Changes of ultrasonographic pattern of the spleen examined with a high-frequency linear transducer during growth in puppies.

A normal spleen is a homogeneous, finely textured, and hyperechoic organ. The development of high-frequency transducers has enabled the examination of the structural features of the spleen. Thus, the spleen can appear mildly mottled, even in normal dogs, and this could be misinterpreted as an abnormality. The purpose of this prospective, longitudinal, descriptive study was to describe the ultrasonographic pattern of the splenic parenchyma using a high-frequency transducer in puppies. The study included nine, normal, client-owned puppies that were born healthy. Transabdominal ultrasonographic examination was performed from 4 to 60 weeks serially every 4 weeks. Ultrasonographic patterns of the spleen were graded as follows: granular, mild reticulonodular, moderate reticulonodular, and marked reticulonodular pattern. The examinations were performed by one veterinary clinician, and the grades of the ultrasonographic patterns were determined by two veterinary clinicians experienced in ultrasonography, based on consensus. Differences and associations between time and the grade of the splenic parenchyma were determined using the paired t-test and scatter plots. There was a strong quadratic relationship between time and the grade of the splenic parenchyma. It was found that the splenic parenchymal patterns changed with increasing age, with a granular appearance initially at 4 weeks, followed by a reticulonodular pattern with well-defined hypoechoic nodules-most marked between 28 and 36 weeks, after which this pattern decreased until there was a homogeneous granular pattern again at 60 weeks. These findings should not be misinterpreted as being indicative of a disease in normal puppies, particularly those aged between 28 and 36 weeks.

Transverse relaxation of selectively excited metabolites in stroke at 21.1 T.

PURPOSE: This study seeks to evaluate in vivo T2 relaxation times of selectively excited stroke-relevant metabolites via 1 H relaxation-enhanced magnetic resonance spectroscopy (RE-MRS) at 21.1 T (900 MHz). METHODS: A quadrature surface coil was designed and optimized for investigations of rodents at 21.1 T. With voxel localization, a RE-MRS pulse sequence incorporating the excitation of selected metabolites was modified to include a variable echo delay for T2 measurements. A middle cerebral artery occlusion (MCAO) animal model for stroke was examined with spectra taken 24 h post occlusion. Fourteen echo times were acquired, with each measurement completed in less than 2 min. RESULTS: The RE-MRS approach produced high-quality spectra of the selectively excited metabolites in the stroked and contralateral regions. T2 measurements reveal differential results between these regions, with significance achieved for lactic acid. CONCLUSION: Using the RE-MRS technique at ultra-high magnetic field and an optimized quadrature surface coil design, full metabolic T2 quantifications in a localized voxel is now possible in less than 27 min. Magn Reson Med 77:520-528, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Design and implementation of embedded 8-channel receive-only arrays for whole-brain MRI and fMRI of conscious awake marmosets.

PURPOSE: The common marmoset (Callithrix jacchus) is a New World primate of increasing interest to neuroscience and in translational brain research. The present work describes the design and implementation of individualized 8-channel receive-only radiofrequency (RF) coil arrays that provide whole-brain coverage and allow anatomical and functional MRI experiments in conscious, awake marmosets. METHODS: The coil arrays were designed with their elements embedded inside individualized restraint helmets. The size, geometry, and arrangement of the coil elements were optimized to allow whole-brain coverage. Coil-to-coil decoupling was achieved by a combination of geometric decoupling and low input impedance preamplifiers. The performance of the embedded arrays was compared against that of one 8-channel receive-only array built to fit the external surface of the helmets. RESULTS: Three individualized helmets with embedded coil arrays were built for three marmosets. Whole-brain coverage was achieved with high sensitivity extending over the entire cortex. Visual stimulation of conscious awake marmosets elicited robust BOLD fMRI responses in both primary and higher order visual areas of the occipitotemporal cortex. CONCLUSION: The high sensitivity provided by embedded receive-only coil arrays allows both anatomical and functional MRI data to be obtained with high spatial resolution in conscious, awake marmosets. Magn Reson Med 78:387-398, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

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.

Effect of anisotropy and spatial compound imaging on renal cortical echogenicity in dogs.

