Functional MRI Techniques.

1. Functional MRI Techniques
and its Applications
-Dr. R. Mohan Sundaram, DMRD,
Senior Resident, Dept. Of
Radiodiagnosis, GVMCH

2. Introduction to fMRI
fMRI : Functional MRI
fMRI is a noninvasive MR technique to map or
localize brain areas which are responsible for a
particular task. Patient is asked to perform a
particular activity, e.g. finger-thumb apposition and
a T2*-weighted EPI sequence is run. The brain areas
responsible for the activity (e.g. sensory or motor
cortex) show increased signal.

3. Principle behind fMRI
fMRI is based on the concept of Blood Oxygen
Level- Dependant (BOLD) imaging.
Deoxyhemoglobin is paramagnetic while the
oxyhemoglobin is diamagnetic relative to the
surrounding tissues. Presence of deoxyhemoglobin
causes microscopic field variation in and around the
microvasculature resulting into signal drop on T2 or
T2*-weighted images.

4. Technique used in fMRI
When any brain area is activated by the particular
task blood flow to that area increases (Fig. 20.1).
This increase in the blood flow is much more than
the metabolic demand with resultant increased
amount of oxyhemoglobin and relatively less
deoxyhemoglobin in that area. This leads to
increased signal in the area from less
deoxyhemoglobin. fMRI includes paradigm or
tasks to stimulate brain areas. Active paradigms
include motor, language and cognitive tasks.

5. fMRI image indicating a tumor in left frontal lobe
White arrow points central sulcus

6. Clinical Applications of fMRI
Apart from ongoing research in understanding brain
functional areas and understanding psychiatric
diseases, fMRI has clinical uses like
1. Mapping of eloquent cortex in intracranial tumors,
seizure foci and other lesions to determine the surgical
risk and the optimal surgical approach.
2. Estimation of risk of postoperative deficit, e.g. if the
particular functional area is more than 2 cm away from
the tumor or lesion to be resected, then patient is less
likely to develop postoperative deficit.
3. Determination of hemispheric dominance for the
language.

7. Magnetic Resonance
Angiography Techniques
-Dr. R. Mohan Sundaram, DMRD,
Senior Resident, Dept. Of
Radiodiagnosis, GVMCH

8. Introduction to MRA
Magnetic Resonance Angiogram (or) Angiography is a non-
invasive technique employs RF pulses to assess the vascular
system of brain and skull.
MR Angiogram can be done through both contrast and non –
contrast enhancement but non contrast technique is
preferably used due to TOF technique.
Time of Flight is a technical sequence which works by
saturating the area, other than the areas having particles in
motion, with high frequency RF pulses.
TOF acquires signals from the areas showing motions as
inflowing blood will take much time to magnetize accordingly
to the field. The program neglects signals from saturated
areas thereby visualizes only the areas of circulation.

9. There are two types of MRA namely black
blood and bright blood imaging
Black blood imaging. All the vessels are dark on this axial HASTE (single-shot fast spin-echo) image of the chest. As
Ao = ascending aorta; Ds
Ao = descending aorta;
MPA = main pulmonary artery and
SVC = superior vena cava

10. Bright blood imaging. All the vessels are bright on this axial
TrueFISP image of abdomen, which is a gradient echo sequence

11. • Noncontrast MRA Techniques
Basic two types of NCMRA commonly used in
routine practice include:
– 1. Time of Flight MRA (TOF-MRA).
– 2. Phase contrast MRA (PC-MRA).
There are also several new techniques that are
being increasingly used and include SSFP-based
MRA and ECG-gated fast spin-echo (FSE) MRA.
Time of Flight MRA (Tof-MRA):
Employs Steady-State Acquisition and Inflow
Enhancement techniques by saturating stationary
tissues with high frequency RF pulses.

