Radiological characterization of gilthead seabream (Sparus aurata) by X-ray computed tomography.

In recent years, the increasing use of fish as new animal models in scientific research and the growth of fish farming (mainly for human consumption) have highlighted the need for advanced technology to deepen our knowledge of fish biology. Hence, the present study was carried out to radiologically analyse the whole body of gilthead seabream (Sparus aurata) specimens using X-ray computed tomography (CT). Images were acquired in an Albira SPECT/PET/CT tri-modal preclinical-scanner. Segmentation, measurements and three-dimensional reconstruction were made using the Carestream Molecular imaging Albira CT system in conjunction with Pmod, AMIDE and Amira software packages. The results showed that the density values of gilthead seabream are in the range -700 to +2500 HU for the whole body. We also determined the density ranges that topographically coincide with the swim bladder, soft tissues, fat, skin and skeleton. This work describes, validates and demonstrates the application of a fully automated image analysis technique to study and quantify fish body composition, whether segmented or as a whole. In addition, the basis for applying this image technique in other in vivo studies is established.

Use of iDXA spine scans to evaluate total and visceral abdominal fat.

OBJECTIVES: Abdominal fat may be a better predictor than body mass index (BMI) for risk of metabolically-related diseases, such as diabetes, cardiovascular disease, and some cancers. We sought to validate the percent fat reported on dual energy X-ray absorptiometry (DXA) regional spine scans (spine fat fraction, SFF) against abdominal fat obtained from total body scans using the iDXA machine (General Electric, Madison, WI), as previously done on the Prodigy model. METHODS: Total body scans and regional spine scans were completed on the same day (N = 50). In alignment with the Prodigy-based study, the following regions of interest (ROI) were assessed from total body scans and compared to the SFF from regional spine scans: total abdominal fat at (1) lumbar vertebrae L2-L4 and (2) L2-Iliac Crest (L2-IC); (3) total trunk fat; and (4) visceral fat in the android region. Separate linear regression models were used to predict each total body scan ROI from SFF; models were validated by bootstrapping. RESULTS: The sample was 84% female, a mean age of 38.5 ± 17.4 years, and mean BMI of 23.0 ± 3.8 kg/m2 . The SFF, adjusted for BMI, predicted L2-L4 and L2-IC total abdominal fat (%; Adj. R2 : 0.90) and total trunk fat (%; Adj. R2 : 0.88) well; visceral fat (%) adjusted R2 was 0.83. Linear regression models adjusted for additional participant characteristics resulted in similar adjusted R2 values. CONCLUSIONS: This replication of the strong correlation between SFF and abdominal fat measures on the iDXA in a new population confirms the previous Prodigy model findings and improves generalizability.

Retrospective Evaluation of Whole Body Computed Tomography for Tumor Staging in Dogs with Primary Appendicular Osteosarcoma.

OBJECTIVE: To evaluate whole body computed tomography (CT) for staging canine appendicular osteosarcoma. STUDY DESIGN: Retrospective case series. ANIMALS: Client-owned dogs diagnosed with appendicular osteosarcoma (n=39). METHODS: Medical records for client-owned dogs diagnosed with appendicular osteosarcoma from August 2008 to July 2014 were reviewed. Dogs were included if they had a confirmed diagnosis of appendicular osteosarcoma and were staged using whole body CT. Data collected included signalment, body weight, primary tumor location, serum alkaline phosphatase (ALP) activity, findings on 3-view thoracic radiographs, cytologic or histologic results, and findings on CT. RESULTS: Thirty-nine dogs (median age 8.5 years; median body weight 37 kg) had osteosarcoma of the distal radius (n=17), proximal humerus (11) and other sites. Serum ALP activity was elevated in 14 dogs. Bone metastasis was not detected in any dog on whole body CT. Pulmonary metastasis was considered definitive on CT based on board certified radiologist assessment in 2/39 dogs (5%). Two additional dogs (2/39, 5%) had soft tissue masses diagnosed on CT, consistent with concurrent, non-metastatic malignancies. CONCLUSION: Bone metastases were not identified in any dog with whole body CT. Thoracic and abdominal CT detected lung lesions and concurrent neoplasia in dogs with primary appendicular osteosarcoma. Whole body CT may be a useful adjunct to other screening tests for disseminated malignancy.

