principle of cardiac MRI

1. PRINCIPLE
OF CARDIAC
MRI
Present by Thaiwat
Advisor Narumol

2. Clinical approach to CVMR
techniques
 Coils
 Cardiac motion
compensation
 Respiratory motion
compensation
 Pulse sequence
 Survey
 Anatomy
 Function
 Perfusion
 Delayed enhancement
 Flow
 Coronary magnetic
resonance angiography
 Vessel wall imaging
 Cardiovascular magnetic
resonance image
processing
 Reduced data acquisition

3. Coils
 Standard body coil
 Standard surface coil
 Single circular coil
 Cardiac phases array coil
constructed of multiple
elements
 Best
 Application SENSE
technique (SENSitivity
Encoding)
 Reduced k-space data
 Reduced MR scan time

4. Cardiac motion compensation
 Synchronizing the
image acquisition to
ECG.
 ECG-triggering 
filled k-space in
multiple steps, based
on the timing within
the cardiac cycle.

5.  ECG triggering  2 type
 Prospective triggering – image
acquisition starts at a fixed delay
after QRS complex and stops
around 80% of cardiac cycle.
 Suitable for systolic heart function.
 Retrospective triggering – after MR
acquisition finished, computer
calculates afterward for appropriate
cardiac phases
 Available in combination with faster
scan techniques.
 Standard  Retrospective ECG
triggering.
Cardiac motion compensation

6.  Major problems
 Reliable ECG signal  2-5% of case have no
reliable ECG signal.
 Electrical ECG signal is distorted by magneto
hemodynamic effect.
 Vector ECG (VCG)  three-dimensional
orientation of QRS complex.
 Not trigger by T wave or ECG distortion.
Cardiac motion compensation

7. Respiratory motion
compensation
 Respiratory ordered phase
encoding (ROPE) and Phase
encoding artifact reduction (PEAR)
 k-space reordering technique
combine with respiratory tracking
device.
 Faster image (EPI, TFE) 
acquire image during short breath-
hold around 15 seconds.
 Disadvantage – reproducibility of
breath-hold level.
 High-resolution require longer
time (coronary artery MR)  for
optimal quality, respiratory
navigator technique is require.

8.  The respiratory navigator pencil beam (A, white line; B, white dot) is positioned on
the right hemidiaphragm at the interface between lung and liver, based on a survey
image in the coronal (A) and sagittal (B) planes. The one-dimensional navigator
image is acquired repeatedly over time, thereby constructing an image of
diaphragmatic motion (C). The edge between lung and liver is traced automatically

9.  The MR acquisition is gated to a predefined acceptance window (two solid horizontal
lines) based on the traced respiratory signal (curved solid line) around end-
expiration. K-space data are acquired continuously, but only data are stored that
fulfill the requirement that
 (a) before data acquisition, the navigator was within the acceptance window (leading
navigator); or that
 (b) before and after data acquisition, the navigator was within the acceptance window
(leading and trailing navigator).
 Other acquired image data are deleted. This is the principle of a real-time prospective

10.  Recent technical
 Possible to acquire a stack of 12 slices, with around
25 cardiac phases each, in a single breath-hold of up
to 20 seconds.
 These ultrafast techniques are combinations of turbo-
field echo, echo-planar, or spiral k-space acquisition.
 However, the image spatial resolution of this
technique is still quite low, allowing only evaluation of
ventricular volume changes and some rough
estimation of wall motion abnormalities.
 In the future
 Ultrafast whole heart functional imaging in a single
breath-hold is the so-called k-t BLAST technique.
 Real-time imaging of the heart without the need for
ECG-triggering or breath-holding .
Respiratory motion
compensation

11. Pulse sequence

12. Pulse sequence
 Imaging engines
Fast spin-echo (FSE)
Gradient-echo (GRE)
Steady-state free
precession (SSFP)
Echo-planar imaging
(EPI)
 Modifiers
 Fat suppression
 Inversion prepulse
 Saturation prepulse
 Velocity- encoded
 Parallel imaging

13.  Dark Blood Imaging
 Bright Blood Imaging
 Modifiers
 Contrast-Enhanced Techniques and Other
Applications of Pulse Sequences
Pulse sequence