The echogenicity of the renal cortex is an important parameter to consider in dogs that are suspected to have renal dysfunction. Focal increases in echogenicity have been attributed to neoplasia, infection, calcification, fibrosis, gas, and infarction. Anisotropic backscatter has been described as a source of focally increased renal cortical echogenicity in several species. The source of anisotropy appears to be the medullary rays, which are oriented perpendicular to the renal capsule. Spatial compound imaging (SCI) is an ultrasound setting that uses beam steering to acquire and average several overlapping scans of an object from different view angles, creating a compound image that is updated in real time. The impact of insonation angle and SCI on renal cortical echogenicity was evaluated ex vivo in eight kidneys from four dogs. Significant angle-dependent differences in cortical echogenicity were detected with both microconvex and linear transducers (P < 0.0001). Furthermore, the angle-dependent echogenicity differences persisted when SCI mode was used. Our finding that echogenicity was increased using a perpendicular insonation angle (90°) relative to the tubules, compared to a parallel insonation angle (0°) should assist in the interpretation of ultrasonographic images of the dog kidney.

Ultrasonographic examination of the abdomen of the goat. I. Reticulum, rumen, omasum, abomasum and intestines.

This review article summarizes the ultrasonographic findings of the reticulum, rumen, omasum, abomasum and intestines of goats. Ultrasonographic examination is done on both sides with the goat in a standing position using a linear array or convex transducer with a frequency of 5.0 to 7.5 MHz. The shape, contour and motility of the reticulum are assessed; this organ appears as a crescent-shaped structure with a smooth contour immediately adjacent to the diaphragm. There are 0.8 to 2.1 reticular contractions per minute, which may be mono-, bi- and triphasic. The rumen is examined from the 8th to 12th intercostal spaces (ICSs) and flank on the left, and from the 12th ICS and flank on the right. The ruminal wall appears as a thick echoic line. The dorsal and ventral sacs of the rumen are differentiated based on the longitudinal groove, which forms an echoic notch. Differentiation of the dorsal gas cap, fibre mat and fluid layer is not always straightforward and varies among goats. The omasum is examined from the 6th to 11th ICSs on the right. Only the wall closest to the transducer can be imaged and it appears as a crescent-shaped echoic line medial to the liver. The omasal folds and the wall furthest from the transducer cannot be seen. In about two thirds of goats, active omasal motility is apparent as a transient reduction in size of several centimetres, followed by relaxation and return to its original size. There is an average of 1.1 contractions per minute. The abomasum is examined from the ventral midline and the left and right paramedian regions and can always be seen from the ventral midline. In all but a few goats the abomasum is also visible from the left and right paramedian areas. It appears as a heterogeneous, moderately echoic structure with echogenic stippling. The abomasal folds appear as prominent echoic bands in about two thirds of all goats. The small and large intestines are examined on the right from the 8th to the 12th ICSs. Loops of jejunum and ileum are seen mainly in cross-section and have a strong motility. The intestinal content is usually homogeneous and echoic and the diameter of the intestinal loops varies from 0.8 and 2.7 cm. The spiral colon and in many cases also the caecum can be imaged. The former is recognized by its garland-like appearance brought about by the centripetal and centrifugal coils of the intestine. In the spiral colon and the caecum, only the wall closest to the transducer can be imaged because of intraluminal gas. The wall appears as a thick echoic and slightly undulating line 5.6 to 8.0 cm in length. Ultrasonography is an imaging technique that is very well suited for the examination of the gastrointestinal tract of goats.

Quantitative assessment of crystal material and size on the performance of rotating dual head small animal PET scanners using Monte Carlo modeling.

