Pulmonary System Quiz

Introduction to Respiratory System Imaging

• The chest, or thorax, is the upper portion of the torso between the neck and abdomen.
• Radiographic anatomy of the chest is divided into three sections: bony thorax, respiratory system, and mediastinum.

Bony Thorax

• The bony thorax is part of the skeletal system providing a protective framework for the structures involved in breathing and blood circulation within the chest.
• The bony structure includes ribs, sternum, and thoracic spine.

Respiratory System

• The respiratory system includes the pharynx, trachea, bronchi, and lungs.
• The dome-shaped diaphragm is a critical muscle for inspiration, the process of drawing air into the lungs.
• The diaphragm moves down, creating a "sucking" action. Air is drawn through the nose, mouth, pharynx, larynx, trachea, and bronchi. This fills the lungs.

Trachea

• The trachea is a fibrous muscular tube, approximately 2 cm in diameter and 11 cm long.
• It contains C-shaped rings of cartilage that prevent it from collapsing during exhalation.
• The trachea sits anterior to the esophagus. It branches into the right and left primary bronchi.

Lungs

• Lungs are located on each side of the thoracic cavity.
• The right lung is divided into three lobes (superior, middle, and inferior), separated by fissures (horizontal and oblique).
• The left lung is divided into two lobes (superior and inferior), separated by a single oblique fissure.

Mediastinum

• The mediastinum is the medial portion of the thoracic cavity between the two lungs.
• Four radiographically important structures within the mediastinum are the thymus gland, heart and great vessels, trachea, and esophagus.

Methods of Imaging the Respiratory System

• Plain films
• Computed tomography (CT)
• Radionuclide imaging (V/Q scans)
• Ultrasound (US) - for pleural, chest wall, and diaphragm disease
• Magnetic resonance imaging (MRI)
• Positron emission tomography (PET)

CT Scan of the Thorax - Indications

• Assessing pulmonary masses, chest wall, or pleural disease.
• Staging and follow-up of malignancy in the chest.
• Evaluation of known/suspected thoracic vascular issues, including pulmonary embolus, aortic dissection, or arteriovenous malformations.
• Assessing airway disease like bronchiectasis and large airway stenosis.
• Evaluating trauma to the chest.
• Performing CT-guided interventions, such as lung, pleura, or chest wall mass biopsy.

CT Scan of the Thorax - Contraindications

• Intravenous (IV) contrast medium administration requires evaluation for impaired renal function, use of nephrotoxic drugs, and history of previous adverse reactions to iodinated contrast media.

Technique CT Chest - Types

• Standard/Conventional CT (Volume scan): Typically performed with intravenous contrast enhancement at a rate of 3-5 mL/sec with a delay of 25-40 seconds. This quickly covers the entire lung. Delayed imaging at 60-65 seconds can assist in assessing otherwise hidden pleural thickening, particularly in cases of large pleural effusions.
• High-resolution CT (HRCT): Noncontrast scan acquired during full inspiration. 1mm (or thinner) slices at 10-20mm intervals (or volumetric acquisitions) are ideal. High resolution image reconstruction techniques are important to maximize visualization of detailed lung anatomy. Additional expiratory images can assist in evaluating suspected air-trapping. Prone images might be needed to distinguish reversible changes from fibrosis.
• Low-dose CT: Utilizes reduced radiation doses while maintaining diagnostic quality. This technique is useful for follow-up exams (infections, post-lung transplant, metastases).

CT Angiography (CT with contrast)

• Evaluation of mediastinum (lymph nodes, infection)
• Assessment of suspected cancer
• Evaluation of pleural masses

Windowing (CT)

• Windowing (grey-level mapping, contrast stretching, histogram modification) is used to manipulate the CT image grayscale to highlight certain structures. It adjusts brightness (Window level) and contrast (Window width) of the image.

Window Width (WW)

• Wide window: displays a broader range of CT numbers, including more tissues. (400-2000 HU)
• Narrow window: displays a limited range of CT numbers, showing fewer tissues. (50-350 HU)

Window Level/Center (WL)

• WL or window center is the midpoint of the range of CT numbers displayed.

