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1. MAGNETIC RESONANCE IMAGING
3 marks
B.Sc Medidcal imaging technology – 3rd
year
QUESTIONS AND ANSWERS
BY
2020 BATCH
MS. KEERTHNA
Guided By
Mr. Yogananthem Dr. Harshavardhan B
B.Sc MIT course coordinator Head of Medical Technology Course

2. MAGNETIC RESONANCE IMAGING
1. Define atomic structure. (UNIT – I)
2. Define magnetism.
3. Classify types of magnet.
4. Define eddy current.
5. Define precession.
6. Define larmor frequency.
7. Define solenoids.
8. Define contrast.
9. Define resolution.
10.What is RF coil? (UNIT – II)
11.What is gradient coil?
12.What is shim coil?
13.Define transmitter and receiver of coils.
14.Why needa MRI safety?
15.Do and don’t in MRI.
16.Types of coils?
17.Safe zones in MRI?
18.What is pulse sequence? (UNIT – III)
19.Define spin echo.
20.Define turbo spin echo.
21.What is a gradient?
22.Define inversion recovery.
23.Define proton density.
24.Give a abbreviation of TSE, SE, IR and PD.

3. 25.Define angiography. 26.Define Venogram.
27.Define spectroscopy.
28.Classify the protocols of brain. (UNIT – IV)
29.Classify the protocols of spine.
30.Classify the protocols of abdomen.
31.Classify the protocols of hand.
32.Classify the protocols of pelvis.
33.Classify the protocols of shoulder.
34.What are the steps involved in MRI scan.
35.How you will do MRI for uncooperative patient?
36.What is the contrast used in MRI?
37.Classify the plain studies in MRI.
38.What is axial, coronal and sagittal?
39.Define SNR.
40.List the artifacts in MRI.
41.Define the resolution and its types.
42.Define perfusion. (UNIT – V)
43.Define tractography.
44.What is a functional MRI?
45.What are the advantages of MRI scan?
46.What are the advantages of perfusion?
47.What are the advantages of tractography?
48.What is post processing?
49.Define 3D images.
50.What are the recent advances in MR Imag

4. 1. Define atomic structure.
Atomic structure refers to the structure of an atom comprising a nucleus (centre)
in which the protons (positively charged) and neutrons (neutral) are present. The
negatively charged particles called electrons revolve around the centre of the
nucleus.

5. 2. Define magnetism.
Magnetism is mainly defined as the property to attract or repel a material, the
material which shows this property is known as magnets. When we apply an
external magnetic field on a material the electron present in it tries to align itself
in the direction of the field and forms a domain in many directions.

6. 3. Define eddy current.
Eddy currents are loops of electrical current induced within conductors by a
changing magnetic field in the conductor according to Faraday's law of
induction. Eddy currents flow in closed loops within conductors, in planes
perpendicular to the magnetic field .in transformer due to eddy current we are
energy loss.
4. Classify types of magnet
There are three types of magnets
1. Resistive magnet
2. Permanent magnet
3. Superconductive magnet

7. 5. Define precession.
Spin is rotation of a proton around its own axis while precession is rotation of the
axis itself under the influence of external magnetic field such that it forms a ‘cone.
6. Define Larmor frequency?
 Larmor equation states that precession frequency is directly proportional
to magnetic field strength (Bo).
 The gives relation between magnetic field strength and angular
frequency.
w0= Bo y
Where wo = Precession frequency in Hz
Bo = Strength of external magnetic field in Tesla
γ = Gyromagnetic ratio,

8. which is specific to particular nucleus Precession frequency of the
hydrogen proton at 1, 1.5 and 3 Tesla is roughly 42, 64 and 128 MHz
respectively
7.Define Solenoids?
 A coil of wire which is designed to generate a strong magnetic field
within the coil is called a solenoid.
 Wrapping the same wire many times around a cylinder creates a
strong magnetic field when an electric current is passed through it.

The magnetic field strength of a solenoid coil is directly proportional to
number of turns.

