排序方式： 共有49条查询结果，搜索用时 15 毫秒
1.
Tommaso Gregori Richard Lam Simon L. Priestnall Christopher R. Lamb 《Veterinary radiology & ultrasound》2016,57(6):582-586
The truncation artifact in magnetic resonance (MR) images is a line of abnormal signal intensity that occurs parallel to an interface between tissues of markedly different signal intensity. In order to demonstrate the truncation artifact in sagittal images of the canine spinal cord and the effect of changing spatial resolution, we conducted an experimental in vitro study. A section of fixed canine spinal cord was imaged using a 1.5T magnet. Spatial resolution was increased by increasing the acquisition matrix and reconstruction matrix, producing series of T2‐weighted (T2w) images with the following pixel sizes: A, 1.6 (vertical) × 2.2 mm2 (horizontal); B, 1.2 × 1.7 mm2; C, 0.8 × 1.1 mm2; D, 0.4 × 0. 6 mm2. Plots of mean pixel value across the cord showed variations in signal intensity compatible with truncation artifact, which appeared as a single, wide central hyperintense zone in low‐resolution images and as multiple narrower zones in high spatial resolution images. Even in images obtained using the highest spatial resolution available for the MR system, the edge of the spinal cord was not accurately defined and the central canal was not visible. The experiment was repeated using an unfixed spinal cord specimen with focal compression applied to mimic a pathologic lesion. Slight hyperintensity was observed within the spinal cord at the site of compression although the cord was normal histologically. Results of this study suggest that caution should be applied when interpreting hyperintensity affecting the spinal cord in T2w sagittal images of clinical patients because of the possibility that the abnormal signal could represent a truncation artifact. 相似文献
2.
EFFECTS OF FLUID AND COMPUTED TOMOGRAPHIC TECHNICAL FACTORS ON CONSPICUITY OF CANINE AND FELINE NASAL TURBINATES 
下载免费PDF全文
下载免费PDF全文 Raimonda Uosyte Darren J. Shaw Danielle A. Gunn‐Moore Eduardo Fraga‐Manteiga Tobias Schwarz 《Veterinary radiology & ultrasound》2015,56(5):494-502
Turbinate destruction is an important diagnostic criterion in canine and feline nasal computed tomography (CT). However decreased turbinate visibility may also be caused by technical CT settings and nasal fluid. The purpose of this experimental, crossover study was to determine whether fluid reduces conspicuity of canine and feline nasal turbinates in CT and if so, whether CT settings can maximize conspicuity. Three canine and three feline cadaver heads were used. Nasal slabs were CT‐scanned before and after submerging them in a water bath; using sequential, helical, and ultrahigh resolution modes; with images in low, medium, and high frequency image reconstruction kernels; and with application of additional posterior fossa optimization and high contrast enhancing filters. Visible turbinate length was measured by a single observer using manual tracing. Nasal density heterogeneity was measured using the standard deviation (SD) of mean nasal density from a region of interest in each nasal cavity. Linear mixed‐effect models using the R package ‘nlme’, multivariable models and standard post hoc Tukey pair‐wise comparisons were performed to investigate the effect of several variables (nasal content, scanning mode, image reconstruction kernel, application of post reconstruction filters) on measured visible total turbinate length and SD of mean nasal density. All canine and feline water‐filled nasal slabs showed significantly decreased visibility of nasal turbinates (P < 0.001). High frequency kernels provided the best turbinate visibility and highest SD of aerated nasal slabs, whereas medium frequency kernels were optimal for water‐filled nasal slabs. Scanning mode and filter application had no effect on turbinate visibility. 相似文献
3.
