Transcript Nuclear Medicine 4203 Scanning & Imaging

Nuclear Medicine 4203
Scanning & Imaging
Respiratory System
Anatomy and Physiology
Trachea divides into the right and left
mainstem bronchi
These divide to form lobar bronchi
Right side has upper, middle and lower lobe
bronchi
Left side has upper and lower bronchi
Lobes further divide into segments
Lung Segments
Lung Anatomy
Main pulmonary arteries divide into
each lung and follow the divisions of
the bronchi and bronchioles to the
level of the alveoli.
Each alveolus is supplied by a
terminal pulmonary arteriole, which
turns to capillaries.
Adults have 250-300 million alveoli
Figure 3 Schematic diagram of lung anatomy with cross-sections of bronchi,
bronchioles alveolar ducts, and alveoli.
GI Motility online (May 2006) | doi:10.1038/gimo73
Lung Physiology
Gravity and patient position have a
significant impact on both ventilation and
perfusion.
In upright position, intrapleural pressure is
significantly more negative at the apices
than at the base of the lung.
Also in upright position, the apex receives
only 1/3 of the blood flow compared to the
base.
Radiopharmaceuticals
Perfusion:
99mTc
macroaggregated albumin (MAA)
Localizes by capillary blockage
Fewer than 1 in 1000 capillaries are blocked
Injection should include 200,000-600,000 particles
Normal adult dose is 3-5 mCi of activity and 1-2 ml of
volume
Syringe should be agitated before injection
Should be injected while patient is supine during
respiration (some radiologists will prefer upright injection)
Care should be taken not to draw back blood into the
syringe~this will cause small labeled blood clots~causing
focal hot spots on the image.
Radiopharmaceuticals
Perfusion:
Contraindication to injecting 99mTc MAA
Severe pulmonary hypertension
Known Right-to Left shunt
In both cases, number of particles should be
reduced to 100,000-200,000 particles.
Radiopharmaceuticals
Radioactive Inert Gas:
133
Xe
Half life 5.3 days
Gamma ray energy of 81 keV
Usual dose of 10-20 mCi
Usually done prior to 99mTc MAA perfusion
Imaged in posterior view
1-initial breath
2-equilibrium
3-washout
Requires patient cooperation
Administered using delivery and rebreathing unit.
Radiopharmaceuticals
Radiolabeled Aerosols
Map the distribution of aerated lung volume
99mTc diethylene triamine pentaacetic acid
(DTPA)
30-50 mCi of activity in 2-3 ml volume.
Oxygen is supplied to the delivery system.
Patient breaths in and out through a
mouthpiece and the nose should be pinched
off.
Advantage is views can be taken in all 8
camera positions, to match perfusion.
Radiopharmaceuticals
Technegas and Pertechnegas
Delivered in a micro-aerosol generator
Still in FDA trials in U.S., but used
commonly in other countries.
Advantage: pertechnegas can be
delivered in only 1-2 breaths and
multiple images can be obtained.
Indications
Suspected pulmonary embolus
Chest pain
Shortness of Breath
Hypoxia
Coughing
Chest radiograph should be done 12-24 hrs. prior
to VQ scan for comparison.
CTA is generally preferred, but a VQ scan will still
be warranted if:
Pt. has contrast allergy
Renal failure
Pregnant (this is debatable)
Normal Perfusion Lung Scan
Uniform activity seen except a
decreased area of cardiac silhouette
and aortic knob.
Normal Perfusion
Normal Ventilation
133
Xe
Normal half-time washout for Xenon is 30-45
seconds.
May be deposited in the liver and result in
increase activity in right upper quadrant.
Normal 99mTc Aerosol images resemble
perfusion images.
Normal to see trachea and bronchi
Swallowed activity can be seen in the
esophagus and stomach.
Perfusion Defects
Area of absent or diminished perfusion.
Classified as segmental or nonsegmental.
Segmental may involve all or part of a
bronchopulmonary anatomic segment. These
are classically wedge shaped.
Nonsegmental do not correspond to anatomic
segments and are generally not wedge shaped.
These are NOT associated with pulmonary
emboli. Can be caused by hilar or mediastinal
structures, neoplasms, bullae, pneumonia,
edema or other infiltrates.
High Probability Study
Pulmonary Embolus
Do they Match?
A mismatch refers to a defect seen on
perfusion, but is normal on the
ventilation.
Segmental mismatch is a classic
pulmonary emboli.
Analysis of Images
Perfusion defect: is it segmental?
Yes, then further evaluation is
required.
Compare to Ventilation scan: It is a
mismatch? If yes,
Compare to CXR : are there
infiltrates, effusions, or masses?
PIOPED II Criteria
Prospective Investigation Of Pulmonary Embolism Diagnosis
High probability
Greater than 80% likelihood of pulmonary emboli
Intermediate probability
20-80% likelihood of pulmonary emboli
Low probability
Less than 20% likelihood of pulmonary emboli
Very low probability
Less than 10% likelihood of pulmonary emboli
Indeterminate
Should be used only when technical factors limit the
study
Normal
No perfusion defects
Stripe sign ~ Very unlikely to be
pulmonary emboli
Fissure sign~ caused by pleural fluid
in the fissures, pleural scarring or
thickening, or COPD.
Other indications
Follow-up on pulmonary embolus
To determine if treatment is working
Management of patients with COPD
Assess lung function in patients with
lung cancer
Assess lung function pre-operative to
lung resection