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1.
Radiographic diagnosis of equine bone disease using digital radiography is prevalent in veterinary practice. However, the diagnostic quality of digital vs. conventional radiography has not been compared systematically. We hypothesized that digital radiography would be superior to film-screen radiography for detection of subtle lesions of the equine third metacarpal bone. Twenty-four third metacarpal bones were collected from horses euthanized for reasons other than orthopedic disease. Bones were dissected free of soft tissue and computed tomography was performed to ensure that no osseous abnormalities were present. Subtle osseous lesions were produced in the dorsal cortex of the third metacarpal bones, and the bones were radiographed in a soft tissue phantom using indirect digital and conventional radiography at standard exposures. Digital radiographs were printed onto film. Three Diplomates of the American College of Veterinary Radiology evaluated the radiographs for the presence or absence of a lesion. Receiver operator characteristic curves were constructed, and the area under these curves were compared to assess the ability of the digital and film-screen radiographic systems to detect lesions. The area under the ROC curves for film-screen and digital radiography were 0.87 and 0.90, respectively ( P =0.59). We concluded that the digital radiographic system was comparable to the film-screen system for detection of subtle lesions of the equine third metacarpal bone.  相似文献   

2.
Major advantages of computed radiography are the potential reduction of dose and the possibility of postprocessing. In our study, we compared conventional radiographs to digital radiographs of the equine stifle by subjective evaluation of diagnostic quality when using a decreasing photon flux (mAs). Twelve equine stifle joints from horses of different weight and size were examined. Conventional and digital radiographs were performed identically in a caudocranial projection with the tube angled 15 degrees. A series of four radiographs was performed in each technique with an increasing photon flux starting with 2.5 mAs and going up to 5, 10, and 20 mAs. All radiographs were evaluated subjectively in a blinded fashion by seven readers in terms of contrast, bone structure, and diagnostic value and were graded using a 1-5 scale. Results from conventional and digitized radiographs were compared, and differences between the individual observers were analyzed statistically. Contrast, bone structure, and diagnostic value from digital images were rated significantly better than from conventional images (p < .001). For both techniques, a decrease in ranking was found with a decrease of photon flux. There was only slight interobserver variability. A dose reduction up to a factor of 4 compared to a 100 speed film-screen system seems to be possible without loss of information. Weight and size of the horse are not major influences.  相似文献   

3.
This study tested whether the supplement (Aquacid), high in calcium and other minerals, can alter markers of bone metabolism and mineralization of the equine third metacarpus bone. Radiographs were taken of the left third metacarpus of 14 yearlings. Radiographic bone aluminum equivalence (RBAE) of each cortex was calculated to estimate mineral content. Blood samples were also taken at this time. Horses were ranked according to RBAE and gender, were pair-matched, and randomly assigned to two treatment groups. Each group was provided one of two mineral supplements in addition to their normal diet. The treated group (Aq) received 75 g Aquacid/horse/d, which provided an additional 15 g of calcium. The control group (Co) received 39.5 g of limestone to provide similar amounts of calcium. The study lasted for 112 days, with blood being taken every 28 days. At day 56 and 112, additional radiographs was taken to track changes in RBAE. Blood was analyzed for osteocalcin (a bone formation marker) and serum C-telopeptide crosslaps of type I collagen (a bone resorption marker) to detect alterations in bone metabolism. Using day 0 values as a covariate for bone markers, there was a trend (P = .07) for osteocalcin concentrations to be greater in Aq horses than in Co. Likewise, C-telopeptide crosslaps of type I collagen concentrations were greater (P < .0001) in Aq horses than in Co. There were minimal differences in RBAE values. These findings suggest Aquacid, while not altering bone mass, increases bone turnover and may aid in repairing damaged bone and preventing injuries.  相似文献   