In this work, among different proposed designs we have studied dual-head coincidence detectors (DHC) with pixelated crystals in order to optimize the design of detector systems of small animal PET scanners. Monte Carlo simulations and different detector components and materials, under different imaging conditions and geant 4 application for tomographic emission (GATE) were used for all simulations. Crystal length and inter material space on system performance were studied modeling several pixel sizes, ranging from 0.5 x 0.5mm² to 3.0 x 3.0mm² by increment of 0.5mm and using epoxy intermaterial with pitch of 0.1, 0.2 and 0.3mm. Three types of scintillator crystals:bismuth germinate orthosilicate, cerium-doped lutetium orthosilicate and gadolinium orthosilicate were simulated with thicknesses of 10mm and 15 mm. For all measurements a point source with the activity of 1MBq was placed at the center of field of view. The above simulation revealed that by increasing pixel size and crystal length in scintillator material of a pixelated array, sensitivity can be raised from 1% to 7%. However, spatial resolution becomes worse when pixel size increases from 0.6mm to 2.6mm. In addition, photons mispositioned events decrease from 76%to 45%. Crystal length decrease, significantly reduces the percentage of mispositioned events from 89% to 59%. Moreover increase in crystal length from 10mm to 15 mm changes sensitivity from 2% to 6% and spatial resolution from 0.6mm to 3.5mm. In conclusion, it was shown that pixel size 2mm with 10mm crystal thickness can provide the best dimensions in order to optimize system performance. These results confirmed the value of GATE Monte Carlo code, as being a useful tool for optimizing nuclear medicine imaging systems performance, for small animal PET studies.

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.

In vitro activity of human chorionic gonadotropin (hCG) on myometrium contractility.

LH/hCG receptor has been found in extragonadal tissues in human and animals. The myometrium presents such receptors but their functional role is still not clear. Aim of our study was to test the activity of human chorionic gonadotropin (hCG) on bovine uterine contractility. Uterine strips from cows both during follicular and luteal phases were mounted in an organ bath and then exposed to increased doses of hCG. The amplitude of the myometrium contractions were significantly decreased in the follicular and luteal phase but the frequency was not affected. These findings prove a relaxing effect of hCG in the bovine uterus, as already shown in the sow and human, and its possible functional role in modulating uterine contractility.

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.

Design and evaluation of a low-cost respiratory monitoring device for use with anaesthetized animals.

This report describes a simple, non-invasive electronic device that employs a compact accelerometer integrated circuit to transduce movements in the chest wall of an anaesthetized animal into an analogue signal that can be used to calculate the rate and relative depth of respiration. The device requires amplification by signal processing hardware/software which are common to most experimental laboratories. We assessed the sensitivity of the device by its ability to detect changes in respiratory patterns produced by modulating the depth of anaesthesia in isoflurane-anaesthetized Wistar rats. It is widely accepted that many anaesthetic agents affect respiratory patterns, especially respiratory rate (RR), which is often used as an important index of anaesthetic depth. Respiratory parameters obtained with the device were compared with concurrently recorded electroencephalographic and cardiac measures. Different concentrations of anaesthetic agent produced four depths of anaesthesia, identified using established electroencephalographic criteria. The accelerometer was attached easily and securely to the location of maximal chest wall movement and produced a strong respiratory signal that was detectable in all four anaesthetic stages. Deepening the anaesthesia produced a gradual decrease in RR, a decrease in dominant spectral frequency of the electroencephalogram (EEG) but no change in the heart rate. There was a significant correlation between RR and the dominant spectral frequency of the EEG, indicating that one useful application of the monitor could be to identify anaesthetic stages. The results demonstrate that respiratory parameters can be recorded using a simply constructed, low-cost device and suggest an application in the monitoring of anaesthetic depth.

Design of a superconducting volume coil for magnetic resonance microscopy of the mouse brain.

We present the design process of a superconducting volume coil for magnetic resonance microscopy of the mouse brain at 9.4T. The yttrium barium copper oxide coil has been designed through an iterative process of three-dimensional finite-element simulations and validation against room temperature copper coils. Compared to previous designs, the Helmholtz pair provides substantially higher B(1) homogeneity over an extended volume of interest sufficiently large to image biologically relevant specimens. A custom-built cryogenic cooling system maintains the superconducting probe at 60+/-0.1K. Specimen loading and probe retuning can be carried out interactively with the coil at operating temperature, enabling much higher through-put. The operation of the probe is a routine, consistent procedure. Signal-to-noise ratio in a mouse brain increased by a factor ranging from 1.1 to 2.9 as compared to a room-temperature solenoid coil optimized for mouse brain microscopy. We demonstrate images encoded at 10x10x20mum for an entire mouse brain specimen with signal-to-noise ratio of 18 and a total acquisition time of 16.5h, revealing neuroanatomy unseen at lower resolution. Phantom measurements show an effective spatial resolution better than 20mum.