Nathalie Rademacher Romain Pariaut Julie Pate Carley Saelinger Michael T. Kearney Lorrie Gaschen 《Veterinary radiology & ultrasound》2014,55(4):447-452
Pulmonary edema is the most common complication of left‐sided heart failure in dogs and early detection is important for effective clinical management. In people, pulmonary edema is commonly diagnosed based on transthoracic ultrasonography and detection of B line artifacts (vertical, narrow‐based, well‐defined hyperechoic rays arising from the pleural surface). The purpose of this study was to determine whether B line artifacts could also be useful diagnostic predictors for cardiogenic pulmonary edema in dogs. Thirty‐one normal dogs and nine dogs with cardiogenic pulmonary edema were prospectively recruited. For each dog, presence or absence of cardiogenic pulmonary edema was based on physical examination, heartworm testing, thoracic radiographs, and echocardiography. A single observer performed transthoracic ultrasonography in all dogs and recorded video clips and still images for each of four quadrants in each hemithorax. Distribution, sonographic characteristics, and number of B lines per thoracic quadrant were determined and compared between groups. B lines were detected in 31% of normal dogs (mean 0.9 ± 0.3 SD per dog) and 100% of dogs with cardiogenic pulmonary edema (mean 6.2 ± 3.8 SD per dog). Artifacts were more numerous and widely distributed in dogs with congestive heart failure (P < 0.0001). In severe cases, B lines increased in number and became confluent. The locations of B line artifacts appeared consistent with locations of edema on radiographs. Findings from the current study supported the use of thoracic ultrasonography and detection of B lines as techniques for diagnosing cardiogenic pulmonary edema in dogs. 相似文献
4.
5.
超声回波强度的影响因素及临床声像图问题研究 总被引：3，自引：0，他引：3
目的：为医学超声诊断水平的提高。方法：以超声传播所遵循的物理规律、超声成像的物理原理以及医学超声诊断仪的基本设置为基础，佐以实验观察，系统地分析了影响超声回波强度的因素和规律并重点讨论了介质薄层的透声规律。结果与结论：超声回波的强度可受多种因素的影响：提出“介质薄层伪像”和“隐现声影”等新观点。 相似文献
6.
CAROLINA I. URRACA DEL JUNCO DARREN J. SHAW MARTIN P. WEAVER TOBIAS SCHWARZ 《Veterinary radiology & ultrasound》2011,52(6):634-639
Magnetic susceptibility artifacts as a result of metal debris from shoeing are a common problem in magnetic resonance imaging of the equine foot. Our purpose was to determine the suitability of radiography as a screening tool for the presence and location of metallic particles in the equine foot and to predict the size of the resultant magnetic susceptibility artifact. Radiography had 100% sensitivity for detection of metal particles ≥1 mm diameter. Metal particles of known diameter were placed within the hoof wall of 22 cadaver feet and scanned with a low‐field strength MR imaging unit (0.21 T). Magnetic resonance images were characterized by a signal void with a hyperintense rim and adjacent image distortion at the level of the known metal location. T2* weighted sequences were the most and fast spin echo (FSE) sequences the least affected. For all four sequences (T1 gradient echo [GRE]; T2*W GRE; T2 FSE; and short tau inversion recovery FSE), linear relationships were observed between particle and resultant artifact size. Magnetic susceptibility artifact size, location and superimposition on clinically relevant anatomic structures can be predicted radiographically for particles larger than 1 mm. If metal debris cannot be removed, the least artifact‐prone FSE sequences should be selected. 相似文献
7.
Paul Y Barthez DVM René Léveillé DVM Peter V Scrivani DVM 《Veterinary radiology & ultrasound》1997,38(5):387-393
Side lobes and grating lobes are both unwanted parts of the ultrasound beam emitted off axis that produce image artifacts due to error in positioning the returning echo. The purpose of this study was to reproduce artifacts associated with side lobes and grating lobes in vitro using different transducer types and recognize these artifacts in vivo. A phantom, composed of a water bath, a metallic wire, and a wooden tongue depressor, was imaged using a linear array, a curved linear array, a vector array, and a sector mechanical transducer. When imaging the metallic wire in a transverse plane, an echogenic artifact was constantly seen on each side of the wire, with a shape and intensity variable with the transducer type. The artifact was curvilinear and concave (linear and curved linear arrays), or curvilinear and convex (vector array and the mechanical transducer). When the tongue depressor was imaged in a longitudinal plane, the artifact was a straight line (linear array), a curved convex line(curved array), a series of convex curvilinear echo (vector array) or a small convex curvilinear echo (mechanical transducer). In vivo situations similar to the phantom experiment were investigated using clinical patients. Artifacts produced in vitro were recognized in vivo when a highly reflective object (urinary bladder wall) was imaged adjacent to an anechoic region (urine). These artifacts corresponded to the principle of secondary ultrasound lobes, and were therefore interpreted as such. 相似文献
8.