4.
Objective: To determine the effect of core decompression surgery and bone mineral density (BMD) on the mechanical properties of equine navicular bones. Study Design: Experimental, in vitro study. Sample Population: Fore limb navicular bones (n=36 pairs) from sound 2–5‐year‐old horses with no radiographic abnormalities of the distal aspect of the forelimbs. Methods: Navicular BMD was measured using dual energy X‐ray absorptiometry. One randomly assigned navicular bone from each pair served as control. The contralateral test specimen was allocated to 1 of 6 treatment groups defined by drill bit size (3.2 versus 2.5 mm diameter) and by the number of drill channels (1, 2, or 3) created in the proximal border of the bone. Bones were then tested until failure in 3‐point bending. Data were statistically analyzed using ANOVA and regression analysis. Results: There were significant (P<.001) positive correlations between BMD and biomechanical data. A significant (P<.001) reduction in breaking strength was noted between intact and drilled bone pairs; however, the diameter and number of decompression channels did not significantly (P>.05) influence the extent of the reduction in mechanical strength. Conclusion: In vitro core decompression significantly decreases the breaking strength of the equine navicular bone.  相似文献   

5.
Variations in hoof conformation may alter stress distribution, thus predisposing horses to pathologies and lameness; however, experimental studies are scarce. Our objective was to investigate the correlation between midstance hoof kinetics at the walk and hoof conformation in horses. Nine clinically sound, unshod horses were walked over a pressure plate, and force (F), contact area (CA), contact pressure (CP), and peak contact pressure (PCP) were recorded at the dorsal, palmar, medial, and lateral regions, as well as for the whole hoof. By using digital radiography and digital pictures, 55 variables of internal and external hoof shape and dimensions of the hoof were measured. Correlations between kinetic and anatomical measurements were investigated using Pearson correlation coefficient. P-values ≤ 0.05 and r values ≥ 0.5 were considered. Several anatomical variables showed correlations with biomechanical variables. Toe angle was negatively correlated with CA (r = –0.72). Several heel height measurements were negatively correlated with dorsal F (–0.59 ≤ r ≤ –0.50), suggesting a trend. Measurements of the dorsal hoof wall thickness and length/width of the distal phalanx showed correlations with F and CP (0.5 ≤ r ≤ 0.71). Our study was focused on midstance biomechanics and at the walk; further investigation on other gaits and parts of the stance phases is warranted. Patterns of correlations between internal structural arrangement and hoof kinetic parameters encourage more research and should be considered by veterinarian and farriers for routine and therapeutic trimming/shoeing.  相似文献   

6.
Subchondral cyst‐like lesions (SCLs) of horses have been found in various locations, but SCLs of the talus have been reported rarely. In this report, we describe 4 horses affected with a SCL of the talus. Each SCL was identified using digital radiography, and each horse was treated by intralesional injection of triamcinolone acetonide. Case details, history, findings during clinical and radiographic examination, treatment, and outcome of each horse are discussed.  相似文献   

7.
Radiography is part of evaluating horses with poor performance and pelvic limb lameness; however, the radiographic appearance of the sacroiliac region is poorly described. The goal of the present study was to describe the use of a simple technique to obtain radiographs of the sacroiliac region in the anesthetized horse and to describe the radiographic appearance of this region. Seventy-nine horses underwent radiography of the pelvis under general anesthesia in dorsal recumbency. During a 5s exposure time the horse was actively ventilated to blur the abdominal viscera, which allowed assessment of individual bone structures in 77 horses. A large variation in the shape of the sacral wings, their articulation with the transverse processes of L6, and the relation of the sacrum to the ilium were observed. Females had significantly narrower width of the sacral wings. Broad sacral wings and bony proliferations at the caudal aspect were commonly observed features and their size was highly correlated with gender. In males, caudal osteophytes were significantly larger than in females. Five horses had transitional or hemitransitional vertebrae. Radiography with the ventilation-induced blurring technique is a simple approach that results in diagnostic quality radiographs and delineation of the highly variable bone structures of the sacroiliac region.  相似文献   

8.
Damage to the subchondral bone has been associated with a number of orthopaedic diseases. Diagnostic imaging is, therefore, critical in identifying disease and damage of the subchondral bone, not only for the diagnosis of joint and subchondral bone disease causing lameness, but also for identifying early/pre-symptomatic damage. The aims of this Critically Appraised Topic (CAT) were to assess the published evidence for the use of advanced imaging techniques (magnetic resonance imaging [MRI] and computed tomography [CT]) in the diagnosis of subchondral bone disease in the distal limb joints (metacarpo/metatarsophalangeal and interphalangeal joints) of the adult horse, and to compare the diagnostic value of these techniques with radiography. In the studies reviewed in this CAT, advanced imaging modalities (MRI and CT) were superior to routine radiography for the diagnosis of subchondral bone injury of the distal limb joints. In a small percentage of horses, post-MRI reevaluation of the initial radiographs or acquiring further lesion-orientated radiographs allowed the identification of the subchondral bone injury. Extended radiographic examinations, including non-standard views, might increase the sensitivity of radiography to detect subchondral bone injuries, however, currently CT and MRI may be considered the “gold standard” imaging modalities. More studies comparing the identification of subchondral bone lesions on imaging and by histopathological/gross examination would be useful to assess more precisely the sensitivity and specificity of the different modalities.  相似文献   