Effects of head-down positioning on regional central nervous system perfusion in isoflurane-anesthetized horses.

OBJECTIVE: To test the hypothesis that head-down positioning in anesthetized horses increases intracranial pressure (ICP) and decreases cerebral and spinal cord blood flows. ANIMALS: 6 adult horses. PROCEDURES: For each horse, anesthesia was induced with ketamine hydrochloride and xylazine hydrochloride and maintained with 1.57% isoflurane in oxygen. Once in right lateral recumbency, horses were ventilated to maintain normocapnia. An ICP transducer was placed in the subarachnoid space, and catheters were placed in the left cardiac ventricle and in multiple vessels. Blood flow measurements were made by use of a fluorescent microsphere technique while each horse was in horizontal and head-down positions. Inferential statistical analyses were performed via repeated-measures ANOVA and Dunn-Sidak comparisons. RESULTS: Because 1 horse developed extreme hypotension, data from 5 horses were analyzed. During head-down positioning, mean +/- SEM ICP increased to 55+/-2 mm Hg, compared with 31+/-2 mm Hg during horizontal positioning; cerebral perfusion pressure was unchanged. Compared with findings during horizontal positioning, blood flow to the cerebrum, cerebellum, and cranial portion of the brainstem decreased significantly by approximately 20% during head-down positioning; blood flows within the pons and medulla were mildly but not significantly decreased. Spinal cord blood flow was low (9 mL/min/100 g of tissue) and unaffected by position. CONCLUSIONS AND CLINICAL RELEVANCE: Head-down positioning increased heart-brain hydrostatic gradients in isoflurane-anesthetized horses, thereby decreasing cerebral blood flow and, to a greater extent, increasing ICP. During anesthesia, CNS regions with low blood flows in horses may be predisposed to ischemic injury induced by high ICP.

A chronic in situ coil system adapted for intracerebral stimulation during MRI in rats.

BACKGROUND: We describe the fabrication and performance of a chronic in situ coil system designed to allow focal brain stimulation in rats while acquiring functional MRI data. NEW METHOD: An implantable receive-only surface radiofrequency coil (iCoil) was designed to be fitted subcutaneously, directly onto to the rat skull surface during the intracerebral cannulation procedure. The coil is fixed in place using acrylic dental cement anchored to four screws threaded into the skull. To demonstrate the use of this coil system in situ, whole-brain functional MRI scans were acquired during various stimuli, including intracranial microinfusions of bicuculline and morphine in the prefrontal cortex and ventral tegmental area, respectively. RESULTS/COMPARISON TO OTHER METHODS: SNR performance of the iCoil was superior to three commercially-available coils, in some instances by a factor of two. Widespread BOLD activation was observed in response to bicuculline and morphine microinfusions. CONCLUSION: A new approach was demonstrated for high-SNR MR imaging of the brain in rats with intracranial implants using an implantable surface coil. This approach enables mapping the functional response to highly targeted stimuli such as intracranial microinfusions.

Simultaneous Multiparametric PET/MRI with Silicon Photomultiplier PET and Ultra-High-Field MRI for Small-Animal Imaging.

UNLABELLED: Visualization of biologic processes at molecular and cellular levels has revolutionized the understanding and treatment of human diseases. However, no single biomedical imaging modality provides complete information, resulting in the emergence of multimodal approaches. Combining state-of-the-art PET and MRI technologies without loss of system performance and overall image quality can provide opportunities for new scientific and clinical innovations. Here, we present a multiparametric PET/MR imager based on a small-animal dedicated, high-performance, silicon photomultiplier (SiPM) PET system and a 7-T MR scanner. METHODS: A SiPM-based PET insert that has the peak sensitivity of 3.4% and center volumetric resolution of 1.92/0.53 mm(3) (filtered backprojection/ordered-subset expectation maximization) was developed. The SiPM PET insert was placed between the mouse body transceiver coil and gradient coil of a 7-T small-animal MRI scanner for simultaneous PET/MRI. Mutual interference between the MRI and SiPM PET systems was evaluated using various MR pulse sequences. A cylindric corn oil phantom was scanned to assess the effects of the SiPM PET on the MR image acquisition. To assess the influence of MRI on the PET imaging functions, several PET performance indicators including scintillation pulse shape, flood image quality, energy spectrum, counting rate, and phantom image quality were evaluated with and without the application of MR pulse sequences. Simultaneous mouse PET/MRI studies were also performed to demonstrate the potential and usefulness of the multiparametric PET/MRI in preclinical applications. RESULTS: Excellent performance and stability of the PET system were demonstrated, and the PET/MRI combination did not result in significant image quality degradation of either modality. Finally, simultaneous PET/MRI studies in mice demonstrated the feasibility of the developed system for evaluating the biochemical and cellular changes in a brain tumor model and facilitating the development of new multimodal imaging probes. CONCLUSION: We developed a multiparametric imager with high physical performance and good system stability and demonstrated its feasibility for small-animal experiments, suggesting its usefulness for investigating in vivo molecular interactions of metabolites, and cross-validation studies of both PET and MRI.

