1. Radiation
-Absorbed dose in grays, biological effects in sieverts
-PA CXR: 0.04-0.06 mSv
-Standard thoracic CT: 4-6 mSv
-Low dose thoracic CT: 1-2 mSv
-CT Abd/pelvis: 10 mSv
-Natural background rad: 2.5-3.5 mSv/year - higher in high altitude locations like Denver.
-Risk of mortality from radiation is inversely related to age-- highest in infants, drops over time; higher in women than men. Kids' cells are more actively dividing, more have replicating DNA, vs old people with quiescent cells.
2. Pneumoperitoneum 
-May be 2/2 g-tube placement
-hard to see on portable, especially if they are not sitting up straight
3. Pneumothorax
-in young people, edges of lungs are hard to see-- not fibrosed at all.
-Can be hairline. Always check for this in young people with chest pain.
4. Multi detector CTs:
-320 slice Ct can get through 32 cm length of tissue (small child) in less than 1 second at sub-1mm resolution
-Less motion artifact
-Better temporal resolution if you want to say track a bolus.
5. Hounsfield Units
-every AM, the technologist puts water in the CT to zero it
-bigger electron cloud, more white (i.e. calcium)
+1000 : metal
+400 : bone
+40-60: liver
+46 White matter
+43: grey matter
+40: blood
+10-50: soft tissue (kidneys, muscles)
+15: CSF
0: water
-50-100 Fat
6. Uses of Hounsfield Units 
-1000 air
-Can use HU to do emphysema mapping-- separate different densities of lungs
-Can filter out bone, program to remove everything over HU of a certain number.
-Can subtract soft tissues from CTA
-Can segment liver, calculate total volumes, estimate residual volume (ie after resection, donation) to ensure there's enough liver left.
7. Contrast
-PO: drink 60-90 mins prior to exam.
Positive agent (barium, iodine) lights everything up
Negative agent: milk, water, volumen: good for seeing the mucosal (ie crohns dx, panc cancer to see duodenum) because the white whites out the walls of the bowell
-IV
Shellfish allergy not a CI
Power injector, good flush, 75-120cc
-IA
-Intrathecal
-Bladder
8. Phases of contrast
-Non contrast
-Arterial
-Portovenous (contrast goes through mesentery, portal v, light up liver)
-Delayed (collecting system)
9. Basic Body CT protocol
-PO + IV contrast: (inflammation/cancer) bowel obstruction, perforation (pain), hernia, abd abscess/infections (fever), appendicitis, diverticulitis (pain + white count)
-Non contrast: (stones, blood) kidney stones (flank pain), retropertioneal bleed (anticoagulated, recent cath), abd bleed (AAA rupture)
10. Allergy to contrast
-Anaphylactoid: 1-2/10,000: low osmolarity contrast; Tx: 1:1000 epi, 0.3 mL IM (epi pen)
-Other: n/v, pulmonary edema, seizure, renal failure
-Delayed: fever, chills, rash, pruritis, arthralgia, n/v, headache.
-For other and delayed reactions, pre-medicate with steroids/benadryl (everything from mild bronchospasm and milder).
-For serious circulatory collapse