9. 8. Define MRI Contrast?
Contrast is the difference in density between two adjacent tissues.
The tissue (image) contrast in MRI is determined by 3 things:
1 Density of 'mobile' protons, (Proton density image)
2. T1 characteristics, (T1 Image)
3. T2 characteristics. (T2 image)
Also repetition time (TR), echo time (TE) and flip angle is used to control image
contrast and the weighting of the MR image.
9. Define Resolution?
 Resolution is the ability of human eyes to distinguish one structure
from the other.
 In MRI,the resolution is determined by the no.of pixel in a specified
FOV.
 The higher the image resolution,the better the small pathologies can
be diagnosed.
 There are two resolution parameters:
 Basic resolution
 Phase resolution
 Factors affecting resolution are matrix size, field of view,slice
thickness.

10. 10. What is RF Coil?
 A loop of wire is a coil.
 Radio Frequency (RF) is an electromagnetic radiation with frequency
range of 1MHz-10GHz.
 Radio frequency coil are used to transmit RF pulses into the patient
and to receive the signals from the patient.
 RF coil can be transmitters, receivers or both.
 Energy is transmitted in the form of short intense bursts of radio
frequency known as radio frequency pulses.
Example: Volume coils, Surface coil &Phased array coils.

11. 11.What is Gradient Coil?
Gradient coils are used to produce deliberate variations in the main magnetic field (B0).
There are three sets of gradient coils, one for each direction.
The variation in the magnetic field permits localization of image slices as well as phase encoding
and frequency encoding.
Both phase encoding and frequency encoding gives us information where the MRI signals are
coming from the body.
Simply saying it is helps us to localize the signal.
There coil are switched on and off rapidly (about 1 ms) that makes loud noise.

12. 12. What is shim coil?
 Shimming means making uniform
➢ The main Magnetic field should be uniform all over its extent to get correct information from
the patient.
➢ Even though magnetic field is more or less uniform there might be minor in homogeneity.
➢ The process of making the magnetic field homogeneous is called shimming the coil used for
shimming are called shim coil.
➢ These coil superimpose over the main field and correct field difference.
13. Types of Shimming ?
Shimming can be active or passive.
Passive shimming is done by keeping metal pieces, called shim plates, in the field to oppose the
inhomogeneity.
Active shimming is done by passing current through the gradient coils, which generate small
magnetic field gradients superimposed on main magnetic field (B0). These coils are called shim
coils. Shim coils make field homogeneous by adding or subtracting from the field at desired
points.
Passive shimming- keeping metal plate inside

13. 13.Define Transmitter and Receiver coils?
➢ Transmitter:
Transmitter coil is a loop of wire with a current passed through it at Larmor frequency, situated
at right angles to the main magnetic field. Example :RF coil
➢ Receiver coil:
A coil or antenna positioned within the imaging volume and connected to the receiver circuitry
that is used to detect or receive an MR signal from the patient
Example: RF coil (surface coil)(body coil). RF coils can be transmitters, receivers or
both(transceivers).
14.Do and Don’t in MRI?
Do’s :
➢ Wear comfortable cotton clothes.
➢ Make sure all clothing is metal free.
➢ Remove all metal objects like jewelers.
➢ Check the patient with metal detector.
 Follow MRI safety guidelines.
Don’ts:
➢ Don’t wear makeup.
➢ No metal objects allowed.
➢ Metal implant s like pacemaker, dental implants are not allowed.
➢ don’t drink too much of fluid beforehand
15. Why need a MRI safety?
MRI machine uses a powerful magnet which can pose real risks to people in the room. If an
object is highly attracted to the magnet, if can be picked up and pulled into the magnet like a
projectile. There can be significant safety rules should be followed, when taking an MRI scan.
Patients (and employees) may have implants or devices, like pacemakers, neurostimulators,
cochlear implants, and aneurysm clips and coils, which can harm patients if scanned
unknowingly. Equipment, like wheelchairs, oxygen cylinders, and trolleys, can become attracted
to the strong magnetic field and become a projectile.
Because of these potential dangers, employee access is limited to MRI rooms unless appropriate
screening has been undertaken for patients and staffs..