Windowing Examples

• Soft Tissue (mediastinal) window
• Lung window
• Bone window

CT-Guided Lung Biopsy

• Investigation of new or progressive pulmonary opacities
• Assessing new lung, pleural, or chest wall lesions in patients with existing malignancies.
• Obtaining tissue samples when other procedures fail to yield sufficient diagnostic material.
• Genetic testing of tissue samples in patients with known lung malignancy, to identify epidermal growth factor receptor (EGFR) mutations, for example

Patient Preparation

• Procedures can often occur on an outpatient basis with several hours of observation afterwards.
• Patients should have clotting screen (INR and platelets assessments).
• Certain medications, like aspirin and clopidogrel, may need to be stopped before the procedure.
• Pulmonary function tests (like spirometry) may be ordered.

Pulmonary Embolism Methods of Imaging

• Plain film chest radiograph
• Radionuclide scanning
• Multidetector CT pulmonary angiography (CTPA); consider the gold standard nowadays
• Pulmonary arteriography (less common now)
• MR angiography (alternative for scenarios where radiation or IV contrast is contraindicated.)

Pulmonary Embolism Technique CTPA

• Patients receive IV contrast using an injector pump at a high rate.
• Images are taken when the contrast reaches the pulmonary arteries.
• Normal scan shows contrast filling pulmonary blood vessels. An embolus appears as a filling defect (dark shadow).

Pulmonary Arteriography

• Procedures are aimed at identifying emboli and other peripheral abnormalities.
• Treatment planning and performing interventions like catheter-directed thrombolysis or embolectomy for pulmonary embolism.

Contrast Medium (for Pulmonary Embolism Imaging)

• LOCM 370 mg I/mL; 0.75 mL kg-1 at 20-25 mL/sec (max. 40 mL).

Equipment (for Pulmonary Embolism Imaging)

• Digital subtraction angiography facilities
• Pump injector
• Catheter: pigtail (coiled, end-hole and side holes)

Seldinger Technique

• The Seldinger technique is used to introduce catheters via the right femoral vein; the catheters are advanced through an introducer sheath, then placed within 1-3 cm of the pulmonary valve under fluoroscopic guidance.
• Pulmonary pressures are routinely monitored during the procedure. Lower injection rates should be used if pressures are elevated.

MRI of the Respiratory System

• MRI has a limited role in the respiratory system due to artefacts from air in the lungs.
• Mediastinum and chest wall can be assessed well because of MRI's ability to image in coronal and sagittal planes.

MRI of Pulmonary Embolism

• Technically adequate images are often difficult to achieve with MRI for pulmonary embolism.
• MR pulmonary angiography (MRPA) is generally reserved for specific situations; most often, when standard imaging tests are contraindicated (e.g. pregnant patients, patients allergic to contrast media).

PET and PET-CT of the Respiratory System

• Positron emission tomography (PET), a noninvasive technique, measures radioactivity in vivo. This is useful in showing radioactivity distribution, post injection of a radiopharmaceutical, to help identify issues.
• PET/CT scan together give both morphological (CT) and metabolic (PET) information about a lesion.
• Typical radiopharmaceutical used is F-18 fluorodeoxyglucose (FDG).
• A standardized uptake value (SUV) < 2.4 suggests less chance of malignancy compared to SUV > 3.5.

PET-CT Procedure

• Patients must fast 4-6 hours before the scan. Diabetic patients should fast for 12 hours.
• Blood glucose levels are usually under 150 mg/dL.
• Strenuous exercise should be avoided 24 hours prior to the scan.
• Scan is carried out 60 minutes after FDG injection.

PET-CT Applications

• Oncological applications include baseline staging, treatment planning, assessing treatment response, and monitoring changes post-therapy.
• Non-oncological applications include cardiology, neurology.

Test your knowledge on the anatomy and diagnostics of the respiratory system with this quiz. From the primary muscle of inspiration to the specifics of CT pulmonary angiograms, this quiz will challenge your understanding of pulmonary health. Perfect for students and professionals in the medical field.