Gastrografin can be detected in ex vivo biological specimens by dual-energy CT scanning.

BACKGROUND: Dual-energy CT is able to distinguish between materials based on differences in X-ray absorption at different X-ray beam energies. The strong k-edge photoelectric effect of materials with a high atomic number makes this modality ideal for identifying iodine-containing compounds. We aim to evaluate dual-energy CT for the detection of Gastrografin (GG) (diatrizoate, Bayer PLC, Reading, UK) enteric contrast medium and validate the conditions for the measurement in ex vivo samples. METHODS: Dual-energy CT acquisitions were performed to detect Gastrografin in serial dilutions of water, saline and body fluids. We also evaluated the stability of Gastrografin solutions over time at room temperature. Stool specimens were examined to validate the proposed study protocol for clinical applications. RESULTS: Concentrations as low as 0.2% of Gastrografin were reproducibly detected in vitro and ex vivo samples by DECT, with linear readings ranging from 0.2% to 25% Gastrografin. Gastrografin was shown to be stable in ex vivo biological samples, and there was no difference in detection over time. Gastrografin was detected in stool specimens when administered orally. The detection curves followed the expected saturation effect at high concentrations of iodine. CONCLUSIONS: Dual-energy CT offers a convenient, quick, reliable and reproducible method for detecting and quantifying the presence of Gastrografin in ex vivo clinical specimens. Biological solutions containing Gastrografin are stable over time. A minimum dilution level of 25% is suggested to avoid beam saturation and inaccurate results.

Dual-Energy Computed Tomography Pulmonary Angiography: Comparison of Vessel Enhancement between Linear Blended and Virtual Monoenergetic Reconstruction Techniques.

INTRODUCTION: Optimal opacification of the pulmonary vasculature is a fundamental factor of a diagnostic quality computed tomography pulmonary angiogram (CTPA). This retrospective study examined the feasibility of utilising a noise-optimised monoenergetic reconstruction of the dual-energy computed tomography pulmonary angiogram (DE-CTPA) as an additional protocol to increase vessel opacification. METHOD: The study involved a retrospective analysis of 129 patients, 69 males (average age 58 years), 60 females (average age 56 years) who underwent a DE-CTPA at a tertiary referral hospital. Linear blended 120 kilovoltage (kV) images (LB120) dual-energy (DE) data sets (50% 100 kV and 50% 140 kV) were compared to noise-optimised virtual monoenergetic image reconstruction (VMI+) at 40 kiloelectron volts (VMI+40). The attenuation of the pulmonary trunk measured in Hounsfield units (HU) between the equivalent axial slices of the LB120 data set and the VMI+40 data set underwent statistical analysis via a Wilcoxon paired-sample test. RESULTS: VMI+40 (1161.500 HU) yielded a statistically significant increase in median attenuation within the pulmonary trunk compared to the LB120 (304.400 HU), with a median difference between monoenergetic reconstruction and standard dual energy of data sets of 827.5 HU (P < .001). CONCLUSIONS: VMI+40 of the DE-CTPA scan demonstrates a statistically significant increase in vessel attenuation in all cases and may have utility in reducing the rates of indeterminate or repeated studies.

Surface ECG and Fluoroscopy are Not Predictive of Right Ventricular Septal Lead Position Compared to Cardiac CT.

BACKGROUND: Controversy exists regarding the optimal lead position for chronic right ventricular (RV) pacing. Placing a lead at the RV septum relies upon fluoroscopy assisted by a surface 12-lead electrocardiogram (ECG). We compared the postimplant lead position determined by ECG-gated multidetector contrast-enhanced computed tomography (MDCT) with the position derived from the surface 12-lead ECG. METHODS: Eighteen patients with permanent RV leads were prospectively enrolled. Leads were placed in the RV septum (RVS) in 10 and the RV apex (RVA) in eight using fluoroscopy with anteroposterior and left anterior oblique 30° views. All patients underwent MDCT imaging and paced ECG analysis. ECG criteria were: QRS duration; QRS axis; positive or negative net QRS amplitude in leads I, aVL, V1, and V6; presence of notching in the inferior leads; and transition point in precordial leads at or after V4. RESULTS: Of the 10 leads implanted in the RVS, computed tomography (CT) imaging revealed seven to be at the anterior RV wall, two at the anteroseptal junction, and one in the true septum. For the eight RVA leads, four were anterior, two septal, and two anteroseptal. All leads implanted in the RVS met at least one ECG criteria (median 3, range 1-6). However, no criteria were specific for septal position as judged by MDCT. Mean QRS duration was 160 ± 24 ms in the RVS group compared with 168 ± 14 ms for RVA pacing (P = 0.38). CONCLUSIONS: We conclude that the surface ECG is not sufficiently accurate to determine RV septal lead tip position compared to cardiac CT.

