhaled xenon gas. Applications of this paradigm in the thorax include characterization of the pulmonary blood pool in the setting of acute or chronic pulmonary embolism (PE) and characterization of diseases of the lung parenchyma. Selective xenon detection is being explored for imaging of lung ventilation. In addition, the usefulness of DECT-based selective iodine uptake measurements has been described for the diagnosis and surveillance of thoracic malignancies. This article reviews the current applications of DECT-based imaging techniques in the chest with an emphasis on the diagnosis and characterization of pulmonary thromboembolic disorders. CONCLUSION DECT can provide both anatomic and functional information about the lungs in a variety of pulmonary disease states based on a single contrast-enhanced CT examination. This quality has been shown to improve the diagnosis of acute and chronic PEs, other vascular disorders, lung malignancies, and parenchymal diseases. Further developments in DECT techniques and CT scanner technology will further foster and enhance the utility of this application and open new avenues in lung imaging.

Detection of Pulmonary Embolism Using Dual-Energy Computed Tomography and Correlation with Cardiovascular Measurements: A Preliminary Study

Background: Detection of a suspected pulmonary embolism (PE) 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 PE, but the studies on this topic are few. Purpose: To assess the clinical value of dual-source, dual-energy CT (DECT) for the diagnosis of suspected PE and to correlate with cardiovascular measurements. Material and Methods: 31 patients with suspected PE underwent contrast-enhanced DSCT scanning with dual-energy mode. Dedicated software for lung perfusion blood volume (PBV) was used in postprocessing. The numbers and locations of PE in PBV images and CT pulmonary angiography (CTPA) were recorded. Sensitivity and specificity were measured, comparing to CTPA as a standard of reference. The relationship between range of iodine mapping abnormality in PBV images and cardiovascular measurements was analyzed. Results: 33 DECT scans were performed in 31 patients. Seventeen patients had PE, while 14 patients had negative results. Filling defects were detected in pulmonary arteries in 44 pulmonary lobar and 99 segmental arteries. Compared to CTPA as a standard of reference, sensitivity and specificity of PBV images were 93.8% and 93.3% on a per-patient basis, 93.2% and 94.7% on a per-lobe basis, and 76.1% and 97.6% on a per-segment basis, respectively. Spearman correlation test showed good positive correlation between the right ventricle (RV)/left ventricle (LV) diameter ratio and pulmonary lobes with emboli for PBV images (R=0.663; P=0.004). Conclusion: DECT can provide morphological and functional information of the whole lung in a single contrast-enhanced acquisition; the perfusion defects visualized in PBV images appear to have a positive relationship with the patients’ right heart dysfunction.

Pulmonary Embolism and Renal Vein Thrombosis in Patients with Nephrotic Syndrome: Prospective Evaluation of Prevalence and Risk Factors with CT