14.  Dark Blood Imaging
 low-signal- intensity appearance of fast-flowing blood
 mainly used to delineate anatomic structures
 Traditionally, spin-echo (SE) sequences  FSE, TSE
 TSE and FSE
 lower signal-to-noise ratio than SE,
 faster imaging than SE  minimizes the effects of respiratory and
cardiac motion.
 Basic consist of radiofrequency pulses with flip angles (α) of 90º
and 180º followed by acquisition
 FSE and TSE sequences can be T1- or T2-weighted acquired over a
series of single or double R-R intervals.
Pulse sequence  SE

15. Fast spin echo diagram
Pulse sequence  SE

16.  Dark Blood Imaging
 Artifact  slow-flowing blood which can appear bright and
can blend in with anatomic structures.
 Gadolinium can interfere with nulling of blood signal
 should be administered after dark blood imaging.
 However, real-time nongated black blood sequences with
gadolinium contrast administration have proven to be effective
for evaluating myocardial ischemia
Pulse sequence  SE

17.  Bright Blood Imaging
 High signal intensity of fast-flowing blood
 Typically used to evaluate cardiac function
 The main pulse sequences
 GRE
 Steady-state free precession (SSFP)
 EPI
Pulse sequence

18.  Bright Blood Imaging
 GRE sequences
 spoiled gradient recall [SPGR]
 turbo FLASH
 turbo field echo
 fast-field echo [FFE])
 Emitting an excitation radiofrequency pulse that is
usually less than 90
 Followed by gradient reversals in at least two
directions, which create an echo signal that can
be detected
Pulse sequence  GRE

19. Pulse sequence GRE
Gradient echo diagram

20.  Steady-state free precession (SSFP)
 Fast imaging employing steady-state acquisition [FIESTA]
 Fast imaging with steady-state precession [FISP]
 Balanced FFE
 short TR with gradient refocusing
 less vulnerable to T2* effects
compared with standard GRE.
 providing greater contrast-to-noise
and signal-to-noise ratios than GRE sequences.
Pulse sequence  SSFP

21. Pulse sequence  SSFP

22.  Steady-state free precession (SSFP)
 Once this equilibrium is reached
 Two types of signals are produced.
 postexcitation signal (S+) that consists of FID arising
from the most recent RF pulse.
 echo reformation that occurs prior to excitation (S-)
and results when residual echo is refocused at the
time of the subsequent RF pulse.
Pulse sequence  SSFP

23. Pulse sequence  SSFP
• FID (S+) has mixed T1 and T2* weighting.
• SE (S-) is strongly T2 weighted and has
negligible T2* weighting.

24.  Steady-state sequences  Classified
 Postexcitation refocused steady-state sequences
 only the FID (S+) component
 (eg, FISP [Siemens], GRASS [GE Medical Systems], FFE, Fourier-
acquired steadystate technique [FAST; Picker International,
Cleveland, Ohio]).
 Preexcitation refocused steady-state sequences
 only the spin-echo (S-) component
 (eg, PSIF [reversed FISP, Siemens]; steady-state free precession
[SSFP, GE Medical Systems]; T2-FFE).
 Fully refocused steady-state sequences
 both FID (S+) and spin-echo (S-) components
 balanced SSFP, since gradients applied in all three axes are
balanced (eg, true FISP, FIESTA [GE Medical Systems], balanced
FFE).
Pulse sequence  SSFP

25. Pulse sequence  SSFP

26. Pulse sequence  SSFP

27. Pulse sequence  SSFP

28.  EPI  rapid sequence
 application of a single
radiofrequency excitation
pulse, usually with flip
angles of less than 90º
 This sequence can also
be combined with GRE.
 EPI is often used for
functional assessment in
cases in which
arrhythmia precludes
adequate gating.
Pulse sequence  EPI

29. Pulse sequence
 Imaging engines
 Fast spin-echo (FSE)
 Gradient-echo (GRE)
 Steady-state free precession
(SSFP)
 Echo-planar imaging (EPI)
Modifiers
 Fat suppression
 Inversion
prepulse
 Saturation
prepulse
 Velocity- encoded