Whole-body systemic transcapillary filtration rates, coefficients, and isogravimetric capillary pressures in Bufo marinus and Rana catesbeiana.

Whole-body and organ-level transcapillary filtration rates and coefficients are virtually unexamined in ectothermal vertebrates. These filtration rates appear to be greater than in mammals when plasma volume shifts and lymphatic function are analyzed. Gravimetric techniques monitoring whole-body mass changes were used to estimate net systemic filtration in Bufo marinus and Rana catesbeiana while perfusing with low-protein Ringer's and manipulating venous pressure. Capillary pressures were estimated from arterial and venous pressures after measuring the venous to arterial resistance ratio of 0.23. The capillary filtration coefficient (CFC) for the two species was 25.2+/-1.47 mL min-1 kg-1 kPa-1. Isogravimetric capillary pressure (Pci), the pressure at which net fluid is neither filtered nor reabsorbed, was 1.12+/-0.054 kPa and was confirmed by an independent method. None of these variables showed a significant interspecific difference. The anuran CFC and Pci are significantly higher than those found using the same method on rats (7.6+/-2.04 mL min-1 kg-1 kPa-1 and 0.3+/-0.37 kPa, respectively) and those commonly reported in mammals. Despite the high CFC, the high Pci predicts that little net filtration will occur at resting in vivo capillary pressures.

Efficacy of linear and convex transducers for ultrasound-guided transvaginal follicle aspiration.

A new device was developed to hold linear transducers for transvaginal follicle aspiration. Efficacy of follicle aspiration was compared using a linear 6 MHz and a convex 5 MHz transducer. Fifty-five cows were submitted to follicle aspiration at random days of the estrous cycle. Aspirations were conducted with linear (n=28) and convex (n=38) transducers with 18 G needles at a negative pressure corresponding to 13 ml H(2)O/min. A greater number of follicles were aspirated using convex than to linear probe (12.4 versus 7.8, respectively, P<0.05). Mean number of oocytes and recovery rates were similar for convex (5.4 and 48.6%) and linear (4.6 and 59.3%) transducers. Limited space between the linear transducer and needle guide restricted access to some portions of the ovary, reducing the number of follicles aspirated using a linear transducer. The newly developed adaptor allowed greater stability, holding the ovaries firmly against the linear transducer. This diminished mobility permitted a similar number of oocytes to be recovered with both transducers. In conclusion, this new adaptor provided a low cost alternative for routine follicle aspiration and oocyte recovery in cattle.

Motility of the large intestine and flow of digesta in pigs.

The motor function of the large intestine of pigs is incompletely understood. Here the ileo-caecal-colonic motility is investigated by means of chronically implanted extraluminal strain gauge transducers and simultaneous videofluoroscopy in six pigs. Motility parameters were evaluated by computer and manually. The dominant feature of the ileal motility were aborally propagating giant contractions (velocity: 3.9 (0.7) cm sec(-1)) occurring at intervals of 7-12 minutes. They pushed the ileal digesta into the caecum. Despite a fed-state, migrating motor complexes occurred at intervals of 131.5 (8.1) minutes consisting of repetitive peristaltic waves. The motility of the caecum showed clustered contractions representing haustral movements. Transfer of caecal digesta and gas into the colon was caused by peristaltic contractions. The motility of the proximal colon was characterised by long peristaltic waves resulting in a rapid aboral transport of gas and a slow aboral flow of digesta. The propagation velocities along the centripetal and centrifugal loops of the colonic coil were 2.8 (0.6) and 5.7 (0.8) cm sec(-1), respectively. About half of the colonic waves were coordinated with the ileal giant contractions and the caecal peristaltic waves. The contraction parameters showed pronounced differences between the ileum and large intestine. The contraction rise time of the caecal and colonic contractions was about twice that of the ileal contractions (5.1 (0.2) and 4.4 (0.6) seconds versus 2.2 (0.1) seconds). Consequently, the maximal frequencies of the caecal and colonic contractions were about half compared with the ileal contractions (5.3 (0.4) and 6.1 (0.1) contractions min(-1) versus 11.8 (0.3) contractions min(-1)). Results show that the contractile patterns and motor functions of the individual intestinal segments differ markedly.