A prototype PET/SPECT/X-rays scanner dedicated for whole body small animal studies.

OBJECTIVE: To present a prototype tri-modal imaging system, consisting of a single photon emission computed tomography (SPET), a positron emission tomography (PET), and a computed tomography (CT) subsystem, evaluated in planar mode. MATERIALS AND METHODS: The subsystems are mounted on a rotating gantry, so as to be able to allow tomographic imaging in the future. The system, designed and constructed by our group, allows whole body mouse imaging of competent performance and is currently, to the best of our knowledge, unequaled in a national and regional level. The SPET camera is based on two Position Sensitive Photomultiplier Tubes (PSPMT), coupled to a pixilated Sodium Iodide activated with Thallium (NaI(Tl)) scintillator, having an active area of 5x10cm2. The dual head PET camera is also based on two pairs of PSPMT, coupled to pixelated berillium germanium oxide (BGO) scintillators, having an active area of 5x10cm2. The X-rays system consists of a micro focus X-rays tube and a complementary metal-oxide-semiconductor (CMOS) detector, having an active area of 12x12cm2. RESULTS: The scintigraphic mode has a spatial resolution of 1.88mm full width at half maximum (FWHM) and a sensitivity of 107.5cpm/0.037MBq at the collimator surface. The coincidence PET mode has an average spatial resolution of 3.5mm (FWHM) and a peak sensitivity of 29.9cpm/0.037MBq. The X-rays spatial resolution is 3.5lp/mm and the contrast discrimination function value is lower than 2%. CONCLUSION: A compact tri-modal system was successfully built and evaluated for planar mode operation. The system has an efficient performance, allowing accurate and informative anatomical and functional imaging, as well as semi-quantitative results. Compared to other available systems, it provides a moderate but comparable performance, at a fraction of the cost and complexity. It is fully open, scalable and its main purpose is to support groups on a national and regional level and provide an open technological platform to study different detector components and acquisition strategies.

IMAGING DIAGNOSIS--USE OF RADIOGRAPHY AND COMPUTED TOMOGRAPHY IN THE DIAGNOSIS OF A MINERALIZED YOLK SAC IN A BROWN KIWI (APTERYX MANTELLI).

A 12-day-old Brown Kiwi (Apteryx mantelli) was presented with anorexia, torticollis, head-tilt, and coelomic distension. Radiographs showed an ill-defined, fat-opaque, coelomic mass displacing viscera craniodorsally. Curvilinear mineral opacities were superimposed over the ventral aspect of the mass. Computed tomography demonstrated the presence of mineral within the periphery of a fat attenuating mass consistent with a retained yolk sac. A deutectomy (yolk sac excision) was performed. Histopathology of the excised tissue confirmed the diagnosis of a retained yolk sac with multifocal mineralization.

Research Note: A deep learning method segments chicken keel bones from whole-body X-ray images.

Most commercial laying hens suffer from sternum (keel) bone damage including deviations and fractures. X-raying hens, followed by segmenting and assessing the keel bone, is a key to automating the monitoring of keel bone condition. The aim of the current work is to train a deep learning model to segment the keel bone out of whole-body x-ray images. We obtained full-body x-ray images of laying hens (n = 1,051) and manually drew the outline of the keel bone on each image. Using the annotated images, a U-net model was then trained to segment the keel bone. The proposed model was evaluated using 5-fold cross validation. We obtained high segmentation accuracy (Dice coefficients of 0.88-0.90) repeatably over several validation folds. In conclusion, automatic segmentation of the keel bone from full-body x-ray images is possible with good accuracy. Segmentation is a requirement for automated measurements of keel geometry and density, which can subsequently be connected to susceptibility to keel deviations and fractures.