9.
Hoof balance radiographs are commonly used as the basis for corrective farriery decision‐making in horses, however there are limited published data quantifying effects of the stance of the horse or the horizontal radiographic beam angle. In this analytical study, the influence of variation of the horse's stance in the craniocaudal and lateromodial plane on hoof balance measurements as well as the influence of variation of the horizontal radiographic beam angle on dorsopalmar hoof balance measurements was examined. Distal left thoracic limb lateromedial radiographs were acquired using a standardized protocol while varying the craniocaudal stance of five horses, each selected to be sound and conformationally normal. Dorsopalmar foot radiographs were acquired while varying the lateromedial stance; and variable angle horizontal beam dorsopalmar foot radiographs were acquired while keeping the limb position constant. Analyses of measurements demonstrated that hoof pastern angle had a linear relationship (R2 = 0.89, P < 0.001) with craniocaudal stance of the horse. The relationship of joint angle and stance was greater for the distal interphalangeal joint angle (R2 = 0.89, P < 0.001) than the proximal interphalangeal joint angle (R2 = 0.65, P = 0.001). The distal phalanx angle did not change with craniocaudal stance variation. The proximal interphalangeal joint width, distal interphalangeal joint width, or distal phalanx height did not change with lateromedial stance variation, nor within a 15 degree dorsolateral to caudomedial and dorsomedial to caudolateral variation from the dorsopalmar axis. Findings indicated that positioning of the thoracic limb needs to be considered during radiographic interpretation and decision‐making for corrective farriery.  相似文献   

10.
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11.
Objective: To (1) determine prevalence of radiographically detectable meniscal mineralization in domestic cats and (2) to evaluate the association between meniscal mineralization and degenerative joint disease (DJD). Study Design: Prospective study. Animals: Client‐owned cats (n=100) and 30 feline cadavers. Methods: Randomly selected client‐owned cats were used to determine the prevalence of meniscal mineralization. Stifles from feline cadavers were used to evaluate the relationship between meniscal mineralization (using high‐resolution X‐ray), radiographic DJD, and cartilage damage. Menisci were evaluated histologically. Results: Forty‐six percent of the client‐owned cats had meniscal mineralization detected in 1 or both stifles. Pain scores were not significantly different between stifles with meniscal mineralization and those with no radiographic pathology (P=.38). Thirty‐four of 57 cadaver stifles had meniscal mineralization, which was always located in the cranial horn of the medial meniscus. Percentage mineralization of the menisci was significantly correlated with the cartilage damage score of the medial femoral (r2=0.6; P<.0001) and tibial (r2=0.5; P<.0001) condyles as well as with the total joint cartilage damage (r2=0.36; P<.0001) score and DJD score (r2=0.8; P<.0001). Conclusion: Meniscal mineralization is a common condition in domestic cats and seems to indicate medial compartment DJD. Clinical Relevance: Clinical significance of meniscal mineralization is uncertain. Further work is needed to determine if the meniscal mineralization is a cause, or a consequence of joint degeneration.  相似文献   

