BRAIN
MRA BRAINMRV BRAINPEDIATRIC BRAINORBITIAMSDWI IAMSPNSSELLAEPILAPSYTMJ'STRIGEMINALFACENECK sialographyC SPINEMRA NECKB PLEXUSMRA SUB CLAVIANSCHESTSTRENUMT SPINECARDIACKIDNEYSMRA RENALADRENALLIVERMRCPPANCREASSECRITEN MRCPSMALL BOWELmrv abdomenBREASTIMPLANT BREASTRECTAL CA BLADDERURETHRAPROSTATEPENIS TESTISGYNE PELVISPLACENTAVEGINAL FISTULAFISTULAProctogramHIPSARTHROGRAM HIPPSOSL SPINESI JOINTSL PLEXUSKUBMR UROGRAPHYTHIGHKNEETIB AND FIBANKLEFOOTMRA LEGSSHOULDERARTHROGRAM SHOULDERHUMORUSELBOWFOREARMWRISTHANDMRA ARMMRA HANDMRA WHOLE BODYmiscellaneous

 

 

 

 

 

 

 

 

LIVER

Introduction

MRI is one of the most useful and rapidly developing diagnostic tools for the evaluation of liver pathologies. MRI allows acquisition of images with excellent tissue contrast and anatomical detail. It is particularly good at visualising liver tissue and is capable of detection and characterisation of focal liver lesions. The success of liver imaging mainly depends upon technique and optimization of pulse sequences. Fast breath hold T1 and T2 sequences with smaller slice thickness and high resolution matrix are routinely used for liver imaging. Contrast enhanced T1 weighted scans play a main role in liver imaging because of their high sensitivity and specificity for detection and characterisation of focal hepatic lesions.

Contrast Agents for liver imaging

Intravenous contrast can increase the sensitivity and specificity of MRI scans for lesion detection and characterization, and to distinguish benign from malignant liver masses. Contrast enhancement characteristics are often used for specific diagnosis of pathologies. Several contrast agents are available for liver imaging. Nonspecific extracellular contrast agents, hepatocyte-Specific contrast agents, or a combination of both are used.

Extracellular contrast agents:-

These are gadolinium based contrast agents, which have been widely used in liver MRI for several years. Gadolinium is a paramagnetic metal ion, which shortens T1 relaxation time and produces positive enhancement on T1 weighted scans. Gadolinium agents initially enhance the vessels then rapidly disperse throughout the extracellular space and are eliminated by renal excretion. The best liver-to-lesion contrast will be possible within the first 90 seconds after the injection. It is therefore important to acquire the dynamic sequences during this timeframe. Liver-specific agents have been developed recently to increase and prolong the contrast between normal and abnormal tissues and to improve lesion detection.

Hepatocyte-specific contrast agents:-

Hepatocyte-targeted contrast agents are taken up by hepatocytes in the liver and are eliminated through the biliary system. In hepatocyte-targeted contrast agents the maximum contrast between normal and abnormal tissue occurs 10–40 minutes after injection. Liver-specific contrast agents  are designed to distinguish between benign and malignant hepatocellular lesions based on their contrast uptake pattern by functioning hepatocytes and Kupffer cells. Tumours of non-hepatocytic origin (e.g. metastases, cholangiocellular carcinoma, non-functioning hepatocytic tumours etc.) are unable to take up hepatocyte-targeted contrast agents and remain unenhanced in the post contrast scans.

Indications for liver MRI

> Evaluation of diffuse liver disease such as haemochromatosis, haemosiderosis, fatty infiltration
> Detection of focal hepatic lesions metastasis, focal nodular hyperplasia, hepatic adenoma
> Lesion characterization, e.g. cyst, focal fat, haemangioma, hepatocellular carcinoma
> Clarification of findings from other imaging studies or laboratory abnormalities
> Evaluation of tumour response to treatment, e.g. post-chemotherapy or surgery
> Evaluation of known or suspected congenital abnormalities
> Evaluation for known or suspected metastasis
> Liver iron content determination
> Potential liver donor evaluation
> Evaluation of vascular patency
> Evaluation of cirrhotic liver