A throughput-optimized array system for multiple-mouse MRI.

MRI is a versatile tool for the systematic assessment of anatomical and functional changes in small-animal models of human disease. Its noninvasive nature makes it an ideal candidate for longitudinal evaluations of disease progression, but relatively long scan times limit the number of observations that can be made in a given interval of time, imposing restrictions on experimental design and potentially compromising statistical power. Methods that reduce the overall time required to scan multiple cohorts of animals in distinct experimental groups are therefore highly desirable. Multiple-mouse MRI, in which several animals are simultaneously scanned in a common MRI system, has been successfully used to improve study throughput. However, to best utilize the next generation of small-animal MRI systems that will be equipped with an increased number of receive channels, a paradigm shift from the simultaneous scanning of as many animals as possible to the scanning of a more manageable number, at a faster rate, must be considered. This work explores the tradeoffs between the number of animals to scan at once and the number of array elements dedicated to each animal, to maximize throughput in systems with 16 receive channels. An array system consisting of 15 receive and five transmit coils allows acceleration by a combination of multi-animal and parallel imaging techniques. The array system was designed and fabricated for use on a 7.0-T/30-cm Bruker Biospec MRI system, and tested for high-throughput imaging performance in phantoms and live mice. Results indicate that up to a nine-fold throughput improvement of a single sequence is possible compared with an unaccelerated single-animal acquisition. True data throughput of a contrast-enhanced anatomical study is estimated to be improved by just over six-fold.

Recovery of chemical estimates by field inhomogeneity neighborhood error detection (REFINED): fat/water separation at 7 tesla.

PURPOSE: To reduce swaps in fat-water separation methods, a particular issue on 7 Tesla (T) small animal scanners due to field inhomogeneity, using image postprocessing innovations that detect and correct errors in the B0 field map. MATERIALS AND METHODS: Fat-water decompositions and B0 field maps were computed for images of mice acquired on a 7T Bruker BioSpec scanner, using a computationally efficient method for solving the Markov Random Field formulation of the multi-point Dixon model. The B0 field maps were processed with a novel hole-filling method, based on edge strength between regions, and a novel k-means method, based on field-map intensities, which were iteratively applied to automatically detect and reinitialize error regions in the B0 field maps. Errors were manually assessed in the B0 field maps and chemical parameter maps both before and after error correction. RESULTS: Partial swaps were found in 6% of images when processed with FLAWLESS. After REFINED correction, only 0.7% of images contained partial swaps, resulting in an 88% decrease in error rate. Complete swaps were not problematic. CONCLUSION: Ex post facto error correction is a viable supplement to a priori techniques for producing globally smooth B0 field maps, without partial swaps. With our processing pipeline, it is possible to process image volumes rapidly, robustly, and almost automatically.

Radioluminescent nanophosphors enable multiplexed small-animal imaging.

We demonstrate the ability to image multiple nanoparticle-based contrast agents simultaneously using a nanophosphor platform excited by either radiopharmaceutical or X-ray irradiation. These radioluminescent nanoparticles emit optical light at unique wavelengths depending on their lanthanide dopant, enabling multiplexed imaging. This study demonstrates the separation of two distinct nanophosphor contrast agents in gelatin phantoms with a recovered phosphor separation correlation of -0.98. The ability to distinguish the two nanophosphors and a Cerenkov component is then demonstrated in a small animal phantom. Combined with the high-resolution potential of low-scattering X-ray excitation, this imaging technique may be a promising method to probe molecular processes in living organisms.

CT-PET weighted image fusion for separately scanned whole body rat.

