pulmonary diagnostic imaging Flashcards
What is the benefit of using US and/or MRI imaging in pulmonary diagonistics
no ionizing radiation
which diagnostic imagining is often the initial study to evaluate respiratory symptoms
chest xray
describe the inherent contrast of chest xray
- air in lungs is black
- soft tissue (light grey)
- bone (nearly white)
- metal (white)
what are the chest xray views? which two are used most often?
- PA
- Lateral
- AP: (anything on anterior part of chest is magnified)
- Decubitus
silhoutette sign
when you see a nice silhouette of heart border
How is the lateral view chest xray taken
- taken from right to left so that the heart does not appear abnormally large
when is is appropriate to order a decubitus CXR
- suspect pleural effusion
benefits of CXR
- non-invasive
- low radiation exposure (0.1 mSv)
- inexpensive
- widely available
what do you look for on CXR when you suspect pneumothorax
look for edge of pleura as a light line that has advanced inward toward heart
what condition does this wedge shaped sign suggest
Hampton’s hump -> pulmonary infarct
Computed tomography (CT scan) takes what kind of pictures
cross sectional images (slices) through the body
Why would you order a CT
- clarify abn CXR
- characterize pulmonary nodules
- detection and staging of primary and metastatic lung neoplasms
- evaluate suspected mediastinal or hilar masses
What are the various types of CT scans
- conventional
- helical
- high resolution
- low dose CT
- CT angiography
conventional CT scan
- 10 mm slice
- “step and shoot:
- 25-30 min
helical CT
- continuous
- < 5 min
high resolution CT (HRCT)
- better detail
- 1 mm slice
- used to figure out what is going on with lung tissue; ex: chronic lung diseases
multi_detector CT
- also called multislice CT
- 4-620 slides
- conventional or helical scans
- very fast; higher radiation
what are the benefits of CT
- fast
- real-time imaging
- can be performed even if patient has implantable device
- less expensive and sensitive to patient movement than MRI
what contrast is used in CT
- iodine
why is constrast used
to enhance differences in densities of various structures
does the following require CT with or without contrast:
Masses, CA, metastatic disease, obstructive processes, PE or dissection
CT chest with contrast
does the following require CT with or without contrast:
pulmonary fibrosis; interstitial lung disease; follow up of known pulmonary nodules
- CT chest without contrast
- pulmonary fibrosis; interstitial lung disease: use HRCT
risk of CT
- radiation exposure 8 mSv
- increased CA risk
- pregnancy exposure
- body habitus > 450 lbs
CT chest and CT chest with contrast can be approximated to have the radiation exposure equivalent to how many plain chest xrays
- CT chest: 80
- CT chest with contrast: 150
why should CTs be avoided in pediatric patients
- more radiosensitive than adults
- increased risk of leukemia and brain tumors with CT scans
what are the risks of getting a CT with contrast
-
allergic reaction
- w/in 5-60 min of administration
- risk factors: prior reaction, asthma, atopy (NOT shellfish allergy)
- can pretreat with prednisone and benadryl
- contrast induced nephropathy
which imaging modality should you use cation with in patients taking metformin (Glucophage)
CT with contrast
- hold medication for 48 hours after exam
- recheck creat/BUN before restarting
- can cause lactic acidosis
what is contrast induced nephropathy
- serum creatinine increase > 25% form baseline or > 0.5 mg/dL
- usually reversible
- best treatment is prevention
-
caution with impaired kidney function
- creat > 1.5 mg/dL or GFR < 60
when should you check renal function prior to iodine contrast
- age > 60 yo
- history of renal disease
- dialysis, single kidney, kidney transplant, renal CA, renal sx
- h/o HTN treated with medication
- h/o DM
- taking metformin
which imaging modiality assess vasculature in the body
angiography
- CT-> CTA
- MRI-> MRA
- xray with catheter
which imaging modality should be used for suspected PE, aortic dissection, superior vena cava syndrome; or vascular malformation
CT pulmonary angiography (CTPA)
risks and limitations of CTPA
- can miss sub-segmental PEs
- allergy to contrast
- nephrotoxicity from contrast
- radiation exposure: 10-15 mSv
- body habitus > 450 lbs
what imagining modality is the gold standard in evaluation of PE
direct pulmonary angiography
describe direct pulmonary angiography technique
- catheter inserted into right femoral or internal jugular vein -> Rt heart -> pulm arteries
- dye injected; xrays taken
- used if V/Q scan or CTPA are inconclusive and 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
- radiation exposure (5 mSv)
benefits of using MRI over CT
- no bone artifact as with CT
- no ionizing radiation
the following indicate evaluating with what imaging
hilar or mediastinal densities, sulcus tumors, possible cysts and lesions of chest wall; allergy to iodinated contrast or renal disease (GFR <30)
MRI
functio of Magnetic resonancy angiograph
- high quality images of many blood vessels
- less detailed view of lung parenchyma and diminished spatial resolution compared to CT
what is the contrast material used for MRI and MRA
Gadolinium
limitations/risk of MRI/MRA
- patient must remain still
- claustrophobia
- body habitus
- risk of nephrogenic systemic fibrosis ( GFR <15 ml/min)
contraindications of MRI/MRA
- pacemaker or defibrillator
- metal in eye
- clips used in brain aneurysms
- cochlear implant
when is V/Q scan used
- to evaluate for PE
- for pre-op assesment prior to lung resection
how does V/Q scan work
emitted radiation is captured by external detectors in 2 phases
- 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
test of choice for diagnosis of PE in pregnant women
V/Q scan
benefits of V/Q scan
- allergic reaction is rare
- low dose radiation 2-2.5 mSv
which imaging is the acquisition of physiologic images based on the detection of radiation emitted from FDG (radioactively labeled glucose) which is injected into patient
positron emission tomography (PET)
where does FDG (radioactively labeled glucose) accumulate
- is tissues/organs with high metabolic activity (cancer cells***)
- PET scan most often used to detect CA
in a PET scan, patient is scanned and measurements of the uptake are made in standardized uptake value (SUV). and SUV > X raises the possibility of malignancy
SUV > 2.5
limitations of PET scan
- radiation exposure 14 mSv
- false results occur with metabolic imbalances
- radioactive substance decays quickly
- high cost