PURPOSE To prospectively determine the prevalence of pulmonary embolism ( PE pulmonary embolism ) and renal vein thrombosis ( RVT renal vein thrombosis ) with computed tomography (CT) and to identify markers predictive of PE pulmonary embolism and/or RVT renal vein thrombosis in a large consecutive cohort of patients with nephrotic syndrome. MATERIALS AND METHODS This study was approved by the local institutional review board, and all patients or their guardians provided written informed consent. Consecutive patients with nephrotic syndrome (24-hour urine protein > 3.5 g) underwent combined CT pulmonary angiography for PE pulmonary embolism and renal CT venography for RVT renal vein thrombosis . Prevalence of PE pulmonary embolism and/or RVT renal vein thrombosis was estimated for different ages, sexes, and histopathologic types of nephrotic syndrome. Multivariate analysis was used to determine independent predictors for PE pulmonary embolism and/or RVT renal vein thrombosis in patients with nephrotic syndrome. RESULTS There were 512 patients in the study cohort (331 male patients, 181 female patients; mean age, 37 years ± 17 [standard deviation]; range, 9-81 years), including 80 children. One hundred eighty (35%) of 512 patients had PE pulmonary embolism and/or RVT renal vein thrombosis , with PE pulmonary embolism the more common condition (85% [153 of 180]). PE pulmonary embolism was associated with RVT renal vein thrombosis in 85 (56%) of 153 patients and was isolated in 68 patients (44%). Most patients with PE pulmonary embolism (84% [128 of 153]) were asymptomatic. One hundred twelve (22%) of 505 patients had RVT renal vein thrombosis . PE pulmonary embolism and/or RVT renal vein thrombosis was found in 15 (19%) of 80 children with nephrotic syndrome, while 165 (38%) of 432 adult patients with nephrotic syndrome had PE pulmonary embolism and/or RVT renal vein thrombosis (P = .001). Membranous nephropathy was the most common histopathologic type associated with PE pulmonary embolism and/or RVT renal vein thrombosis (48% [88 of 183]). Membranous nephropathy, age greater than 60 years, high hemoglobin level, long prothrombin time, and high creatinine level were independent predictors of PE pulmonary embolism and/or RVT renal vein thrombosis (P < .05 for all). CONCLUSION PE pulmonary embolism and RVT renal vein thrombosis are common in patients with nephrotic syndrome. PE pulmonary embolism is more common than RVT renal vein thrombosis , is most often asymptomatic, and is most frequently found in patients with membranous nephropathy. A high index of suspicion and a low threshold for diagnostic work-up is warranted in these patients.

Image Quality and Radiation Dose of Lower Extremity CT Angiography Using 70 kVp, High Pitch Acquisition and Sinogram-Affirmed Iterative Reconstruction

Objectives The purpose of this study was to assess image quality and radiation dose of lower extremity CT angiography (CTA) with 70 kVp, high pitch acquisition and sinogram-affirmed iterative reconstruction (SAFIRE). Methods Lower extremity CTAs were performed on 44 patients: 22 patients were examined using protocol A (120 kVp, pitch of 0.85 and 120 ml of contrast agent on a first-generation dual-source CT) (120 kVp group) and 22 patients were evaluated with protocol B (70 kVp, pitch of 2.2 and 80 ml of contrast agent on a second-generation dual-source CT) (70 kVp group). Images from the 120 kVp group were reconstructed with filtered back projection (FBP) and images from the 70 kVp group with SAFIRE. The attenuation, image noise, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. Two radiologists subjectively assessed image quality of lower extremity arteries, plantar arterial enhancement and venous contamination of all patients. Radiation dose was compared between the two groups. Results Higher mean intravascular attenuation was obtained in the 70 kVp group (70 vs. 120 kVp group, 555.4±83.4 HU vs. 300.9±81.4 HU, P<0.001), as well as image noise (20.0±2.8 HU vs. 17.5±3.2 HU, P = 0.010), SNR (32.0±7.0 vs. 19.1±6.9, P<0.001) and CNR (28.1±6.6 vs 15.9±6.3, P<0.001). No difference in subjective image quality and plantar arterial enhancement was found between 120 kVp group and 70 kVp group (all P>0.05). The venous contamination score was 1.5±0.8 for 120 kVp group while no venous contamination was found in 70 kVp group. The inter-observer agreement was moderate to good for both groups (0.515∼1, P<0.001). The effective dose was lower in 70 kVp group (0.3±0.1 mSv) than in 120 kVp group (1.6±0.7 mSv)(P<0.001). Conclusions Lower extremity CTA using 70 kVp, high pitch acquisition and SAFIRE, except increasing imaging noise, allows for lower radiation dose and contrast material volume without compromising image quality.