Contraindications





Any electrically, magnetically or mechanically activated implant (e.g. cardiac pacemaker, insulin pump biostimulator, neurostimulator, cochlear implant, and hearing aids)
Intracranial aneurysm clips (unless made of titanium)
Pregnancy (risk vs benefit ratio to be assessed)
Ferromagnetic surgical clips or staples
Metallic foreign body in the eye
Metal shrapnel or bullet

Patient preparation




 


A satisfactory written consent form must be taken from the patient before entering the scanner room
Ask the patient to remove all metal object including keys, coins, wallet, any cards with magnetic strips, jewellery, hearing aid and hairpins
Ask the patient to undress and change into a hospital gown

Instruct the patient to hold their breath for the breath hold scans and breathe gently for the gated scans (its advisable to coach the patient two to three times before starting the scan)
An intravenous line must be placed with extension tubing extending out of the magnetic bore
Claustrophobic patients may be accompanied into the scanner room e.g. by staff member or relative with proper safety screening
Offer headphones for communicating with the patient and ear protection
Explain the procedure to the patient and answer questions
Note down the weight of the patient

Positioning




 

Position the patient in supine position with head pointing towards the magnet (head first supine)
Position the patient over the spine coil and place the body coil over the upper abdomen (nipple down to iliac crest)
Securely tighten the body coil using straps to prevent respiratory artefacts
Give a pillow under the head and cushions under the legs for extra comfort
Centre the laser beam localizer over xiphoid process of sternum

 

position liver

Suggested protocols, parameters and planning

localiser

A three plane TrueFISP localiser must be taken initially to localise and plan the sequences. These are fast single shot localisers with under 25s acqusition time which are excellent for localising abdominal structures.

position liver

T2 tse BLADE(PROPELLER) axial gated

Plan the axial slices on the coronal localiser; angle the position block across the liver as shown. Check the positioning block in the other two planes. Slices must be sufficient to cover the whole liver from the diaphragm down to the iliac crest. Adding saturation bands on top and bottom of the axial block will help to reduce arterial pulsation and breathing artefacts. Use motion correction sequences like BLADE (PROPELLER) for further artefact reduction. For respiratory gated scans it is important to place the respiratory navigator box correctly ie. in the middle of the right dome of diaphragm with half the box over the right lobe of the liver (segment 8) and the other half over the lungs. Planning must be done in a non-breath hold localizer because the diaphragm will push down the liver during inhalation and that will lead to an improper planning of slices and respiratory navigator box. It is important to instruct patient to breathe gently throughout the sequence. The effectiveness of the navigator will be reduced with very shallow or erratic breathing.

liver MRI protocols and planning of axial t2 scans

Navigators:-

Navigators have recently been introduced to allow free-breathing scans of the abdomen and chest, and allow the production of images free from motion artefacts. A navigator consists of an intermittent two-dimensional pulse that excites a cylinder of spins, followed by a readout gradient in the direction of the long axis of the cylinder to acquire a 1-dimensional profile of the area of interest. The sequence employs a low flip angle(10) to minimize saturation and the sharp change in the signal intensity of the lungs and liver along the axis of the box is used to determine the position of the diaphragm. The navigator pulse is about 20ms long and is executed every 200 milliseconds. A scan acceptance window is calculated from the preliminary pre-scan data after which the actual scan acquisition starts. The navigation box detects the position of the diaphragm during each slice acquisition, and imaging only occurs when the diaphragm falls within the acceptance window.

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BLADE(PROPELLER)

BLADE is a newly developed MRI technique used to reduce the motion sensitivity of MRI examinations. During BLADE acquisition the k space data is collected in concentric rectangular strips that rotate around the k space. The central portion of   k space is sampled during each strip acquisition. An average strip is used for the phase, translation, rotation correction.