12.
Reasons for performing study: There are no data concerning the accuracy of conventional and computed or digital radiography for evaluation of the equine foot. Objectives: To compare conventional film‐screen and computed radiography with magnetic resonance imaging (MRI) for detection of distal border fragments of the navicular bone; and to establish which type of fragment was more likely to be detected radiologically. Methods: Horses were included if forelimb lameness was localised to the foot and both radiography and high‐field MR images had been acquired. Horses were divided into 2 groups based on acquisition of conventional (Group A) or computed (Group B) radiographs. The presence of distal border fragments was recorded. From MR images, distal border fragments were graded based on their size and changes in signal intensity in the adjacent navicular bone. Sensitivity and specificity of conventional and computed radiography for detection of fragments were calculated using MRI as the gold standard. A Chi‐squared test was used to test for associations between specific radiological and MRI findings in the distal border of the navicular bone. Results: In Group A 46 and 18 fragments were identified on MR and radiographic images, respectively; in Group B 45 and 17 fragments were seen. There was no significant difference between computed and conventional radiography. Grades 4 and 5 fragments or large‐sized fragments were identified most frequently; low‐grade fragments were unlikely to be observed. There was a significant correlation between radiological and MRI abnormalities of the distal border of the navicular bone. Conclusions: Conventional and computed radiography had similar, rather low sensitivity for identification of distal border fragments of the navicular bone, but specificity was high. Large‐sized and high‐grade fragments were most likely to be identified radiologically. Potential relevance: Fragments observed radiologically are likely to be associated with other pathological abnormalities of the distal border of the navicular bone.  相似文献   

13.
A better understanding of imaging characteristics of equine stifle osteoarthritis (OA) may allow earlier detection and improve prognosis. Objectives of this ex vivo, prospective, methods comparison study were to (1) describe the location and severity of naturally acquired OA lesions in the equine stifle using ultrasound (US), radiography (XR), computed tomography (CT), and macroscopic evaluation (ME); (2) compare the diagnostic performance of each imaging modality with ME; and (3) describe subchondral bone mineral density (BMD) in equine stifle joints with OA using CT. Radiographic, CT, and US evaluations were performed on 23 equine cadaver stifles and compared with ME. Significant associations were found between osteophyte global scores for all imaging modalities (CT, P ? 0.0001; XR, P = 0.005; US, P = 0.04) vs. ME osteophyte global scores. Osteophytes were detected most frequently in the medial femorotibial (MFT) joint. A specific pattern of osteophytes was observed, with a long ridge of new bone at the insertion of the MFT joint capsule cranially on the medial femoral condyle. A novel caudo‐10°proximo‐5°lateral‐cranio‐disto‐medial oblique radiographic projection was helpful for detection of intercondylar osteophytes. Multiplanar CT reformatted images were helpful for characterizing all osteophytes. Osteophyte grades at most sites did not differ among modalities. Low sensitivity/specificity for subchondral bone sclerosis and flattening of femoral condyles suggested that these signs may not be reliable radiographic and CT indicators of equine stifle OA. Equine stifle OA was associated with a decrease in BMD and specific sites of focal subchondral bone resorption/cyst formation were found in some specimens.  相似文献   

14.
In mammals, the release from growth‐inhibiting conditions results in catch‐up growth. To investigate animal evidence for whether prenatal dexamethasone (DEX) treatment leads to the development of growth restriction especially reduced mineralization of skeleton, and release from it leads to the phenomenon of catch‐up, piglets were prenatally exposed to DEX (3.0 mg/sow per day?2) during the last 24 days of prenatal life and tested further in two different ways: discontinued at birth and continued administration of DEX (0.5 mg/kg day?2) to piglets through 30 days of neonatal life. Using dual energy X‐ray absorptiometry methods, bone mineral density (BMD) and bone mineral content (BMC) were measured. The three‐point bending test was applied to determine the mechanical properties of the bones. Furthermore, geometric properties of the bones were assessed. Serum concentration of osteocalcin (OC) was determined. Histomorphological analysis of the ribs was also performed. The consequences of neonate DEX treatment and in utero DEX exposure were reflected in a dramatic decrease of BMD, BMC and blood serum OC concentration and geometric parameters of piglets’ bones. Prenatal action of DEX during the last 24 days of pregnancy resulted in continued neonatal modification of bone tissues, thus diminishing bone quality, and negatively influenced structural development and mechanical properties, finally increasing the risk of fractures of ribs and limb bones. Prenatal DEX treatment limited to the last 24 days of foetal life did not reduce the term birth weight and the growth of suckling piglets followed up to 30 days of neonatal life, and catch‐up in bone mineralization did not occur.  相似文献   

