Pulmonary Anatomy, Physiology, Lung scintigraphy principles

NMT631

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Position of heart & lungs in thoraxReview of Respiratory System (1)

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Cardiac notch (cardiac silhouette)

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Lobes of the Lung

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Right, left lungs:

-apex, base

- lobes, segments

- cardiac impression (Cardiac silhouette/ cardiac notch)

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Lung SegmentsReview of Respiratory System (1)

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Lung Pleura Pleura: parietal visceral (pulmonary)

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Diaphragm

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Airways

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- Larynx

- Trachea

- carina

- left, right main bronchus

- Secondary bronchi

- Bronchioles

- alveoli

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Pulmonary CirculationReview of Respiratory System (1)

Circulatory system:

superior/inferior vena cava, right atrium, right ventricle, pulmonary arteries, lungs, pulmonary veins, left atrium, left ventricle, aorta

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Oxygenated – Deoxygenated blood flow pathwayReview of Respiratory System (1)

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Pulmonary circulation: arteries, arterioles, alveolar capillaries

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Effect of Gravity on Pulmonary Circulation

• At or below level of heart (Zone 2 & Zone 3), arterial pressure in smaller vessels greater so effect of gravity less noticeable

• Lung apices are above level of heart, so not well perfused. The reason is PA > Pa resulting in collapsed small vessels

As a general rule, blood flow through a capillary in an alveoli occurs only if: Pulmonary artery pressure (Pa) > Alveloar pressure (PA) & Pulmonary vein pressure (Pv)

Upright

Thus Zone 1 is ventilated but not perfused in compromised individuals

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Effect of Gravity on Pulmonary Circulation

– Apices of lung and heart about at same level, so effect of gravity minimized

– Apical blood flow increases to equal to the blood flow to bases of lung (Pa > Pv > PA)

– Clinical implication: Administer radiopharmaceutical used to demonstrate lung perfusion with patient supine

Supine

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Respiratory cycle

Inspiration

Expiration

Compliance(ability to stretch)

Elastic recoil

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VentilationAir moves down a pressure gradient

Highpressure

Lowpressure

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Regulation of VentilationR

evie

w o

f Res

pira

tory

Sys

tem

(1)

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Respiration

Includes processes of:- ventilation- gas exchange- gas transport- regulation of ventilation

- can be monitored with nuclear medicine

techniques

The transport of O2 to and CO2 from cells

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In a healthy lung, ventilation (V) and perfusion (Q) are matched for efficient and optimal gas exchange (V/Q ratio = 1)

The disparity between alveoli surface area and volume of blood in pulmonary capillaries affected by gravity, regulatory mechanisms, and disease

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Patients on whom nuclear medicine lung examinations are ordered may suffer from hypoxia.

• Hypoxia: insufficient oxygen due to decreased lung function and/or decreased oxygen supply to tissues caused by decreased blood flow or decreased cardiac output

• Symptoms of hypoxia:

– Lethargy

– Dyspnea

– Cyanosis

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A Brief overview of

Lung Ventilation Perfusion Imaging

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Lung Perfusion Imaging

Clinical Indications

Radiopharmaceutical used

Dosage & Administration

Technique

The Normal Scan

Artifacts & Pitfalls

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Pulmonary Embolsm

• Rule out/follow-up pulmonary embolism

– Most often a blood clot in the lung resulting from a thrombus in the veins of the pelvis/leg

Clinical Indications

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• Evaluate COPD (chronic obstructive pulmonary

disease)

Clinical Indications

- Any disease that causes decreased ability of lungs to perform ventilatory function

- Symptoms: persistent dyspnea on exertion

chronic cough

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• Evaluate lung perfusion– In area of tumor

– To contralateral lung prior to surgery

• Other lung pathologies

Clinical Indications

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Radiopharmaceutical used

Generic name Chemical name

Pulmolite® 99mTc-Macroaggregated Albumin TechneScan ® Macrotec®

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Dosage• Dosage: 2-5 mCi (adult

dose)

• Particle size: 10-150 microns

• Number of particles: 500,000

Dosage & Administration

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• None• However, ask scheduling physician’s

office for any contraindications:- Severe pulmonary hypertension- In patients with ‘right to left’ cardiac shunt reduce injected particles to 100,000

Patient preparation (before arrival)

Technique

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Patient preparations (after arrival)

1) ID patient; verify order; review clinical indication for exam

2) Verify that patient has had a recent chest x-ray - needed for interpretation of NM images- rules out other possible causes of patient’s symptoms and increases the specificity of perfusion lung imaging- a normal chest x-ray increases the likelihood of PE

Technique

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Relevant Medical History for Lung Imaging

• Symptoms of PE: chest pain (location, duration), SOB, cyanosis, hemoptysis, fever

