• the cooling liquid used by the cryostat (c.g. liquid Helium a15k, liquid Nitrogen >7 K). • The magnet is housed insulated container (Dewar) that Functions like a thermos battle. • 1200 liters: typical volume of liquid Helium Used. • Quenching: the rapid heating of electromagnets that vaporize the cryogens.

proton density AKA

- The process nuclei undergo as they release their excess energy through interaction amongst themselves. • Usually labelled as spin-spin relaxation • Measured also in milliseconds • Involves a types of relaxation: spin-spin , transverse relaxation time.

- Parameters that are controlled by the techndo-gist depending on the capabilities of the mRl scanner. • Repetition time • Echo time • Inverse time • Flip angle

• ratio of the average signal intensity over the unavaidable background noise. • mababa SNR = mababa image quality

uses GE with short TR, enabling mz and Mxy be equal.

2 types relaxation of T2 sequence

TRUE OR FALSE characteristics of a Resistive magnet - Operates at room temperature. - Uses standard conducting materials (e.g. copper) shaped into a solenoid. - Requires high electric current to produce magnetic Field. - Produces a uniform magnetic Fied. - Limited to low Field applications.

(BI): the secondary field.

TRUE OR FALSE Advantages of using a superconducting magnet - induces high intensity magnetic Field - High Field homogeneity - Low power consuption - High signal noise rotio = Faster scanning time - Scamers are built horizontally

• method of bringing magnets to a superconductive state via cryogenic cooling (use of special cooling agents).

• Relaxation Time: the most important Factor in tissue discrimination. • Tissues can be distinguished From one another based on relaxation rates of their nuclei. • Types : T, and Ta sequences.

TRUE OR FALSE Characteristics of a superconducting Magnet - Made oF (superconductive) coils of Niobium Titanium alley filament wrapped around a large loop of copper. • Super conductive materials when exposed to low temperantures has no resistance which eliminates problems regarding those of resistive magnets. • Ramping: method of bringing magnets to a superconductive state via cryogenic cooling (use of special cooling agents).

- The most popular and commonly used, introduced by Herman Carr and Edward purcell - Uses 20° and 180° RFpulses (refocusing pulse) 50 TE • sequences: short TR and TE For Ti weighting, long FR and TE For Te weighting both are usually obtained. • Use: in almost all (general) applications.

- The process nuclei undergo as they release their excess energy to the general environment • Usually labelled as spin lattice relaxation. • Measured in milliseconda. • Inuelves a types of relaxation: spin lattice longitudinal, end thermal celaxation time.

True or false Permanent Magnet - An artificially induced magnet in nature. - Created by means of exposing a Ferromagnetic material to an external magnetic Field to induce magnetism. • Bo: up to 0.3 Tesla • Bo: Direction: can be transverse or longitudinal • Very heavy, inexpensive maintenance and materials, temperature sensitive. • Low Fringe field. - Made up of Ferrous material (e. magnetized ceramics, Ferrous plates, iron, cobalt, nickel) - magnetic Field is always active. - No power is required to activate magmetic Field - Can only produced low Field strengthe - Usually oF vertical Field direction, - Produces a weak Fringe Fiold.

true or false Use of signals in MRI - The signals produced in mRI techniques contain a combination of proton density and relaxation (Ti and Tz) • Rates of Relaxation (Ti, Tz) depends on the environment in which the nucleus is located. • Chemical environment among tissues difFer. • Relaxation rates of nuclei in diFFeren+ tissues differ = mRl signals in different tissues also diFFer = difFerent appearance on image.

TRUE OR FALSE Disadvantages of using a Superconducting Magnet - High capital cost requirement - High specific absorption rate (SAR) - Production oP chemical shiFt artifact - Increased production of motion artifact - Louder noises produced by the scanner. - InsufFicient research.

3 types relaxation of T1 sequence

true or false Common MRl pulses - Most common mRl pulses: ao and 180 degrees • B1 = determines the distance that magnetic moment (mo) processes from 2 axis. • A 90 degrees pulse tips 90° From 2 axis, the y exis • The spinning mo induces an Em Fore that creates detectable voltage in the coil oF wire.

- Connected to the mR scanner system to help maintain the bore cool and avoid high tempe ratures. • High temperatures causes damage to the system and loss oF eFficiency in producing magnetic Field. • Chiller system has a close circuit where glycol (cooling liquid) circulates through. • Glycol carries heat as it passes through the mRI system, then cooled down as it passes through the chiller.

: an insulating chamber that contains thy cryogens and electromagnet

TRUE OR FALSE - Current passing through the loop: the higher the electric current, the stronger the magnetic Field.

patial saturation AKA

true or false • Most soft tissues and fat have similar proton sensity thus poorly distinguished. • Bone and hair air in the lungs have low proton density and produces weak signals, thus easily distinguished From other tiesues.

Ultra high field strength

- Diameter of the loop: the smaller the diameter of the loops, the stronger the magnetic Field.

uses long T1 techniques for fluid suppression

• used to recondense some helium vapor back into the liquid helium bath.

Extrinsic parameters angle of inclination Fronen longitudinal axis.

uses GE low FA and TR to deplase Mxy.

- AKA Saturation Recovery, uses a series of 90° RF pulses to create repeated Free induction decays. • Contrast: depends on pD and T12 • • Sequence: short TR T1 partial saturation. • Use: demonstrating the presence oF cysts, subdural Fluids, and blood Flow.

- the time requred after : • Precessing spins hove aligned with the external magnetic Field due to the RE pulse • hosing 63% oF coherence due to interactions between spins.

(Bo) : the primary Field produced by the main magnet of the scanner.

