1 Pulmonary Diagnostic Imaging Flashcards
Pulmonary diagnostic imaging that exposes the patient to ionizing radiation
Chest Radiography (CXR)
Computed Tomography (CT)
Pulmonary Angiography (CTPA/Direct)
Nuclear Scanning
• V/Q scan
• PET scan
Pulmonary diagnostic imaging that DOESN’T expose the patient to ionizing radiation
Ultrasound
Magnetic Resonance Imaging (MRI/MRA)
Bronchoscopy
CTs account for ____% of average ionizing radiation exposure each year
24%
Often the initial study to evaluate respiratory symptoms
Chest X-Ray
X-ray beam penetrates through the body and provides images of structures in and around the thorax (lung parenchyma, pleura, chest wall, diaphragm, mediastinum, and hilum)
On CXR, air appears ____, fat ______, and bone ______.
Air = black Far = dark gray Bone = nearly white
Indications for chest x-ray
Shortness of breath
Persistent cough
Hemoptysis
Chest pain or injury
Fever
What views are utilized when taking chest x-rays?
Posterior-anterior (PA)
Anterior-posterior (AP)
Lateral
Decubitus
Combo of CXR views most often used
PA and lateral
AP is used if bedridden (but may make heart look bigger than it actually is)
The ABCDEFs of viewing chest X-rays
Airway (trachea, bronchi)
Bones (ribs, clavicle)
Cardiac (borders, cardiomegaly)
Diaphragm
Edges (look for pneumothorax or effusion)
Fields of lungs (look for infiltrates, nodes)
Which CXR view allows for best visualization of the right lower lobe?
Lateral
Because the RLL is mostly posterior, very little of it can be visualized from a PA view
What is an Apical Lordotic view?
Variation on an AP view, where patient’s feet are some distance from the film and the lean back upon it.
Indicated when TB is suspected because it gives the best view of the apex of the lungs, where TB typically starts
Example of use of the lateral decubitus view on CXR
Subpulmonic effusion
The PA film shows an apparently elevated right diaphragm
On the decubitus view, the effusion flows up along the side of the lung
What are the primary benefits of CXRs?
Non-invasive
Low radiation exposure
Inexpensive
Convenient - Imaging is fast, easy, and particularly useful in emergency Dx and Tx
Widely available (esp with portable units)
Though uncommon to see, a Hampton’s Hump on CXR indicates…
PE - it’s an area of ischemia due to the infarct
Risks and Limitations of CXR
Radiation exposure
• 0.1 mSv, minimal but cumulative
• PA/LAT, about what you receive from background radiation in 10 days
Pregnancy - some exposure but smaller risk than CT
Some conditions of the chest cannot be detected (ie very small cancers, pulmonary emboli)
Why might you order a CT?
Clarify an abnormal CXR
Help diagnose the cause of clinical SSx (SOB, cough, CP, fever)
Characterize pulmonary nodules
Detection and staging of primary and metastatic lung neoplasms
Evaluate suspected mediastinal or hilar masses
Who should get a CT screening for lung cancer?
55-80 year olds with a 30 pack year history and currently smoke or quit within the past 15 years
Types of CT scans
Conventional - 10 mm slice, “step-and-shoot”, 25-30 min
Helical - aka spiral CT, faster, continuous, <5 min
High Resolution (HRCT) - better detail, 1mm slice
Low Dose CT - usually used for lung cancer screening, but less detail
CT Angiography
“Multidetector” or “multislice CT” - capable of conventional and helical scans, but 64x faster (though with higher radiation)
How does bronchiectasis appear on CT?
Thickening/dilation of airways
What does subcutaneous emphysema sound like?
Rice crispiest
Benefits of CT
Fast, widely available
Detailed images
Real-time imaging useful for biopsies
Can be performed even if patient has an implanted device
Less expensive and less sensitive to patient movement than MRI
Risks/Limitations of CT
Radiation exposure (~8 mSv or 80 times that of Xray) - about the same a person receives from background radiation in three years
Increased CA risk
Fetal exposure during pregnancy
Problems associated with contrast (allergy, renal problems)
Body habitus >450lbs may not fit in machine
What’s special about kids and CTs?