14. 16.Types of Coil?
A loop of wire is a coil.
➢ Based on design RF coils can be divided into Volume coils,Surface coil, Phased array coil.
➢ Volume coil: A Volume coil typically surrounds either the whole body or a specific region.
Example: Body& Head coil.
➢ Surface coil: A surface coil is placed on the surface of a region of interest to acquire image
with very high SNR. Example: Lumber spine,knee and orbit.
➢ Phased array coil: A phase array coil consists of two or more geometrically aligned surface
coils used in conjunction .
17.What is Pulse sequence?
An MRI pulse sequence is a programmed set of changing magnetic gradients. Each sequence
will have a number of parameters, and multiple sequences grouped together into an MRI
protocol to form images.
A pulse sequence is generally consists of by multiple parameters, including:
• time to echo (TE)
• time to repetition (TR)
• flip angle
• field of view and matrix size
• inversion pulse(s) and etc

15. 18.Safe Zones in MRI?
They are four zones inMRI.
Each zone is indicated with different color coding
ZONE 1:GREEN MRI access area
ZONE 2: BLUE MRI Patient screening & preparation.
ZONE 3:YELLOW Restricted asses screened MRI Patient &MRI personal only.
ZONE 4:RED Screened MRI Patient under direct supervision of trained MRI personal only.

16. 19. Define Spin Echo?
➢ The Spin Echo sequence is made up of a series of events.
➢ 90 degree pulse (Excitation pulse)
➢ 180 degree pulse of TE/2 (Refocusing pulse)
➢ Single reading at TE.
➢ This series is repeated at each time interval TR(Repetition time)

17. 20.Define Turbo spin echo or FSE( fast spin echo )?
 In fast SE sequence we are giving multiple 180 degree rephasing pulses are sent after each 90
degree pulse.
 In these sequence multiple echoes are obtained per TR once echo with each 180 degree pulse.
 All echoes are used to fill a single k-space.
 Since k-space is filled much faster with multiple echoes in a single TR the scanning speed is
increases considerably.
Reduce phase encoding and spatial resolution

18. 21. What is a gradient?
 Gradient or gradient coils are used to vary magnetic field strength over the extent of
magnetic field.
 Because of gradient coils rapidly on &off sound is produced in MRI.
 Gradient system consists of three sets of coils that produce field which changing strength in
X,Y,Z direction.
 The three gradients applied along X, Y, Z axes are perpendicular.
 The three gradients applied along X, Y, Z axes are perpendicular to each other and are used
for slice selection phase encoding and frequency encoding by the way it helps to localize the
RF signal from the body.
22. What is inversion recovery?
 Inversion recovery sequence consists of an inverted 180° pulse before the usual spin echo or
gradient echo sequence.
 The time inversion 180° and excitatory 90° pulses is called as time to invert or a time to
recovery.
 TI, Time of inversion, is the main determinant of contrast in IR sequence.
 Flair and Stir are the most useful inversion recovery sequences in MRI
 TI for Stir is around 140ms and Flair is around 2900ms

19. 23. Define proton density?
In PD image contrast is determined by the density of protons in the tissue.
 Long TR and short TE give PD weighted image.
 T1 effect is reduced by keeping long TR and T2 effect is reduced by keeping the TE short
 Very useful for brain imaging (because of good in White matter Gray matter
contrast)
 Useful for extremity imaging for ligaments and tendons(e.g. ankle, knee, elbow
shoulder and hips)
 Can be useful in thighs, lower legs, upper arms and forearms imaging
 Very useful for temporomandibular joint imaging
24. Give a abbreviation of TSE,SE,IR and PD
 TSE – Turbo Spin Echo also called Fast Spin Echo
 SE - Spin Echo
 IR - Inversion recovery
 PD – proton density
No useful

20. 25.Classify the protocols of Brain.
 It is a simple non contrast protocol comprising a group of basic MRI sequence as a useful
approach.
 Localiser – three plane localizer must be taken in the beginning to localise and plan the
sequences.
 DWI – plan the DWI on sagittal plane useful for the identification of ischemic stroke.
 FLAIR – plan the FLAIR in axial plane- supress fluid
 T2 axial, T2 sag for evaluation of ventricular system and good visualization of flow void.
 SWI for identify bleed products or disorders.
 T1 3D (T1- FSE) for anatomical.
 Then Flair and T2 coronal.
 Angio,veno for blood vessels.
27. Define Angiography?
• MR Angiography is an attractive method to image blood vessels.
• It is used to generate image of arteries in order to evaluate them for stenosis, occlusion,
aneurysms or other abnormalities.
• It is to produce 3D image of blood vessels.
• MRA can be broadly divided into non contrast and contrast enhanced MRA
• Position the saturation band at the top of the block in the sagittal and coronal plane to
avoid signals from veins.