Parameters

TR

3000-4000

TE

90

FLIP

140

NXA

1

SLICE

3MM

MATRIX

320x320

FOV

350

PHASE

A>P

OVERSAMPLE

100%

TRIGGER

YES

 

T2 tse fat suppressed BLADE or T2 STIR axial gated

Plan the axial slices on the coronal localiser; angle the position block across the liver as shown. Check the position in the other two planes. Slices must be sufficient to cover the whole liver from the diaphragm down to the iliac crest. Adding saturation bands on top and bottom of the axial block will help to reduce arterial pulsation and breathing artefacts. Use motion correction sequences like BLADE (PROPELLER) for further artefact reduction. For respiratory gating scans it is important to place the respiratory navigator box correctly ie. in the middle of the right dome of diaphragm with half the box over the right lobe of the liver (segment 8) and the other half over the lungs. Planning must be done in a non-breath hold localizer because the diaphragm will push down the liver during inhalation and that will lead to an improper planning of slices and respiratory navigator box. It is important to instruct patient to breathe gently throughout the sequence. The effectiveness of the navigator will be reduced with very shallow or erratic breathing.

liver MRI protocols and planning of axial stir respiratory gated scans

Parameters

TR

5000-6000

TE

90

FLIP

140

NXA

1

SLICE

3MM

MATRIX

320x320

FOV

350

PHASE

A>P

FAT SAT

SPAIR

TRIGGER

YES

T1 VIBE 3D fat suppressed breath hold coronal

Plan the coronal slices on the axial image; position the block across the liver as shown. Check in the other two planes. Slices must be sufficient to cover the whole liver from the anterior abdominal wall to the posterior abdominal wall. Adding saturation bands on top (over chest) and bottom (over lower abdomen) of the coronal block will help to reduce the arterial pulsation and breathing artefacts. Phase oversampling and, in the case of 3D blocks, slice oversample, must be used to avoid wrap around artefacts. Instruct the patient to hold their breath during image acquisition. (In our department we instruct the patients to breath in and out twice before the “breath in and hold” instruction.)

liver MRI protocols and planning of coronal t1 breath hold scans

VIBE

VIBE stands for Volumetric Interpolated Breath-hold Examination. VIBE is a modified 3D-FLASH MR technique which provides high spatial resolution images under breath-hold. VIBE sequences are particularly useful for the evaluation of soft tissue and vasculature simultaneously.

Parameters

TR

4-5

TE

2-3

FLIP

10

NXA

1

SLICE

3MM

MATRIX

256x256

FOV

350

PHASE

R>L

OVERSAMPLE

50%

TRIGGER

NO

 

 

T1 In-opposed phase breath hold axial

Plan the axial slices on the coronal vibe image; angle the position block as shown. Check the position in the other two planes. Slices must cover the whole liver from the diaphragm down to the iliac crest. Adding saturation bands on top and bottom of the axial block will reduce arterial pulsation and breathing artefacts. Instruct the patient to hold their breath during image acquisition.

liver MRI protocols and planning of axial t1 vibe breath hold scans

Planning must be done in the breath hold vibe coronal because the diaphragm will push down the liver during inhalation and that will change the position of liver from the initial localizer scans.

position liver

In-opposed phase

In and opposed phase imaging uses multi-echo techniques in which two echoes per excitation pulse are acquired simultaneously. The main difference between in and opposed phase is that in-phase imaging uses a long TE of 4.5 where as opposed-phase imaging uses a short TE of 2.3. In phase and opposed phase GRE imaging is very useful for the diagnosis of focal or diffuse fatty infiltration. Fat and water protons have different resonance frequencies in different TE’s. In and opposed images are acquired when fat and water protons are resonating either “in-phase’’ or 180 degrees “out-of-phase’’ with each other. The normal liver shows same signal intensity on in and opposed images and it is always greater than the signal intensity of the spleen. But fatty liver shows reduced signal intensity on opposed phase images which may be equal to or less than that of the spleen. Chemical shift imaging is also useful for lesion characterization by demonstrating fat within tumours.

