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CT SCAN CHEST LEARNING OBJECTIVES At the end of lecture, the student should be able to know: • About different structures that can be identified on CT chest • About Different levels of mediastinal CT • About Different levels of CT scan showing bronchial cross section • About the appearance of lung parenchyma on CT chest COMPUTERIZED AXIAL TOMOGRAPHY, OR COMPUTED TOMOGRAPHY (CT) • Way of using x-rays to create cross sectional views of the body. • Thin beam of x-rays is moved around the patient • Electronic detectors opposite the beam produce an electrical output • The output varies according to the tissues traversed by the x-ray beam. Each axial slice can be divided into a a grid of pixels, or picture elements representing a small part of the overall image • Ct scanner rotates the x-ray beam around the patient to create each slice • Information obtained from the beam detectors is analyzed by a computer that computes the brightness of each pixel. • The resulting image can be displayed on a monitor or printed onto x-ray film. HOW DIFFERENT TISSUE LOOK ON X-RAY AND CT SCAN • AIR ---------- JET BLACK ( AIR IN LUNG AND GIT) • FAT ---------MODERATLY BLACK ( FAT IN S/C TISSUE) • WATER------ GRAY ( NEITHER BLACK NOR WHITE) • MUSCLES---- SLIGHT WHITE • BONES ------- WHITE • CALCIFICATION---- DENSE WHITE LEVELS OF SECTIONAL ANATOMY ON COMPUTED TOMOGRAPHY HOW TO INTERPRET CT CHEST • MEDIASTINAL WINDOW • LUNG WINDOW • BONE WINDOW MEDIASTINUM • Broad central partition that separates the two laterally placed pleural cavities • Imaginary plane passes through T 4 divides it into superior and inferior mediastinum • Inferior mediastinum is further divided – Heart enclosed in pericardium occupies middle mediastinum – From sternum to anterior pericardium anterior mediastinum – From posterior pericardium to vertebrae posterior mediastinum LATERAL SURFACE AND RADIOGRAPHIC NORMAL MEDIASTINAL AND LUNG ANATOMY CT MEDIASTINUM supra aortic level • At sternoclavicular joint T3 • Trachea—air filled round structure in center • Clock wise from right anterolateral to posterior from trachea are – Brachiocephalic trunk – Left common carotid artery(LCCA) – Left subclavian artery(LSCA) – Oesophagus(E) • Anterior to this ring right and left Brachiocephalic vein RBCV and LBCV • On lower sections: these veins join to form SVC on right of ascending aorta CT MEDIASTINUM AORTIC ARCH LEVEL At the level of manubriosternal joint Arch of aorta curving to left of trachea Superior vena cava on right of anterior part of arch Esophagus on right of posterior part of arch Thymus starts appearing as an arrow head anteriorly CT MEDIASTINUM SUBAORTIC LEVEL Ascending aorta Descending aorta Thymus lies anterior to ascending aorta Azygous vein posterolaterally to right of esophagus o Passes forward to join superior vena cava over the top of junction between the right main bronchus and right upper lobe bronchus CT MEDIASTINUM SUBAORTIC LEVEL STERNUM THYMUS ASCENDING AORTA AORTICOPULMONARY WINDOW TRACHEA OESOPHAGUS AZYGOUS VEIN SVC DESCENDING AORTA CT MEDIASTINUM AT CARINA Trachea divides into right and left main bronchus RMB and LMB Left pulmonary artery LPA passes over the LMB CT MEDIASTINUM AT CARINA STERNUM AA THYMUS LPA SVC SPV RUPA LMB RULB DA RMB OESOPHAGUS CT MEDIASTINUM AT THE LEVEL OF PULMONARY TRUNK Sections at a lower level shows Main pulmonary artery MPA Right pulmonary artery RPA Course from the left to right CT MEDIASTINUM BELOW CARINA SHOWING ATRIA • Left atrium LA appears anterior to esophagus and descending aorta DA • Superior vena cava blends into right atrium RA • Pulmonary trunk passes anterior to aortic root to arise from right ventricle RV • Posterior to ascending aorta,AA superior pericardial recess may cause a weak density mass CT MEDIASTINUM BELOW CARINA SHOWING ATRIA RIGHT ATRIUM ASCENDING AORTA INFERIOR PULMONA RY VEIN MPA LEFT ATRIUM DA CT MEDIASTINUM HEART BRO NCH EAL TRE E AND BRO NCH EAL CRO SS SEC TIO NAL BRONCHIAL TREE trachea Right upper bronchus Apical Posterior anterior Middle lobe Right Lower lobe bronchus Left main bronchus Apical posterior and anterior lingual Left lower lobe bronchus BRONCHIAL CROSS SECTION AND CT AT RESPECTIVE LEVEL BRONCHIAL CROSS SECTION CT IMAGE Right apical segment Apical posterior segment NORMAL LUNG ANATOMY ON COMPUTED TOMOGRAPHY COLOUR ISCHEMATIC REPRESENTATION OF DIFFERENT LUNG SEGMENTS