Kids are more radiosensitive than adults
CT has increased risk of leukemia and brain tumors
Radiation risk compounded by longer lifespan
What do we need to know about pregnant women and CTs?
In uterine exposure linked to pediatric cancer mortality - always ask LMP prior to imaging
What type of contrast does CT use?
Iodine
Used to enhance differences in densities of various structures - ie a large blood vessel with a tumor encasing/constricting it
When is CT with contrast needed?
Masses, cancer, metastatic disease, obstructive processes, PE or dissection (CT angiography)
When do we want a CT WITHOUT contrast
High resolution CT for evaluation of diffuse lung disease and to follow up known pulmonary nodules
Special risks of CT with contrast
Allergic reaction (mild-moderate vs major)
Potential for contrast induced nephropathy
Development of lactic acidosis if taking Glucophage (Metformin) - consider holding metformin for 48 hours after imaging
Tell me more about iodine contrast allergies…
Reaction develops within 5-60 min of administration of contrast
SSx - flushing, Pruitt is, urticaria, angioedema, bronchospasm and wheezing, stridor, hypotension, loss of consciousness
Risk factors - prior reaction, asthma, atopy
Can pre-treat with prednisone and diphenhydramine (Benadryl)
Is a shellfish allergy a contraindication for CT contrast?
Nope.
Contrast induced nephropathy is defined as …
Serum creatinine >25% from baseline or >0.5 mg/dL
Usually reversible
Best treatment is prevention
Caution using contrast in patients with impaired kidney function
In whom should we be concerned for development of contrast induced nephropathy
If Creatinine >1.5 mg/dL or GFR <60
Age >60
Hx of renal disease, HTN treated with meds, DM (esp if taking metformin)
Use alternative - either CT w/o contrast, MRI w/o gadolinium, or U/S
Patients taking metformin and CT contrast…
If eGFR ≥ 30 ml/min, metformin does not need to be withheld
If Acute kidney injury or severe CKD with eGFR <30 ml/min - temporarily hold metformin when contrast administered x 48 hours, resume only after re-evaluation of renal function
When do we use angiography?
To assess vasculature in the body
• Brain, kidneys, pelvis, legs, lungs, heart, neck
• Injection/timing controlled, dye is where you want it during the scan
Performed in conjunction with imaging modalities
• CT —> CTA
• MRI —> MRA
• X-ray with catheter (direct/conventional)
Imaging procedure that provides anatomical detail of blood vessels and is useful for suspected pulmonary embolism, aortic dissection, and superior vena cava syndrome
CT Pulmonary Angiography (CTPA)
Identifies vascular malformations and assesses pulmonary arterial invasion by a neoplasm
Benefits of CTPA
Has largely replaced conventional (catheter-directed) pulmonary angiography
If surgery is warranted, can provide precise anatomical guidance
Less invasive, less expensive, and safer compared to conventional angiography
Risks/Limitations of CTPA
Can miss sub-segmental PEs
Allergy to contrast material (iodine)
Nephrotoxicity from contrast
Radiation exposure (10-15 mSv)
Body habitus (>450lbs)
Gold standard in the evaluation of PE
Direct pulmonary angiography
CTA is more useful now but this is still the gold standard
How is direct pulmonary angiography performed
Needle/catheter inserted into right femoral or internal jugular vein —> R side heart —> pulmonary arteries
Dry injected, x-rays taken
Used if V/Q scan or CTPA inconclusive and still a high clinical suspicion
Invasive and expensive
Risks of direct pulmonary angiography
Bleeding or hematoma at insertion site
Heart arrhythmia
Allergic reaction to contrast
Impaired kidney function (though usually reversible)
Radiation exposure (5 mSv)
How are MRIs used in pulmonary disease?
Limited usefulness
Hilar or mediastinal densities, sulcus tumors, possible cysts and lesions of the chest wall
Who cannot receive an MRI?