30.  Inversion recovery (IR)
 Applying additional 180º pulses
 Double or triple IR can be used to further null
signal from blood for black blood imaging, thereby
improving contrast between the cardiac tissues
and blood pool.
 This sequence is particularly useful for tumor
imaging, delayed enhancement imaging, and
coronary angiography.
 Fat suppression is accomplished in a similar
manner, in which the inversion time of the
additional selective 180º pulse is set to match the
Pulse sequence  IR

31. Pulse sequence  IR

32. Pulse sequence  IR

33. Pulse sequence  IR

34.  Saturation-recover preparatory pulses
 Improve T1-weighted imaging
 Applying a 90º flip angle
 less subject to signal intensity variations than IR
techniques
 The saturation-recover pulse is often used in
combination with GRE and hybrid GRE-EPI pulse
sequences for perfusion-weighted imaging and
myocardial tagging.
Pulse sequence
 Saturation preparatory

35.  Myocardial tagging
 Tagging involves labeling the
myocardium with a low-signal-
intensity grid.
 This enables quantification of
myocardial strain and assessment of
pericardial constriction.
 Tagging is also a more accurate
method of assessing infarct-related
dysfunction than wall thickness
analysis.
 Unfortunately, the grid tends to fade
by early diastole.
Pulse sequence
 Saturation preparatory

36.  Phase-contrast imaging
 Velocity-encoded imaging
 Noncontrast technique
 Used to estimate pulmonary blood flow (Qp) and
systemic blood flow (Qs)  calculate the pulmonary-
to-systemic flow ratio (Qp:Qs) {shunt fraction}.
 Qp:Qs > 1.5 usually indicates a significant left to-right shunt
that requires surgical or percu- taneous correction.
 Used to calculate regurgitant fractions and valve area
 continuity equation
 usually implemented via GRE pulse sequences  temporal
resolution 50 milliseconds.
 The gradient strength  match the expected velocities.
 Susceptible to gradient field artifacts, and
correction with phantoms is recommended to
improve the accuracy of these measurements.
Pulse sequence  Phase
contrast

37.  Sensitivity-encoding (SENSE) and
simultaneous acquisition of spatial harmonics
(SMASH)
 Accelerated imaging acquisition with short breath-
hold times.
 Parallel imaging can be applied to most forms of
cardiac imaging.
 Use of multiple coil arrays and sample limited
portions of k-space over time.
 As a result, parallel imaging compromises the
signal-to-noise ratio and is especially subject to
artifacts.
Pulse sequence
 Parallel technique

38. Contrast-Enhanced Techniques
 Integral part of a myocardial viability study.
 Based on the phenomenon of delayed
enhancement.
 Consists of performing IR GRE approximately 10
minutes after injection of a gadolinium-based
contrast medium.
 Imaging performed at an inversion time at which
signal in the myocardium is maximally nulled .
Dynamic perfusion imaging is also useful
 Infarct  enhance

39.  For tumor imaging
 T1-weighted IR FSE pulse sequences
immediately after gadolinium injection
 long–inversion time imaging (i.e., 500–600 ms)
with gating every 3 or 4 R-to-R intervals to
distinguish between tumor and thrombus.
 Thrombus  maximally nulled much later than the
signals from other tissues and can be readily
distinguished using this technique.
Contrast-Enhanced Techniques

40.  Combination of sequences often enables
specific tumor characterization and may be
helpful for distinguishing between malignant and
benign tumors.
 Static
 T2-weighted
 T1-weighted
 Gadolinium enhanced T1-weighted sequences
 Dynamic
 cine SSFP sequence
 double IR T1-weighted FSE
 double IR T2-weighted FSE
 Spectral presaturation with IR (SPIR)
Contrast-Enhanced Techniques

41.  The first step  acquisition of a localizer 
determine general anatomy
 Purpose  to image the cardiac region in three
basic orientations: coronal, transverse, and
sagittal planes
 Using 15 slices of 10 mm each for every orientation.
 A decade ago  multislice spin-echo technique
+/- turbo spin-echo.
 A faster technique  turbo-field-echo or turbo-
field-echo-planar MR sequence.
Survey

42.  Recently
 Balanced gradient echo (bFFE, bTFE, true-FISP)
techniques became available, yielding images
with high contrast between blood and
myocardium
 Excellent images can be obtained using
balanced-FFE without respiratory motion
compensation, with an acquisition time of only 15
seconds.
Survey

