Imaging the Respiratory System PDF

College of Medical and Health Technology Department of Radiology Techniques 3th Academic Special Radiological Procedures 2024-2025 lecture 4: Methods of Imaging the Respiratory System Hayd...

College of Medical and Health Technology Department of Radiology Techniques 3th Academic Special Radiological Procedures 2024-2025 lecture 4: Methods of Imaging the Respiratory System Hayder Suhail Najm, Medical Imaging Technology, PhD Anatomy review:  The chest, or thorax, is the upper portion of the trunk between the neck and the abdomen.  Radiographic anatomy of the chest is divided into three sections: A. bony thorax, B. respiratory system, C. mediastinum. The bony thorax: Is the part of the skeletal system that provides a protective framework for the parts of the chest involved with breathing and blood circulation. The respiratory system:  pharynx, trachea, bronchi, and lungs.  An important structure of the respiratory system is the dome-shaped diaphragm, the primary muscle of inspiration.  While the diaphragm moves down creates a "sucking" action, resulting in air being drawn into the lungs through the nose and mouth, pharynx, larynx, trachea, and bronchi. This causes the lungs to fill with air, which is known as inspiration.  Trachea: It is a fibrous muscular tube about (2 cm) in diameter and (11 cm) long. Approximately 16 to 20 C-shaped rings of cartilage are embedded in its anterior wall.  These rigid rings keep the airway open by preventing the trachea from collapsing during expiration.  The trachea, located just anterior to the esophagus, extending downward where it divides into right and left primary bronchi.  Lungs: are located on each side of the thoracic cavity.  The right lung is made up of 3 lobes: the superior (upper), (middle), and inferior (lower) lobes-divided by two deep fissures. o The horizontal fissure separates the superior and middle lobes. o The oblique fissure, which separates the inferior and middle lobes,  The left lung has only two lobes-the superior (upper) and inferior (lower)- separated by a single deep oblique fissure  Mediastinum:  The medial portion of the thoracic cavity between the 2 lungs.  Four radiographically important structures located in the mediastinum are: 1. thymus gland. 2. heart and great vessels. 3. trachea. 4. esophagus..  METHODS OF IMAGING THE Respiratory System 1. Plain films 2. Computed tomography (CT) 3. Radionuclide imaging (V/Q scans) 4. Ultrasound (US)—for pleural, chest wall disease and diaphragm 5. Magnetic resonance imaging (MRI) 6. Positron emission tomography (PET)  CT SCAN OF THE THORAX Indications: 1. In assessing pulmonary masses, chest wall, or pleural disease. 2. For the staging and follow-up of malignancy in the chest 3. Evaluation of known/suspected thoracic vascular assessment (congenital or acquired pulmonary embolus, aortic dissection, arteriovenous malformation, etc.) 4. In the assessment of airway disease, bronchiectasis and large airway stenosis 5. Trauma of the chest 6. Performing CT-guided intervention e.g. lung, pleura, or chest wall mass biopsy. Contraindications:  Where intravenous (i.v.) contrast medium is to be administered, the presence of impaired renal function, nephrotoxic drugs,  history of previous reaction to i.v. iodinated contrast media must be evaluated.  Technique CT CHEST – TYPES 1. Standard or conventional CT(Volume scan):  usually performed with intravenous contrast enhancement at a rate of 3–5 mL s−1 with a delay of 25–40 s.  It covers the full lung, very quickly.  Delayed imaging at 60–65 s can be useful in cases of large pleural effusion to assess for otherwise occult underlying soft tissue pleural thickening. 2. High-resolution CT (HRCT): Noncontrast scan obtained on full inspiration. A. 1 mm (or less) slice at 10–20 mm intervals or B. volume acquisition through the lungs with a reconstruction of contiguous 1 mm slices:  Spatial resolution should be maximized using the smallest field of view possible.  Reconstruct images using a high-resolution (high spatial resolution) ‘bone’ algorithm.  A volume acquisition with reconstruction of contiguous slices benefits postprocessing capabilities, particularly multiplanar reformatting, which can help illustrate the craniocaudal distribution of lung changes.  Additional expiratory images can be performed in suspected air-trapping and airway disease.  Additional prone images are indicated to differentiate reversible-dependent change from early interstitial fibrosis. 3. Low Dose CT:  Uses low doses of radiation. As much as 30 to 50 % less than regular CT  Details of the image acquired decreased  Uses:  Follow up in case of 1. Infections 2. Post lung transplant 3. Metastases. 4. CT angiography: 5. CT with contrast:  Evaluation of the mediastinum (lymph nodes, infection)  Evaluation of the suspected cancer.  Evaluation of the pleural masses. Windowing (CT):  Windowing, also known as grey-level mapping, contrast stretching, histogram modification or contrast enhancement is the process in which the CT image grey scale component of an image is manipulated via the CT numbers; doing this will change the appearance of the picture to highlight particular structures.  The brightness of the image is adjusted via the window level.  The contrast is adjusted via the window width. Window width:  The window width (WW) : is the range of CT numbers that an image contains, Could be:-  Wide window Defined 400-2000 HU (wide range) which means more tissues are included in the image because more CT numbers are included in the range. o Narrow window Defined as 50-350 HU (narrow range) which means less tissues are included in the image because less CT numbers are included o Window level/center The window level (WL), often also referred to as window center, is the midpoint of the range of the CT numbers displayed. o A 'window' can be set to look at certain tissues. o Soft tissue (Mediastinal) window o A soft tissue window cannot be used for lung parenchyma, as lung density (-500 HU) is outside range and will appear completely black. Window Level: +50 HU Window Width: 350 HU (Range: -125 to +225) Axial lung window Mediastina (soft tissue) Sagittal bone window Axial C+ CTPA Axial bone window  CT-GUIDED LUNG BIOPSY Indications:  Investigation of a new or progressing pulmonary opacity.  