Prelim-Endterm Flashcards
A greek philosopher in 4000 B.C theorize that all matter is made of both indivisible and invisible particles “atoms.”
Democritus
west turkey discovered “loadstones.” Used for navigation religiory and magical purpose.
Magnesia
in 1819 discovered that electricity produces magnetism.
Hans christian oersted
1831 twelve years after the discovery of oersted discovered electricity.
Michael faraday
made the heart of MRI mathematics “Fourier transform.”
Jean-Baptiste-Joseph Fourier
1860 discovered magnetic lines of force could be mathematically expressed. Electrical and magnetic fields coexist at a 90-degree angle.
Sir James clerk Maxwell of Scotland
1868 discovered invisible electromagnetic waves exist with varying frequencies.
Heinrich hertz of Germany
discovered rotating magnetic field.
Nikola Tesla
First described and measured in molecular beams on magnetic resonance, Rabi method involved using electromagnetic of approximately 0.21 and a hairpin coil producing an oscillatory RF-field of about 3.5 MHz. The RF-field was maintained at a constant frequency and the main magnetic field was varied by changing its current. Rabi then passed a “molecular beam” of lithium chloride (LiCi) molecules through a vacuum chamber and subsequently into the magnetic apparatus in 1938 he and his team reported energy absorption/resonance peak for both Li and Ci as predicted. Rabi named this phenomenon “nuclear magnetic resonance”.
Isidor Isaac Rabi
their development of new ways and methods for nuclear magnetic precision measurements, expanded the technique for use on liquids and solids in NMR, for which they shared the Nobel prize 1952.
Felix Bloch and Edward Purcell
physician/physicist July 3, 1977, performed the 1st MRI whole body transaxial proton density weighted slice image. It took 4 hrs and 45 mins for the 1st scan, father of MRI (Magnetic Resonance Imaging), indomitable name of Damadian’s whole body scanner.
Dr. Raymond Damadian
demonstration of use of magnetic gradients for spatial localization and actual demonstration of 1-D imaging (1D MR image) which lead to the experiments of…
1952
designed the gradient coils, developed a way to generate the 1st MRI image in 2D and 3D, using gradients
Dr. Paul Lauterbur
from university of Nottingham then developed a mathematical technique that would allow scans to take seconds rather than hours and produce clearer images than Lauterbur had.
Peter Mansfield-
Owing to __ a mathematical technique called a __ could then be used to recover the desired image greatly speeding up the image process
Larmor precession, Fourier transformation
selective excitation or sensitization of tomographic image slice was invented by sir Peter Mansfield’s group.
1974
Richard ernst’s group invented the two dimensional Fourier transformation.
1975
Clow and Young produced the 1st published image of human head.
1978
General electric introduced high field 1.5 tesla systems
1984
for their discoveries concerning magnetic resonance imaging Paul Lauterbur and Sir Peter Mansfield were awarded the Nobel prize for medicine & physiology.
2003
a magnet whose magnetic field originates from permanently ferromagnetic materials (permanent magnet) to generate a magnetic field between two poles of magnet. There is no requirement for additional electrical power or cooling, and the iron-core structure of the magnet leads to a limited fringe field and no missile effect. Due to weight considerations __ magnets are usually limited to maximum field strength of 0.3-.5T
Permanent magnet
A type of magnet that utilizes the principle of electromagnetism to generate magnetic field. Typically large current values and significant cooling of the magnet coil is required. The resistive magnets does not require cryogens but needs a constant power supply to maintain a homogenous magnetic field and can be quite expensive to maintain. Resistive magnets fall into two general categories- iron core and air core.
Electromagnets or resistive system
Magnets that are partially built from superconducting materials and therefore reach much higher magnetic field intensity. Coil windings of superconducting magnets are made of wires of a type 2 superconductor. Liquid helium (-459F,0 K -273C) is commonly used as a coolant, which consequently conclude refilling. There are cryogen-free superconducting magnets with a closed-cycle refrigerating system at horizon. Superconducting magnets typically exhibits field strengths of greater than 0.5T, operate Clinically up to 3T and have a horizontal field orientation which makes them prone to missile effects without significant magnetic shielding.