PURPOSE: The limited resolution and lack of spatial information in positron emission tomography (PET) images require the complementary anatomic information from the computed tomography (CT) and/or magnetic resonance imaging (MRI). Therefore, multimodality image fusion techniques such as PET/CT are critical in mapping the functional images to structural images and thus facilitate the interpretation of PET studies. In our experimental situation, the CT and PET images are acquired in separate scanners at different times and the inherent differences in the imaging protocols produce significant nonrigid changes between the two acquisitions in addition to dissimilar image characteristics. The registration conditions are also poor because CT images have artifacts due to the limitation of current scanning settings, while PET images are very blurry (in transmission-PET) and have vague anatomical structure boundaries (in emission-PET). METHODS: The authors present a new method for whole body small animal multimodal registration. In particular, the authors register whole body rat CT image and PET images using a weighted demons algorithm. The authors use both the transmission-PET and the emission-PET images in the registration process emphasizing particular regions of the moving transmission-PET image using the emission-PET image. After a rigid transformation and a histogram matching between the CT and the transmission-PET images, the authors deformably register the transmission-PET image to the CT image with weights based on the intensity-normalized emission-PET image. For the deformable registration process, the authors develop a weighted demons registration method that can give preferences to particular regions of the input image using a weight image. RESULTS: The authors validate the results with nine rat image sets using the M-Hausdorff distance (M-HD) similarity measure with different outlier-suppression parameters (OSP). In comparison with standard methods such as the regular demons and the normalized mutual information (NMI)-based nonrigid free-form deformation (FFD) registration, the proposed weighted demons registration method shows average M-HD errors: 3.99 ± 1.37 (OSP = 10), 5.04 ± 1.59 (OSP = 20) and 5.92 ± 1.61 (OSP = ∞) with statistical significance (p < 0.0003) respectively, while NMI-based nonrigid FFD has average M-HD errors: 5.74 ± 1.73 (OSP = 10), 7.40 ± 7.84 (OSP = 20) and 9.83 ± 4.13 (OSP = ∞), and the regular demons has average M-HD errors: 6.79 ± 0.83 (OSP = 10), 9.19 ± 2.39 (OSP = 20) and 11.63 ± 3.99 (OSP = ∞), respectively. In addition to M-HD comparisons, the visual comparisons on the faint-edged region between the CT and the aligned PET images also show the encouraging improvements over the other methods. CONCLUSIONS: In the whole body multimodal registration between CT and PET images, the utilization of both the transmission-PET and the emission-PET images in the registration process by emphasizing particular regions of the transmission-PET image using an emission-PET image is effective. This method holds promise for other image fusion applications where multiple (more than two) input images should be registered into a single informative image.

Development of a pixelated GSO gamma camera system with tungsten parallel hole collimator for single photon imaging.

PURPOSE: In small animal imaging using a single photon emitting radionuclide, a high resolution gamma camera is required. Recently, position sensitive photomultiplier tubes (PSPMTs) with high quantum efficiency have been developed. By combining these with nonhygroscopic scintillators with a relatively low light output, a high resolution gamma camera can become useful for low energy gamma photons. Therefore, the authors developed a gamma camera by combining a pixelated Ce-doped Gd(2)SiO(5) (GSO) block with a high quantum efficiency PSPMT. METHODS: GSO was selected for the scintillator, because it is not hygroscopic and does not contain any natural radioactivity. An array of 1.9 mm × 1.9 mm × 7 mm individual GSO crystal elements was constructed. These GSOs were combined with a 0.1-mm thick reflector to form a 22 × 22 matrix and optically coupled to a high quantum efficiency PSPMT (H8500C-100 MOD8). The GSO gamma camera was encased in a tungsten gamma-ray shield with tungsten pixelated parallel hole collimator, and the basic performance was measured for Co-57 gamma photons (122 keV). RESULTS: In a two-dimensional position histogram, all pixels were clearly resolved. The energy resolution was ∼15% FWHM. With the 20-mm thick tungsten pixelated collimator, the spatial resolution was 4.4-mm FWHM 40 mm from the collimator surface, and the sensitivity was ∼0.05%. Phantom and small animal images were successfully obtained with our developed gamma camera. CONCLUSIONS: These results confirmed that the developed pixelated GSO gamma camera has potential as an effective instrument for low energy gamma photon imaging.