• Medications/dietary supplements/birth control pills

• Surgery, esp recent• Malignancies• History of prior PE or

thrombophlebitis

• Chronic/acute lung disease• Cardiac history: CHF,

pericarditis, cardiomegaly• Lifestyle: smoking, physical

activity• Previous medical imaging• Lab results• Pregnancy

Technique

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Administration

• Intravenous• Administer with patient in supine position• Invert syringe before injection• Do not draw blood into syringe• Inject slowly• Have patient take a few deep breaths

Dosage & Administration

Arrangement of recommended injection set for albumin particles

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Imaging the patient

- Remove attenuating materials before imaging

- Standard views: 8 views- anterior- posterior- laterals (Rt.Lat. & Lt. Lat.)- anterior/posterior

obliques(RAO, LAO, RPO, LPO)

Technique

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Normal Lung Perfusion The Normal Scan

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R R

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Labeled Blood ClotsIf blood and MAA particles remain in the syringe for extended periods, radioactive clots may form and appear as “hot spots” on the images

Artifacts & Pitfalls

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Artifacts & Pitfalls

If the radiopharmaceutical is not administered while the patient is in the supine position, the apices of the lung may show decreased tracer accumulation. This biodistribution could be misleading to the physician interpreting the images.

Patient posture

Lung Ventilation Imaging (3)

Clinical Indications

Radiopharmaceutical used

Dosage & Administration

Technique

The Normal Scan

Artifacts & Pitfalls

• Lung perfusion imaging is a sensitive, but not specific technique.

• Its specificity is increased with additional information from tests such as chest x-ray and lung ventilation imaging.

• Lung perfusion and ventilation imaging are often performed together for this reason.

Clinical Indications

Distribution PatternsV/Q Imaging

Perfusion (Q) Ventilation (V)

Normal Normal Normal

PE(VQ mismatch)

Abnormal Normal

COPD(VQ match)

Abnormal Abnormal

A. The most common indication for lung scintigraphy is to determine the likelihood of pulmonary embolism. However, PE determination may not always require the Ventilation component.

B. Less common indications

- Evaluate COPD (chronic obstructive pulmonary disease)

- evaluation of lung transplantation- preoperative evaluation

Clinical Indications

- Mostly same for both perfusion & ventilation studies

Do not let patients confuse our study with a ‘Pulmonary Function Test’!

Radiopharmaceutical used

Inert Gas

Gas Half-life Gamma EnergyXenon-133 5.8 days 80 keV

Other less popular inert gas Ventilation agents : Xenon-127; Krypton – 81m

Radiopharmaceutical used

Inert GasGas Half-life Gamma EnergyXenon-133 5.8 days 80 keV

Aerosol (a suspension of fine solid or liquid particles in a gas)

1) Tc-99m pentetate aerosols (DTPA = diamine triethyl pentaacetic acid)

2) Technegas - ultrafine dispersion of Tc99m labeled carbon particles (not marketed in the United States)

Other less popular inert gas Ventilation agents : Xenon-127; Krypton – 81m

Dosage

• Xe-133 gas : 5-20 mCi (adult dose)

• 99mTc-DTPA aerosol : The usual administered activity of 99mTc DTPA is 25–35 mCi in the nebulizer, from which the patient receives approximately 0.5–1.0mCi to the lungs.

• Technegas : 10 to 15 mCi

Dosage & Administration

Ventilation first!!!

Administration

Dosage & Administration

• Both the gas and the aerosol are inhaled, but each requires a different type of administration equipment and a different imaging protocol.

• It is important to elicit patient cooperation by practicing with the equipment prior to tracer administration.

Patient preparation

1) ID patient; verify physician’s order; review clinical indication for exam; ascertain that recent chest x-ray has been performed.

2) Explain procedure; obtain relevant medical history (see medical history page for lung perfusion imaging)

Technique

Before Arrival: None

After Arrival:

Relevant Medical History for Lung Imaging

• Symptoms of PE: chest pain (location, duration), SOB, cyanosis, hemoptysis, fever

• Medications/dietary supplements/birth control pills

• Surgery, esp recent• Malignancies• History of prior PE or

thrombophlebitis

• Chronic/acute lung disease

• Cardiac history: CHF, pericarditis, cardiomegaly

• Lifestyle: smoking, physical activity

• Previous medical imaging• Lab results• Pregnancy

Xenon-133 Gas Administration

Requires a closed breathing system (xenon machine/xenon trap) to keep the radioactive gas contained in the patient or the xenon machine. Radioactive xenon is a radiation hazard if it escapes into the room.

