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Screening
Tech must go over the form
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Public - on the street
Zone 1
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Zone 1
Public - on the street
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Reception
- Zone 2
- - insurance information is provided
- - feel the form
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Zone 2
- Reception
- - insurance information is provided
- - feel the form
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Zone 3
- Tech console area
- - screening
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Zone 4
Scan area - must screen before
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5G line
Safe limit for pace maker
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Safe limit for pace maker
5G line
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SAR
- Specific Absorb Rate
- RF absorbed by blood stream and dissipated as heat.
- Head: 3.2 Watts/kg
- 1 gr of tissue: 8 Watts/kg
- Whole body: 0.4 Watts/kg
- Eyes and testes more sensitive to RF b/c do not sweat
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If the parameters selected for an imaging sequense will expose the Pt to SAR levels in excess of FDA defined level of no concern, they should never be employed on the Pt who are:
Febrile seizure
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SAR & TR depend on Slice thickness
Thinner slice - ↥ TR - ↧ SAR
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SAR - Head
Head: 3.2 Watts/kg
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SAR for 1 gr of tissue:
1 gr of tissue: 8 Watts/kg
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SAR - Whole body
Whole body: 0.4 Watts/kg
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Shielding B0
Steel around the wall (passive)
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Shielding B1
- Faraday Cage (active - electrical)
- use copper (best conducter)
- exclude bad RF
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Magnetic Field components:
- 1) B0 - Main Magnet (3T)
- 2) RF - 2nd order
- 3) Gradients - 3 pairs mini resistive:
- - add strength to 6T/1sec (ON/OFF)
- - noise from gradients
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Gradients
- - 3 pairs mini resistive
- - add strength to 6T/1sec (ON/OFF)
- - noise from gradients
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If gradients ON > 1 sec
- 1) Peripheral Nerve Stimulator
- 2) Arrythmic
- 3) Magnetophosphenes - illusion of light caused when changing of MF creates current within the retina or visual cortex
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Magnetophosphenes
illusion of light caused when changing of MF creates current within the retina or visual cortex
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What PS makes loudest noise?
EPi - Echo Planer imaging
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What makes more noise from gradients?
- Slice section thickness
- FOV
- RF Pulse bandwidth
- ↧ in slice section thickness
- ↧ in FOV
- ↧ in RF Pulse bandwidth
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Noise can effect ...
the Internal Auditory Canal
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Threshold
TH - the point or level at which something begins or changes
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Safe TH noise dose (%?)
66-80% does not cause any tympanic membrane damage
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TH noise dose is safe for tympanic membrane (%?)
66-80%
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dB/dt
Changint MF over time
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Changint MF over time is denoted by...
dB/dt
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Damage on analog wathces and credit catd strips can be at...
10.0 Gauss
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Quench
- first to do
- demagnetization of the magnet
- explosion (not combustion - fire)
- dangerous event in MRI process
- cause b/c Helium level to low and remain boil-off to the air
- - evacuate the room
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Dewar (capacity, pressure)
- container to keep He
- He should never be < 40%
- Pressure not > 5 PSI (rate of circulation)
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MRI facility must be in:
T - ?
Humidity - ?
- T = 65-70 F (room T)
- Humidity = 55-70%
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Quench causes...
- 1) Asphyxiation (chock)
- 2) Frostbite
- 3) Demagnetization
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MRI compatibles
MRI safe testing is done @ 3T by Bio-Met
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MRI and Aneurysm clip
- Conditional:
- - steel NO
- - titanium YES, but low field magnet 0.5T
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MRI and Cochlear implants
- NO MRI - Soundbridge implant device
- YES for - external hearing aids can be removed
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MRI and Pacemaker
- NO MRI
- YES for:
- - Gordon Wells Patch - temporary pacemaker (good for MRI)
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MRI contraindications
- 1) Pacemaker
- - Gordon Wells Patch - temporary pacemaker (good for MRI)
- 2) Aneurysm clip - conditional:
- - steel NO
- - titanium YES, but low field magnet 0.5T
- 3) Cochlear implants
- - Soundbridge implant device
- - external hearing aids can be removed
- 4) Whatever use bettery
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Pregnancy & MRI
- No MRI w contrast
- - crossing placenta
- Pregnant tech can work in MRI (NOT forbidden)
- - RF main concern, but it is in isocenter
- 10 days rool:
- - save to do MRI within beginning of menstr to 10 days
- Life-death situation:
- - can be done w consent from the doctor and radiologist
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Eyeliner taattoo
- YES MRI - give Pt instruction
- transient skin irritation or cutaneous swelling of the eyes and surrounding tissue
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Eyeliner makeup containing ferrous pigment
- YES MRI - give Pt instruction
- transient skin irritation or cutaneous swelling or the eyes and surrounding tissue
- Fabio eyeliner - NO MRI
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Vascular stents
- 99% compatible with MRI
- Swan-Ganz Catheters - NO MRI b/c Eddy Current inductive heating may melt the catheter
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Boolet & MRI
MRI can be done unless it is close to spinal cord
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Metall worker
- Best way to deterct metal - x-ray
- x-ray of the orbit before MRI
- radiologist must to read
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MRI sedated Pt's
- should be monitored (Pulse rate, O2 level & BP)
- MRI compatable Pulse Oxymeter and Sphygmomanometer
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Claustrophobia
- - health threat to the Pt
- 1) Give clear, detailed and concise instruction (easiest, safest, most effective)
- 2) Provide ear plugs
- 3) Provide music
- 4) Talk to the Pt b/w sequences. Can bring Pt out of the magnet.