12. Time of Flight MR Angiography of
intracranial arteries, coronal projection

13. Other types of MRA
• Phase Contrast MRA
• Electrocardiogram gated Fast Spin Echo MRA
• Steady-State Fast Projection MRA
• Contrast Enhanced MRA

14. Magnetic Resonance Cholangio
Pancreatography
Dr. R. Mohan Sundaram, DMRD,
Senior Resident, Dept. Of
Radiodiagnosis, GVMCH

15. Introduction to MRCP
Magnetic Resonance Cholangiopancreatography (MRCP) has got a
widespread clinical acceptance and has almost completely replaced
diagnostic ERCP. MRCP visualizes biliary and pancreatic tree noninvasively
without use of any contrast injection or radiation. Principles,
sequences, technique and clinical applications of MRCP are discussed.
Principles:
Heavily T2-w images are used to visualize static fluid or bile in the
pancreatobiliary tree. The images are made heavily T2-w by using longer
echo times.
At this long TE, only fluid or tissues with high T2 relaxation time will retain
signal. Background tissues with shorter T2 do not retain sufficient signal at
longer TEs and are suppressed.

16. Sequences employed in MRCP
• 3D FSE sequence (Axial / Coronal/ Sagittal)
• Balanced SSFP – with breath-hold or
respiratory gating.
• Single shot FSE
CONTRAST ENHANCED SEQUENCES :
• Contrast enhanced T1 weighted GRE thick slab
SPECIAL SEQUENCES:
• Secretin Cholangiopancreatography (S-MRCP)

17. MRCP demonstrating pancreatic ducts
and GB

18. Secretin MRCP
Secretin, an artificially synthesized enzyme, is injected
intravenously (1 ml/kg) and imaging takes place for
every 30 seconds with a total duration of 10 minutes.
Secretin is an enzyme which causes dilatation of
pancreatic ducts in response to an acid stimulation.
This enzyme secreted in duodenal areas causes
secretion of water and bicarbonates which keeps the
duodenal ducts dilated. Heavily t2 weighted images are
taken through thick slab sequences demonstrating the
areas of pancreatic side branches. The only drawback
of this procedure is the high cost of secretin.

19. MRCP PROTOCOL AND TECHNIQUES
• Patient should be in fasting for 8 – 10 hours
before the procedure to distend the GB and
bile ducts.
• Fluid should be avoided in the upper GIT. If
fluid is still present, then barium or blue berry
juice should be suppress fluid secretion.

20. Clinical applications of MRCP
• Cystic diseases of bile duct including
choledochocele and Caroli’s disease.
• Congenital Anomalies : parallel cystic and hepatic
duct insertion, medial cystic duct insertion and
low hepatic duct insertion.
• Choledocholithiasis – stones in the CBD.
• Sclerosing Cholangitis
• Post – operative evaluation of pancreatic and bile
duct areas.
• Chronic Pancreatitis

21. MR Urography
• MR urography is a procedure involves MR
imaging of urinary tract abnormalities which can
be congenital, obstructive or neoplastic.
• The urinary tract will be evolved either through
heavy T2 images or through contrast enhanced
T1 images.
• Non-contrast sequences demonstrate lesions
which can be obstructive or congenital whereas
contrast enhanced sequences demonstrate
excretion of contrast by kidneys and urinary tract.

22. Techniques of MRU
• Patient is started on intravenous ringer lactate
(10 ml/kg) 30 minutes before the scan.
• Intravenous furosemide (1 mg/Kg) is injected
approximately 15 minutes before the gadolinium
injection.
• Multiple runs of coronal oblique (along long axis
of kidneys and ureters) T1-w 3D GRE
(VIBE/THRIVE/LAVA) are acquired during dynamic
intravenous injection of routine dose of
gadolinium-based contrast media

23. MRU images

24. Clinical Applications of MRU
• The MRU serves one stop shop method for the
following abnormalities in the excretory
system:
– Congenital
– Obstructive
– Neoplastic.

25. MRI K-Space
• K-Space is an imaginary raw
data matrix space between
reception of signals and
image formation.
• The raw data from k-space is
further converted and
processed into images
through Fourier
Transformation.
• K-space has two axes. The
horizontal axis represents
the phase axis where the
signals are received and the
vertical axis represents the
frequency axis where the
signals are processed.

26. Parameters of Scanning
• Matrix
• FOV
• Number of Excitations.
• Flip Angle
• Bandwidth.

27. THANK YOU STUDENTS
FOR WONDERFUL CO-OPERATION.
THIS SESSION WILL BE VERY USEFUL FOR
YOU.
ALL THE BEST FOR YOUR EXAMS.