Radiology and Imaging for the Nurse Anesthetist

Perianesthetic Indications: Suspected history/physical abnormalities, rales, advanced COPD, bullae, blebs, pulmonary edema, pneumonia, masses, tracheal deviation, and cardiomegaly.
Nitrous Oxide Warning: Do not use with patients exhibiting bullae, as these can fill with nitrogen and explode.
Radiodensities:
- Gas/Air: Radiolucent (black), seen in trachea or stomach.
- Fat: Gray; less radiolucent than air.
- Water/Soft Tissue: Light gray/whitish; seen in heart and muscle.
- Bone/Metal: Radiopaque (white).
Orientation Views:
- Posteroanterior (PA): Preferred view; beam passes back to front. No rotation is ideal to prevent abnormal appearance of structures.
- Anteroposterior (AP): Beam passes front to back; causes heart magnification and widening of the mediastinum.
- Lateral: Used to detect lesions behind the heart or near the diaphragm.

"NO ABCDEFGH" Evaluation: Name, Orientation, Appliances, Bones, Cardiovascular, Center of Chest, Diaphragm, Extrathoracic tissues, Fluid, Gas, and History.
Endotracheal Tube (ETT): Placed $3-5\,cm$ above the carina ( $T4-T5$ or 6th posterior rib levels). Neck flexion/extension can move the tube $2\,cm$ respectively.
Tracheostomy Tube (TT): Tip should be halfway between the stoma and the carina ( $\approx T3$ ).
Feeding Tubes: Dobbhoff tubes are recognizable by weighted metallic ends; tip should be in the duodenum (crossing midline) to reduce aspiration risk.
Central Lines (CVC/PICC): Tip should reside in the Superior Vena Cava (SVC) above the junction of the right atrium.
Cardiovascular: Normal cardiothoracic ratio is $\le 1:2$ . Anything greater suggests cardiac enlargement.

Pulmonary Edema: Indicated by interstitial edema, peribronchial cuffing, "bat-wing" or "butterfly" patterns, and Kerley B lines (thickening of interlobular septa).
Pleural Effusion: Identified by a meniscus sign and blunted costophrenic angles (requires approximately $250\,mL$ of fluid).
Tension Pneumothorax: A medical emergency characterized by hyperlucency, absence of lung markings, and tracheal/mediastinal shift to the opposite side.
Atelectasis: Linear increased density resulting from volume loss; associated with a raised diaphragm.
COPD/Hyperinflation: Indicated by a flattened diaphragm with $11-12$ posterior ribs visible.

Biological Damage: Ionizing radiation creates free radicals leading to DNA mutation and cell death. The Linear No-Threshold (LNT) model is used to estimate risk.
Measurement Units:
- Gray (Gy): Quantity of radiation ( $1\,Gy = 1\text{ rad}$ ).
- Sievert (Sv): Biological risk/equivalent dose ( $1\,Sv = 1\text{ rem}$ ).
- For radiographs, $1\,Gy = 1\,Sv$ .
Safety Thresholds:
- Annual Occupational Limit: $50\,mSv$ .
- Lifetime Limit: $350\,mSv$ .
- Background Radiation: General public receives $\approx 3\,mSv$ annually.
Safety Practices (Time, Distance, Shielding):
- Distance: Follows the Inverse Square Law; doubling distance reduces dose to $1/4th$ . Standard distance is $6\,feet$ .
- Shielding: Lead aprons with $0.5\,mm$ thickness reduce exposure to $25\%$ of original dose. Lead should be hung, never folded.
Pregnancy: Fetus is most sensitive during first trimester. Fetal limit is <5\,mSv. Pregnant providers should wear $1.0\,mm$ wraparound lead and two film badges (collar and waist).

CT Scanning: Uses computer-processed 2D X-ray slices to create 3D cross-sectional images.
Iodinated Contrast: Enhances vascular structures. Ionic agents have higher osmolality and higher allergic predisposition than non-ionic agents.
Reactions:
- Type I (Acute): Within $1\,hour$ . Symptoms include pruritus, bronchospasm, and CV collapse.
- Delayed: More than $1\,hour$ (rashes, N/V).
- Prophylaxis: Prednisolone ( $50\,mg$ ) at $12$ and $2\,hours$ before; Diphenhydramine ( $50\,mg$ ) immediately prior.
Nephropathy: Contrast-induced nephropathy is a leading cause of hospital-acquired renal failure; prevention requires adequate hydration.

Principles: Utilizes magnetic fields and radio waves to align hydrogen protons, creating a magnetic vector. Field strength measured in Tesla ( $1\,T = 10,000\text{ gauss}$ ).
MRI Safety Zones: Zone I (Public) through Zone IV (Scanner room).
Anesthetic Challenges:
- Antenna Effect: Monitoring wires can form loops, attracting magnets and causing patient burns.
- Compatibility: PACs, wire-reinforced ETTs, and certain tattoos (iron oxide) may be hazardous.
- Environment: Access to patient is limited; acoustic noise can exceed $90\,dB$ .

Physics: High-frequency sound ( $1-5\,MHz$ ) reflects "echoes" from tissue boundaries based on the Piezoelectric effect.
Echogenicity:
- Hyperechoic (White): Nerves, fascia, bone rim.
- Hypoechoic (Gray): Muscle, fat, cartilage.
- Anechoic (Black): Blood vessels.
PART Nomenclature: Pressure, Alignment, Rotation, Tilt.
Probe Management: Higher frequencies offer better resolution but attenuate faster (less penetration depth). Always maintain visualization of the needle tip.