Computed Tomography (CT) of the Chest - Dijlah University College PDF

Dijlah University College ‫كلية دجلة الجامعة‬ Department of Radiology technologies ‫قسم تقنيات االشعة‬ ‫المرحلة الرابعة‬ Topic: Computed tomography...

Dijlah University College ‫كلية دجلة الجامعة‬ Department of Radiology technologies ‫قسم تقنيات االشعة‬ ‫المرحلة الرابعة‬ Topic: Computed tomography ‫التصوير المقطعي‬ Lecture16&17&18 Subject: CT scan of the chest ‫ ريم عبد الجليل خليل‬.‫د‬  Chest CT is used primarily to evaluate and further defined disease identify by routine chest X-ray.  Although many lung disorders can be diagnosed by plain chest radiograph but its limitation in providing definite diagnosis are widely known.  Advantages of CT are shorter examination time, thinner sections and higher resolution.  Importance of CT in Chest Imaging: o Detects diseases affecting the lungs, mediastinum and chest wall. o Assists in planning interventions such as biopsies or surgeries. Anatomy:  The thoracic cavity lies between the neck and the abdomen.  It is bounded by the thoracic wall and extends from the diaphragm (below) to the superior thoracic aperture (above).  Thoracic apparatus comprises of the first thoracic vertebrae, upper border of manubrium sterni and the first ribs on either side.  Anteriorly, the thoracic cavity is limited by the sternum, while posteriorly it is bounded by the thoracic part of the vertebral column.  The thoracic cavity is divided into two compartments. These include the mediastinum in the center, bounded by a pleural cavity on either side. The pleural cavities house the lungs inside them. Whereas, the mediastinum contains heart and the associated big vessels and several important structures. The lungs :  Are composed of a spongy material called the parenchyma. The parenchymal tissue contains the fine structures of the bronchial trees and pulmonary circulation. The exchange of oxygen and carbon dioxide takes place at the alveolar level within the parenchyma.  Divisions of the Lungs : o The right lung is composed of 3 lobes. They are named according to location as the upper, middle and lower lobes. The upper and middle lobes are separated by a fissure called the horizontal fissure. An additional oblique fissure separates the middle and lower lobes. o The left lung is composed of 2 lobes , a superior and inferior lobe divided by an oblique fissure.  The hilum: is the central area of each lung, where the bronchi, blood vessels, lymph vessels and nerves enter and leave the lungs RUL. Right upper lobe, LUL: Left upper lobe , RML: right middle lobe, RLL: right lower lobe, LLL: left lower lobe The Chest Wall : Includes ribs, sternum, clavicles, chest muscles, neurovascular bundles, skin and subcutaneous tissues. The diaphragm :  Is a muscular structure located immediately below the lung bases.  It is divided into 2 sections called the right and left hemidiaphragm  The right hemidiaphragm is higher on a chest radiograph because of the location of the liver, which is immediately inferior to it.  The term cardio-phrenic angles is sometimes used to describe the area where the heart’s border comes in contact with the diaphragm. The pleura :  Each lung is surrounded by a thin walled sac called the pleura which completely encases the lung with an inner layer called the visceral layer and an outer layer called the parietal layer.  The potential space between these 2 layers is called the pleural space. Radiographically, this space is important because it can fill with fluid (pleural effusion), air (pneumothorax) or blood (hemothorax).A chest tube can be placed within the pleural space to drain accumulated fluid or air. The mediastinum :  Is the space between the lungs that houses the heart and great vessels, including the proximal pulmonary arteries and aortic root.  Additionally, the proximal bronchial trees, pulmonary veins, a portion of the esophagus ,thymus gland and lymphatic vessels are important structures found in the mediastinum. Imaging Technique: Patient Preparation:  Ensure patients are fasting for at least 4-6 hours if IV contrast is used.  Explain the procedure, including the importance of breath-holding to minimize motion artifacts.  Position the patient supine with arms raised above the head to reduce beam hardening artifacts. Scanning Parameters:  kVp: 120-140 for optimal image contrast.  mA: Automated dose modulation based on patient size.  Slice Thickness: Thin slices (1-3 mm) for high-resolution images, especially for the lungs.  Pitch: 0.8-1.2 for optimal spatial resolution. Contrast Media Protocols:  Use iodinated IV contrast to enhance mediastinal structures, vascular anatomy and masses.  Injection rate: 3-5 mL/s.  Typical dose: 1-2 mL/kg body weight.  Timing: 1. Pulmonary Arterial Phase: 15-25 seconds after injection, ideal for evaluating pulmonary embolism. 2. Venous Phase: 45-70 seconds for mediastinal and chest wall evaluation.  Breath-Hold Technique: o Patients are instructed to hold their breath during scanning to avoid respiratory motion artifacts.  Reconstruction Algorithms: o Use high-spatial-frequency algorithms for lung parenchyma. o Soft tissue algorithms for mediastinal structures and chest wall.  