Technique

Exam must be performed in a negatively pressurized room to contain any xenon that may escape

Xenon Traps

Xenon traps utilizing activated charcoal are employed to prevent its escape into the room atmosphere and Xenon trap monitors like the ones show on the right can monitor any escape.

Technique

Bacterial filters

Bacteria filters are used to reduce the possibility of cross contamination. The single-use filter is placed in line between a delivery tube and disposable mouthpiece or face mask. Electrostatically charged filter media is 99.9% effective in bacteria/virus retention while maintaining low breathing resistance. Two filters can be piggy-backed together for potential high-risk studies.

Technique

Face Mask

• The syringe luer locks tightly to the direct dose tube, away from the patient’s face.

• The one-way valve prevents the gas from reversing through the mask luer connector, allowing the technologist to disconnect immediately after injecting.

Technique

CO2 & Moisture Absorbers

The Carbon Dioxide absorberand moisture absorber cartridges are located in the upper cabinet

Soda lime absorbs exhaled carbondioxide“Drierite”, “Dry-All” –

absorbs exhaled moisture(calcium sulfate + cobalt chloride; turns from blue to pink as it absorbs moisture)

O2 or air must be added to the system because it is closed to surrounding air

Technique

Connectors for the bore hose and Valve assembly are located on the back panel.

• Patient wears nose clamps and breathes Xe/O2 through a mouthpiece connected by tubing to the xenon administration machine.

Technique

Xenon Imaging Protocol• View: single, usually posterior projection, upright or

supine

• Three stage dynamic acquisition:– Wash in – patient inhales Xe/O2 (initial single breath and

breath hold)– Equilibrium – Xe rebreathed until concentration in lungs

and rebreathing system is constant (Xenon is distributed throughout the lungs)

– Wash out – patient exhales Xe and rebreathes O2 until Xe cleared from lungs

Technique

Single breath phase bypassed for patients too sick to hold their breath

Operation

Front panel controls

Position One: Start - Patient breathes room air. System is charged with oxygen.

Position Two:Single breath and equilibrium imaging - This is when you add Xe-133, either a bolus or a homogeneous mixture. When the patient equilibrates, the user switches the handle to washout position.

Position Three: Washout - The patient is now breathing room air from a one-way valve through the delivery system and exhaling into the built-in charcoal trap. During washout a pump draws the patient's expired breath through the activated charcoal trap. The xenon is stripped away and only clean air leaves the trap exit port.

Technique

Tc-99m Pentetate Aerosol Administration

• A nebulizer is used to break the liquid tracer into small particles by directing a stream of air or O2 through the liquid; the gas moves the particles forward and the patient breathes them in

• Patient breathes the aerosol through a mouthpiece or face mask connected by tubing to the nebulizer; the patient is disconnected from the nebulizer after inhaling the aerosol

Technique

Nebulizer Used to Generate Radioaerosols

Pharmaceutical practice - Arthur J. Winfield, R. Michael E. Richards

Technique

• The size of the aerosol particles must be small enough to be inhaled down into the smaller airways; particle size/deposition is controlled by rate of gas flow, pressure, tubing diameter and length, and other factors

• Radiation safety considerations:– Contamination of floor, patient’s upper chest, and area

around nose/mouth– Coaching the patient before and during the exam has

shown to decrease the amount of contamination

Technique

Give

water to

drink!!

Tc-99m Pentetate Imaging Protocol

• Tc99m DTPA aerosol must have correct oxygen flow rate through nebulizer (at least 8 to 10 L/min)

• Take precautions not to allow contamination of patient’s nose, mouth, upper chest, floor under patient and camera

• Views: multiple views; same as acquired for perfusion portion of the exam

• All images are equilibrium images and no single breath or washout images possible; wash out images are not possible because the particles become stuck in the lung once they are inhaled.

Technique

Technegas Generator• Vapourises Tc99m

Pertechnetate injected into a carbon crucible in the presence of argon.

• Generates Technetium labeled carbon nano-particle suspended in argon gas.

• The gas inhaled by patient through a disposable breather kit.

• 1-3 breaths delivers the required full dose

Technique

Normal Lung Ventilation

The Normal Scan

Xenon - 133

Distribution Patterns – NormalPerfusion Xenon Aerosol

Greater activity central lung area (greatest tissue mass)

Slightly decreased activity lung apices (normal thinning)

Well defined cardiac impression

Uniform tracer distribution throughout lungs

90% clearance (washout) 3-4 min post administration

Symmetric tracer distribution from apex to base in both lungs

• Gut activity due to pt. swallowing• Upper esophagus activity• Improper breathing through mask/mouth

piece• Missing proper start time on computer for

Xenon breath hold image• Patient motion

Artifacts & Pitfalls

Alternatives to lung perfusion imaging

Spiral CT

Pulmonary angiography