43.  Balanced FFE pulse sequences
belong to the group of “Steady
State Free Precession”
techniques.
 Time-balanced gradients are
applied for all gradient directions:
slice selection, phase encoding,
and frequency readout.
 In combination with the alternating
phase of the excitation pulse, this
enables acquisition of both FID
and Echo signal.
 The sequence produces a high
image intensity for tissues with a
high T2/T1 ratio, independent of
the repetition time TR.
 Balanced FFE images are
obtained after field shimming,
because field homogeneity is very

44. PLANSCAN
 Based on survey images, further MR scans
can be planned.
 Update
 planning can be performed in real-time, even in
combination with balanced-TFE.
 Once the desired imaging plane is reached,
the geometry settings can be stored for later
use during the cardiovascular MR exam.

45.  Manual planscan
 Automatic planscan
 Use the survey images as input for an algorithm
 Software package finds automatically the position of the
heart in the survey images and uses this information for
planning of the other acquisitions
 Reliable quantification  end-diastolic volume and ejection
fraction and
 Suitable for patient follow-up to evaluate therapy effects
such as antihypertensive or lipid-lowering drugs
 However, the automatic planscan procedure is
currently available only off-line as a research tool, and
the time efficiency of the real-time planning alternative
seems to be higher.
PLANSCAN

46. ANATOMY
 Main patient category congenital heart disease
evaluation of global cardiovascular anatomy
 In the past, the time-consuming (turbo) spin-echo
was the technique of choice.
 Disadvantage of this technique was the presence of
major breathing artifacts, hampering routine
evaluation of cardiac anatomy.
 The latest technique is a multiple breath-hold,
dual inversion black blood turbo spin-echo
technique
 Disadvantage  breath-hold level reproducibility.
 In the future, this technique combining with
SENSE, allowing single breath-hold or respiratory
navigator gated acquisitions.

47. Black blood preparation

48.  Schematic diagram of a black blood pulse
sequence.
 A nonselective 180° pulse inverts all signal.
 Subsequently, a slice-selective 180° pulse resets
signal of the studied slice.
 Blood with inverted signal flows into the slice plane.
 After a delay (Tinv, inversion time) the blood signal is
nulled
 Data acquisition is performed with a fast spin-echo
pulse train.
 The image is obtained in a breath-hold.
 Note that Tinv is dependent on the heart rate.

49.  The “black blood”
image
 dual inversion fast
spin-echo
technique,
 combination with
SENSE
 Echo spacing 4.3
ms,
 FOV 350 × 350
mm,
 Matrix 192 × 146,
 Slice thickness 8
mm.
 Scan time was 6

51. FUNCTION
 The second most frequent indication for cardiac
MR is evaluation of myocardial wall motion
abnormalities in patients with suspected
myocardial ischemia.
 Most of these patients are hard to image using
ultrasound  obese or have lung emphysema.
 The expectation is that, due to the experience
cardiologists are obtaining with MR through the
aforementioned patient group, there will be an
increasing demand for MR analysis of cardiac
function.

52.  The short-axis view of the left
ventricle is the working horse view in
cardiovascular MR.
 First  two long-axis views need to be
acquired
 Which can yield diagnostic information
itself
 Apical wall motion pattern of both
ventricles
 Valvular function
 Ventricular anatomy and dimension
 Vertical long-axis ( two-chamber view)
 Horizontal long-axis (four-chamber
view)
FUNCTION

53.  Vertical long-axis ( two-chamber
view)
 Based on a transverse survey image
 Center of the slice  middle of the
mitral valve
 Angulation  slice cuts through the
left ventricular apex on a lower
transverse survey image
 For selection of the end-systolic
cardiac time frame
 Using a dynamic gradient echo
technique.
 During continuous breathing
 Ultrafast breath-hold technique such as
EPI  better
 Currently, the optimal option  balanced-
TFE sequence
FUNCTION

54.  Horizontal long-axis (four-chamber
view)
 Based on the diastolic and systolic
images of the two-chamber view
 Center of the slice one third of
the lower part of the mitral valve on
the end-systolic two-chamber
image
 Angulation  through the apex
 Afterward  the position of the
slice in the diastolic two-chamber
image needs to be checked to
ensure that the atrium is imaged
properly.
 Dynamic imaging technique 
balanced-TFE.
FUNCTION