Effects of inflammatory periodontal disease ('broken mouth') on the mobility of the sheep incisor.

Loads directed linguolabially and between 0.01 N and 0.2 N were applied to a mandibular central incisor in each of 12 four-year-old ewes with evidence of inflammatory periodontal disease ('broken mouth'). For every incisor, tooth position was monitored continuously with an ultrasonic displacement transducer. Each load chosen was suddenly applied and then maintained for five minutes, producing a biphasic, viscoelastic-like response (a phase of rapid displacement being followed by a more gradual phase of creep). A similar biphasic recovery response was seen on suddenly removing the load. Comparing the findings with those obtained in a previous study for incisors in healthy dentitions, there was a considerable increase in mobility with inflammatory periodontal disease. Surprisingly, however, the patterns of the responses did not differ. The reason for the change in the amount of mobility may be related simply to the quantity of the tooth supporting tissues which is lost, although there is some evidence that qualitative changes occurring in these tissues may also be important.

Evaluation of pulse oximetry in anaesthetised foals using multiple combinations of transducer type and transducer attachment site.

A commercially available pulse oximeter was evaluated in anaesthetised foals to determine its accuracy for estimating arterial haemoglobin saturation (SaO2). Five different transducer/transducer attachment site (TTAS) combinations were evaluated; 1-3) a fingertip transmission transducer attached to the foal's ear, lip and tongue, 4) an adhesive transmission transducer positioned on the foal's ear and 5) a forehead reflectance transducer placed on the ventral aspect of the foal's tail-base. Eight normal, Quarter Horse foals (age 5-10 days) were studied while under general anaesthesia. Alterations in arterial carbon dioxide tension (PaCO2) were produced by changing the level of ventilation. At each level of ventilation, alterations of arterial haemoglobin saturation (SaO2) were produced by varying the inspired fraction of oxygen (FIO2). At each level of ventilation and each level of FIO2, arterial blood samples were obtained for blood gas analysis while pulse oximeter readings were recorded simultaneously for each TTAS combination. Arterial blood oxygen saturation (SaO2) was calculated from arterial blood gas values and the equine blood oxygen dissociation curve. Pulse oximeter readings from each TTAS combination were compared with SaO2 values with linear regression analyses. Bias and precision values were determined and the sensitivity and specificity of each TTAS combination for detecting desaturation (SaO2 < 90%) were determined. Linear regression analyses indicated significant (P < 0.05) linear correlation between oxygen saturation determined by pulse oximeter (SpO2) and SaO2 for each of the 5 TTAS combinations. The combinations TTAS-1, TTAS-3 and TTAS-4 tended slightly to underestimate SaO2 at high SaO2 ranges, but overestimated SaO2 at low ranges of SaO2. Combination TTAS-2 overestimated SaO2 over all ranges of SaO2. Combination TTAS-5 consistently underestimated SaO2 at all ranges of SaO2. In general, accuracy and precision of each TTAS combination decreased at lower SaO2 ranges. All TTAS combinations, except TTAS-2 and TTAS-4, had good sensitivity for detecting SaO2 less than 90%. All TTAS combinations except TTAS-5 demonstrated good specificity. We concluded that pulse oximetry appears to be a valuable method for assessing SaO2 and detecting desaturation in anaesthetised foals. Clinicians should be aware that the type of transducer used and the anatomical site to which it is attached can have marked effects on the accuracy of pulse oximetry; and that different TTAS combinations may behave differently over various ranges of SaO2.