Superconducting magnet
4-7 tesla
Ultrahigh field
1.5-3 tesla
High field
0.5-1.4 tesla
Mid field
0.2-0.4
Low field
<0.2 tesla
Ultra low field
Substance having no unpaired orbital electrons weakly repelled by either magnetic poles Ex: water and plastic
Diamagnetic
Materials lie somewhere between ferromagnetic and non-magnetic
Paramagnetic
Strongly magnetized by a magnetic and usually can be permanently magnetized by exposure to a magneticfield Ex: ALNICO (aluminum, nickel, cobalt)
Ferromagnetic
An atom is composed of?
Nucleus and revolving electron
The nucleus is composed of?
Protons and neutrons
Atoms with odd numbers of protons in their nuclei exhibits the property of?
Magnetic resonance
Has a single proton and thereby a large magnetic moment, also abundantly present in the body in the form of water and fat therefore, it produces the best magnetic resonance signals
Hydrogen
Therefore used in magnetic resonance imaging
Hydrogen ions
Is a vector quantity consisting of both a north and south pole
Magnetic field
A magnetic field characterized by its own magnetic north and south poles separated by a finite distance
Magnetic dipole
Refers to spinning motion of positive protons and the negative electrons that create a small magnetic field about the atom.
Magnetic moment
The amount of magnetic flux in a unit area perpendicular to the direction of magnetic flow
Magnetic intensity
A device that attracts iron and produces a magnetic field, the biggest and most important part of MRI system
Magnet
Precess or tumble
Spin
The phenomenon of magnetic field spinning or gyrating around imaginary axis of its own creation
Precession
Is the rate at which the nuclei complete a revolution about the precession path (megahertz or millions of cycle per second)
Frequency precession
Ratio between magnetic moment and angular momentum (disintegration constant in nucmed)
Gyromagnetic ratio
Angle formed between a precessing object and its imaginary axis
Angular momentum
Refers to that portion of the electromagnetic spectrum in which electromagnetic waves can be generated by alternating current to an antenna
Radiofrequency pulse
Specific frequency of resonance. Is located based on the particular tissue and strength of the main magnetic field
Larmor frequency
Phenomenon resulting in the absorption or emission of electromagnetic energy by nuclei or electrons in a static magnetic field, after exitation by a suitable magnetic field
Resonance
Time usually in fraction of a second in w/c the hydrogen nuclei switches from a magnetized state go a demagnetized state when magnetic pulse is turned off
Relaxation time
A biological parameter that is used in MRI to distinguish between tissue types, is a measure of the time raken to realign with the external
T1 relaxation time/spin lattice/longtudinal relaxation
Time required for a component of net magnetization vector to return __of its original value following an exitation pulse
T1 relaxation time, 63%
In the rotating frame, the net magnetization vector decays as spins lose phase coherence and begin to cancel each other out, they do this because they experience slightly different magnetic field strength due to interaction between spins, this cause some spin to “lag behind” the average and some “get ahead” of the average.
Free induction decay
Time required for a component of net magnetization vector to return __ of its orginal value following exitation pulse is?
T2 relaxation time, 37%
Interaction between individual spins
T2 relaxation time/spin-spin relaxation/transverse relaxation
Interaction between spins and bo inhomogeneity
T2*/t-two-star
Time between middle of exciting
TE/echo delay time/time echo
Period of time between the beginning of a pulse sequence and the beginning of the succeeding (esentially identical) pulse sequence
TR/repetition time
When an MRI is set to produce a PDWI image, the tissue with higher concentration or density of protons (hydrogen atoms) which produce the strongest signal and appears brightest on the image, produces contrast mainly by minimizing the impact of T1 and T2 differences with long TR (2000-5000ms) and short TR (10-20)
Proton density
Very useful for brain imaging (because of great white matter matter gray contrast), useful for extremity imaging (ankle, knee, elbow, shoulder, and hips), can be useful in thighs, lower legs, upper arm and forearm imaging, very useful for temporomandibular joint imaging.
PDWI (proton density weighted image)
Tr and te for T1W
short, short
Tr and te for T2W
long, long
Tr and te for PDW
Long, short
In clinical practice: TE is always shorter than?
TR
A short TR = value approximately equal to the average?
T1 value usually lower than 500 ms
A long TR = 3 time the?