Principles and Clinical Application of Dual-energy Computed Tomography in the Evaluation of Cerebrovascular Disease.

Dual-energy computed tomography (DECT) simultaneously acquires images at two X-ray energy levels, at both high- and low-peak voltages (kVp). The material attenuation difference obtained from the two X-ray energies can be processed by software to analyze material decomposition and to create additional image datasets, namely, virtual noncontrast, virtual contrast also known as iodine overlay, and bone/calcium subtraction images. DECT has a vast array of clinical applications in imaging cerebrovascular diseases, which includes: (1) Identification of active extravasation of iodinated contrast in various types of intracranial hemorrhage; (2) differentiation between hemorrhagic transformation and iodine staining in acute ischemic stroke following diagnostic and/or therapeutic catheter angiography; (3) identification of culprit lesions in intra-axial hemorrhage; (4) calcium subtraction from atheromatous plaque for the assessment of plaque morphology and improved quantification of luminal stenosis; (5) bone subtraction to improve the depiction of vascular anatomy with more clarity, especially at the skull base; (6) metal artifact reduction utilizing virtual monoenergetic reconstructions for improved luminal assessment postaneurysm coiling or clipping. We discuss the physical principles of DECT and review the clinical applications of DECT for the evaluation of cerebrovascular diseases.

Imaging and Right Ventricular Pacing Lead Position: A Comparison of CT, MRI, and Echocardiography.

BACKGROUND: Right ventricular nonapical (RVNA) pacing may reduce the risk of heart failure. Fluoroscopy is the standard approach to determine lead tip position, but is inaccurate. We compared cardiac computed tomography (CT), magnetic resonance imaging (MRI), two-dimensional and three-dimensional transthoracic echocardiography (TTE), and chest x-ray (CXR) to assess which provides the optimal assessment of right ventricular (RV) lead tip position. METHODS: Eighteen patients with MRI-conditional pacemakers (10 RVNA and eight apical [RVA] leads) underwent contrast CT, MRI, TTE, and a standard postimplant posteroanterior and lateral CXR. To compare images, the RV was arbitrarily partitioned into three long-axis segments (right ventricular outflow tract, middle, and apex), and two short-axis segments (septal and nonseptal). Agreement between modalities was assessed. RESULTS: RV lead tip position was identified in all patients on CT, TTE, and CXR, but was not identified in seven (39%) patients on MRI due to device-related artifact. Of 10 leads deemed to be nonapical/septal during implant, 70% were identified as nonapical on CXR, 60% on CT, 60% on MRI, and 80% on TTE. On CT imaging only 10% were truly septal, 20% on MRI, 30% on CXR, and 80% on TTE. Agreement was better between modalities when assessing position of the designated RVA leads. CONCLUSION: During implant leads intended for the septum are not confirmed as such on subsequent imaging, and marked heterogeneity is apparent between modalities. MRI is limited by artifact, and discrepancy exists between TTE and CT in identifying septal lead position. CT gave the clearest definition of lead tip position.

Can MRI accurately detect pilon articular malreduction? A quantitative comparison between CT and 3T MRI bone models.

BACKGROUND: Pilon fracture reduction is a challenging surgery. Radiographs are commonly used to assess the quality of reduction, but are limited in revealing the remaining bone incongruities. The study aimed to develop a method in quantifying articular malreductions using 3D computed tomography (CT) and magnetic resonance imaging (MRI) models. METHODS: CT and MRI data were acquired using three pairs of human cadaveric ankle specimens. Common tibial pilon fractures were simulated by performing osteotomies to the ankle specimens. Five of the created fractures [three AO type-B (43-B1), and two AO type-C (43-C1) fractures] were then reduced and stabilised using titanium implants, then rescanned. All datasets were reconstructed into CT and MRI models, and were analysed in regards to intra-articular steps and gaps, surface deviations, malrotations and maltranslations of the bone fragments. RESULTS: Initial results reveal that type B fracture CT and MRI models differed by ~0.2 (step), ~0.18 (surface deviations), ~0.56° (rotation) and ~0.4 mm (translation). Type C fracture MRI models showed metal artefacts extending to the articular surface, thus unsuitable for analysis. Type C fracture CT models differed from their CT and MRI contralateral models by ~0.15 (surface deviation), ~1.63° (rotation) and ~0.4 mm (translation). CONCLUSIONS: Type B fracture MRI models were comparable to CT and may potentially be used for the postoperative assessment of articular reduction on a case-to-case basis.

