coil types in MRI

COIL TYPES IN MRI

RESISTIVE COILS:
-air core
-either 1 coil pair (2 coils) (Helmholtz coil) or
2 pairs (4 coils)
-diameter of coils describe surface of a sphere
-magnetic field (either longitudinal or transverse
-iron core
-windings directly around poles of electromagnet
(either C or H configuration)
-transverse field

SUPERCONDUCTIVE COIL:
-winding solenoid (around gantry)
-made of NbTi filaments in a copper matrix
-longitudianl field

RF COILS:
-for transverse fields
(solenoidal configuration
(2 times more SNR than saddle shaped coils
-for longitudinal fields
(saddle shaped coils
-surface coil
(circular coils placed directly over ROI
(RF receiver

GRADIENT COILS:
-Maxwell pair
(current flow in opposite direction
(used in slice selection gradient- in direction of Bo
-Golay coil
(opposing parallel side coils
(curved over the cylindrical surface of the gantry bore
(2 sets – 90 degree to each other- used in x , y plane
gradients

SHIM COILS:
-small coils
-within gantry
-make Bo more uniform


Ravi
BS (RT)

maximize x ray tube life

HOW TO MAXIMIZE X-RAY TUBE LIFE ?
Good work practices can significantly prolong tube life.
Recommendations :
Minimize filament boost ("prep") time
Use lower tube current (mA)Follow rating charts and anode heating/cooling curves.Limit operation to 80% of maximum single exposure ratings
Do not exceed anode thermal capacity or dissipation rate of the target
Do not make high mA exposures on a cold targetAvoid long intervals between spot-filmsLimit rotor start/stop operations

pituitary gland

PITUITARY GLAND
-Imaging indications:
-endocrine disturbances
-visual failure
-pituitary fossa:
-above sphenoid
-cavernous sinuses on each side
-superiorly -suprasellar cistern (optic pathways and circle of Willis)
-varies in size
-normally ( thin rim of soft tissue at base of sella
(partially empty sella)
-in females of child bearing age(will fill sella with
with superior convex margin
-infundibulum:
-larger in females than in males but should not exceed diameter of the basilar artery
-pituitary (no more than 9mm in height
(should enhance both on CECT & CEMR
-anterior and posterior lobes can be identified on MRI
-sometimes posterior pituitary returns high signal on T1WI due to neurosecretory granules so this high signal can vary on sequential scans of same patient
-uniformly bright in neonates
Ectopic pituitary : may originate from -- posterior lobe of pituitary—rounded high signal soft tissue mass