Abdominal MRI - Technical Solutions Notes
Greg Brown SMRT       vision@adelaide.on.net

These notes deal with technical issues governing sequence choice in upper abdominal imaging, the appearance of key pathologies, suggested protocols and associated references.
 
Technical Challenges Generic Protocols
Current Solutions  Liver  
Pancreas  
MRCP 
Breath Hold Sequence Consideration 
T1 Weighted Techniques  
T2 Weighted Techniques  
Breath Hold Scans - Getting the Best Results 
Imaging Characteristics of Liver Mass Lesions 
Sequence Options  Stages of Enhancement 
Respiratory Artefact Reduction  
Flow Artefact Reduction  
Gut Motion Artefact Reduction  
Fat Suppression 
Readings & References  

Back to Greg's MRI page

Technical Challenges
Current Solutions

Breath Hold Sequences Considerations

Top of page
T1 Weighted Techniques T1 Out of Phase (OOP) images Te for in phase and out of phase GRE at 3 field strengths
 
FIELD In Out In Out In Out In
1.5 T 0 2.2 4.4 6.8 9 11.2 13.4
1.0 T 0 3.4 6.8 10.2 13.6 17 20.4
0.5T 0 6.8 13.6 20.4 27.2 34 40.8
T1 in-phase breathhold abdomen T1 out of phase breathhold abdoment
T1 In Phase S-GRE (FLASH)  Te = 4 msec T1 Out of phase S-GRE (FLASH)  Te = 2
T1 Fat Suppressed
  • Intended to distinguish bright lesions on T1 images (blood from fat) and to improve display of the pancreas (especially when atrophic)
  • Standard spectral saturation routines are too time consuming (10 msec/slice)

  • Water excitation (non spatial, spectral selective) works well
T1 fat suppressed BH abdomen
T1Breath hold FLASH with interleaved Fatsat

T2 Weighted Techniques
Breath Hold T2 TSE (RARE, FSE)
  • Higher ETL allows use of long TR and long Te for very strong T2 weighting.
  • Primary aim is discrimination between fluid filled lesions and solid tumours.
  • The MTC effect of multiple refocusing pulses decreases contrast between liver and solid tumours. GRASE or multi-shot EPI sequences should minimize this effect
T2 images should have fat suppression, especially for the pancreas.
T2 fatsat BH abdomen
T2 breathhold Fatsat TSE
T2 non-breath hold TSE
  • Allows very high spatial resolution with phased array coils.
  • Fat suppression and spatial saturation largely eliminate artefacts

  • Can use lower ETL to reduce MTC effects and better discriminate solid lesions. (But they won't classify the lesion so this is a minor point)
T2 TSE breathing abdomen
 T2 TSE non breathhold
Long TE STIR
  • Fat suppression is extremely uniform and robust
  • Appearances virtually identical to a fat suppressed T2 TSE

  • Double echo sequences offer a reverse T1 fat suppressed image as well 
  • Usually a non-breath hold sequence
T2 STIR abdomen
 Non-breathhold TSE STIR 
 Te 85 msec TI 160 msec
Top of page


Breath Hold scans - Getting Best Results Top of page
Sequence Options

Respiration Artefact Reduction

 ROPE
Respiratory Gating Respiratory Triggering Multiple Acquisitions
  • Average motion artefacts over multiple acquisitions
  • Typically only works with NEX >4

  • [repeat phase step n times then increment, average over TR x NEX]
  • Better with "SMART" averaging (Philips)

  • (collect all phase steps then repeat acquisition, average over TR x N.phase x NEX)
  • Only moderately effective
  • Increased scan time and opportunity for other patient motion
  • Breath Hold Sequences Ultrafast Acquisition
    Top of page
    Flow Artefact Reduction Gradient Motion Nulling Spatial Saturation
    Gut Motion Artefact reduction Reduce gut motility
  • Fast totally for 6 hours prior to exam (cheap & effective
  • Buscopan or Glucagon (expensive & side effects)

  • Fat Suppression
    Fat signal causes high signal respiration induced ghosts on T1 weighted images and T2 weighted Turbo Spin Echo images. Basic fat suppression methods are used in different combinations by different equipment so take time to learn how your scanner suppresses fat signal. These notes only give a basic outline. For a comprehensive discussion of fat suppression issues see the Fat Suppression paper elsewhere on this web. Top of page
    Generic Protocols

    Standard Liver
    To detect and characterize focal liver lesions

    Post Contrast (0.2ml/kg rapid injection followed by 10 ml saline flush) Notes Top of page
    Pancreas

    To detect and characterize focal pancreatic lesions

    Post Contrast (0.2ml/kg rapid injection followed by 10 ml saline flush) Notes
    Pancreatic carcinoma appears with low signal on unenhanced fat suppressed T1 images, but a tumour may be mimicked by age related changes. Immediately post contrast, the normal pancreas enhances avidly leaving the pancreatic carcinoma as a low signal region. Normal pancreatic enhancement drops off rapidly.

    Top of page


    MR Cholangiopancreatography (MRCP) MRCP Parameters
     
    Thick Slice
    • Localiser or simple display of ductal anatomy: 
    • Fat saturated single shot HASTE Axial and oblique coronal planes 
    • TR 2800 TE 1100 ETL 128 Slice thickness 70 mm FOV 300 mm Matrix 256 x 240 Resolution 1.27 x 1.2 mm Acquisition time 7 seconds ( uses 2 TR to establish steady state) 
     
    Thick Axial MRCP
    Thin Slice - For detailed depiction of gallstones or ductal obstruction 
    • Fat suppressed single shot HASTE Coronal 

    • TR 11.9 (infinite) Te 95 ETL 128 13 slices 4 mm thick FOV 270 mm (7/8) matrix 256 x 240 resolution 1.13 x 1.05 mm Acquisition time 20 seconds
    Coronal MIP MRCP
    Top of page
    Stages of Enhancement
    Imaging Characteristics of Liver Mass Lesions
     
    Early enhancement & Washout 
    • Hepatocellular Carcinoma
    • Hepatic Adenoma
    • Cholangiocarcinoma
    • Hypervascular metastases (unusual)
    Bright on T2
    • Haemangioma
    • Hepatocellular Carcinoma
    • Cholangiocarcinoma
    • Metastases
    • Simple Cysts (very bright esp on Te > 120)
    Contains Fat or blood 
    • Hepato-cellular Carcinoma
    • Adenoma (most drop signal on OOP image)
    Pseudo-capsule (compressed liver)
    • Hepato-cellular Carcinoma

    • Adenoma
    Decreased Signal on OOP image
    • Adenoma
    • Fatty infiltration (cirrhosis, post chemotherapy)
    Uniform enhancement
    • Fibro-nodular Hyperplasia
    • Adenoma
    Persistent rim enhancement
    • metastases
    • Late enhancement & delayed washout
    • Haemangioma

    • very rarely hypervascular metastases
    Rim enhancement and peripheral washout
    • hypervascular metastases
    Top of page
    READING & REFERENCES
    Click Me to Mail to Me
    If you would like this paper presented at your MRI meeting or you have comments or suggestions, please contact the author by e-mail by clicking on the picture. 
    Top of page