21. 28. Define Venography?
• MR Venography is used to examine veins of the brain.
• It is used to visualize the cerebral viens and venous sinuses allowing their anatomy.
• It is used to produce 3D image of blood vessels.
• MRV can be broadly divided into non contrast and contrast MRV(CE MRV)
• By using saturation band below we are getting MRV.
• Position the saturation band at the bottom of the block in the sagittal and coronal plane to
void the arterial signals.

22. 29.Define Spectroscopy?
X- axis for ppm and Y-axis for intensity of metabolites
• Spectroscopy is the study of amount of metabolites present in the tissues.
• Metabolites are the byproduct of metabolism.
• Example: Choline is the byproduct of cancer cells.

23. • The aim of the MRS is to detect the small metabolites.
• Most metabolites of clinical interest have their signal resonate between frequencies of water
and fat.
• It the large signal from the water protons is suppressed small metabolites are detected.
• Example
• NAA(2.02PPM)
• Creatine (3.0 PPM)
• Choline (3.2 ppm)
• Lactate(1.3PPM)
30. Classify the protocols of abdomen?
Use respiratory gating in abdomen mri imaging to avoid breathing artifacts. Also we can use navigator to
overcome breathing artifacts.
• Localizer
• Axial T1
• Axial T2
• STIR Axial
• T2 FS
• Sag T2
• Cor T2.
• DWI in needed

24. 31. What are the steps involved in MRI Scan?
There are four major steps involved in getting an MRI scan.
• Placing the patient in the magnet.
• Sending Radiofrequency pulse by coil.
• Receiving signals from the patient by coil.
• Transformation of signals into image by complex processing in the computers.
It also includes following steps also
Patient preparation and screening. ...
Patient positioning. ...
Protocol selection. ...
Localizer scans. ...
Calibration scans for parallel imaging. ...
Position slices and saturation bands. ...
Automatic prescan. ...
Acquire images.
Post processing
32. Define SNR?
On MRI the signal-to-noise ratio is measured frequently by calculating the difference in signal intensity
between the area of interest and the background (usually chosen from the air surrounding the object).
In air, any signal present should be noise.
• It is the ratio of useful signal to unwanted signal (noise) in the signal.
• An image with high SNR is less grainy and has more details.
• SNR improves with number of average ,FOV,surface and phased array coils.
• Factor affecting SNR could be fixed or changeable.

25. 33.List the Artifact’s in MRI?
• Ghost /Motion Artifact
• Susceptibility Artifact
• Aliasing or wrap around Artifact
• Chemical shift Artifact
• Zipper Artifact
• Truncation /Ringing Artifact
• Parallel imaging Artifact.
34. What is the Contrast used in MRI?
• The contrast used in MRI is Gadolinium
• Atomic number:64
• Paramagnetic agent
• Reduces T1&T2 relaxation time of the tissue where it accumulates
• Usual dose :0.1mmol/kg
• Ionic : Magnevist-1960m mol/kg
• Non -Ionic Omniscan-789 mmol/kg
• Prohance-620m mol/kg.
35.What is axial, coronal, and sagittal?
• Sagittal: Imaginary vertical planes passing through the body parallel to the median plane.
• Coronal. These are imaginary planes passing through the body at right angles to median
plane,dividing into anterior and posterior portion.
• Axial: These are imaginary planes passing through the body at right angles to both the
median and coronal plane this plane is parallel to the ground. The plane divides the body
into superior and inferior parts.

