Pulmonary Imaging

CHAPTER 12 PULMONARY IMAGING

Pulmonary Imaging The lung examination is performed to determine  the distribution of the air space (ventilation) and  the distribution of blood flow (perfusion–sometimes abbreviated as Q) in the lungs.

the ventilation and perfusion scans (sometime called V/Q scans) are frequently used to diagnose pulmonary emboli.

PART I. PERFUSION IMAGING 1 Radiopharmaceuticals  The distribution of pulmonary arterial blood flow is usually demonstrated by the intravenous injection of radioactive particle, 99mTc-MAA  which measure 30 to 40μm(microns) in diameter.

1 Radiopharmaceuticals 

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After intravenous injection the particle, which pass through the right atrium and right ventricle, where they are well mixed with blood, and then into the pulmonary artery. They pass out into the blood vessels of the lung until they become impacted in the terminal arteriales and capillaries because they are too large to pass through them. 30 to 40μm Diameter of capillary is about 8~9 μm.

Safe?

Yes!

1 Radiopharmaceuticals 

SAFE 

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With the usual dose of particulate material of the appropriate size, fewer than 1 in 1000 pulmonary arterioles are blocked.

Special care should be taken in patients known to have 

severe pulmonary hypertension 

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right to left shunts 

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because their available vascular bed is reduced. because the particles will pass through to the systemic circulation and embolize to the brain, kidneys, heart, and other organs.

Pneumonectomy Pediatric patients Pregnancy

2 Method of injection 

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There is a difference in the patterns of perfusion depending on whether the particles are injected with the patient in the upright or supine position. As gravity plays an important role in the pressure relationships with the lungs. 

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Patients injected upright will tend to have a larger proportion of the particles distributed toward the bases. Patients injected supine demonstrate a more homogeneous distribution of particles from the bases to the apices.

3 Positioning Standard perfusion imaging includes six basic views: posterior (POST), Anterior (ANT), right and left laterals (RL,LL), and right and left posterior obliques (RPO,LPO).

Presently, tomography of lung has been widely performed in this study.

PART II. VENTILATION IMAGING The body maintains a precise regulation of the distribution of perfusion based upon a continuous sampling of the level of oxygen in the alveoli. When the partial pressure of oxygen in a segment of lung is low, pulmonary blood flow is directed away from that area. If an imaging of the regional distribution of perfusion is recorded without any knowledge of the regional distribution of ventilation, it is difficult to determine if the blood flow was directed away from that area because of

decreased local oxygen content or secondary to a mechanical (embolic) obstruction.

PART II. VENTILATION IMAGING   

Xe 133 Xenon 133

The xenon exam consists of 3 phases: 1. 2. 3.

Single breath Equilibrium Washout

Xenon-133 1. 

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Single breath The patient takes a single deep inspiration and holds it for as long as possible. This view reflects regional ventilation and can detect approximately 66% of ventilation defects associated with obstructive airway disease.

Xenon-133 2. 

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Equilibrium During this phase, the patient performs normal tidal respirations for at least 3 minutes, and 5 minutes if possible, while rebreathing a mixture of 133Xe and oxygen. This view demonstrates the overall lung volume as tracer equilibrates between all aerated portions of the lungs. It is the least sensitive for detecting obstructive airway abnormalities. However, adequate duration of rebreathing ensures diagnostic quality washout phase.

Xenon-133 3. 

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Washout Inhalation of 133Xe is discontinued and the patient breaths room air or oxygen while exhaling the xenon into a charcoal trap. 133 Xe should clear from the lungs normally in 2-3 minutes. Retention of tracer activity beyond 3 minutes is observed in areas of air trapping (obstructive airway disease).

Xenon-133 

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The washout phase of the exam will detect about 90% of abnormalities associated with obstructive airway disease. It is therefore more sensitive than the single breath view in this regard.

The other radiopharmaceuticals    

Tc-99m DTPA Aerosol, Xenon-127 , Tc-99m Technegas, Krypton-81m .

Characteristic Patterns: 

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By combining studies of ventilation and perfusion one can determine whether defects in blood flow are associated with defects in ventilation. The pulmonary diseases commonly met with in clinical nuclear medicine tend to fall into two categories:  V/Q mismatch  V/Q match

Characteristic Patterns: (1) V/Q mismatch 

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With abnormal regional pulmonary blood flow, but normal (or almost normal) regional ventilation. Pulmonary embolism is by far the most important one of these, but early heart failure, interstitial lung disease, some lung cancers and other abnormalities of the pulmonary vasculature may show this pattern.

(2) V/Q match  

with abnormal ventilation and abnormal blood flow. Here the most common conditions are chronic bronchitis, emphysema, and asthma, with cystic fibrosis and bronchial tumors, or foreign bodies obstructing a bronchus can all produce localized abnormalities of ventilation and blood flow.

CLINICAL APPLICATIONS 1. Pulmonary Embolism A pulmonary embolus occurs when a thrombus forms the wall of the vein, and circulates through the heart to enter the lung. These events are more likely to occur in bedridden or sedentary people that in active, healthy individuals.

Clinical Findings 

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No single, or combination of, clinical findings is either specific or sensitive enough to diagnose or exclude PE. Symptoms of pulmonary embolism include tachypnea (most common), tachycardia, hypoxia, pleuritic chest pain, hemoptysis, and atrial fibrillation. Massive PE may be associated with cor pulmonale and the ECG may show right axis deviation, P-pulmonale, RBBB, or other evidence of right heart strain. A normal arterial blood gas does not exclude the presence of a PE. Although PE occurs most commonly from deep venous thrombosis in the lower extremity, about 10% arise from clot in the upper extremity primarily associated with an indwelling catheter.

Risk Factors 

In the PIOPED (Prospective Investigation of Pulmonary Embolism Diagnosis) study, 92% of the patients with pulmonary embolism had at least one of the following risk factors:    

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immobilization, recent surgery, underlying malignancy, history of deep venous thrombosis or pulmonary embolism, estrogen use, pre-existing cardiac disease.

In patients without prior cardiac or pulmonary disease only immobilization and surgery are significant discriminating predisposing factors.

CLINICAL APPLICATIONS 

On V/Q scanning, a pulmonary embolism is characterized by a ventilation-perfusion mismatch:  An area of normal ventilation corresponding to a segmental wedge-shaped area of decreased or absent perfusion which extends to the surface of the lung.

CLINICAL APPLICATIONS 2 Chronic Obstructive Airway Disease  chronic bronchitis, emphysema, and asthma, with cystic fibrosis and bronchial tumors, or foreign bodies obstructing a bronchus can all produce localized abnormalities of ventilation and blood flow.  with abnormal ventilation and abnormal blood flow------ V/Q match.

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Interpret the EF, PER, PFR, the amplitude image and the phase image. What are the clinical application of equilibrium multiple-gated blood pool imaging. What are the clinical application of ventilation-perfusion studies. What is the characterized of pulmonary embolism on V/Q scanning?