Pulmonary anat phys lung scint principles
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Transcript of Pulmonary anat phys lung scint principles
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
Review of Respiratory System (1)
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)
Review of Respiratory System (1)
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Diaphragm
Review of Respiratory System (1)
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Airways
Review of Respiratory System (1)
- 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
Review of Respiratory System (1)
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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
Review of Respiratory System (1)
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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
Review of Respiratory System (1)
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Respiratory cycle
Inspiration
Expiration
Compliance(ability to stretch)
Elastic recoil
Review of Respiratory System (1)
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VentilationAir moves down a pressure gradient
Highpressure
Lowpressure
Review of Respiratory System (1)
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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
Review of Respiratory System (1)
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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
Review of Respiratory System (1)
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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
Review of Respiratory System (1)
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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