Short TR, usually greater than 1500 ms
A short TE is usually lower than?
30 ms
A long TE = 3 times the short TE, usually greater than?
90 ms
is referred to as the longitudinal magnetization.
MZ
There is no (if it returns to normal equilibrium or relax that is T1)
transverse (Mxy) magnetization
__ referred to as __(if it returns to normal equilibrium or relax that is T2)
Mxy, transverse magnetization
Structures in short T1 (bright appearance)
Fats, proteinogenous fluids, subcutaneous blood
Structures in LONG T1 (dark appearance)
Neoplasm, Edema, inflammation, Pure fluid, CSF
Structure in short T2 (dark appearance)
Blood breakdown products
Structures in LONG T2 (bright appearance)
Neoplasm, Edema, Pure Fluid, CSF
Different in PWDI: Bone marrow (fatty marrow is usually __)
equal to or higher than that of muscle, (bright)
Different in PWDI: Fat (__ than the fat signal in T1 images)
bright (slightly darker)
Diffrent in PWDI: Fluids (__ than the fluid signal in T2 images)
bright (darker)
Diffrent in PWDI: White matter
darker than bright gray
Diffrent in PWDI: Gray matter
bright gray
Diffrent in PWDI: Moving blood
dark
Diffrent in PWDI: Muscles
gray
Diffrent in PWDI: Bone
dark
Diffrent in PWDI: Air
dark
optimum signal intensity
Hyperintense
weak signal intensity
Hypointense
same signal intensity
Isointense
The magnet is the most expensive part of the whole scanner. The earliest systems were based around water-cooled resistive magnets, and for particular applications it is possible to use permanent magnets, but the majority of modern scanners use superconducting magnets.
External magnets
are loops of wire or thin conductive sheets on a cylindrical shell lying just inside the bore of an MR scanner. When current is passed through these coils a secondary magnetic field is created
Gradients coils
Three of gradient coils are used in nearly all MR systems
X, Y, Z gradients
__ is usually based on circular (Maxwell)
Z gradients
typically have a saddle (Golay) coil configuration.
X- and Y- gradients
Supplied by computer manufacturer and modified and programmed for use in an MRI system. Attached to it is the user interface, the fourier transformer. The signal converter, and a preamplifier, a display device and a laser printer are also included.
Computer
the electromagnetic components of the __ may be provided by outside suppliers and assembled by the MRI manufacturer. These components are attached to the RF coils, which are made with varying designs
RF system
Make the magnetic field homogenous
Shim coils
Detect the returning radio signals
Receiver coils
are the ‘antenna’ of the MRI system that broadcast the RF signal to the patient and/or receives the return signal RF coils can be receive only, in which case the body coil is used as a transmitter, or transmit and receive (transceiver).
RF coils
are the simply a loop of wire, either circular or rectangular, that is placed over the region of interest. The depth of the image of a surface coil is generally limited or about one radius. Commonly used in spines, shoulders, TMJ’s and other relatively small body parts.
Surface coils
provide better homogeneity of the RF in the area of interest and are used as volume coils, unlike surface coils. Also used of the X and Y gradient coils. Commonly used for imaging of the knee.
Paired saddle coil
consist of two circular coils parallel to each other. They are use as gradient coils in MRI scanners. They also used occasionally RF coils for pelvis imaging and spine imaging
HELMHORTZ PAIR COIL
provides the best RF homogeneity of all the RF coils. It has the appearance of a bird cage; hence, its name. This coil is commonly used as a transceiver coil for imaging of the head. This type of coil is also used occasionally for imaging of the extremities such as the knees.
BIRD CAGE COIL
Power Supply of MRI
2.4 Kw, 5% Voltage Ripple
To provide Radio Frequency shielding, uses aluminium, or in certain conditions galvanized steel, to form the Shielded Faraday cage. To function properly, an MRI scanner needs to sit in a specialized room or chamber shielded against Radio Frequency (RF) interference. Without such protection the very weak RF signals that emanate from the patient when scanned would be overwhelmed.
Faraday cage
is used in MRI to describe the relative contributions to a detected signal of the true signal and random superimposed signals (‘background noise’)
Signal-to-noise ratio
Old name of signal to noise ratio (SNR)?
