Finger protocol (MRI)

The MRI finger protocol encompasses a set of MRI sequences for the routine assessment of the finger pathology.

Note: This article aims to frame a general concept of an MRI protocol for the assessment of the fingers and or the thumb. Protocol specifics will vary depending on MRI scanner type, specific hardware and software, radiologist and perhaps referrer preference, patient factors e.g. implants, specific indications and time constraints

Indications

Typical indications are pain and swelling or decreased range of motion of the fingers including the following pathologies:

• collateral ligament injury
• tendon injury
• finger pulley injury
• injury of the palmar plate

1.5 vs 3 tesla

Musculoskeletal examinations are generally done on both 1.5 and 3 tesla. In particular, an examination of the fingers and/or thumb profits from an improved spatial and contrast resolution of 3 tesla. Postoperative examinations in patients with metallic implants, however, should be done on 1.5 tesla with metal artifact reduction sequence.

Patient positioning

There are two options:

• the patient in a prone position with the arm in an overhead and elevated position and the elbow joint in pronation (superman position)
• the patient is supine with the arm adducted close to the hip in mild supination

A disadvantage of the superman position is that it is uncomfortable for the patient and possible advantages in fat saturation due to the hand being in the center of the magnet might be mitigated by movement artifacts.

The hand of the patient should be positioned with the finger in question being approximately in axis with the forearm.

Technical parameters

Coil

Multi-phased array coils are recommended.

• dedicated wrist or hand coil
• flexible small extremity coil

Scan geometry

• in-plane spatial resolution: ≤0.3 x 0.3 mm
• field of view (FOV): 60-120 mm (might be rectangular)
• slice thickness: ≤2 mm to ≤3 mm depending on the plane

Planning

Images are angulated on the specific finger.

• axial images:
  • angulation: perpendicular to the finger axis and parallel to the joints
  • volume: depends on the specific question
  • slice thickness: ≤3 mm with a gap of 0,3
• coronal images:             
  • angulation: parallel to the fingers and wrists
  • volume: entire finger from the skin to skin
  • slice thickness: ≤2 mm without a gap
• sagittal images:
  • angulation: sagittal to the finger axis
  • volume: includes the fingers of interest
  • slice thickness: ≤2 mm without a gap
• 3D images (optional)
  • angulation: coronal
  • spatial resolution: isotropic ≤0.6 mm
• axial oblique images*: for better illustration of the proper collateral ligaments

Sequences

The mainstay in musculoskeletal imaging are water-sensitive sequences, this can be achieved with conventional STIR or fat-saturated images or with intermediate-weighted images.

At least one T1-weighted sequence should be included to ease the assessment and interpretation of bone marrow and/or soft tissue lesions.

Standard sequences

• intermediate-weighted (fat-saturated)​
  • purpose: bone and/or soft-tissue characterization and detailed anatomy of radiocarpal and intercarpal ligaments as well as the triangular fibrocartilage complex
  • technique: IM fast spin echo
  • planes: coronal or sagittal, axial
• T1 weighted
  • purpose: bone and/or soft-tissue characterization
  • technique:  T1 fast spin echo
  • planes: coronal or sagittal depending on the clinical question, axial*

Optional sequences

• T2* weighted
  • purpose: bone and/or soft-tissue characterization, collateral ligaments, palmar plate
  • technique: T2 GRE
  • planes: axial* (optional)
• 3D images
  • purpose: joint pathology, collateral ligaments, palmar plate
  • technique:  3D GRE
  • acquisition plane: coronal – sagittal and oblique multiplanar reconstructions
• T1 weighted C+ (fat-saturated)
  • purpose: joint pathology, collateral ligaments, palmar plate
  • technique:  T1 fast spin echo
  • planes: coronal, sagittal, axial depending on the pathology

(*) indicates optional planes

Practical points

• the superman position is preferred on that protocol
• the hand or wrist should be in the center of the scanner
• the protocol can and should be tailored to the specific indication or clinical question
• in case of suspected tendon pathology, additional imaging of the wrist might be necessary
• the examination will benefit if every plane is imaged
• a typical native protocol will contain 4-5 sequences