Radiation dose efficiency of dual-energy CT benchmarked against single-source, kilovoltage-optimized scans.

OBJECTIVE: This study evaluated the radiation dose and image quality implications of dual-energy CT (DECT) use, compared with kilovoltage-optimized single-source/single-energy CT (SECT) on a dual-source Siemens Somatom(®) Definition Flash CT scanner (Siemens Healthcare, Forcheim, Germany). METHODS: With equalized radiation dose (volumetric CT dose index), image noise (standard deviation of CT number) and signal-difference-to-noise ratio (SDNR) were measured and compared across three techniques: 100, 120 and 100/140 kVp (dual energy). Noise in a 30-cm-diameter water phantom and SDNR within unenhanced soft-tissue regions of a small adult (50 kg/165 cm) anthropomorphic phantom were utilized for the assessment. RESULTS: Water phantom image noise decreased with DECT compared with the lower noise SECT setting of 120 kVp (p = 0.046). A decrease in SDNR within the anthropomorphic phantom was demonstrated at 120 kVp compared with the SECT kilovoltage-optimized setting of 100 kVp (p = 0.001). A further decrease in SDNR was observed for the DECT technique when compared with 120 kVp (p = 0.01). CONCLUSION: On the Siemens Somatom Definition Flash system (Siemens Healthcare), and for equalized radiation dose conditions, image quality expressed as SDNR of unenhanced soft tissue may be compromised for DECT when compared with kilovoltage-optimized SECT, particularly for smaller patients. ADVANCES IN KNOWLEDGE: DECT on a dual-source CT scanner may require a radiation dose increase to maintain unenhanced soft-tissue contrast detectability, particularly for smaller patients.

Metal artifacts from titanium and steel screws in CT, 1.5T and 3T MR images of the tibial Pilon: a quantitative assessment in 3D.

Radiographs are commonly used to assess articular reduction of the distal tibia (pilon) fractures postoperatively, but may reveal malreductions inaccurately. While magnetic resonance imaging (MRI) and computed tomography (CT) are potential three-dimensional (3D) alternatives they generate metal-related artifacts. This study aims to quantify the artifact size from orthopaedic screws using CT, 1.5T and 3T MRI data. Three screws were inserted into one intact human cadaver ankle specimen proximal to and along the distal articular surface, then CT, 1.5T and 3T MRI scanned. Four types of screws were investigated: titanium alloy (TA), stainless steel (SS) (Ø =3.5 mm), cannulated TA (CTA) and cannulated SS (CSS) (Ø =4.0 mm, Ø empty core =2.6 mm). 3D artifact models were reconstructed using adaptive thresholding. The artifact size was measured by calculating the perpendicular distance from the central screw axis to the boundary of the artifact in four anatomical directions with respect to the distal tibia. The artifact sizes (in the order of TA, SS, CTA and CSS) from CT were 2.0, 2.6, 1.6 and 2.0 mm; from 1.5T MRI they were 3.7, 10.9, 2.9, and 9 mm; and 3T MRI they were 4.4, 15.3, 3.8, and 11.6 mm respectively. Therefore, CT can be used as long as the screws are at a safe distance of about 2 mm from the articular surface. MRI can be used if the screws are at least 3 mm away from the articular surface except for SS and CSS. Artifacts from steel screws were too large thus obstructed the pilon from being visualised in MRI. Significant differences (P<0.05) were found in the size of artifacts between all imaging modalities, screw types and material types, except 1.5T versus 3T MRI for the SS screws (P=0.063). CTA screws near the joint surface can improve postoperative assessment in CT and MRI. MRI presents a favourable non-ionising alternative when using titanium hardware. Since these factors may influence the quality of postoperative assessment, potential improvements in operative techniques should be considered.