Mean Signal/Standard Deviation of Background Noise
Factor affecting Snr- relationship
Bo-
T1-
T2-
TE-
TR-
NEX-
pixel size-
Matrix size-
Slice thickness-
Fov-
Rf bandwith-
Increase
Decrease
Increase
Decrease
Increase
Increase
Increase
Decrease
Increase
Increase
Decrease
• The smaller the sensitive volume of a coil, the lower the noise from the adjacent structures of the selected slice plane which it can detect, and the better the signal to noise ratio will be.
• A local coil, or better, a surface coil have a higher signal to noise ratio than a body coil.
If all parameters are constant
Refers to the frequencies associated either with RF-excitation (transmitter bandwidth, tBW) or signal reception (receiver bandwidth, rBW) or the highest or lowest signal.
RF bandwidth
the range of frequencies accepted by the receiver to sample the MR signal.
receiver (or acquisition) bandwidth (rBW)
rBW has a direct relationship to?
Signal to noise ratio (SNR) snr = 1/squareroot (rBW)
refers to the RF excitation pulse required for slice selection in a pulse sequence. The slice thickness is proportional to the bandwidth of the RF pulse (and inversely proportional to the applied gradient strength). Lowering the pulse bandwidth can reduce the slice thickness.
Transmit bandwidth
Slice Thickness in MRI is determined
Bandwidth of RF (longer BW, lower ST)
Steepness of the slope of gradient coil (strength)
MRI uses techniques called __ to acquire images with different tissue contrast mechanisms. __ are a set of specific instructions programmed into the computer with an expectation as to how the images should appear.
pulse sequences
•diffusion movement of molecules due to random motion. If an incident occurs less than 72 hours prior to the scan, swelling due to edema occurs.
•Used for CVA and CNS
•the combination of actual diffusion values and T2 signal.
diffusion weighted imaging (DWI)
DWI is most applicable when?
tissue of interest is dominated by isotropic
water movement
DWI also remains sensitive to?
T1 and T2 relaxation
are images representing the actual diffusion values of the tissue without T2 effects.
• They are therefore much more useful, and objective measures of diffusion values can be obtained, however they are much less pretty to look at.
• They appear basically as grayscale inverted DWI images.
Apparent diffusion coefficient maps (ADC)
most widely used. Starts with 90 pulse and
ends with 180 degree pulse.
Spin echo
a gradient to refocus the spins. Gradient echoes are more susceptible to blood flows. They utilize
flip angles lesser than 90 degrees in addition to TR and TE.
• Are an alternative technique to spin echo sequences
• Utilization of gradient fields to generate transverse magnetization
• flip angles of less than 90°
• AKA Reverse Polarity of Gradient
Gradient echo sequences
fast gradient imaging technique. For turbulent blood flow.
Fast gradient echo
is quicker because it covers a wide range of tissue, however it does increase the specific absorbed rate. FSE starts with a 90 degree pulse and followed with a series of 180
degree pulse.
Fast spin echo
a pulse sequence used to saturate fat. This is important because fat may mask underlying pathology in areas such as the orbits or the liver. Use different method such as STIR and Dixon Method
Fat saturation (fat-sat)
also called short T1 inversion recovery is a fat suppression technique with an inversion time, Where the signal of fat is zero.
Short tau inversion recovery (STIR)
Exploits the fact that water and fat molecules precess at different rates.
• hybrid techniques combining several of these fat suppression techniques ( use four suppression)
Dixon technique
In phase
Water+fat
Out phase
Water - fat
Fat only
In phase - out phase = (water + fat) - (water-fat)
Water only
In phase + out phase = (water+fat) + (water-fat)
Starts with a 180 degree pulse and ends with a 90 degree pulse.
•Utilizes an inversion time in addition to the TE used.
•Acquired from SE.
Inversion recovery
Suppresses signal from CSF. (fluid)
•Most applicable in the brain for seizure disorders and for spinal cord injuries.
Fluid attenuation inversion recovery (flair)
It has been shown to be superior in the assessment of osteomyelitis in bone 1 and in the assessment of head and neck tumors
•Fast Technique of Inversion Recovery
Turbo inversion recovery magnitude (TIRM)
is a MRI pulse sequence which suppresses signal from the CSF as well as from the white matter and hence enhances any inflammatory lesion.
