XRay and CT PDF

Dr Syed Faizan Raza Jafri MBBS,MD (medicine) RMP Medical specialist XRAY and Computed tomography  XRAY Plain radiographs, also known as x-rays or plain films, produce two-dimensional images. X-rays are generated by the machine and directed towards the s...

Dr Syed Faizan Raza Jafri MBBS,MD (medicine) RMP Medical specialist XRAY and Computed tomography  XRAY Plain radiographs, also known as x-rays or plain films, produce two-dimensional images. X-rays are generated by the machine and directed towards the subject (e.g. a wrist or chest). The detector on the other side of the subject is a piece of film or (more commonly) a digital plate. This records the magnitude of x-rays that have managed to make it to the detector and we can thereby infer where x-rays have been attenuated.  X-rays can be used in a wide variety of situations, such as investigating fractures, pneumonia or confirming nasogastric tube position. They are quick and relatively simple to perform and compared to other imaging modalities, relatively inexpensive. The image is available almost immediately. However, they do make use of ionizing radiation and their use is limited to the situations where there is a clinical need because of the risk of cancer induction.  When x-rays meet the detector and create an image, there are five main densities that can be visualized. They are a direct result of how many x-rays have passed through the subject and arrived at the detector. If all of the x-rays continue through (e.g. air), that area of the image has little density and is black. If the x-rays are blocked (e.g. bones), that area of the image is very dense and is therefore white.  air: the blackest part of the radiograph. May include areas outside the patient or air within the body (e.g. lungs). fat: lighter grey shade compared to air soft tissue or fluid: consists of denser organs and fluid within the body. More white than fatty tissue bones or calcium: bones are very dense and allow little x-rays to get through them. Calcifications elsewhere (e.g. in arteries) will also appear white.  Computed tomography (CT) CT scans also use x-rays to create a picture. The patient lies down on a table that passes into the CT scanner. A rotating x-ray source and detector spin around the outside of the patient gathering data similar to the plain radiograph above. Once all the data has been gathered, a computer can build up the data and present it as a series of images. These two-dimensional cross-sectional images can be scrolled and viewed in the axial, sagittal or coronal planes. This also means that overlapping structures are not an issue, as they are in x-rays. Depending on the type of imaging, 3D reconstructions can be created.  CT images are comprised of pixels or varying density. In the same manner as conventional radiographs, the density of each pixel corresponds to the type of tissue imaged. High density substances absorb more x-rays and appear whiter. Low density substances absorb few x-rays and appear darker. The density of each pixel is measured in Hounsfield units (HU), where air is assigned - 1000 HU, water is 0 HU and bone is around 500 HU.  The range of Hounsfield units included in a study is called the window. Windowing is very important in diagnostic images at it allows optimization of the CT to identify different types of pathology - all without having to rescan the patient. A widely used example of this is in chest CTs - where different windows can show the bones, lung fields and mediastinum in detail. This may reveal fractures, emphysema or heart disease respectively. By adjusting the window you can highlight certain fields to maximize the diagnostic power of the CT. Radiological anatomy of chest. Bony Structures Ribs: Seen as curved structures on the periphery of the chest. The posterior ribs are better seen on frontal X- rays. Sternum: Appears faintly on lateral X-rays but is not clearly visible on frontal X-rays. Clavicles (Collarbones): Appear above the lung fields on a frontal chest X-ray. Vertebrae: The thoracic spine is seen in the center of the chest, with vertebral bodies faintly visible behind the heart.  Soft Tissue Structures Diaphragm: The dome-shaped muscle separating the chest cavity from the abdomen. The right hemidiaphragm is usually higher than the left due to the liver's presence underneath. Breast shadows: These may be seen as soft tissue densities on a frontal X-ray, especially in women. Heart: The cardiac silhouette is prominent in frontal views. The heart's size, shape, and contour can give clues to pathology. Aortic arch: Seen as a distinct contour on the left side in frontal views  Lung Fields Lungs: Appear as radiolucent (dark) areas on X- rays due to air content. Key landmarks include: Hila: The area where the bronchi, blood vessels, and nerves enter and exit the lungs. The left hilum is usually higher than the right. Fissures: These separate lung lobes and can sometimes be seen in X-rays (e.g., the horizontal fissure in the right lung). Lobes: The right lung has three lobes (upper, middle, lower), while the left lung has two lobes (upper and  Airways Trachea: A vertical air column located in the midline that divides into the right and left main bronchi. Right main bronchus: Wider, shorter, and more vertical than the left, which is important for the likelihood of foreign body aspiration. Carina: The bifurcation of the trachea into the right and left bronchi is an important landmark.  Vascular Structures Pulmonary Arteries: Seen near the hila of the lungs; they transport deoxygenated blood to the lungs. Aorta: The aortic arch is usually visible on the left side. The descending thoracic aorta may be seen as a shadow next to the vertebrae. Superior Vena Cava: Located on the right side, it drains venous blood from the upper body into the heart. Pleura Pleural Spaces: Normally not visible, but when fluid accumulates (pleural effusion), the fluid can be seen between the lung and chest wall. The costophrenic angles (where the diaphragm meets the ribs) are important in detecting small effusions.  