In vitro qualitative and quantitative CT assessment of iodinated aerosol nasal deposition using a 3D-printed nasal replica.

Computed tomography can provide high-resolution details on nasal anatomy being potentially useful for the assessment of nasal spray deposition. The purpose of this technical note was to present a method based on CT imaging to assess qualitatively and quantitatively the in vitro spray deposition patterns within the sinonasal cavities of a nasal replica obtained by three-dimensional (3D) printing, using iodinated contrast agent labelled solutions with high spatial and temporal resolution. Using a third generation dual-source CT scanner in single energy mode, scans of a nasal replica were acquired following application of iodinated contrast agent labelled aerosols with an iodine concentration of 92.5 mgl/mL. Two software programmes were then utilised (Osirix MD v.9.0, Pixmeo, Geneva, Switzerland; 3mensio, Pie Medical Imaging, Bilthoven, Netherlands) to generate three-dimensional reconstructions of the scans, thus enabling the rapid detection and visualisation of administered single droplets and their voxel-by-voxel localisation. Using this approach, we achieved recovery rates between 84-98% and 89-109% (depending on the software programme) of the total applied aerosol volume

Development of an anthropomorphic spine phantom suitable for fusion of MR neurography with interventional flat-panel CT

PURPOSE To design a spine phantom suitable for fusion of MR neurography (MRN) with interventional flat panel computed tomography (FPCT) images from tissue-equivalent agarose gels and artificial nerves in MRI, including material with equal attenuation to bone in computed tomography (CT). METHODS T1-/T2-relaxation times of target tissue were determined in vivo (n = 5) using MR mapping-techniques. Serial dilution of castor oil lipogels was performed ex vivo in order to define correct composition for tissue-equivalent relaxation times. Similarly, serial dilution series of calcium carbonate (CaCO) and barium sulphate (BaSO) in synthetic resin were used to adjust radiodensity of selected vertebral bodies (L1-L5) and sacrum in CT. Nerve tissue was simulated with agarose-impregnated polyethylene fibers. Spine phantom was assembled using respective components in anthropomorphic geometry. A fat-saturated, T2-weighted 3D SPACE STIR sequence was acquired for MRN and subsequently fused with an on-site FPCT scan of the phantom. RESULTS In vivo T1-/T2-values for fat tissue were found to be at 394 ± 16 ms and 161 ± 16 ms, corresponding to a castor oil concentration of 50%. Analogously, bone marrow-equivalent values were measured at 822 ± 21 ms and 67 ± 6 ms, simulated with 40% castor oil. Cortical bone-like radiodensity of 1'115 ± 80 HU was achieved for artificial bone with 30% CaCO and 1.5% BaSO. Simulated nerves were successfully depicted in MRN and fused with FPCT, combining optimal contrasts for nerves and bones on-site. CONCLUSIONS The customized phantom showed analogous tissue contrasts to in vivo conditions in both MRN and FPCT, facilitating simulations of fusion-image guided spine interventions

Realistic Kidney Tissue Surrogates for Multienergy Computed Tomography-Feasibility and Estimation of Energy-Dependent Attenuation Thresholds for Renal Lesion Enhancement in Low-kV and Virtual Monoenergetic Imaging

PURPOSE The aims of this study were to assess if kidney tissue surrogates (KTSs) are superior to distilled water-iodine solutions in the emulation of energy-dependent computed tomography (CT) attenuation characteristics of renal parenchyma and to estimate attenuation thresholds for definite lesion enhancement for low-kV single-energy and low-keV dual-energy virtual monoenergetic imaging. METHODS A water-filled phantom (diameter, 30 cm) with multiple vials was imaged on a dual-source dual-energy CT (DS-DE) and a single-source split-filter dual-energy CT (SF-DE), both in single-energy mode at 80, 100, 120, 140 kVp and in dual-energy mode at 80/Sn150, 90/Sn150, and 100/Sn150 kVp for DS-DE and AuSn120 kVp for SF-DE. Single-energy images, linear-blended dual-energy images, and virtual monoenergetic imaging at energy levels from 40 to 190 keV were reconstructed. First, attenuation characteristics of KTS in solid and liquid consistencies were compared. Second, solid KTSs were developed to match the CT attenuation of unenhanced renal parenchyma at 120 kVp as retrospectively measured in 100 patients. Third, CT attenuation of KTS-iodine and water-iodine solutions at 8 different iodine concentrations (0-10 mg I/mL) were compared as a function of tube voltage and of keV level using multiple linear regression models. Energy-dependent attenuation thresholds for definite lesion enhancement were calculated. RESULTS Unenhanced renal parenchyma at 120 kVp measured on average 30 HU on both scanners in the patient cohort. Solid KTS with a water content of 80% emulated the attenuation of unenhanced renal parenchyma (30 HU) more accurately compared with water-iodine solutions (0 HU). Attenuation difference between KTS-iodine and water-iodine solutions converged with increasing iodine concentration and decreasing x-ray energy due to beam-hardening effects. A slight attenuation difference of approximately 2 HU was found between the 2 CT scanners. Attenuation thresholds for definite lesion enhancement were dependent on tube voltage and keV level and ranged from 16.6 to 33.2 HU and 3.2 to 68.3 HU for single-energy and dual-energy CT scan modes for DS-DE and from 16.1 to 34.3 HU and 3.3 to 92.2 HU for SF-DE. CONCLUSIONS Kidney tissue surrogates more accurately emulate the energy-dependent CT attenuation characteristics of renal parenchyma for multienergy CT compared with conventional water-iodine approaches. Energy-dependent thresholds for definite lesion enhancement could facilitate lesion characterization when imaging at different energies than the traditional 120 kVp