15.
Cool-season grass mixtures are rarely evaluated for preference, yield, and persistence under horse grazing. The objectives of this research were to evaluate horse preference, forage yield, and persistence of cool-season grass mixtures under horse grazing. Eight commercially marketed and four experimental perennial cool-season grass mixtures were planted in 2009 in a randomized complete block with five replicates and grazed by four adult horses during 2010, 2011, and 2012. All mixtures contained four to six cool-season perennial grass species. Specie density measurements were taken in each spring and fall, and yield was mechanically measured before each grazing period. After grazing, preference was determined by visually assessing percentage of forage removal on a scale of 0 (no grazing) to 100 (100% of vegetation removed). Data were analyzed using a mixed-model analysis of variance and liner regression. Horses preferred mixtures containing tall fescue, perennial ryegrass, Kentucky bluegrass, and timothy (P < .001). Horses had less preference for mixtures containing ≥30% orchardgrass (P < .001). Mixtures had similar (P = .11) forage yields that ranged from 6,100 to 7,082 kg ha−1. After 2 years of grazing, orchardgrass and tall fescue increased; Kentucky bluegrass remained stable; and festulolium, meadow fescue, and perennial ryegrass had the greatest rate of decline in mixtures. Orchardgrass became the dominate species, regardless of initial percentage in the mixture. Mixtures containing tall fescue, perennial ryegrass, Kentucky bluegrass, and timothy should be planted in midwestern US horse pastures; however, mixtures will likely transition to tall fescue and Kentucky bluegrass–dominated pastures.  相似文献   

16.
Fuel loading information is important for prescribed fire planning, evaluating wildfire risk, and understanding fire effects in grassland. Yet fuel loads in grasslands often go unmeasured because of the time required to clip plots and process samples, as well as limited access or proximity to a drying oven. We tested the digital photography biomass estimation technique for measuring fuel load in grasslands in two national parks in the eastern Great Plains. The method consists of using percentage image obstruction, as determined by digital photography, to estimate vegetation biomass based on a linear transformation (i.e., regressing dry clipped weights against percent digital obstruction). We used the technique with some modification and measured digital obstruction at two sites at Wilson’s Creek National Battlefield, Missouri (WICR), and three sites at Tallgrass Prairie National Preserve, Kansas (TAPR). The method did not result in strong correlations at either of the two sites at WICR (Site 1: r2=0.02; Site 2: r2=0.32), but performed relatively well at TAPR (Site 1 [<1 yr since burn]: r2=0.82; Site 2 [2 yr since burn]: r2=0.57; Site 3 [1 yr since burn]: r2=0.88). Linear regressions for the three sites at TAPR did not differ in slope (P>0.05). In general, the denser the vegetation, the weaker the relationship between the vegetation biomass of clip plots and the percentage image obstruction of digital images. The digital photography technique may not be useful for estimating fuel loads in grasslands with relatively high biomass (>80 g · 0.1 m?2) or digital image obstruction >50%. Large amounts of litter may also potentially reduce the accuracy of the technique.  相似文献   

17.
Background: Echocardiographic prediction of congestive heart failure (CHF) in dogs has not been prospectively evaluated. Hypothesis: CHF can be predicted by Doppler echocardiographic (DE) variables of left ventricular (LV) filling in dogs with degenerative mitral valve disease (MVD) and dilated cardiomyopathy (DCM). Animals: Sixty‐three client‐owned dogs. Methods: Prospective clinical cohort study. Physical examination, thoracic radiography, analysis of natriuretic peptides, and transthoracic echocardiography were performed. Diagnosis of CHF was based upon clinical and radiographic findings. Presence or absence of CHF was predicted using receiver‐operating characteristic (ROC) curve, multivariate logistic and stepwise regression, and best subsets analyses. Results: Presence of CHF secondary to MVD or DCM could best be predicted by E : isovolumic relaxation time (IVRT) (area under the ROC curve [AUC]=0.97, P < .001), respiration rate (AUC=0.94, P < .001), Diastolic Functional Class (AUC=0.93, P < .001), and a combination of Diastolic Functional Class, IVRT, and respiration rate (R2=0.80, P < .001) or Diastolic Functional Class (AUC=1.00, P < .001), respiration rate (AUC=1.00, P < .001), and E : IVRT (AUC=0.99, P < .001), and a combination of Diastolic Functional Class and E : IVRT (R2=0.94, P < .001), respectively, whereas other variables including N‐terminal pro‐brain natriuretic peptide, E : Ea, and E : Vp were less useful. Conclusion and Clinical Importance: Various DE variables can be used to predict CHF in dogs with MVD and DCM. Determination of the clinical benefit of such variables in initiating, modulating, and assessing success of treatments for CHF needs further study.  相似文献   