55.  Planning of the short-axis view
 based on the systolic and diastolic images
of the four-chamber view and the systolic
two-chamber view.
 Level  mid-mitral point to the left
ventricular apex
 Angulation  perpendicular to the long
axis of the left ventricle
 Position
 10 to 12 slices
 8- to 10-mm thickness
 Be sure to include the entire ventricle in
end-diastole, which can be checked on the
end-diastolic images  important for
calculation
 End-diastolic volume
 Stroke volume
 Ejection fraction
 Other derived functional parameters
FUNCTION

56.  The short-axis scan
 Conventional GRE sequence during continuous
breathing  time-consuming
 EPI with breath-hold  better
 Balanced-TFE MR sequence with multiple breath-holds
in expiration the best
 In the near future  entire short-axis slices in single
breath-hold for up to 15 seconds  balanced-TFE k-t
SENSE
 Real-time imaging of the short-axis stack  seems
perfectly suitable for cardiac stress imaging during
continuous increasing dobutamine dosage and for
imaging of the heart in the presence of arrhythmias.
FUNCTION

57. PERFUSION
 Myocardial perfusion  ischemic heart
 Most perfusion analysis  intravenously injected
gadolinium-based MR contrast agents.
 Principle
 Reduces the T1-relaxation time
 Relatively increases the MR-signal intensity of well-
perfused tissues.
 Ischemic myocardial regions  no or little signal
intensity change as compared to well-perfused
myocardium.
 Fast T1-weighted MR-techniques should be used 
magnetization prepared turbo-field echo/EPI/FLASH
 A very promising technique  k-t BLAST perfusion will
allow full cardiac coverage cardiovascular magnetic
resonance (CMR) perfusion imaging during first pass of

58. Myocardial perfusion

59.  Quantitative image analysis
 Parameters  characterize the
bolus passage immediately after
administration of the contrast
agent
 Rate
 Level of enhancement
 Time-to-peak
 Mean transit time
 Display
 Each image pixel
 Graphically  parametric images
 Visualizing the anatomic location of
abnormalities
PERFUSION

60.  Ischemic model illustrates the distribution of extracellular
MR contrast media in normal and infarcted myocardium.
Extracellular MR contrast media distribute exclusively in the
extracellular space in normal myocardium (10%-18% of the
tissue volume, left). For infarction the fractional distribution
volume of the contrast agent increases because of the
formation of interstitial edema and loss of membrane
integrity of the necrotic cells.
CHARACTERIZATION OF
MYOCARDIAL VIABILITY AND
SALVAGE

61. DELAYED ENHANCEMENT
Injection
Plasma
concentration
Interstitial space
Renal wash
out Capillary bed
Diffusion
Reabsorb
Tissue
damage
delayed
enhancement
imaging
15-30 min

62. DELAYED ENHANCEMENT
 Currently, the principle “bright
is dead,” indicating that bright
areas on a delayed MR-
image after contrast injection
correspond with nonviable
myocardium
 Delayed enhancement
CVMR, in combination with
first-pass perfusion and wall
motion imaging at rest, has
an important clinical value
when stress CVMR cannot be
performed

63. FLOW
 One of the advantages of MR 
measure flow velocity (cm/sec) and
flow volume (mL/sec)
 Principle of “spin phase”
 Postprocessing  two images which
grey values represent
 Spatial localization of the protons
 Velocity of the protons  velocity map
 The measurement of flow velocity, taken
from a region of interest at many time
frames
 Flow-velocity versus time curve
 Flow-velocity changes during the cardiac
cycle
 Area under the curve  amount of blood
passing through the region of interest
during a cardiac cycle

64.  Velocity map
 Static tissue  intensity zero
 Moving blood  positive or
negative value (direction of
flow)
 Additional magnetic field may
be applied
 in-plane  parallel to flow
direction
 through-plane  perpendicular
to flow direction
 Calculating the pressure
gradient  modified Bernoulli
FLOW

65.  Flow encoding MR
 Based on gradient-echo pulse sequences
 Combination with prospective or retrospective ECG-
gating
 Diastolic ventricular function  retrospective
ECG-gating
 Currently  duration of 2 to 3 minutes 
represent the average flow during the acquisition
period
 Recent developments  real-time flow
measurement
 The k-t BLAST technique can also be used in
FLOW

