Radiographic Techniques Lecture 1 - Thorax, Larynx, PDF

Radiographic Techniques Lec 1 Radiographic Techniques of The Thorax: larynx BY Ahmed Jasem Abass MSC of Medical Imaging 1  Plain radiography is requested to investigate the presence of soft-tissue swellings and their effects on the air passages, as well as to...

Radiographic Techniques Lec 1 Radiographic Techniques of The Thorax: larynx BY Ahmed Jasem Abass MSC of Medical Imaging 1  Plain radiography is requested to investigate the presence of soft-tissue swellings and their effects on the air passages, as well as to locate the presence of foreign bodies or assess laryngeal trauma. Tomography, computed tomography (CT) magnetic resonance imaging (MRI) may be needed for full evaluation of other disease processes.  It is common practice to take two projections, an anteroposterior (AP) and a lateral. 2  Positioning patient and image receptor  The patient lies supine with the median sagittal plane adjusted to coincide with the central long axis of the couch.  The chin is raised to show the soft tissues below the mandible.  The image receptor is centred at the level of the 4th cervical vertebra.  Direction and location of the X-ray beam  The collimated vertical beam is directed 10° cranially and centred in the midline at the level of the 4th cervical vertebra.  Essential image characteristics (Figs 7.1b, 7.1c)  The beam should be collimated to include an area from the occipital bone to the 7th cervical vertebra. 3 4  Position of patient and image receptor  The patient stands or sits with either shoulder against the CR cassette or vertical Bucky.  The median sagittal plane of the trunk and head are parallel to the image receptor.  The jaw is slightly raised so that the angles of the mandible are separated from the bodies of the upper cervical vertebrae.  A point 2 cm posterior to the angle of the mandible should be coincident with the vertical central line of the image receptor.  The image receptor is centred at the level of the prominence of the thyroid cartilage.  Immediately before exposure the patient is asked to depress the shoulders forcibly so that their structures are projected below the level of the 7th cervical vertebra.  The head and trunk must be maintained in position.  Exposure is made on forced expiration. 5  Direction and location of the X-ray beam  The collimated horizontal central ray is centred to a point vertically below the mastoid process at the level of the prominence of the thyroid cartilage through the 4th cervical vertebra.  Essential image characteristics  The soft tissues should be demonstrated from the skull base to (C7).  Exposure should allow clear visualization of laryngeal cartilages and any possible foreign body. 6 7  Radiographic examination of the lungs is performed for a wide variety of medical conditions, including primary lung disease and pulmonary effects of diseases in other organ systems. Such effects produce significant changes in the appearance of the lung parenchyma and may vary over time, depending on the nature and extent of the disease. 8  The choice of erect or decubitus technique is governed primarily by the condition of the patient, with the majority of patients positioned erect. Very ill patients and patients who are immobile are X-rayed in the supine or semi- erect position. With the patient erect, positioning is simplified, control of respiration is more satisfactory, the gravity effect on the abdominal organs allows for reveal maximum area of lung tissue, and fluid levels are defined more easily with the use of a horizontal central ray. 9  The postero-anterior projection (PA) is generally adopted in preference to the antero-posterior (AP) because the arms can be arranged more easily to enable the scapulae to be projected clear of the lung fields.  Heart magnification is also reduced significantly compared with the AP projection.  This projection also facilitates compression of breast tissue with an associated reduction in dose to the breast tissue.  The mediastinal and heart shadows, however, obscure part of the lung fields, and a lateral radiograph may be necessary in certain situations. 10 11  Images are normally acquired on arrested deep inspiration, which ensures maximum visualization of the air-filled lungs.  Antero-posterior projection  Magnification makes heart size and apical region difficult to assess as well as the mediastinum, which appears artificially widened causing difficulty in interpretation particularly when a traumatic is suspected. 12  Overexposed images reduce visibility of lung parenchymal detail masking vascular and interstitial changes, and reducing the conspicuity of consolidation and masses.  Underexposure can artificially enhance the visibility of normal lung markings, leading to them being wrongly interpreted as disease (e.g. pulmonary fibrosis or oedema).  Underexposure also obscures the central areas causing failure to diagnose abnormalities of mediastinum. 