Investigation of a new lung/pleural/chest wall lesion in a patient with known malignancy.  To obtain material for culture when other techniques have failed.  To obtain histological samples for genetic typing in patients with known malignancy (e.g. identifying epidermal growth factor receptor [EGFR] mutation in a patient with known lung adenocarcinoma). Patient Preparation:  The procedure can routinely be performed on a day-case outpatient basis, with observation for 4–6 hours postprocedure, but a bed should be available in case of complications  Clotting screen (ideally INR ≤1.4 and platelets >100 × 109 L−1). There is no clear evidence that aspirin should be discontinued prebiopsy, but consensus suggests clopidogrel should be stopped 5 days prior to the procedure.  Pulmonary function tests (spirometry).  Technique: 1. Procedures are usually carried out under CT guidance, but if the lesion abuts the peripheral pleural surface. 2. Position the patient in a stable position on the back, front, or side. 3. Inject local anesthetic into skin and subcutaneous tissues down to the pleura. 4. Sampling needle is advanced during suspended inspiration with regular imaging to monitor position/alignment. 5. 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.  PULMONARY EMBOLISM  Pulmonary embolism (PE) is a blockage of an artery in the lungs by a substance that has moved from elsewhere in the body through the bloodstream (embolism).  Symptoms of PE may include shortness of breath, chest pain while breathing in, and coughing up blood.  PE usually comes from a blood clot in the leg that travels to the lung. METHODS OF IMAGING PULMONARY EMBOLISM 1.Plain film chest radiograph. 2.radionuclide scanning. 3.Multidetector CT pulmonary angiography (CTPA) 4.Pulmonary arteriography was traditionally the 'gold standard' and will detect most pulmonary emboli but has been superseded by multidetector CTPA. 5.MR angiography where ionizing radiation exposure or the use of iodinated contrast media is contraindicated. COMPUTED TOMOGRAPHY IN THE DIAGNOSIS OF PULMONARY EMBOLI Technique: 1. The technique will depend on individual CT scanner technology. 2. Individual CT manufacturers will recommend specific scanning protocols, including delivery of i.v. contrast medium. 3. CT will not only identify the presence of thrombus but also allow assessment of secondary right heart strain.  CT Pulmonary Angiography(CTPA)  A CT pulmonary angiogram (CTPA) is a medical diagnostic test that employs computed tomography (CT) angiography to obtain an image of the pulmonary arteries, Its main use is to diagnose pulmonary (PE).  It is a preferred choice of imaging in the diagnosis of PE due to its minimally invasive nature for the patient, whose only requirement for the scan is an intravenous line  The patient receives an intravenous injection of an iodine-containing contrast agent at a high-rate using an injector pump. Images are acquired when contrast in the pulmonary arteries reach its max intensity. This can be done using bolus tracking.  A normal CTPA scan will show the contrast filling the pulmonary vessels, appearing as bright white. Any mass filling defects, such as an embolus, will appear dark in place of the contrast, filling/blocking the space where blood should be flowing into the lungs.  PULMONARY ARTERIOGRAPHY Indication: 1. Demonstration of pulmonary emboli and other peripheral abnormalities. 2. Planning and performing therapeutic procedures such as catheter directed thrombolysis or catheter embolectomy. 3. Prior to embolization of pulmonary arteriovenous malformations. Contrast Medium:  LOCM 370 mg I mL−1; 0.75 mL kg−1 at 20–25 mL s−1 (max. 40 mL). Equipment:  Digital subtraction angiography facilities  Pump injector  Catheter: pigtail (coiled end, end hole and 12 side holes) Technique: 1. The Seldinger technique is used via the right femoral vein. The catheter is introduced via an introducer sheath. 2. The catheter tip is sited, under fluoroscopic control, to lie 1–3 cm above the pulmonary valve. 3. Pulmonary pressures should routinely be measured during the procedure; lower injection rates are advised if the pressures are raised.  MAGNETIC RESONANCE IMAGING OF THE RESPIRATORY SYSTEM  MRI currently has a limited role in assessing the respiratory system due to the artifact from the large volume of air within the lungs.  The mediastinum and chest wall are well assessed by MRI due to the ability to image in the coronal and sagittal planes.  MR OF PULMONARY EMBOLI  It is difficult to obtain technically adequate images for pulmonary embolism patients using MRI.  Magnetic resonance pulmonary angiography (MRPA) should be considered only at centers that routinely perform it well and only for patients for whom standard tests are contraindicated like pregnant ladies with suspicion of pulmonary embolism.  PET AND PET-CT OF THE RESPIRATORY SYSTEM  Positron emission tomography (PET) is a modern non-invasive imaging technique for quantification of radioactivity in vivo. It involves the intravenous injection of a positron-emitting radiopharmaceutical, waiting to allow for systemic distribution, and then scanning for detection and quantification of patterns of radiopharmaceutical accumulation in the body.  CT provides us a morphological information about the lesion.  PET-CT together will provide us with both metabolic and morphological information of the lesion.  Standardized Uptake value: SUV < 2.4 (3.5)= malignancy.  PET-CT imaging is a form of dual-modality imaging that utilizes the advantages of both positron emission tomography (PET) and computed tomography (CT).  The typical PET-CT protocol involves the injection of a given radiopharmaceutical followed by a specified uptake/waiting period.  The most commonly used radiopharmaceutical is F-18 fluorodeoxyglucose (FDG).  PET and CT scans are performed sequentially with the patient in the same position to allow co-registration of both sets of images.  Images can be displayed side-by-side or fused to overlay the PET data on the CT scan Procedure:  Fasting for 4-6 hours - diabetic patients should fast overnight (12 hours)  Blood glucose level