• Its main application is to delineate white matter plaques in multiple sclerosis, estimate lesion load, differentiate juxta cortical from mixed grey matter- white matter plaques and detect infratentorial or spinal cord lesions.
Double inversion recovery (DIR)
is an MRI-based neuroimaging technique which makes it possible to estimate the location, orientation, and anisotropy of the brain’s white matter tracts.
Diffusion tensor imaging (DTI)
cause a reduction in the T1 relaxation time they are typically small molecular weight compounds containing as their active element. Gadolinium , Manganese , or Iron all of these elements have unpaired electron spins in their outer shells and long relativities.
Positive contrast agent
are small particulate aggregates often termed superparamagnetic iron oxide (SPIO). These agents produce predominantly spin relaxation effect (LOCAL FIELDINHOMOGENETIES). Which results in shorter T1 and T2 relaxation time.
Negative contrast agent
Adverse reactions of contrast agent (+)
Headache 6.5%
Injection site coldnesss 3.6%
Injection site pain or burning 2.5%
Nausea 1.9%
MAGNETIC FIELD HAZARDS
- Projectile/ Missile effect
- Effect on surgically implanted devices
- Magnetic foreign bodies
- Life support devices
- Object that may be damage
MRI uses a very strong magnetic field to image the body. This may create dangers for more serious than the somatic effects of ionizing radiation, therefore, particular attention should be taken to ensure the safety of both patient and the technologist.
MRI safety
the magnet is continuously cooled with cryogens. However, if the cryogen level becomes excessively low, the remainder will “boil off” into the air
Quenching
In quenching the ff will then occur:
• A cloud of gas will evaporate into the air.
• The magnet becomes demagnetized.
• Patient asphyxiation and frostbite may occur.
• If a quench does occur, evacuate the pt. immediately.
• It takes approx. 72hrs to ramp the magnet up to full magnetic potential.
Tips to prevent quenching and provide safe enviroment as possible in quench situation
Maintain proper hilum levels and appropriate percentage of helium pressure as prescribe by the system manufacturer
Continuous monitoring of ‘cold head’ functioning by listening to chirping sounds.
occurs on MR images when the object imaged is under sampled (the object is larger than the field of view) and the object outside the field of view is superimposed onto the opposite side of the imaged volume. The appearance is a though the image that was not properly sampled has been folded over onto the opposite side of the image.
Aliasing or wraparound artifact
appear as a dark band on one side of the interface between fat and water and a bright band on the other side. The term __ refers to the difference in resonant frequency of protons due to local differences in chemical environment.
Chemical shift artifacts
appears as multiple rings of regular periodicity or duplication at transitions between high- and low-intensity signals.
Truncation artifact
is more apparent because of higher spatial frequencies that exist at the boundaries.
Gibbs phenomenon
occur when the image displayed demonstrates overlapping anatomic structures within the same pixel. Caused by thickness too thick and pixel size too large.
Partial volume averaging artifacts
How to correct aliasing or wraparound artifact?
Increase the FOV. By choosing a larger FOV there are more samples to assign the area of interest.
Use “no phase, no frequency wrap” technique.
The use of surface coils is often helpful in
minimizing this artifact.
How to correct chemical shift arifact?
Change scan direction. Patient may be rescanned with the axis parallel to the fat-water interface.
Use steeper gradients/Increase gradient strength.
Use specialized pulse sequence (STIR).
3 significant features of truncation
Ring artifacts that parallel high-contrast interfaces
Artifactural false widening of edges at these interfaces
Edge enhancement of the interface with distortion of tissues immediately adjacent to the interface.
How to correct Truncation/Gibbs phenomenon/ Ring Artifacts
Use larger matrix size
Use of smaller pixel size the more accurate the edge detail.
Filter raw data. Filters remove high frequency signals that cause the truncation.
How to correct partial volume averaging artifact?
Decrease FOV
that parallel high-contrast interfaces. Artifactural false widening of edges at these interfaces. Edge enhancement of the interface with distortion of tissues immediately adjacent to the interface.
Ring artifacts
produce ghost images of the anatomy in the phase encoding direction. Motion can cause blurring and is proportional to the distance moved. This may result in fuzziness on the image or a lack of crispness or detail.