Detection of Pulmonary Embolism: Comparison Between Dual Energy CT and MR Angiography in a Rabbit Model

RATIONALE AND OBJECTIVES The purpose of this study was to compare the efficacy of dual-energy computed tomography (DECT), time-resolved magnetic resonance (MR) imaging (MRI) perfusion measurements, and high-resolution MR angiography (MRA) for the detection of pulmonary embolism (PE) in a rabbit model. MATERIALS AND METHODS Two hours after Gelfoam (n = 16) or saline (n = 2) injection into the femoral vein, 18 rabbits were first imaged using dual-energy computed tomographic pulmonary angiography (CTPA), from which blood flow imaging (BFI) were produced. Next, the rabbits underwent time-resolved MR perfusion measurements and MRA using a 3.0-T scanner. Two radiologists who were blinded to histopathologic findings independently evaluated the results of CTPA, BFI, time-resolved MR perfusion, and MRA for each rabbit and recorded the locations and number of pulmonary clots on a per lobe basis. Immediately after MRI examination, pathologic determination of the locations and numbers of lung lobes with PE was recorded. Histopathologic results served as the reference standard to determine the sensitivity and specificity of DECT (BFI and CTPA) and MRI (time-resolved MR perfusion and high-resolution MRA) for the detection of PE. RESULTS The induction of PE was successful in all animals, but three rabbits were excluded because of death prior to MRI procedures (caused by complications during the embolization procedure); only data from the remaining 15 rabbits were included in the final analysis. Histopathology demonstrated 24 lobes with clots and 51 lobes without clots. CTPA, BFI, and MRI correctly identified PE in 23, 23, and 20 lobes, respectively, and the absence of emboli in 48, 46, and 46 lobes, respectively; these results corresponded to sensitivities of 95.8%, 95.8%, and 83.3% and specificities of 94.1%, 90.2%, and 90.2% for reader 1 and sensitivities of 91.7%, 91.7%, and 87.5% and specificities of 90.2%, 88.2%, and 88.2% for reader 2 for CTPA, BFI, and MRI, respectively. Good or excellent intermodality and interreader agreement among CTPA, BFI, and MRI were found. CONCLUSIONS DECT can simultaneously provide high-resolution pulmonary artery and lung iodine mapping with slightly high diagnostic accuracy for the detection of PE compared to MRI in an experimental rabbit model of PE. This improvement was not statistically significant given the study sample size.

Image quality and radiation dose of lower extremity CT angiography at 70 kVp on an integrated circuit detector dual-source computed tomography

Background Despite the well-established requirement for radiation dose reduction there are few studies examining the potential for lower extremity CT angiography (CTA) at 70 kVp. Purpose To compare the image quality and radiation dose of lower extremity CTA at 70 kVp using a dual-source CT system with an integrated circuit detector to similar studies at 120 kVp. Material and Methods A total of 62 patients underwent lower extremity CTA. Thirty-one patients were examined at 70 kVp using a second generation dual-source CT with an integrated circuit detector (70 kVp group) and 31 patients were evaluated at 120 kVp using a first generation dual-source CT (120 kVp group). The attenuation and image noise were measured and signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. Two radiologists assessed image quality. Radiation dose was compared. Results The mean attenuation of the 70 kVp group was higher than the 120 kVp group (575 ± 149 Hounsfield units [HU] vs. 258 ± 38 HU, respectively, P < 0.001) as was SNR (44.0 ± 22.0 vs 32.7 ± 13.3, respectively, P = 0.017), CNR (39.7 ± 20.6 vs 26.6 ± 11.7, respectively, P = 0.003) and the mean image quality score (3.7 ± 0.1 vs. 3.2 ± 0.3, respectively, P < 0.001). The inter-observer agreement was good for the 70 kVp group and moderate for the 120 kVp group. The dose-length product was lower in the 70 kVp group (264.5 ± 63.1 mGy × cm vs. 412.4 ± 81.5 mGy × cm, P < 0.001). Conclusion Lower extremity CTA at 70 kVp allows for lower radiation dose with higher SNR, CNR, and image quality when compared with standard 120 kVp.

Seventy-Peak Kilovoltage High-Pitch Thoracic Aortic CT Angiography without ECG Gating: Evaluation of Image Quality and Radiation Dose.