Possibilities and limitations for high resolution small animal MRI on a clinical whole-body 3T scanner.

OBJECT: To investigate the potential of a clinical 3 T scanner to perform MRI of small rodents. MATERIALS AND METHODS: Different dedicated small animal coils and several imaging sequences were evaluated to optimize image quality with respect to SNR, contrast and spatial resolution. As an application, optimal grey-white-matter contrast and resolution were investigated for rats. Furthermore, manganese-enhanced MRI was applied in mice with unilateral crush injury of the optic nerve to investigate coil performance on topographic mapping of the visual projection. RESULTS: Differences in SNR and CNR up to factor 3 and more were observed between the investigated coils. The best grey-white matter contrast was achieved with a high resolution 3D T (2)-weighted TSE (SPACE) sequence. Delineation of the retino-tectal projection and detection of defined visual pathway damage on the level of the optic nerve could be achieved by using a T (1)-weighted, 3D gradient echo sequence with isotropic resolution of (0.2 mm)(3). CONCLUSIONS: Experimental studies in small rodents requiring high spatial resolution can be performed by using a clinical 3 T scanner with appropriate dedicated coils.

Estimation of percent body surface area in cats with use of computed tomography.

OBJECTIVE: To establish a baseline reference and create a user-friendly chart for normal body surface area (BSA) in the adult domestic cat similar to the "Rule of Nines" chart. DESIGN: Prospective cadaveric study. SETTING: University Teaching Hospital. ANIMALS: Seven adult domestic short-haired feline cadavers of normal body condition (4-6/9) and body weight. INTERVENTION: Individual whole-body computed tomography (CT) scan was performed on all cats. Images were analyzed with 3-dimensional technology to measure the BSA. A chart was created, illustrating the individual surface area of each body part. MEASUREMENTS AND MAIN RESULTS: Obtained measurements of the cats are different from surface areas of people and dogs. Percentage of total BSA for cats was as follows: head 13%, neck 5%, thorax 20%, abdomen 15%, pelvis and tail 9%, front legs 7% each, and pelvic legs 12% each. CONCLUSION: The distribution of BSA between body parts is different in cats compared to dogs and people. A species-specific chart was created to assure a more accurate estimation of BSA in cats.

Optically detunable, inductively coupled coil for self-gating in small animal magnetic resonance imaging.

An inductively coupled coil concept is presented, which improves the compensation of physiological motion by the self-gating (SG) technique. The animal is positioned in a conventional volume coil encompassing the whole animal. A small, resonant surface coil (SG-coil) is placed on the thorax so that its sensitive region includes the heart. Via inductive coupling the SG-coil amplifies selectively the MR signal of the beating heart. With an optical detuning mechanism, this coupling can be switched off during acquisition of the MR image information, whereas it is active during SG data sampling to provide the physiological information. In vivo experiments on a mouse show an amplification of the SG signal by at least 40%.

A 20-channel receive-only mouse array coil for a 3 T clinical MRI system.

A 20-channel phased-array coil for MRI of mice has been designed, constructed, and validated with bench measurements and high-resolution accelerated imaging. The technical challenges of designing a small, high density array have been overcome using individual small-diameter coil elements arranged on a cylinder in a hexagonal overlapping design with adjacent low impedance preamplifiers to further decouple the array elements. Signal-to-noise ratio (SNR) and noise amplification in accelerated imaging were simulated and quantitatively evaluated in phantoms and in vivo mouse images. Comparison between the 20-channel mouse array and a length-matched quadrature driven small animal birdcage coil showed an SNR increase at the periphery and in the center of the phantom of 3- and 1.3-fold, respectively. Comparison with a shorter but SNR-optimized birdcage coil (aspect ratio 1:1 and only half mouse coverage) showed an SNR gain of twofold at the edge of the phantom and similar SNR in the center. G-factor measurements indicate that the coil is well suited to acquire highly accelerated images.