Motion artfiacts
How to correct motion artifact?
Sedate px
Use spong
Breath hold
Cardiac gating
Use fast scan technique
Respiratory gating
When molecules lie at 54.74°, there is lengthening of T2 times with corresponding increase in signal. Thus in short TE sequences, the T2 signal does not decay significantly before the scanner picks up the signal. On the other hand, in long TE sequences (like T2WI), by the time the scanner picks the signal, T2 signal has already decayed.
Magic angle artifact
Typical sites in magic angle artifact
Proximal part of posterior cruciate
Supraspinatus tendon
Peroneal tendons
Cartilage
Triangular fibrocatilage complex
Infrapatellar tendons
How to correct magic angle artifacts
Used longer te (t2 including fse t2)
The slice-overlap artifact (also known as __- __ artifact) is a name given to the loss of signal seen in an image from a multi-angle, multi-slice acquisition, as is obtained commonly in the lumbar spine.
Crosstalk artifact
How to correct crosstalk artifact?
Decrease slice thickness by 30%
Apply interleave scanning method
System noise causes a bright signal at the isocenter or central reference point with a linear dashed pattern along the frequency axis.
FID/zipper artifacts (may also appear star artifact)
How to correct fid/zipper artifact
Increasing number of acquisitions (NEX)
• Shift in central reference line.
__ , which often appears as static on the image, can be caused by a medical device located anywhere in the MR procedure room. RF noise is a result of excessive electromagnetic emissions from the device that interference with the proper operation of the MR scanner. The interference is attenuated and aliased in the frequency direction.
Rf noise artifact
How to correct rf noise artifact
Improve RF shielding
• Remove monitoring devices if possible
• Close the door of the MRI room
appears as a faint to gross herringbone fabric pattern throughout the image. Others describe it as a screen-door.
Criss-cross/Herringbone
Causes of criss-cross/herringbone
RF discreets
• Gradient power supply (surge in the power)
• A/D converter
• Fluctuating currents
are interference pattern most commonly seen when doing gradient echo images.
Moire fringes (zebra artifacts)
How to correct moire fringes (zebra artifacts)
Appropriate shimming coils (autoshimming)
2nd most common artifact, usually the clip artifact which manifests as a high intensity where the signal has been misregistered and a void, or loss of signal, in the area where the metal is located in the body.
• Ferromagnetics
• Paramagnetics
Diamagnetics
Metal artifacts
Metal artifact solution
Screening is the best solution
Patients should remove eye make up if their upper body is being imaged
are small electric currents that are generated when the gradients are rapidly switched on and off (resulting sudden rises and falls in the magnetic field produce electric currents). These currents will result in a distortion in the gradient profile and in turn cause artifacts in the image.
Eddy current
Ideal gradients are linear. However, as in other aspects of life, there is no such thing as an ideal
gradient or perfect. These nonlinearities cause local magnetic distortions and image artifacts.
The effect is similar to artifacts related to Bo inhomogeneities.