26. 36. Classify Protocols of knee?
• Survey
• STIR Coronal
• PD axial
• PD sagittal
• PD coronal
• MFFE
• Sag T2
• 3D T1.
• 3D WATS
• PD SPIR oblique coronal.
37.Classify the Protocols of Hand?
• Survey
• PD Axial
• PD sagittal
• PD coronal
• Sag T1
• STIR Coronal
• T2 coronal
• T2 axial
• T2 sagittal
38.Classify the Protocols of pelvis?
• Survey
• STIR coronal
• T2 coronal
• T2 Axial
• T1 coronal
• T1 Axial
• DWl
• Sagittal T2
• MFF

27. 39. How will you do MRI for uncooperative patient?
• Oral medication to minimize anxiety.
• Speak to the patient in a confident tone.
• Speaker inside the scanner will enable the technologist to communicate with patient.
41. Define the Resolution and its types?
• Resolution is the ability of human eyes to distinguish one structure from the other.
• In MRI, the resolution is determined by the number of pixels in a specified FOV.
• Types:
Spatial resolution:
It is the ability to resolve two closely spaced object.
Smaller the points that are seen seperately better is the resolution.
It improves with matrix size and number of pixels.
Temporal resolution:
It is ability to resolve event in time.
Temporal resolution relates to the duration of time for acquisition of a single frame of a dynamic
process
Contrast Resolution:
 It is the single intensity difference of the adjacent structure.
 Contrast in an image is determined by T1, T2, PD etc..
Factors affecting Resolution:
 Matrix size: Increase in matrix size improves resolution.
 Field of view: Increase in field of view decrease resolution.

28.  Slice thickness: Increase in slice thickness poorest the resolution.
 Vowel size.
42. Define perfusion?
Blood perfusion is the volume of blood or fluid flow through the capillary and extracellular
spaces per unit time.
MR perfusion also known as bolus tracking of MRI contrast imaging after giving MRI contrast media (
Gadolinium) with series of T2W imaging ( Dynamic Scan)
MR Perfusion can also be done without contrast.
Perfusion is necessary for nutritive supply to the tissue for the clearence of products of metabolism.
Perfusion can help in the diagnosis of certain disease.
43. Define Tractography?
It is a diffusion weighted imaging.
 It is 3D reconstruction technique to assess neural tracts using data collected by Diffusion
Tensor Imaging.
 DTI is a technique that detect how water travel along the white matter tracts in the brain.
Direction on the nerve fibers as follows
1.Red color signifies right to left and right to left.
2. green color signifies anterior–posterior and posterior to anterior
3.blue color signifies craniocaudal orientation of fibers.

29. 44.What is post processing?
 MR image can be manipulated by evaluation in various ways.
 Post processing: Includes substraction, addition, rotation, inversion, multiplaner
reconstruction ( MPR),maximum intensity projection etc..
 Subtraction: it is particularly useful in contrast enhanced MRI examination.
 The pre contrast image are subtracted from the image after the injection of contrast agents
for a better detection.
DSA

30. 45. What is the advantage of MRI scan?
 MRI does not use ionizing radiation.
 MRI produce clear image in three planes ( axial,sagittal,coronal to CT scan.
 MRI provide better soft tissue contrast than CT can differentiate better between fat, water,
muscle and other soft tissue than CT .
 It is a non invasive technique.
 It takes a picture of multiple section of body at once.(using 3D protocols )
46. What are the Advantages of Perfusion?
 Blood perfusion is the volume of blood or fluid flow through the capillary and
extracellular spaces per unit time.
 Perfusion imaging can detect cerebral hypoperfusion, thereby allowing detection of both
potentially reversible ischemia and irreversible cellular damage
 No ionizing radiation exposure.
 It gives more tissue details.
 No contrast medium is used in plain MRI perfusion ( Hence the benefits the cost cutting,
comfortable , no need RFT details and do MRI perfusion immediately.)
47. What are the Advantages of Tractography?
 Used to investigate the structure of white matter.
 Used in preoperative planning could be a useful tool for better prediction of complete tumour
resection.
 Allows direct in vivo examination of aspects of the tissue micro Structure.

31. 48.3D images?
 Usually the images are 2D where the MRI images are usually presentation in slices from top to
bottom.
 Using sophisticated computer calculation these 2 dimensional , very thin, overlapping or without
slice gapping, slices can be joined together to produce a 3- dimensional model of the area of
interest being scanned.
 The 3D mode is used for more compact anatomic regions like the carotid bifurcation, circle of
Willis, or renal arteries.
49. What are the recent advances in MRI?
 Silents MRI
 Helium free
 Portable, bedside, low-field magnetic resonance imaging for evaluation of intra cerebral
hemorrhage
 Latest Perfusion protocols without contrast medium
 FMRI
 Tractography
 Magic sequence from GE, first time ever in the industry, you can generate multiple image
contrasts in a single MRI sequence including T1, T2, STIR, T1 FLAIR, T2 FLAIR* and PD contrasts.

