Biparametric vs Multiparametric MRI: What’s Best for Prostate Cancer Screening?

MRI (Magnetic Resonance Imaging) for prostate cancer has seen significant advancements with the introduction of the PI-RADS (Prostate Imaging-Reporting and Data System) scoring system. This system standardises MRI evaluation, helping to assess the likelihood of prostate cancer, lowering the numbers of men needing a prostate biopsy and increasing the pick up rate of more aggressive cancers.

What is PI-RADS?

PI-RADS is designed to improve the detection, localisation, and risk stratification of prostate cancer. By standardising the reporting and interpretation of MRI results, PI-RADS helps radiologists provide more consistent and accurate assessments. The scoring system ranges from 1 to 5, indicating the probability of clinically significant prostate cancer:

• PI-RADS 1: Very low likelihood
• PI-RADS 2: Low likelihood
• PI-RADS 3: Intermediate likelihood
• PI-RADS 4: High likelihood
• PI-RADS 5: Very high likelihood

Multiparametric MRI (mpMRI) for Prostate Cancer

Multiparametric MRI (mpMRI) is recommended as the standard of care for patients suspected of having prostate cancer. It combines both anatomical and functional imaging, providing a comprehensive view of the prostate:

• Anatomical imaging: Includes T1-weighted and T2-weighted images, which show the structure of the prostate.
• Functional imaging: Involves diffusion-weighted imaging (DWI) for water movement and dynamic contrast-enhanced imaging (DCE) for blood flow within the prostate.

Components of mpMRI:

1. T1-weighted images: Highlight the prostate's anatomy and can detect bleeding or other abnormalities.
2. T2-weighted images: Provide detailed images of the prostate's internal structure, helping to identify suspicious areas.
3. Diffusion-weighted imaging (DWI): Measures the movement of water molecules in the tissue, which can indicate cancerous changes.
4. Dynamic contrast-enhanced imaging (DCE): Involves injecting a contrast medium to observe blood flow, which is often increased in cancerous tissues.

Each sequence requires different amounts of time, making mpMRI a longer procedure overall.

Biparametric MRI (bpMRI) vs Multiparametric MRI (mpMRI)

A biparametric MRI (bpMRI) includes only T2-weighted images and DWI, omitting the DCE sequence. This makes bpMRI faster and more cost-effective:

• bpMRI: Takes about 15-20 minutes.
• mpMRI: Can take up to 45 minutes, as it includes the additional DCE sequence.

The shorter duration and lower cost of bpMRI could make it more accessible in various healthcare settings, potentially having significant implications at a population level.

What Will Be the Benefit of Biparametric MRI in Prostate Cancer Screening?

Introducing bpMRI for prostate cancer screening offers several potential benefits:

1. Reduced Scan Time: bpMRI takes significantly less time than mpMRI, which can increase patient throughput and reduce wait times.
2. Lower Costs: With fewer sequences and no need for contrast medium, bpMRI is cheaper, making it more feasible for widespread use.
3. Increased Accessibility: The shorter duration and lower cost make bpMRI more accessible in various healthcare settings, particularly those with limited resources.
4. Comparable Diagnostic Performance: Preliminary studies, such as the PRIME trial, suggest that bpMRI can offer similar diagnostic performance to mpMRI when image quality is high.

PSA and MRI Screening

Currently, Prostate-Specific Antigen (PSA) tests are used to identify men who might need an MRI. However, ongoing studies are exploring whether MRI could directly screen for prostate cancer, bypassing the PSA test. This could streamline the diagnostic process and potentially improve early detection.

Comparing bpMRI and mpMRI

Several trials have sought to determine whether bpMRI can provide comparable results to mpMRI. Notably, the PRIME trial, presented by Dr. Clare Allen in April 2024, found that when image quality is high, the diagnostic performance of bpMRI and mpMRI is similar in men suspected of having prostate cancer. Other studies, such as PACIFIC, are also investigating this area.

Screening Populations

Screening studies differ from diagnostic studies in patients already identified as high-risk (e.g., those with elevated PSA levels). The Prostagram study at Imperial College, led by Professor Hashim Ahmed, suggested that bpMRI might be suitable for screening, but larger studies are needed. The £42m TRANSFORM trial, set to begin this autumn, will explore this further over the next decade.

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Words of Wisdom from a Consultant Urologist:

MRI technology, when utilised effectively, is a cornerstone in the early detection and management of prostate cancer. As research progresses, we may see significant shifts in screening practices, potentially improving outcomes for many patients. One day we may witness the disappearance of the dreaded finger examination and some experts hint as well that biparametric MRI will replace PSA blood test screeening.

Current evidence supports bpMRI for diagnosing prostate cancer, while its role in population-level screening remains under investigation. What remains clear is the critical importance of well-performed and accurately reported MRI in the prostate cancer care pathway.

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