13  Soft-tissue artifacts are a common cause of confusion. One of the commonest of these is the normal nipple. Other rounded artifacts may be produced by benign skin lesions such as simple seborrhoeic warts. Dense normal breast tissue or breast masses may also cause confusion with lung lesions. Linear artefacts may be due to clothing or gowns, or in thin (often elderly) patients due to skin folds and creases. 14 15  The lungs lie within the thoracic cavity on either side of the mediastinum, separated from the abdomen by the diaphragm. The right lung is larger than the left due to the inclination of the heart to the left side. In the normal radiographs of the thorax, some lung tissue is obscured by the ribs, clavicles and to a certain extent the heart, and also by the diaphragm in the PA projection.  The right lung is divided into upper, middle and lower lobes, and the left into upper and lower lobes. The fissures, which separate the lobes, can be demonstrated in various projections of the thorax, when the plane of each fissure is parallel to the beam. 16  The trachea is seen centrally as a radiolucent air-filled structure in the upper thorax, which divides at the level of the 4th thoracic vertebra into the right and left main bronchi. The right main bronchus is wider, shorter and more vertical than the left, and as a result inhaled foreign bodies are more likely  to pass into the right bronchial tree. The bronchi enter the hila, beyond which they divide into bronchi, bronchioles and finally alveolar air spaces, each getting progressively smaller. As these passages are filled with air.  The hilar regions appear as regions of increased radio-opacity and are formed mainly by the main branches of the pulmonary arteries and veins. The lung markings, which spread out from the hilar regions, are branches of these pulmonary vessels, and are seen diminishing in size as they pass distally from the hilar regions. The right dome of the diaphragm lies higher than the left mainly due to the presence of the liver on the right and the heart on the left. 17 18  a 35 × 43 cm CR cassette is selected, depending on the size of the patient. Orientation of a larger cassette will depend of the width of the thorax.  Position of patient and image receptor  The patient is positioned facing the receptor with the chin extended and centred to the middle of the top of the receptor.  The feet are placed slightly apart so that the patient is able to remain steady.  The median sagittal plane is adjusted at right-angles to the middle of the receptor; the shoulders are rotated forward and pressed downward in contact with the receptor or vertical stand.  This is achieved by placing the dorsal aspect of the hands behind and below the hips with the elbows brought forward, or by allowing the arms to encircle the vertical Bucky device. 19  Direction and location of the X-ray beam  The collimated horizontal beam is directed at right-angles to the receptor and centred at the level of the 8th thoracic vertebrae (i.e. spinous process of T7) which is coincident with the lung midpoint.  The surface marking of T7 spinous process can assessed by using the inferior angle of the scapula before the shoulders are pushed forward.  Exposure is made in full normal arrested inspiration.  In a number of automatic chest film-changer devices the central beam is automatically centred to the middle of the receptor. 20  The ideal PA chest radiograph should demonstrate the following:  Full lung fields with the scapulae projected laterally away from the lung fields.  No rotation, the medial ends of the clavicles should overlap the transverse processes of the spine.  Inferior to the costophrenic angles and diaphragm clearly outlined.  The mediastinum and heart central and sharply defined. 21  Common faults and solutions  The scapulae sometimes obscure the outer edges of the lung fields. If the patient is unable to adopt the basic arm position the arms should be allowed to encircle the vertical Bucky.  Rotation of the patient will result in the heart not being central with assessment of heart size made impossible. Attention to how patients are made to stand is essential to ensure they are comfortable and can maintain the position. The legs should be well separated and the pelvis symmetrical in respect to the vertical Bucky. 22 23 24  Careful patient preparation is essential, with all radiopaque objects removed before the examination.  Patients with underwater-seal bottles require particular care to ensure that chest tubes are not dislodged, and the bottle is not raised above the level of the chest.  A PA side marker is normally used, and the image is identified with the identification marker set to the PA position. Care should be made not to misdiagnose a case of dextracardia.  Long plaited hair may cause artefacts and should be clipped out of the image field. 25 26