Mid field strength

- used to stimulate the nuclei to obtain images that are weighted with any of the three intrinsic parameter. • short T1 = Fast spin lattice relaxation rates incresed mRl signal on T1 weighted images. • long T2 = slow spin-spin relaxation rate increased MRI signal on T2 weighted images.

fastest imaging MRI technique

Low field strength

: causes Field distortions produced by the gradient coils

Extrinsic parameters - the shortest time between a 90° pulse and its echo during a spin echo pulse, usually 10 - 100 ms

Permanent magnet (Bo)

- the release of energy by the excited protons, which occurs at difference rates in different tissues.

most common MEI pulses

• the rapid heating of electromagnets that vaporize the cryogens.

: the amount of power (head) deposited by a radio frequency Field in a certain mass of tissue, expressed in W/kg.

- AKA Spin Density, is the quantity of resonating spins (precessing protons) in agiven evolume tissue: • The signal strength produced by precessing protons is equal to the number of protons present. • Achieved by long relaxation times (TR) between pulses. • Produces low contrast. - Proton density alone poorly separates tissues.

uses GRE with the techniques of SSEP

the time required For the thermally excited system to return to its equilibrium state. • Ti relaxation of water in 3 seconds. • Demonstrates significant different in dehydrated tissues.

TRUE OR FALSE Disadvantages of Using a Permanent Magnet - how magnetic Field strength - Inhomegenous magnetic Field (produces relatively no uniporm Fields - magnets used are very heavy (approx 20 tons) - Low signal to noise ratio • Signal to Noise Ratio (SNR): satio of the average signal intensity oven the unavaidable background noise. • V SNR = L image quality

TRUE OR FALSE

Resistive magnet

- Parameters that are inherent to subject being scammed and uncontrolled by the technologist. • Proton density • T1 sequence • T2 sequence

Resistive Magnet - An electromagnet in nature limited by cooling requirements. - Resistance is due to the amount of solenoid that produce huge amount of heat and requives large amount of electricity. • Bo: 0.02 - 0.4 Tesla • Bo: Direction : longitudinal • High clectrical cost, inexpensive material solenoia, and produces uniform magnetic Fielo. • hongitudinal Fringe Field problem.

TRUE OR FALSE Use of Cryogen in Super conductive mkI scanners - Current posses through the magnet to induce a magnetic Field and rumps it to strength, then super cooled by cryogens to eliminate resistance. • Liquid helium and nitrogen are subject to evaporation and must be replaced periodically • Replacement is a signiFicant cost, since cryogens are very expensive and handling requires special training. • Superconducting magnets do not need continous supply of electric current to Function.

the time required for transverse magnetization to reduce strength by 37% of its maximum.

TRUE OR FALSE Disadvantages of Using a Resistive Magnet - High electric power consumption: a great deal Of power is required to achieved high magnetic Field strength. - Active current is used to induced a magnetic Field. - Heat produced by the magnet needs to be cooled by water (using a water chiller) - High operating cost: large power requirements oF the magnetic coils and the associated cooling system.

used as basic fat suppression sequence

uses multiple rephrasing RF pulses 180 degrees

uses GE with a reverse polarity rephrasing gradient.

TRUE OR FALSE creation of an MRI signal - Frequency of induced voltage matches the larmour frequency making it possible to identify the element of emitting the signal. • The voltage detected is the MRI signal. • Signal emitted by protons decay exponentially because of dephasing. • Free Induction Decay: the gradual loss of MRI signal due to dephasing.

Superconducting magnet

- Spacing between the loops: the smaller the spacing between the loops, the stronger the magnetic Field.

the time required For some of the magnetic moment to regain original orientation after RF excitation.

- Uses a three REpulse sequence that consist of 180° REpulse (inversion pulse) then Followed by a spin echo sequence. • Use: For tissue suppression and modiFying inersion time settings.

TRUE OR FALSE Advantages of Using a Permanent Magnet - much less expensive (to buy and maintain) than the other types of MRI magnets. - Costs virtually nothing to operate. - Scaner table moves in two directions. - Weak Fringe Fields and less SAR to the patient • Specific Absorption Rate (SAR) : the amount of power (head) deposited by a radio frequency Field in a certain mass of tissue, expressed in W/kg.

TRUE OR FALSE - Number of loops in the coil: the more loops the electromaghet has, the stronger the magnetic Field.

- The uses gradient pulses other tham REpulses, usvally gradient pulses of ao degrees. • Contrast: controlled by FA, TI and pD. • Sequence: short TR and 90° FA. • VEe: For neurologic and orthopedic applications.

an Ferrous material made magnetic through exposure to an external magnetic Field.

Extrinsic Parameters - the longest time interval between pulse sequences, usually between 300 - 3000 ms.

Ultra low field strength

Uses 180° gradient pulses and GRE.

• typical volume of liquid Helium Used.

the time required for precessing spins to align with the constant external magnetic Field to 63% of maximum strength.

TRUE OR FALSE - Magnetic Field lines will be present in all forms of magnet : • Bar permanent magnet • Cylindrical coil • Iron core electromagnet • Straight current carrying wire • Circular current carrying wire

TRUE OR FALSE Field Strength of an Electromagnet - Number of loops in the coil - Electric current passing through the loop - Diameter of the lasp - Spacing between loops

- The main magnetic field of the scanner that is used to magnetize the patient's tissue. - Provides the static external magnetic Field, available in different Field strengths and types. • From low to high magnetic Fields. • Permanents and electromagnets • Longitudinal and transverse directions

• has high resistance and requires a large amount of electricity.

Extrinsic parameters the time between a 180 degrees pulse and 90 degrees pulse in the inversion recovery usually 200-2000 ms