Parameters

TR

7-9

TE

IN

2-3

OPP

4-5

FLIP

10

NXA

1

SLICE

3MM

MATRIX

256x256

FOV

350

PHASE

A>P

OVERSAMPLE

50%

BW

IN

350

OPP

240

 

T2 tse breath hold with TE 90 AND TE 180

Plan the axial slices on the coronal vibe; angle the position block across the liver as shown. Check the positioning block in the other two planes. Slices must be sufficient to cover the whole liver from the diaphragm down to the iliac crest. Adding saturation bands on top and bottom of the axial block will help to reduce the arterial pulsation and breathing artefacts. Instruct the patient to hold the breath during image acquisition.

liver MRI protocols and planning of coronal t2 te 90 breath hold scans

Why different TEs?

T2 TSE scans with low and high TE values are very useful for lesion characterization in the liver. Lesions such as haemangioma, HCC and cysts will be hyperintense (white on T2) on T2 weighted scans with 90 TE. On the other hand HCC will be hypointense (dark on T2) on T2 scans with 180 TE and while cyst and haemangiomas remain the same.

Parameters

TR

5000-7000

TE

90

FLIP

150

NXA

1

SLICE

4MM

MATRIX

256x256

FOV

350

PHASE

A>P

OVERSAMPLE

50%

IPAT

ON

 

TR

5000-7000

TE

180

FLIP

150

NXA

1

SLICE

4MM

MATRIX

256x256

FOV

350

PHASE

A>P

OVERSAMPLE

50%

IPAT

ON

T1 flash 3D fat sat axial breath hold pre-contrast

Plan the axial slices on the coronal vibe; angle the position block across the liver as shown. Check the positioning block in the other two planes. Slices must be sufficient to cover the whole liver from the diaphragm down to the iliac crest. Adding saturation bands on top and bottom of the axial block will help to reduce arterial pulsation and breathing artefacts. Instruct the patient to hold their breath during image acquisition. Parallel acquisition technique(IPAT/SENSE) can be used to reduce the scan time.

liver MRI protocols and planning of axial t1 fat sat breath hold scans

Parallel acquisition technique

Parallel imaging is a newly developed techniques used to reduce scan time without affecting the scan resolution. Using parallel acquisition MRI techniques it is possible reconstruct full-FOV images from under sampled k-space data by using the uncorrelated information from RF array coil elements. The main disadvantage of parallel acquisition techniques is the signal-to-noise ratio (SNR) is degraded because of the reduced data samples and the spatially correlated nature of multiple RF receivers.

Parameters

TR

4-5

TE

2

FLIP

12

NXA

1

SLICE

3MM

MATRIX

320X320

FOV

350

PHASE

A>P

OVERSAMPLE

50%

IPAT

ON

contrast administration and timing of scans

Guess timing technique:-

This is one of the simplest methods. It works by estimating the time of contrast travel from the site of injection to the vascular structure of liver. This technique is highly dependent upon the site of contrast injection, age of the patient, cardiac output, and vascular anatomy. Generally the contrast takes about 18-25 seconds to travel from the antecubital vein to the abdominal aorta and 45-60 seconds to reach the portal veins. Therefore the first acquisition of the dynamic sequence should start within 20seconds of contrast administration.

Care bolus technique:-

Care bolus is the most commonly used bolus detection technique. This technique uses a coronal fast gradient refocused sequence. Real-time images are obtained every second through the vascular structure of interest (normally placed over the heart). The operator can then watch the contrast bolus arriving in the heart and then switch to the centric 3D dynamic sequence.

Planning care bolus

Plan the coronal care bolus slice on the sagittal plane; angle the slice parallel to the ascending aorta. Check the positioning block in the other two planes.

liver MRI protocols and planning of coronal care bolus scan

Care bolus scans must start one second prior to the contrast administration. The operator can then watch the scans live and wait for the contrast bolus to arrive in the heart. When the contrast reaches the heart the care bolus must be stopped immediately and the patient instructed to hold their breath before starting the centric 3D dynamic sequence.

position liver

T1 flash 3D fat sat axial breath hold dynamic post contrast

Plan the axial slices on the coronal vibe; angle the position block over the liver as shown. Check the positioning block in the other two planes. Slices must be sufficient to cover the whole liver from the diaphragm down to the iliac crest. Adding saturation bands on top and bottom of the axial block will help to reduce the arterial pulsation and breathing artefacts. Instruct the patient to hold their breath during image acquisition. Parallel acquisition technique(IPAT/SENSE) can be used to reduce the scan time.