18.
BackgroundThe morphometry of the acetabulum is one source of information that assists in the clinical diagnosis of the hip and influences the proper selection of a prosthesis, reducing post-operative complications such as those seen in total hip replacement (THR). However, acetabular parameters in small-breed dogs are rarely reported.ObjectivesTo investigate acetabular parameters using radiography and computed tomography (CT) in small-breed dogs with Maltese and Shih Tzu dogs used as model breeds.MethodsStandard calibrated, extended hip radiographs and CT images were obtained. Subsequently, acetabular width (AW) in various directions was measured using radiography and CT, whereas acetabular depth (AD) was obtained by CT. Acetabular index (AI) is a ratio calculated from AD and AW.ResultsThe values of AW and AD were much higher in Shih Tzu than in Maltese dogs. Male Shih Tzus showed higher values of these parameters than females, while sex-based differences in most of the parameters could not be detected in Maltese. Body weight, but not age, influenced AWs and ADs. While AWs and ADs were influenced by several factors, AI was comparable among the assessed factors and between Maltese and Shih Tzu dogs (p = 0.172; 31.42 ± 1.35 and 32.60 ± 1.80, respectively). Also, AI did not vary with breed, sex, or body size.ConclusionsThe obtained radiographic and CT acetabular parameters could be useful as guidelines for evaluating the acetabulum of small-breed dogs in clinical practice.  相似文献   

19.
The aim of this study was to determine the synergistic effects of centrifuged egg yolk (EY) and soybean lecithin on post-thaw Caspian horse sperm motility, morphological abnormalities, and assessment of membrane integrity. The centrifuged EY (CEY) was added at concentrations of 2% and 4% to a defined INRA plus 1.25% soybean lecithin extender used to freeze Caspian horse semen. In this experiment, ejaculates collected from each Caspian horse (n = 4) were divided into three equal aliquots and diluted in CEY 2% (INRA2), 4% (INRA4) supplemented, and without any CEY (INRA0) in INRA plus 1.25% soybean lecithin extender, respectively. Thereafter, samples were frozen and thawed following a standard protocol. Sperm cryosurvival was evaluated in vitro by microscopy assessments of post-thaw sperm motility (by means of computer-assisted semen motility analysis [CASA]), acrosomal and other abnormalities (head, mid-pieces, and tail) and plasma membrane integrity (evaluated by HOST). In Caspian stallion, semen extended with INRA2 had significantly higher CASA motility and CASA progressive motility than those extended with the rest of extenders after freezing and thawing (P < .001). There was no significant difference in path velocity (VAP), VCL, and ALH among three groups (P > .05). For straight line velocity (P < .01) and LIN (P < .001), the highest values were obtained from the INRA4 group. The highest percentages of acrosomal and other abnormalities were found in semen diluted in INRA4 (P < .001). In the group frozen INRA2, the percentage of membrane integrity was significantly higher than that of the other groups (P < .001). The use of CEY 2% in combination with soybean lecithin significantly improved Caspian horse semen freezability.  相似文献   

20.
Landscapes with structural heterogeneity or patchiness can support diverse and stable wildlife populations. Visual obstruction methods (i.e., Robel pole and Nudd's coverboard) are common and useful techniques for quantifying vegetation structure; however, both rely on ocular estimations, which can be highly variable between observers. Our objectives were to 1) compare measurement and observer variation for visual obstruction among the two standard methods and the digital image method we developed using a digital camera; and 2) compare the performance of the Robel pole and digital image to estimate standing crop. The mean variation across the five observers using the digital image method (6.8%) was significantly lower (P < 0.05) than both the Nudds' coverboard (32.1%) and the Robel pole (52.2). There were no significant differences among locations for the digital image method; however, there were for both the Robel pole and Nudds' cover board (P < 0.05). The digital image method provided a better estimate of standing crop (r2 = 0.89) compared to the Robel pole (r2 = 0.68), accounting for 21% more of the observed variation in biomass. Long-term research programs that utilize seasonal field technicians to quantify habitat structure with a visual obstruction method could benefit from implementing use of the digital image method we developed. The low measurement error observed with this technique relative to the more traditional methods compared in this study might limit year-to-year and within-year variability of habitat structure data collected by numerous technicians with a high annual turnover.  相似文献   

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