32. 50. What is post processing?
 MR images can be manipulated by evaluation in various ways.
Post processing: includes subtraction, addition, rotation, inversion, multiplanar reconstruction
(MPR) maximum intensity projection (MIP) etc.
51. Saturation band MRI.
Saturation Band It is also called REST slab or SAT band and is used to suppress the signal unwanted area.
1. A 90 degrees RF pulse is sent immediately prior to proper sequence tilting the magnetization in
transverse plane in the region of the band.
2 .When proper excitation pulse follows there is no longitudinal magnetization in this region to be tilted.
Hence this region will not have any signal.

33. 52. What is Susceptibility artifact?
Metals ( paramagnet and diamagnetic materials)distorts the magnetic field when it is placed in
the magnetic field and giving booming artifacts. This is known as susceptibility artifact.
MRI, a paramagnetic material produces a susceptibility artifact known as a “Blooming” artifact
due to the interference generated in the magnetic fields.
53 Describe Motion artifact in MRI
Motion Artifact(Ghost Artifact):
• Motion Artifact is due to long scan time patient movement while scanning. (voluntary)
• Respiration and cardiac movements also produce motion artifacts( involuntary)
• Pulsation movements also produce ( involuntary)
• Motion artifacts Cause blurring and reduces the contrast in the image.
• Rectification:
• Use of gating mechanisms like respirative and cardiac gating.
• Sat band in the placed of unwanted area.
• Strips can be used to fix head.

34. 53. Ringing Artifact:
Gibbs artifact, also known as truncation artifact or ringing artifact, is a type of MRI artifact. It
refers to a series of lines in the MR image parallel to abrupt and intense changes in the object
at this location, such as the CSF-spinal cord and the skull-brain interface.
Rectification:
• Increased matrix size
• Reduced FOV.
54.Wrap around Artifact
• Also called aliasing Artifact
• Caused by mismatching of anotomy that lies outside of the FOV but within
the slice volume.
• Rectification:
Increase the FOV and keep FOV in the centre covering anatomy.

35. 55.Partial volume Artifact:
• Aries from finite size of the voxel over the averaged signal and results in lows of details
and spatial resolution.
Rectification:
• Use of smaller pixel size.
• Smaller slice thickness.

36. 56. Chemical shift Artifact:
Water and fat signals from a same voxel gives interfaces destructively and it is the causes for the
chemical shift articats.
Rectification:
1. Fat suppression
2. Increasing bandwidth

37. 57 Explain about Anisotropic diffusion and isotropic diffusion.
Isotropic refers to the properties of a material which is independent of the direction whereas
anisotropic is direction-dependent.
In the Isotropic diffusion, possibility of a water protons moving in any one particular direction is equal
to the probability that it will move in any other direction (isotropy = uniformity in all directions).
In Anisotropic diffusion, water diffusion takes place in particular direction. Water protons move more
easily in that direction than other.

38. 58 .
Describe Helium.
Helium is a colourless, tasteless, and odourless gas. Helium is a chemical element with the He
symbol and having atomic number 2 and atomic mass 4.
Helium is used as a cooling medium (Refrigerant ) for the superconducting magnets in MRI
scanners and NMR spectrometers. One kg of helium cost RS.1000/-. For 1.5 T MRI initially 1500
liters of helium is filled for the operation and daily evaporation is .02% to .04%.
59. Explain K-space in MRI
K-Space is an imaginary space which represents a raw data matrix.
K space is the data space where frequencies are placed during data collection. This space is
strictly a frequency collection site and does not contain any resemblance to an image. After
running this frequency data through the fast Fourier transform processor, signal intensities are
assigned a grayscale
Filling Methods
The process of filling our K space can be done in many different ways. This is done by activating are
phase encoding and frequency encoding gradient in different ways to collect image.
1. Linear: Filling K space line by line, standard method.
2. Centric: Filling from high signal amplitudes or center outward, useful for quick visualization of
contrast media.
3. Elliptical: Spiral filling from center to periphery, beneficial for contrast-enhanced MRA imaging.