Whole-body diffusion-weighted MRI

Whole-body diffusion-weighted MRI (WB-MRI) is an advanced imaging technique that combines anatomical and functional MRI sequences to provide a comprehensive assessment of the whole-body in a single examination.

WB-MRI uses the properties of diffusion-weighted imaging for oncological disease staging and surveillance without the use of ionizing radiation. Other advantages of this technique are that it can be performed on widely available 1.5 or 3 T MRI scanners, no contrast agent is required, and it offers good soft tissue contrast.

WB-MRI is a quantitative technique that allows measurement of parameters such as ADC value and fat fraction, which can be used for objective treatment response assessments.

The disadvantages of this technique are that it has a relatively long acquisition time (core protocol 35 mins, comprehensive protocol 45 mins), it is susceptible to standard MRI artifacts, it may not be suitable for claustrophobic patients, and there is a steep learning curve to perform and interpret WB-MRI.

Indications

There are oncologic and non-oncologic applications of whole-body diffusion-weighted MRI. 

Oncologic indications

• staging and surveillance in patients with known malignancy

  • multiple myeloma

  • solid primary cancer (e.g. prostate and breast cancer)

  • bone or soft-tissue sarcoma

  • any malignancy detected in a pregnant patient

• cancer screening in patients with high-risk genetic predisposition syndromes (e.g. Li-Fraumeni syndrome)

Non-oncologic indications

• muscle disorders (eg. inflammatory myositis, congenital myopathy)

• seronegative arthritis

• chronic non-bacterial or recurrent multifocal osteomyelitis

• fever of unknown origin

1.5 vs 3 Tesla

WB-MRI performed at the field strength of 1.5 T is well established due to its robustness and widespread availability. However, excellent results can also be obtained with increased signal-to-noise ratio (SNR) at 3 T.

For the evaluation of tumor response, repeat examinations should be performed on the same scanner (type and software version) to allow accurate and reliable response assessment.

Patient positioning

These studies are conducted with the patient head-first, in the supine position with their arms by their sides. They can be performed with free-breathing, however breath-hold techniques when scanning the chest and abdomen can reduce motion artifacts.

Patient comfort is important to ensure compliance with the protocol and therefore, extra equipment should be used for comfort (e.g. extra padding, pillows, knee pad, etc.).

Technical parameters

Coil

• standard posterior spine coil

• standard head and neck coil

• 2-3 anterior body coils to allow coverage to mid-thighs

Sequences

Core protocol sequences

These sequences are for lesion detection and characterization.

Duration: 35 minutes

• T1-weighted and STIR

  • coverage: whole spine

  • purpose: detect and characterize bone lesions, assess disease nature, check for spinal cord compression

  • plane: sagittal

  • geometry: field of view (FOV) 380 mm, slice thickness 4 mm

• T1 Dixon technique

  • coverage: whole body (vertex to mid-thighs)

  • purpose: lesion detection and bone marrow fat fraction calculation

  • plane: axial

  • geometry: FOV 430 x 1015 mm, slice thickness 5 mm

• DWI with fat suppression

  • coverage: whole body (vertex to mid-thighs)

  • purpose: lesion detection and characterization, tumor volume measurements, ADC measurements

  • plane: axial

  • two b-values; b50-100 and b800-1000, and calculated ADC

  • geometry: FOV 430 mm, slice thickness 5 mm

Comprehensive protocol sequences

These sequences are for response assessment, as well as lesion detection and characterization.

Duration: 45 minutes

• T1-weighted and STIR

  • coverage: whole spine

  • purpose: detect and characterize bone lesions, assess disease nature, check for spinal cord compression

  • plane: sagittal

  • geometry: field of view (FOV) 380 mm, slice thickness 4 mm

• T1 Dixon technique

  • coverage: whole body (vertex to mid-thighs)

  • purpose: lesion detection and bone marrow fat fraction calculation

  • plane: axial and coronal

  • geometry: FOV 430 x 1015 mm, slice thickness 5 mm

•  DWI with fat suppression

  • coverage: whole body (vertex to mid-thighs)

  • purpose: lesion detection and characterization, tumor volume measurements, ADC measurements

  • plane: axial

  • three b-values; b50-100, b500-600 and b800-1000, and calculated ADC

  • geometry: FOV 430 mm, slice thickness 5 mm

• T2-weighted sequence

  • coverage: whole body (vertex to mid-thighs)

  • purpose: lesion characterization and localization for DWI

  • plane: axial

  • geometry: FOV 430 x 1015 mm, slice thickness 5 mm

• optional: regional assessments

  • head: FLAIR, axial for screening for brain metastases

  • lungs: UTE, coronal or axial for lung lesion detection

Practical points

Scoring systems have been developed for different WB-MRI indications to categorize response assessment and for lesion evaluation, for example MY-RADS (for myeloma), MET-RADS (for metastatic prostate and breast cancer) and ONCO-RADS (for cancer screening).