- 5) Allow family member in the scanning room
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Specific absorption rate limitation problems are more likely to be experienced with ... transmitter coil
... body ...
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Motion artifacts
- - Ghosting
- - phase encoding direction (mismapping the image)
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EKG Triggering
- - MRI compatible electrodes are places on the Pt's chest
- - synchronizint the TR and cardiac
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Synchronizing the TR and cardiac cycle
- Pulse Triggering
- EKG Triggering
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Respiratory gating
- - controlled by Pt's breathing
- - echos are collected when Pt suspends respiration
- - for chest, abdomen and spine
- - synchronizing TR w periodic motion
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Pulse Triggering
- - transduser is placed on the toenail
- - transduser waits for a pulse wave before it begins to scan
- - TR is very limites
- - synchronizing the TR and cardiac
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Synchronizing TR w periodic motion
Respiratory gating
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Motion artifacts can be reduces by...
- ... Gating Techniques - echoes are only collected during the resting phase of the cardiac cycle
- 1) Pulse Triggering
- - transduser is placed on the toenail
- - transduser waits for a pulse wave before it begins to scan
- - TR is very limites
- - synchronizing the TR and cardiac cycle
- 2) EKG Triggering
- - MRI compatible electrodes are places on the Pt's chest
- - synchronizint the TR and cardiac cycle
- 3) Respiratory gating
- - controlled by Pt's breathing
- - echos are collected when Pt suspends respiration
- - for chest, abdomen and spine
- - synchronizing TR w periodic motion
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The faster the blood flow, the ... the signal
brighter
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The slower the blood flow, the ... the signal
lesser
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MRA common techniques:
- 1) Time of flight
- 2) Phase contrast (PC)
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Time of flight types:
- 1) 2DTOF - 2D Time of flight
- - slower blood flow
- - peripheral vascular structures of the lower extremities
- 2) 3DTOF - 3D Time of flight
- - faster moving blood
- - Circle of Willis, Carotid arteries, Aorta, Renal arteries...
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2DTOF
- - 2D Time of flight
- - slower blood flow
- - peripheral vascular structures of the lower extremities
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3DTOF
- - 3D Time of flight
- - faster moving blood
- - Circle of Willis, Carotid arteries, Aorta, Renal arteries
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MRA for Circle of Willis, Carotid arteries, Aorta, Renal arteries...
- 3D Time of flight
- faster moving blood
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MRA for peripheral vascular structures of the lower extremities
- 2D Time of flight
- slower blood flow
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MRA - PC
- PC - Phase contrast
- uses VENC - Velocity Encoding
- signal obtained in all directions
- for very slow blood flow
- imaging venous phase
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VENC
- - Velocity Encoding
- - used in MRA - PC - Phase contrast
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MRA with Gadolinium Pentacetic Acid
- - depends on the weight of the Pt
- - 0.1 mmol/kg or 0.2 ml/kg
- - no contraindication
- Precautions:
- - asthma
- - pregnancy or breast feeding
- - no brest feeding for 2 days
- - any known alergic history
- Used for:
- - dynamic scanning - liver and pituitary gland
- - to determine if BBB is broken of disrupted (enhancement)
- - any spinal surgery to see different b/w scar tissue and disc
- - arthographic studies (joint space)
- - to diagnose Osteomylatis
- Lethal Dose: is in excess of 20cc/kg of body weigth
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