Nonlinearity/non-uniformity artifact
Amplifier artifact caused by unbalanced gain in the two channels of quadrature coil. Combining two signals of different intensity caused some frequencies to become less than zero causing 180 degree ghost
Quadrature artifact
Oldest agent approved in 1988 with historically largest world-wide market share and clinical experience, below average relaxivity probable risk of high risk of NSF
Brand name: Magnevist
Chemical name: gadopentetate (Gd-DTPA)
Structure: linear ionic
Highest relaxivity of all extracellular gadolinium agents due to transient protein binding 3-5% hepatocyte uptake; competitive inhibitor for cMOAT drugs (tamoxifen, methotrexate, cisplatin) QT prolongation
Brand name: multihance
Chemical name: gadobenate (Gd-BOPTA)
Structure: linear ionic
Low thermodynamic stability, disproportionately high risk NSF, may interfere with serum Ca** measurement
Brand name: Omniscan
Chemical name: gadodiamide (Gd-DTPA-BMA)
Structure:linear nonionic
Low thermodynamic stability; probable high risk of NSF; may interfere with measurements of serum Ca, Fe, Cu and Zn
Brand name: Optimark
Chemical name: Gadoversetamide (Gd-DTPA-BMEA)
Structure: linear nonionic
One of oldest agents with largest market share in europe, most recent entry (2013) into us market
Brand name: dotarem
Chemical name: Gadoterate (Gd-DOTA)
Structure: macrocyclic ionic
Low osmolality and viscosity of all agents; below average relaxivity
Brand name: prohance
Chemical name: gadoteridol (Gd-HP-DO3A)
Structure: macrocyclic nonionic
Highest viscosity due to 1.0m formulation (all others 0.5m) above average relaxivity, marketed as gadovist outside US
Brand name: Gadavist
Chemical name: Gabutrol (Gd-BT-DO3A)
Structure: macocyclic nonionic
Designed for liver imaging 50% uptake by hepatocytes after initial extracellular phase, joint renal & biliary excretion very high relaxivity due to size and transient protein binding may interfere with serum Fe measurement QT prolongation
Brand name: Eovist (USA) primovist
Chemical name: Gadoxerate (Gd-EOB-DTPA)
Structure: linear ionic
Highest relaxivity of any agent due to reversible albumin binding intended for MRA; steady state blood pool imaging 20 min- 4 hrs after injection long elimination half-life (16+ hrs) QT prolongation
Brand name: Ablavar
Chemical name: Gadofosveset (Gd-DTPA-DCHP)(MS-325)
Structure: linear ionic
Weekly test in MRI
Qc frequency test
Table positioning accuracy
Set up and scanning test
Daily test in MRI
Magnetic field and radiofrequency warm up
TIPS for SR
• Increase in Slice Thickness =
• Increase in Data Absorbed=
• Increase in Signal=
• Increase in Bo=
Decrease SR
Increase SR
Increase in SR
Increase in SR
After 24 hours post stroke, middle cerebral artery (MCA) strokes appear as low signal intensity on T1-weighted images and high signal intensity on T2-weighted and FLAIR images. Infarctions appear as hyperintense on T2 and FLAIR images due to the development of cytotoxic and edema in the stroke area after 24 hours.
• Diffusion Weighted Imaging is the most sensitive sequence for early stroke diagnosis.
Acute MCA infarction
Typical appearance of affected area in the event of
early stroke
• T2 and FLAIR images will be __
• T1 images will be __
• DWI b value 0 will be __
• DWI b value 1000 will be __
• ADC map will be __
normal
normal
normal
hyperintense
hypointense
Typical appearance of affected area 24 hours post
stroke
• T2 and FLAIR images will be __
• T1 images will be __
• DWI b value 0 will be __
• DWI b value 1000 will be __
• ADC map will be __
hyperintense
hypointense
hyperintense
hyperintense
hypointense
AKA called malignant gliomas, are the most common brain tumours in adults. Approximately 20% of all primary brain tumours are glioblastoma multiforme tumours. Most __ are hypointense on T1-weighted images and hyperintense on T2- weighted images. Very rarely some lesions with hemorrhagic components may mimic glioblastoma multiforme on MRI images e.g. abscesses and infarcts. appear as aheterogeneous mass with low signal intensity on T1- weighted images and high signal intensity on T2- weighted images. These lesions give a typical ring enhancing pattern on T1-weighted gadolinium enhanced images. The hypointense area in the centre on T1-weighted enhanced images represents necrotic cells. The enhancing ring is composed of dense
neoplastic cells with abnormal vessels inside. The peripheral area of hyperintense low attenuation is vasogenic edema containing varying numbers of invasive tumour cells.
Glioblastomas
is the high-grade form of astrocytoma. MRI with and without contrast is the most commonly used diagnostic tool for glioblastoma multiforme.
Glioblastoma multiforme
Most common extra-axial tumours of the central nervous system and accounts for 15 % of all intracranial neoplasms. They are non-glial neoplasms that originate from the mesoderm or meninges. __ are commonly found on the brain surface, either over the convexity or at the skull base. In rare cases, __ occur in an intraventricular or intraosseous location. MRI is the most commonly used diagnostic tool for the characterisation of __.
Meningiomas
Typical of appearance of meningiomas
T1-weighted non enhanced MRI image shows a (rarely
hyperintense ) homogeneous, hypointense round mass with thin capsule.