Radiographic Projections Posteroanterior (PA) View: The standard chest X-ray projection, where the X-ray beam travels from back to front. Lateral View: Taken from the side to evaluate structures behind the heart and diaphragm. Anteroposterior (AP) View: Commonly used in bedridden patients but can distort structures compared to the PA view. Normal chest XRAY vs pathological findings  Normal Chest X-Ray Findings Lung Fields: Clear with no opacities. The lungs appear radiolucent (dark) due to air content. Diaphragm: Dome-shaped, right hemidiaphragm slightly higher than the left. Heart: Normal size and shape. The cardiothoracic ratio (width of heart vs. chest) should be less than 50% in a PA (posteroanterior) view. Mediastinum: Normal width, trachea midline. Costophrenic Angles: Sharp and clear, no fluid present. Bones: Ribs, clavicles, and vertebrae are intact with no fractures or abnormalities Vascular markings: Visible but not overly prominent in lung fields. Pathological Findings in Different Diseases Pneumonia Findings: Opacities (consolidation) in one or more lobes, typically unilateral. Air bronchograms: air-filled bronchi outlined by surrounding alveolar consolidation. Loss of lung volume (atelectasis) in severe cases.  Chronic Obstructive Pulmonary Disease (COPD) Findings: Hyperinflation: Flattened diaphragms, increased retrosternal air space, increased lung volumes. Decreased vascular markings due to lung destruction (especially in emphysema). Bullae: Air-filled spaces indicating areas of lung destruction.  Pulmonary Edema (Heart Failure) Findings: Kerley B lines: Horizontal lines at the lung bases due to interstitial fluid. Bat wing pattern: Bilateral perihilar opacities representing alveolar edema. Cardiomegaly: Enlarged heart silhouette (cardiothoracic ratio > 50% in a PA view). Pleural effusions: Blunting of costophrenic angles.  Pleural Effusion Findings: Blunting of costophrenic angles due to fluid accumulation. Meniscus sign: Curved upper edge of the pleural fluid level. Large effusions may shift the mediastinum to the opposite side. 5. Pneumothorax Findings: Absent lung markings in the affected area (air outside the lung in the pleural space). Collapsed lung visible as a sharp white line with no markings beyond it. Mediastinal shift to the opposite side in a tension pneumothorax.  Tuberculosis Findings: Upper lobe infiltrates: Opacities in the apical and posterior segments of the upper lobes. Cavitation: Hollowed-out areas within consolidated regions, often with air-fluid levels. Lymphadenopathy: Enlarged hilar or mediastinal lymph nodes. Fibrosis and scarring in later stages. 7. Lung Cancer Findings: Solitary pulmonary nodule: A round or irregular mass, typically with sharp margins. Hilar enlargement: Suggesting lymph node involvement. Atelectasis: Due to bronchial obstruction. Pleural effusion: Sometimes associated with advanced disease.  Interstitial Lung Disease (ILD) Findings: Reticular or reticulonodular pattern: Fine lines or nodules throughout the lung fields. Honeycombing: Clusters of small cystic spaces, particularly in the lung bases. Ground-glass opacities: Hazy lung fields indicating early fibrosis or inflammation. 9. Pulmonary Embolism (PE) Findings (on CXR, but often normal): Westermark’s sign: Focal oligemia (decreased lung markings) in the area of the embolism. Hampton’s hump: A wedge-shaped opacity near the pleura, indicating lung infarction. Enlarged pulmonary arteries: Sometimes seen in massive PE.  Atelectasis (Lung Collapse) Findings: Volume loss: Shift of the mediastinum and diaphragm toward the affected side. Opacification of the collapsed lung area. Compensatory hyperinflation of the opposite lung. 11. Rib Fracture Findings: Disruption in the continuity of a rib, visible as a sharp, lucent line. Associated soft tissue swelling or pleural effusion in severe trauma cases.  Emphysema (COPD Subtype) Centrilobular Emphysema Findings: Centrilobular lucencies: Areas of low attenuation, typically affecting the upper lobes. Sparing of the lung periphery. Destruction of alveolar walls, creating small holes within the lung parenchyma. Panlobular Emphysema Findings: Diffuse low attenuation throughout the lungs, involving entire lobules, more uniform than centrilobular emphysema. Associated with conditions like alpha-1 antitrypsin deficiency. Affects lower lobes more prominently. Paraseptal Emphysema Findings: Subpleural bullae or large cystic spaces near the pleura. Predominantly affects the upper lung zones. Can lead to spontaneous pneumothorax if the bullae rupture.  Bronchiectasis Findings: Bronchial dilatation: Airways appear larger than adjacent blood vessels (signet ring sign). Lack of bronchial tapering: Airways maintain abnormal diameter as they branch distally. Thickened bronchial walls. Associated findings like mucus plugging and tree- in-bud pattern (representing small airway inflammation or infection).  Pulmonary Fibrosis Findings: Reticular opacities: Fine, linear opacities due to fibrosis, often with a subpleural and basal predominance. Honeycombing: Small cystic airspaces that form as the disease progresses, particularly in the lung bases. Traction bronchiectasis: Abnormal dilatation of bronchi due to fibrotic pulling.  Viral Pneumonia (e.g., COVID-19) Findings: Ground-glass opacities: Typically bilateral and peripheral in distribution. Consolidations: In more severe cases, dense areas of increased opacity. Crazy paving pattern: Ground-glass opacities with superimposed interlobular septal thickening. Bacterial Pneumonia Findings: Consolidation: Dense opacification, often lobar in distribution. Air bronchograms: Visible air-filled bronchi surrounded by consolidation. Abscess formation or cavitation in certain bacterial infections like Staphylococcus or Klebsiella.  Pulmonary Embolism (PE) Findings: Filling defects: Seen in the pulmonary arteries, indicating the presence of thrombi. Mosaic attenuation: Due to differing blood supply between embolized and non-embolized lung regions. Wedge-shaped opacities: Indicative of pulmonary infarction.