Patients with allergy to iodinated contrast or renal disease (GFR <60)
Benefits to MRI
No bone artifact as with CT
No ionizing radiation
Compared to Chest CT, MRI has _______ detailed view of lung parenchyma and __________ special resolution
Less detailed, diminished special resolution
Contrast material used for MRI and MRA
Gadolinium
Limitations of MRI/MRA
Patient must remain still
Claustrophobia
Body habitus
Risk of nephrogenic systemic fibrosis (irreversible scarring) - avoid use of gadolinium if GFR < 60
Contraindications of MRI/MRA
Pacemaker or defibrillator
Metal in eye
Aneurysm clip
Cochlear implant
Joint replacements aren’t ferrous and are generally safe
Nuclear imaging study used to evaluate for PE
Ventilation-Perfusion (V/Q) scan
Also used for pre-op assessment prior to lung resection
Imbalance of blood flow and ventilation is called
V/Q mismatch
Radioactive material used in V/Q scans
Technicium-99 and Xenon gas
The two phases of V/Q scans
IV Phase - Technetium-99m (labeled to human albumin) is injected and follows distribution of blood flow (PERFUSION)
Inhalation Phase - radio-labeled Xenon gas demonstrates distribution of VENTILATION
If a patient has a high probability of PE but a normal CXR, you should…
Perform V/Q scan to assess for mismatch. Absence of perfusion with normal ventilation indicates PE.
Benefits of V/Q scan
Allergic reaction to radiopharmaceutical is rare
Low-dose radiation (2-2.5 mSv)
Remains test of choice for diagnosis of PE in pregnant women
Useful in estimating post-op reserve capacity for patients undergoing lung resection
Limitations of V/Q scan
Sensitive for Dx of PE but poorly specific (PNA or asthmas might be positive too)
Few false negatives but high number of false-positives
Best utilized in those with a normal CXR w/ high suspicion of PE
No absolute contraindications
Acquisition of physiologic images based on the detection of radiation emitted from fluorodeoxyglucose (FDG)
Positron Emission Tomography (PET)
FDG - radioactively labeled glucose injected into patient and accumulates in tissues/organs with high metabolic activity (ie cancer cells)
In PET scans, measurements of the uptake of FDG are made in ________.
Standardized Uptake Value (SUV)
SUV > 2.5 raises possibility of malignancy
Uses of PET scan
Most often used to detect cancer
Useful to evaluate for metastasis from primary site
Used to examine the effects of cancer therapy (can detect recurrence in previously irradiated, scarred areas of the lung)
Benefits of PET scans
Can detect biochemical changes of anatomy before they are apparent with CT/MRI
However, now being combined with CT or MRI to give anatomic and metabolic info
Radioactivity is short lived
Limitations of PET scans
Radiation exposure ~14 mSv
False results occur with metabolic imbalances
• False (+) inflammatory lesions - granulomas from Cocci and Histo
• False (-) with slow growing tumors
Time-sensitive - radioactive substance decays quickly
High cost
How is ultrasound used in pulmonary diagnostics?
Limited use in evaluation of lung parenchyma
Indications include:
• Bedside detection of pleural fluid or PNA
• Guidance for thoracentesis
• Guidance for placement of thoracostomy tubes
Benefits - no ionizing radiation, portable
What is the FAST exam?
Focused Assessment using Sonography in Trauma
“Seashore sign” on thoracic ultrasound indicates…
Normal condition - Positive lung motion
“Barcode” or “stratosphere sign” on thoracic ultrasound indicates
Abnormal finding - no lung motion
Diagnostic and therapeutic indications for bronchoscopy
Evaluation of PNA, hemoptysis, cough
Dx of tracheoesophageal fistulas and tracheobronchomalacia
Tissue sampling
Removal of excess mucus or FBs
ET tube placement
___________ is most commonly used in patients with obstruction of trachea or a proximal bronchus (for removal of FB)
Rigid bronchoscopy
Benefits of bronchoscopy
Safe procedure with very low complication rates (0.08-6.8%)
• Nasal discomfort, sore throat, mild hemoptysis
• Complications are usually minor (hemorrhage, pneumothorax, hypotension, arrhythmia)
• Most occur during or within first few hours post-procedure
Contraindications for bronchoscopy
Severe refractory hypoxia
Risk of bleeding (anticoagulants, coagulopathy)
Risk of respiratory and CV decompensation (asthma or COPD exacerbation, current or recent MI, poorly controlled CHF, life threatening arrhythmias)