Window Settings: o Lung Window: WL: -600 HU, WW: 1500 HU for optimal visualization of lung parenchyma. o Mediastinal Window: WL: 40 HU, WW: 400 HU for soft tissues. o Bone Window: WL: 300 HU, WW: 2000 HU for chest wall structures. Clinical Indications for CT Chest Imaging: Lungs: Detection of infections (e.g., pneumonia, tuberculosis). Evaluation of lung tumors, nodules and interstitial lung diseases (e.g., fibrosis). Identification of pulmonary embolism and emphysema. Mediastinum: Staging of lung cancer (mediastinal lymph node involvement). Detection of mediastinal masses (e.g., thymomas, lymphomas). Evaluation of vascular abnormalities (e.g., aortic aneurysm, dissection). Chest Wall: Trauma assessment (e.g., fractures, hematomas). Detection of chest wall tumors and infections. Evaluation of post-surgical complications. Benign nodule CT guided lung biopsy: Indications 1. Investigation of a new pulmonary opacity when other diagnostic techniques such as bronchoscopy have failed to make a diagnosis. 2. Investigation of a new lung/pleural/chest wall lesion in a patient with known malignancy. 3. To obtain material for culture when other techniques have failed to identify the causative organism in a patient with persistent consolidation. Contraindications: Contraindications are not absolute but should be carefully evaluated by the relevant multidisciplinary team. 1. Vascular: Bleeding diatheses (including conditions that affect platelet function such as chronic renal failure) Patient on anticoagulants. Significant pulmonary arterial or venous hypertension 2. Respiratory: Contralateral pneumonectomy Presence of significant emphysema Significantly impaired respiratory function. 3. Suspected hydatid disease. 4. Uncooperative patient (including intractable cough). Equipment 1. Sampling needle: Fine needle aspiration: Usually use 20 or 22G needles. Cutting needle biopsy: needles are larger gauge (usually 18 or 20G) and obtain a solid core of tissue for histological examination. 2. Full resuscitation equipment including equipment for pleural aspiration and chest drain insertion. Staff should be prepared for recognition and treatment of complications of pneumothorax, vasovagal episodes, haemoptysis and (very rarely) air embolus. Patient Preparation: 1. Sedative premedication should be avoided if possible, as the patient must remain cooperative so that a consistent breathing pattern can be maintained during the procedure. 2. The procedure can routinely be performed on a day-case outpatient basis, with observation for 4–6 h post-procedure, but a bed should be available in case of complications. 3. Clotting screen 4. Pulmonary function tests Technique Procedure clearly explained to patient particularly with regard to breathing instructions, avoid deep breaths,Valsalva manoeuvres and so on and to obtain a consistent level of breath-hold whilst the needle traverses the lung and samples are taken. Position patient in stable position on back, front or side, determined by the position of mass and the most expeditious route from skin to lesion to avoid fissures, bony structures, cystic/ emphysematous lung tissue and so on. Standard aseptic technique utilized. Inject local anesthetic into skin and subcutaneous tissues down to the pleura. Try to instil a bleb of anaesthetic immediately extra-pleurally without traversing the parietal pleura itself—the anaesthetic will act over a greater area of pleura and reduces the number of times that the pleura is crossed (which may reduce incidence of pneumothorax). Sampling needle is advanced during suspended inspiration with regular imaging to monitor position/alignment. Once an adequate sample has been obtained, a limited CT at the end of the procedure will determine if a pneumothorax or parenchymal bleed is present. After care: 1. Close observation post-procedure for at least 1 hour in a supervised ward or recovery area, with the patient laying in the puncture site down position so the weight of the lung helps seal the pleural puncture site.The patient should avoid raising intra-thoracic pressure unnecessarily—avoid sitting-up unaided, coughing and talking for the first hour or so. 2. Departmental PA chest x-ray at approximately 1–4 h post-procedure. If a pneumothorax has developed (or progressed), then the further management will depend on the size of the pneumothorax and clinical condition of the patient. Small pneumothoraces in asymptomatic patients may be observed; larger pneumothoraces in symptomatic patients will require aspiration or chest drain insertion. 3. High-risk patient particularly those with pre-existing impairment of respiratory function, are best routinely admitted overnight.  Complications: Usually occur early following the procedure: 1. Pneumothorax : Chest drain insertion is necessary. The incidence of pneumothorax is increased if: o the operator is inexperienced o a larger gauge needle is used o there is an increased number of needle passes made there is a greater pleura to lesion depth o smaller lesions are biopsied o the needle traverses a fissure o the patient is coughing 2. Local pulmonary hemorrhage 3. Hemoptysis 4. Other complications, such as haemothorax, implantation of malignant cells along the needle track, spread of infection and air embolism, are all extremely rare. 5. The current documented death rate is 0.15%. References: Chapman & Nakielny’s Guide to Radiological Procedures