Multiple-mouse MRI with multiple arrays of receive coils.

Compared to traditional single-animal imaging methods, multiple-mouse MRI has been shown to dramatically improve imaging throughput and reduce the potentially prohibitive cost for instrument access. To date, up to a single radiofrequency coil has been dedicated to each animal being simultaneously scanned, thus limiting the sensitivity, flexibility, and ultimate throughput. The purpose of this study was to investigate the feasibility of multiple-mouse MRI with a phased-array coil dedicated to each animal. A dual-mouse imaging system, consisting of a pair of two-element phased-array coils, was developed and used to achieve acceleration factors greater than the number of animals scanned at once. By simultaneously scanning two mice with a retrospectively gated cardiac cine MRI sequence, a 3-fold acceleration was achieved with signal-to-noise ratio in the heart that is equivalent to that achieved with an unaccelerated scan using a commercial mouse birdcage coil.

Cerenkov luminescence tomography for small-animal imaging.

Cerenkov radiation is a well-known phenomenon in which optical photons are emitted by charged particles moving faster than the speed of light in a medium. We have observed Cerenkov photons emitted from beta-emitting radiotracers such as (18)F-fluorodeoxyglucose using a sensitive CCD camera. Phantom and in vivo mouse imaging experiments have demonstrated that surface measurements of the emitted Cerenkov optical photons could be used to reconstruct the radiotracer activity distribution inside an object by modeling the optical photon propagation with the diffusion equation and reconstructing the optical emission source distribution iteratively with a preconditioned conjugate gradient method.

Utilization of whole body computed tomography in polytrauma patients.

OBJECTIVE: To determine the safety, feasibility, and utility of whole body computed tomography (WBCT) in polytrauma patients. A second objective was to describe the utilization of the VetMouse Trap for sedated WBCT in polytrauma patients. METHODS: A prospective, observational study in a high-volume private practice. Any cat or dog weighing <20 kg that presented to the emergency department following a polytrauma was eligible. Patients were given analgesia and sedation prior to placement in the VetMouse Trap. A WBCT was then performed. RESULTS: A total of 16 patients (8 dogs and 8 cats) met inclusion criteria. All patients presented with blunt trauma; 3 also had evidence of penetrating wounds. Five (31.25%) patients met inclusion criteria for WBCT based on their neurological evaluation. Five (31.5%) were non-ambulatory with suspicion of orthopedic injury, and 37.5% met additional criteria for WBCT. The most common areas of injury were head (43.7%), lungs (25%), and pelvis (25%). Four patients (25%) had evidence of cavitary effusion that was not seen on focused assessment using sonography for trauma (FAST) scan. No patient had any adverse events during the CT. CONCLUSION: This study demonstrated successful WBCT imaging of the sedated small animal polytrauma patient with the VetMouse Trap.

Time-gated perturbation Monte Carlo for whole body functional imaging in small animals.

This paper explores a time-resolved functional imaging method based on Monte Carlo model for whole-body functional imaging of small animals. To improve the spatial resolution and quantitative accuracy of the functional map, a Bayesian hierarchical method with a high resolution spatial prior is applied to guide the optical reconstructions. Simulated data using the proposed approach are employed on an anatomically accurate mouse model where the optical properties range and volume limitations of the diffusion equation model exist. We investigate the performances of using time-gated data type and spatial priors to quantitatively image the functional parameters of multiple organs. Accurate reconstructions of the two main functional parameters of the blood volume and the relative oxygenation are demonstrated by using our method. Moreover, nonlinear optode settings guided by anatomical prior is proved to be critical to imaging small organs such as the heart.