RATIONALE AND OBJECTIVES To assess the feasibility of 70-kVp high-pitch non-ECG-gated thoracic aortic computed tomography angiography (CTA) with 40-mL contrast agent compared to 100-kVp standard-pitch CTA with 60-mL contrast agent. MATERIALS AND METHODS Sixty-seven patients (51 men and 16 women; mean age, 55 ± 14 years) received non-ECG-gated aortic CTA at 70 kVp, high pitch of 3.4, and 40-mL contrast agent (group A, n = 31) or CTA at 100-kVp, pitch of 1.2, and 60-mL contrast agent (group B, n = 36). Iterative reconstruction was used in all patients. For image quality assessment, CTA images were evaluated on a three-point scale and signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated and compared. Furthermore, computed tomography (CT) dose index was recorded. RESULTS Mean CT values and noise levels were higher in group A compared to group B (all P < .001), whereas SNR and CNR were lower than those in group B (all P < .001). Furthermore, the image quality of the aorta at the level of the diaphragm was lower in group A than that in group B (P < .05). However, image quality was graded as diagnostic in all patients, and motion artifacts of the aortic arch were significantly decreased in group A (P <.05). Interreader agreement was good or excellent for image quality assessment (k = 0.625-0.835). The 70-kVp CTA protocol, which allows dose reduction of 85%, was considered diagnostic in all instances by two readers. CONCLUSIONS Our proposed thoracic aortic CTA protocol provides diagnostic information with substantial reduction of both radiation and contrast agent doses compared to standard-pitch CTA at 100 kVp.

Dual energy CT ventilation imaging after aerosol inhalation of iodinated contrast medium in rabbits.

PURPOSE To assess the feasibility of dual energy CT (DECT) after aerosol inhalation of iodinated contrast medium for the evaluation of ventilation function in rabbits with airway obstruction. MATERIALS AND METHODS The study was approved by our institutional animal experimental committee and performed according to animal care guidelines. Airway obstruction was created by injecting gelatin sponge into the right bronchus of 6 New Zealand rabbits. One additional rabbit served as control without airway obstruction. All 7 rabbits then underwent inhalation of aerosol iodinated contrast medium for 5 min, followed by DECT of the lungs from which ventilation CT images were created. CT number and overlay value (calculated iodine enhancement on the ventilation images in hounsfield unit) of the obstructed and non-obstructed lung lobes were measured at 80-kVp, 140-kVp, and weighted average 120-kVp. Immediately after DECT scan, the rabbits were sacrificed, the lungs were removed and detailed pathological examination of the locations and parenchymal changes of the obstructed lung lobes were performed and correlated with DECT ventilation imaging findings. RESULTS Data from one rabbit with airway obstruction were excluded because of post-procedure pneumatothorax. Seventeen normal lung lobes without airway obstruction proven by histopathology had nearly homogeneous ventilation, while 13 abnormal lung lobes had ventilation defects on DECT ventilation images. CT numbers and overlay values of the normal (CT number, -737.77 ± 71.46 HU, -768.84 ± 73.86 HU, -731.86 ± 65.92 HU for 140-kVp, 80-kVp, and weighted average 120-kVp; overlay value, 46.58 ± 19.49 HU) and abnormal lung lobes (CT number, -183.58 ± 173.37 HU, -124.93 ± 242.23 HU, -166.07 ± 191.57 HU for 140-kVp, 80-kVp, and weighted average 120-kVp; overlay value, 0.00 ± 0.00 HU) were significantly different at 80-kVp, 140-kVp, and weighted average 120-kVp (P < 0.001 for all). Diffuse hemorrhage, inflammatory cell infiltration, and exudation were observed at histopathology in the obstructed lung lobes. CONCLUSIONS It is feasible to study regional lung ventilation function using DECT after aerosol inhalation of iodinated contrast medium in rabbit. The safety of inhalation of iodine contrast medium is unknown, and has to be investigated further before use of this new method in humans.