66.  Clinical
 Mitral valve
 Tricuspid valve
 Ascending
aorta
 Pulmonary
artery
FLOW

67. Quick guide to imaging plane

68. FLOW  Mitral valve
2  early peak filling rate
2-3  early deceleration
5  atrial peak filling rate

69. FLOW  Tricuspid valve
RV two-chamber view
1-2  early acceleration
2  early peak filling rate
5  atrial peak filling rate

70. FLOW  Ascending aorta
An inangulated slice is positioned
perpendicular to the ascending
aorta on a coronal survey image
(A); usually, this is at the level of
the bifurcation of the pulmonary
artery. On a sagittal image of the
original survey, the angulation can
be adjusted, if necessary, although
this is not usually the case (not
shown). An end-diastolic image of
the ascending aorta is shown here
(B), the upper image shows the
normal, or modulus image, and the
lower image shows the velocity-
encoded image.
1-3 AUC  LV stroke
volume
2  peak ejection rate
1-2  aortic acceleration

71.  The flow acquisition through the pulmonary artery is planned in the following
way.
 First, another survey image needs to be acquired of 1 to 3 slices in the
center of and parallel to the pulmonary artery, based on an original sagittal
survey image (A).
 Then, the pulmonary artery flow acquisition can be planned perpendicular to
the pulmonary artery, based on the angulated survey image (B), and on the
original sagittal survey image (C).
 In addition, the slice position in caudo-cranial direction has to be positioned
just before the bifurcation of the pulmonary artery on a transverse image of
the original survey (D). An end-diastolic image of the pulmonary artery is
shown here (E), the upper image shows the normal, or modulus image, and
the lower image shows the velocity-encoded image.
FLOW  Pulmonary artery
1-3 AUC  RV stroke
volume
2  peak ejection rate
2-3  pulmonary
deceleration

72. QUANTIFICATION OF
SHUNTS
Measurement of
pulmonary to
systemic flow
(QP:QS).
Left: Healthy
volunteer with a
QP:QS ratio of 1.03,
which is normal.
Right: A patient with
patent foramen
ovale has increased
volume flow in the
pulmonary trunk
compared to the
aorta, which
demonstrates left-to-
right intracardiac
shunting with a
QP:QS ratio of 1.8.

73. CORONARY MAGNETIC
RESONANCE ANGIOGRAPHY
 Practical point  Three major points of
concerning
 First  cardiac motion  limiting length of image
acquisition to below 100 milliseconds
 Second  respiratory motion which corrected by
respiratory navigators
 Third  image contrast between the coronary vessel
and surrounding tissue  2 alternative
 T2-preparation technique
 contrast agent combined with spiral k-space filling
 Currently resolution is limited to 0.7 mm
 Future  expected that isotropic resolution of 250
µm

74. VESSEL WALL IMAGING
 In general
 Vessel wall imaging  important feature of CVMR
 Cannot be accomplished noninvasively with other
imaging modalities
 Future prospects
 Determine the composition and stability of
atherosclerotic plaque
 Combined with interventional CVMR and
interventional MR procedures

75. CARDIOVASCULAR MAGNETIC
RESONANCE IMAGE
PROCESSING
 Main obstructions  underdeveloped state of
cardiac image analysis
 Currently  manually perform image analysis
 Very time-consuming
 Several software packages are available, such as
the MASS and FLOW software
 Recently  active appearance model algorithm
 Future
 Aimed concept of one-stop-shop cardiac image
processing
 Real-time CVMR image acquisition and real-time
image analysis are combined

76. REDUCED DATA ACQUISITION
METHODS
 SENSE (SENSitivity Encoding) and GRAPPA
(generalized autocalibrating partially parallel
acquisitions)
 Speeding up data acquisition by exploiting the
characteristics of antenna arrays for signal reception
 k-t BLAST (Broad-use Linear Acquisition Speed-
up Techniques) and k-t SENSE  Cine image
series
 Large regions of the image  static or move in a
coherent fashion  lower rate
 Optimized acquisition scheme would need only to
update highly dynamic information at a high rate
 Training data that serve as guidance for image
reconstruction of missing information
 Permit typically fivefold to eightfold accelerations in

77. SENSE

78. k-t BLAST AND k-t SENSE

79. Reference