T1 non enchanced
Typical of appearance of meningiomas
T2-weighted MRI image shows an isointense and
inhomogeneous mass with peripheral oedema indicating a more fibrous and harder character
T2 and FLAIR
Typical appearance of meningiomas
T1-weighted enhanced MRI image shows a hyperintense homogeneous round mass with an enhancing tail involving the dura.
T1 enchanced
__ are isointense to mildly hypointense on T1-weighted images and are hyperintense on T2-weighted images or with fluid attenuation inversion recovery.
Metastatic lesions
is relatively hypointense on T1-weighted images and
are hyperintense on T2-weighted images.
Surrounding edema
are hyperintense on T1-weighted images. On T2-weighted images, mucinous adenocarcinoma
may be hypointense, owing to calcification; hemorrhagic metastases may be hypointense, owing to the chronic breakdown of blood products.
Hemorrhagic metastatic lesions or melanoma lesions
Following administration of a contrast agent, solid, nodular or irregular ring patterns of enhancement are __. Nonenhancing lesions are less likely to be __.
seen, metastases
Pituitary Adenoma
MRI appearance:
• T1:
• T2:
• T1 contrast enhanced:
Hypointense
Unpredicatble variable signal
Hyperintense
Hemorrhage
T1:
Hyperacute- __
Acute - __ to __
Subacute - __
Chronic - __
Hyperintense
Hypointense, isointense
Hyperintense
Hyperintense
Hemorrhage
T2:
Hyperacute- __
• Acute - __
• Subacute - __ to __
• Chronic – __
hyperintense
Hypointense
Hypointense, hyperintense
Hyperintense
Hemorrhage
FLAIR:
hyperintense at all stages
Compartment
Hyperacute- __
Acute - __
Subacute - __ to __
Chronic – __
Intracellular
Intracellular
Intracellular, Extracellular
Extracellular
Hemoglobin
Hypercute (<24 hr)
Acute (1-3 days)
Early subacute (3-7 days)- Late subacute (7-30 days)
Chronic (> 1mo)
Oxhemoglobin
deoxyhemoglobin
Methemoglobin, Methemoglobin
Hemosiderin
Hyperplasia (Focal nodular hyperplasia)
• T1:
• T2: __ with a __ central scar
• Post contrast: __ __ __ in the arterial phase followed by __ in the portal phase and __ in the later phases.
• Iso-or __ in the hepatobiliary phase.
• DWI: __ with normal liver
Iso-hypointense
Iso-slightly hyper, hyperintense
Intense homogeneous enhancement, isointensity, enhancement of the scar
Iso or hyperintense
iso- intense
Hemangioma
• T1: __
• T2: __ markedly __ (referred to as light bulb sign)
• DWI: with low b values (T2 shine through). __ with high b vaule and on ADC map.
homogenous hypointense
homogenous, hyperintense
hyper intense, Iso-intense
Scan best defines abnormality
T1W images
Subacute hemorrhage
Fat containing structures
Anatomical details
T2W images
Edema
Tumor
Infarction
Hemorrhage
FLAIR images
Edema
Tumor
Periventricular lesion
Types of MRI exams
Brain MRI
Pts with headaches, seizures, weaknesss, blurry
Types of MRI exam
Cardiac MRI
Evaluate size and thickness of chamber of heart
Types of MRI exam
Spine MRI
Look for herniated disc or narrowing of spinal canal (stenosis)
Types of MRI exam
Bone and joint mri
Types of MRI exam
Evaluate abnormality seen in other test. Ex liver adrenal and pancreas
Abdomen MRI
Types of MRI exam
Evaluate ovaries and uterus as follow up to an ultrasound exam which showed abnormality. Evaluate endrometrial cancer and prostate cancer
Pelvic MRI
Types of MRI exam
Evaluate blood vessels, in the neck and brain to look for narrowing or dilation, renal arteries also examind
MRA
the flow compensated gradient-echo sequences will be optimized to favor the vascular signal over that of the surrounding tissues
Time of flight (TOF)
Multiple thin (1-2 mm-thick) slices are obtained as a stack in a plane perpendicular to the course of the imaged blood vessels.
2DTOF
is used where the imaged anatomy encompasses a relatively small area and vessels run in various
orientations. 3D methods offer high spatial resolution and high signal-to-noise.
3DTOF