liver MRI protocols and planning of axial t1 post contrast breath hold scans

A dynamic flash 3D sequence consists of three flash 3mm 3D scans with 10s delay between the first and second and 5 minutes delay between the second and third . The first scan is for the arterial phase, the second for the portal venous phase and the last for the equilibrium phase. Timing of each scan is very important especially the arterial and portal venous phase. It is important to give proper breathing instructions during the first and second and second and third scans. Ask the patient to breath normally after the arterial phase scan then ask to hold their breath when there is  about 4 seconds left for the venous scan. Do the same in between the second and third scans.   

A proper arterial phase acquisition should only show up marked enhancement of the hepatic arteries, pancreas, and spleen with no enhancement of hepatic veins. Most liver tumours get their blood supply from the hepatic artery, so the maximum enhancement of the tumour will be in the hepatic arterial phase. Proper timing of arterial phase is very important because   the time frame between the arrival of contrast in the hepatic artery to filling of the hepatic veins is fairly narrow, and many hypervascular lesions are only visible during this time. If imaging is too late the liver parenchyma starts to enhance in the portal venous phase and a hypervascular lesion may be obscured.  The hepatic arterial dominant phase normally occurs 20-50 seconds from the starting of the injection so the arterial phase scans must be acquired during this period. If using Guess timing method the arterial scans must start about 20 seconds from the start of injection and the scan time must be less than 30 seconds. Care bolus technique offers a more reliable timing method, allowing the operator to watch the care bolus scan live and start the liver scan immediately after the contrast reaches the heart (the contrast can pass form heart to hepatic arteries is less than 4s).

Hepatic vein  dominant phase normally occurs 60-90 seconds from the start of the injection so the portal venous  phase scans must be acquired during this period. If you are using Guess timing method portal venous scans must start about 60 seconds from the start of injection and the scan time must be less than 30 seconds. For the care bolus technique give 10-15 seconds delay after finishing the arterial scans (scan starts after 20 seconds + scan time 25 seconds = 45 seconds + 15 seconds delay = 60seconds). In the portal venous phase liver parenchyma enhances maximally so any hypovascular tumours can be easily detected in this phase.

The equilibrium phase starts when contrast is moving away from the liver parenchyma and  liver starts to decrease in density. Equilibrium phase normally occurs 2-5 minutes after the injection so the equilibrium phase scans must be acquired during this period. The tumours that lose contrast slower than normal liver tissue will show up bright in this scan  (e.g. haemangioma). The tumours that wash out fast will show up dark compared to normal liver parenchyma (e.g. HCC).

position liver

TR

4-5

TE

2

FLIP

12

NXA

1

SLICE

3MM

MATRIX

320X320

FOV

350

PHASE

A>P

DYNAMIC

3 SCANS

IPAT

ON

T1 flash 3D fat sat axial delayed 20 minutes

Plan the axial slices on the coronal vibe; angle the position block across the liver as shown. Check the positioning block in the other two planes. Slices must be sufficient to cover the whole liver from the diaphragm down to the iliac crest. Adding saturation bands on top and bottom of the axial block will help reduce the arterial pulsation and breathing artefacts. Instruct the patient to hold their breath during image acquisition. Parallel acquisition technique(IPAT/SENSE) can be used to reduce the scan time.

Delayed phase is very necessary for the characterization of the lesions. Many liver lesions will show progressive filling patterns. Haemangioma normally shows up progressive fill in with lesion density the same as the blood pool. Most hypo vascular metastatic lesions will show a peripheral enhancement pattern with no central enhancement. Cholangiocarcinomas will show progressive enhancement pattern with maximum enhancement in the delayed phase because the fibrous centre will enhance slowly.

position liver

Parameters

TR

4-5

TE

2

FLIP

12

NXA

1

SLICE

3MM

MATRIX

320X320

FOV

350

PHASE

A>P

OVERSAMPLE

50%

IPAT

ON

 

 

CLICK THE SEQUENCES BELOW TO CHECK THE SCANS