Imaging
Alveolar Pulmonary Pattern
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There are different pulmonary radiographic patterns: Alveolar Pattern, Interstitial Pattern, Structured Interstitial (nodular) Pattern, Bronchial Pattern, Vascular Pattern and Mixed Pattern.
The alveolar pattern occurs when fluid (such as exudate, hemorrhage, edema or rarely cells - neoplasic cells) filling up the pulmonary acini and displacing the air (consolidation) or not replaced at all (atelectasis). In either etiology, the lung is no longer aerated increasing the radiographic opacity of lung.
The alveolar pattern is identified by an increase in overall lung opacity that completely obscures the pulmonary vasculature in the opaque area. This pattern is characterized by one or more of the following radiographic features (not all signs seen in every case):
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Uniform opacity
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Air bronchogram (hallmark sign of an alveolar pattern) an air-filled bronchus traversing a region of abnormally opaque lung. Bronchial walls are not seen; only bronchial lumen.
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Lobar sign (the infiltrate extends to periphery) - opacified lobe border and adjacent normal radiolucent lobe.
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Silhouette effect - loss of border visualization between heart and lung lobe.
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Focal or multifocal distribution (depending the disease severity).
References:
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Donald E. Thrall. Textbook of Veterinary Diagnostic Radiology. 7th ed. Elsevier. 2018.
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Ronald L. Burk. Alveolar Pulmonary Patterns. VIN Radiology Atlas. VIN.com
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Martha M. Larsen. Radiographic evaluation of Pulmonary Patterns and Disease (Proceedings). 2008. dvm360.com
DVM 360:
Radiographic evaluation of Pulmonary Patterns and Disease (Proceedings)
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Computed Tomography
Computed Tomography (CT) in animals is an advanced diagnostic imaging modality used extensively in veterinary medicine. It provides detailed cross-sectional images, allowing for superior visualization of internal structures compared to standard radiography. CT is invaluable for diagnosing complex conditions, particularly in neurology, oncology, and orthopedics. Its ability to differentiate tissue densities and visualize both bone and soft tissue makes it ideal for identifying tumors, spinal cord diseases, and intricate skeletal anomalies. CT's high-speed imaging capabilities facilitate dynamic studies like blood flow and respiratory function assessments. However, its use often requires animal sedation or anesthesia.
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CNS Neoplasias Through Diagnostic Tests
Central nervous system neoplasias in animals encompass a range of tumors that can affect the brain and spinal cord, leading to various neurological symptoms. The most frequent neoplasias include meningiomas, gliomas, and pituitary adenomas, among others.
Symptoms indicating the presence of CNS neoplasias can vary widely depending on the tumor’s location and size but often include seizures, behavioral changes, ataxia, paresis or paralysis, and vision problems. These clinical signs are critical for early suspicion of CNS neoplasias.
Diagnostic tests for CNS neoplasias typically involve advanced imaging techniques, with Magnetic Resonance Imaging (MRI) being the gold standard due to its superior detail in visualizing soft tissues. Computed Tomography (CT) scans and cerebrospinal fluid (CSF) analysis are also utilized to aid in diagnosis, with CSF analysis sometimes revealing nonspecific changes that may suggest the presence of a tumor.
Treatment options for CNS neoplasias in animals vary based on the type of tumor, its location, and the overall health of the animal. They can include surgical removal, radiation therapy, and chemotherapy. The prognosis depends on the specific type of neoplasia, its growth rate, and how early the treatment begins.
Please check the Merck Veterinary Manual directly for the most accurate and comprehensive information on this topic: Merck Veterinary Manual - Neoplasia of the Nervous System in Animals.
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Key Factors Influencing X-ray Quality
To set up an X-ray machine in veterinary medicine and calculate the milliamperes (mA), professionals follow a detailed process that ensures the quality of the radiographic images while considering patient safety and minimizing radiation exposure. The setup and calculation of mA are critical for achieving optimal contrast and detail in the radiographs, and several factors influence these settings.
Setting Up the X-Ray Machine and Calculating Milliamperes:
1. Understanding Exposure Parameters: The primary parameters for making a radiographic exposure include kilovoltage peak (kVp), milliamperes (mA), and exposure time. These factors are interdependent, with mA and exposure time so closely related that the term milliampere-seconds (mAs) is commonly used to denote their product. Adjusting these settings affects the image's brightness and contrast, as well as the radiation dose to the patient
2. Adjusting Milliamperes and Exposure Time: Increasing mA or exposure time will increase the number of photons produced, thus darkening the image. To correct for motion blur, it's advisable to minimize exposure time while maintaining an appropriate mAs. Conversely, adjustments in kVp will affect the penetration of photons through the subject, thus altering the image contrast and brightness
3. Technique Charts: Establishing a technique chart for each X-ray machine is crucial. This chart helps operators to quickly determine the appropriate settings based on the animal's size and the anatomical area being examined. Modern X-ray machines often have built-in technique charts where the operator inputs the species, body part, and thickness, and the machine automatically sets the technique. This aids in consistency and reduces the potential for errors.
4. Automatic Exposure Control (AEC): Some X-ray systems feature AEC, which automates exposure timing based on pre-set kVp and mA, ensuring consistent image quality across different subjects. However, accurate positioning and consistent kV settings are essential for AEC to be effective.
5. Collimation and Scatter Radiation Management: Proper collimation, which involves adjusting the X-ray beam's size to match the area of interest, is vital for reducing scatter radiation. Scatter radiation not only degrades image quality but also increases radiation exposure to the patient and staff. Additionally, using a grid can help minimize scatter radiation in thicker subjects, improving image clarity.
6. Positioning the Patient: Correct patient positioning is fundamental for diagnostic accuracy. For example, lateral and dorsoventral positioning are standard for thoracic examinations, ensuring comprehensive visualization of the area of interest. Utilizing positioning aids such as troughs, foam wedges, and sandbags can aid in maintaining the desired position during the exposure.
Impact of Settings on Radiograph Quality:
- mA and Exposure Time: Increasing mA or reducing exposure time, while keeping mAs constant, can reduce motion blur. However, these adjustments can impact the radiation dose and potentially the longevity of the X-ray tube due to heat load.
- kVp: Higher kVp settings increase photon penetration, darkening the image, and can be used to correct underexposed images, particularly in areas of low contrast. However, excessive kVp can lead to overpenetration, reducing image contrast.
- Collimation and Grid Use: Proper collimation and the use of grids to control scatter radiation significantly improve image quality by enhancing contrast and detail.
In summary, the setup of an X-ray machine in veterinary practice involves a careful balance of technical parameters, patient positioning, and radiation safety practices. Each factor, from mA settings to collimation, plays a crucial role in optimizing the radiographic image for diagnostic purposes.
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References:
Radiography of Animals - Clinical Pathology and Procedures - Merck Veterinary Manual
Diagnostic imaging | Veterian Key