Rebecca Manley Andrea R. Matthews Federica Morandi George A. Henry Katherine H. DeAnna Gordon Conklin Ann Reed 《Veterinary radiology & ultrasound》2013,54(3):253-262
Motion artifact is an important limiting factor for abdominal magnetic resonance imaging (MRI) in veterinary patients. The purpose of this study was to determine the effects of pulse sequence on abdominal MRI diagnostic quality in dogs. Ten normal dogs were each scanned using 16 MRI pulse sequences. Sequences included breath‐holding sequences, respiratory navigation sequences, and traditional spin‐echo sequences. Four observers independently scored diagnostic quality for each sequence based on the appearance of specific organs, overall diagnostic quality, and degree of artifactual interference. Signal‐to‐noise ratio and contrast‐to‐noise ratio were also calculated for each sequence. The sequence with the highest overall mean diagnostic quality score was the dorsal T2 turbo spin echo (TSE) with fat saturation and breath‐holding. The sequence with the lowest mean diagnostic quality score was the dorsal T2 fast spin echo. The sequence with the highest signal‐to‐noise ratio for all evaluated organs was the sagittal T1 spin echo. Signal‐to‐noise and contrast‐to‐noise ratios did not correlate with subjective assessment of overall diagnostic quality for the majority of the sequences evaluated (P < 0.05). The three sequences considered to have the highest diagnostic quality for the cranial abdomen were the dorsal T2 TSE with fat saturation and breath‐hold, transverse T1 turbo fast low‐angle shot gradient echo with breath‐hold, and dorsal T2 half‐Fourier acquisition single shot TSE with respiratory navigation. These sequences had short acquisition times, yielded studies of similar diagnostic quality, provided complementary information, and are therefore recommended for routine canine abdominal MRI protocols. 相似文献
9.
David A Jiménez Laura J Armbrust Robert T O'Brien David S Biller 《Veterinary radiology & ultrasound》2008,49(4):321-332
Digital radiography is becoming more prevalent in veterinary medicine, and with its increased use has come the recognition of a number of artifacts. Artifacts in digital radiography can decrease image quality and mask or mimic pathologic changes. They can be categorized according to the step during which they are created and include preexposure, exposure, postexposure, reading, and workstation artifacts. The recognition and understanding of artifacts in digital radiography facilitates their reduction and decreases misinterpretation. The purpose of this review is to name, describe the appearance, identify the cause, and provide methods of resolution of artifacts in digital radiography. 相似文献
10.
Reasons for performing study: Hyperintense signal is sometimes observed in ligaments and tendons of the equine foot on standing magnetic resonance examination without associated changes in size and shape. In such cases, the presence of a true lesion or an artifact should be considered. A change in position of a ligament or tendon relative to the magnetic field can induce increased signal intensity due to the magic angle effect. Objectives: To assess if positional rotation of the foot in the solar plane could be responsible for artifactual changes in signal intensity in the collateral ligaments of the distal interphalangeal joint and in the deep digital flexor tendon. Methods: Six isolated equine feet were imaged with a standing equine magnetic resonance system in 9 different positions with different degrees of rotation in the solar plane. Results: Rotation of the limb induced a linear hyperintense signal on all feet at the palmar aspect of one of the lobes of the deep digital flexor tendon and at the dorsal aspect of the other lobe. Changes in signal intensity in the collateral ligaments of the distal interphalangeal joint occurred with rotation of the limb only in those feet where mediolateral hoof imbalance was present. Conclusions: The position and conformation of the foot influence the signal intensity in the deep digital flexor tendon and in the collateral ligaments of the distal interphalangeal joint. Potential relevance: The significance of increased signal intensity in the deep digital flexor tendon and in the collateral ligaments of the distal interphalangeal joint should be interpreted with regard to the position and the conformation of the foot. 相似文献