UNDERSTANDING MP MRI PROSTATE EVALUATION AND ASSIGNING PIRADS SCORE. NEW IN PIRADS V2

1. Published in European Radiology Experimental, 2019
SUMANTRA DEY
1ST YR PDT

2. BACKGROUND
• Prostate MRI is becoming of central importance in the
contemporary management of PCa by improving the
detection of clinically significant cancer (csPCa) while
minimising overdiagnosis and overtreatment of indolent
disease
• CURRENT USES OF MRI
– detecting and localising csPCa lesions
– triaging biopsy, guiding targeted biopsy or focal therapy
– stratifying the risk before treatment
– monitoring patients during active surveillance
– Planning and choosing surgery or radiation therapy techniques
– assessing recurrence

3. THE MULTIPARAMETRIC STANDARD
• ESUR guidelines 2012
– defined mpMRI as the combination of anatomic T2-
weighted imaging (T2WI) with at least two functional MRI
techniques out of DWI, DCE and MRS
– proposed detailed and stringent technical requirements
for detection and staging
– DWI and DCE to be used mandatorily and MRSI optionally
• protocols were presented together with the first
version of the prostate imaging reporting and data
system (PI-RADS)

4. THE MULTIPARAMETRIC STANDARD
• PI-RADS version 2 (2014) led to consistent
simplification of several technical and
interpretation aspects
– MRSI was excluded from the examination,
restricting the mp standard to the use of T2WI,
DWI, and DCE
– less (even if stringent) technical parameters to
obtain an acceptable mpMRI examination, leaving
space for protocols optimisation
– introducing the concept of dominant sequence

5. Dominant Sequence
• Likelihod that an image represents csPCa is
expressed on a 1 to 5 scale
• Depends on appearance on DWI for the peripheral
zone (PZ) and on T2WI for the transition zone (TZ)
• DCE assigned secondary role of a tiebreaker for PZ
lesions, DWI for TZ lesions

6. Brief discussion on mpMRI

7. T2WI

9. DWI

10. • DWI study consists of 2 images
1. High b value DWI image
2. Apparent Diffusion Coefficient map
• normal PZ demonstrates homogenous low SI
on DWI and high SI on ADC map
• More restricted environment of cancer leads
to high SI on DWI and low SI on the ADC map

12. DCE

14. (A) Axial T2WI
of the prostate
midgland shows a
1.2-cm circumscribed
hypointense nodule
(arrow) in the
enlarged right
transition
zone.
(B)The nodule is
hyperintense on high
b-value DWI
(C)hypointense on
ADC map
(D)shows early
enhancement on the
axial contrast
enhanced
T1WI DCE

15. (A) Axial T2WI
shows a lenticular,
noncircumscribed
mass with low
signal intensity in
the anterior
midgland (arrows)
compatible with a
PI-RADS category
5 lesion.
(B) mass shows
markedly high
signal intensity on
high b-value DWI
(C)markedly low
signal intensity on
ADC map
(D) early
enhancement on
contrast-
enhanced T1WI
DCE

16. THE MP STANDARD - DISADVANTAGES
• mpMRI requires prolonged time (30–45 min)
• use of IV gadolinium-based contrast agents
• drawbacks of PIRADS v2
– Incomplete interpretation criteria for TZ cancers
– lack of definite rules for the CZ or anterior
fibromuscular stroma involvement
• High costs

17. Less-is-better strategies
1. Non-contrast biparametric MRI
2. Reduced acquisition time
3. Abbreviated protocols
4. Less variability from human readers

18. Non-contrast biparametric MRI
• Anatomic T2WI coupled with DWI as the only retained functional
technique
• DCE has been classically assumed to improve the sensitivity of
T2WI alone or T2WI combined with DWI
• Whether DCE should be included in the mp standard has always
been a controversial issue
• PI-RADS v2 revised role for DCE to PZ only and limiting it to a
problem-solving tool
• bpMRI does not apply to the setting of tumour recurrence after
radical prostatectomy, radiation therapy, or focal therapy - DCE still
plays a key-role in this scenario

20. Reduced acquisition time
• T2WI is obtained with 2D turbo spin-echo sequences -
need to acquire transverse, sagittal, and coronal planes
separately; most time consuming
• (3D) volumetric T2WI provides a unique slab with
isotropic voxels, to be reconstructed in any plane –
shortened acquisition time up to 44%
• reduce volume-averaging artefacts, leading to better
delineation of subtle anatomic features affecting the
diagnosis (“erased charcoal sign” around TZ nodules)

21. Reduced acquisition time
• Trade offs with 3D slab technique –
– reduced soft tissue contrast
– blurring and loss of resolution even for subtle
motion
– greater motion artefacts
• 3D T2WI is not yet accepted as a state-of-the-
art tool for detecting and staging PCa

22. Abbreviated protocols
• consist of cutting redundant scans while
preserving the informative core of the test
• Abbreviated bpMRI - transverse T2WI and
DWI only, with total acquisition time of 8 min
45 s (compared to 34 min 19 s of mpMRI)
• Technical solution to face the increasing
demand for prostate imaging
• needs further validation and should be
investigated in terms of cost-effectiveness

23. Less variability from human readers
• Computer-aided diagnosis (CAD) algorithms –
a form of machine learning technology,
trained on real cases to extract and classify
image features, and in turn recognise
intermediate- to-high-risk cancers

24. Different-is-better strategies
• there is a parallel pathway of prostate MRI
development, searching for objective and
reproducible MRI-related biomarkers for the
prediction of PCa aggressiveness or
overcoming inter-reader variability

25. Promised DIFFERENT STRATEGIES

26. TAKE HOME MESSAGE
• Multiparametric magnetic resonance imaging is the standard of
care for assessing prostate cancer.
• Alternative protocols are emerging to increase availability and offer
a patient-centred approach.
• Less-is-better strategies are promising for clinical practice, but
require validation.
• Different-is-better strategies are a matter for intensive research.
• Prostate MRI technical standard and interpretation rules are still
evolving.

27. THANK YOU