Core of the technique (in-bore)
The histological sampling procedure, known in international practice as in-bore MRI-guided biopsy, is performed exclusively inside a magnetic resonance scanner under full MRI guidance. Technically, the process is organized as follows: a specialized biopsy needle guide is inserted into the patient's rectum. Then, the radiologist manually adjusts the position of this guide. The main task of the specialist at this stage is to target the clinically significant area, or suspicious lesion, designated by the term clinically significant region (CSR) as accurately as possible.
Limitations and technological development
Despite the high targeting accuracy, performing a biopsy directly inside the scanner has a number of significant clinical and organizational features. First, the procedure is highly labor-intensive and takes significantly longer when compared to a standard systematic biopsy performed under transrectal ultrasound (TRUS) guidance. Second, for the successful execution of such a procedure, the medical facility must have a specially trained radiologist available.
Currently, active technological development of the method is underway. Due to the complexities associated with lengthy and labor-intensive manual guide adjustment, engineers have developed special MRI-compatible robotic systems. These systems are designed for automated and highly accurate positioning of the biopsy needle.
Comparison of MRI-targeted biopsy methods
In modern prostate cancer (PCa) diagnostics, it is important to evaluate the effectiveness of various approaches. There are three main methods of MRI-targeted biopsy, which are compared with each other and with the standard procedure:
- Tissue sampling directly inside the scanner (in-bore).
- MRI/TRUS fusion registration biopsy, which involves overlaying magnetic resonance images onto real-time ultrasound imaging.
- Cognitive registration biopsy.
The evaluation of the diagnostic accuracy of multiparametric MRI (mpMRI) compared to standard TRUS biopsy is discussed in detail in major scientific works, including the large-scale PROMIS clinical trial.
Standardization, staging, and outcome assessment
To unify radiological reports of the prostate and assess tumor spread, international standardized systems are used:
- PI-RADS (version 2) — the baseline system for describing and processing prostate imaging data.
- MET-RADS — a reporting and data system for assessing multi-organ metastatic disease in advanced cancer.
- Gleason Grading (Gleason Grading) — assessment of tumor malignancy grade based on the 2014 ISUP consensus.
Magnetic resonance imaging has high accuracy for local staging of the disease. The use of ultrasmall superparamagnetic iron oxide particles deserves special attention—this contrast agent is used to detect micrometastases in lymph nodes. In addition, mpMRI plays a key role in monitoring the state of the prostate after treatment and in diagnosing potential recurrences. All patient management tactics are regulated by the current clinical guidelines of the European Association of Urology (EAU-ESTRO-SIOG) and the American Urological Association (AUA).
Briefly: answers to topical questions
How is needle guidance technically performed in cognitive MRI-targeted biopsy?
In cognitive MRI-targeted biopsy, needle guidance is performed by the operator under transrectal ultrasound guidance. The physician mentally projects the suspicious area previously identified on MRI scans and performs a targeted biopsy.
Which parameters and scanning sequences are evaluated using the PI-RADS v2 system in multiparametric MRI of the prostate?
According to the PI-RADS v2 system, multiparametric MRI of the prostate evaluates a combination of anatomical and functional scanning sequences.
The standard examination protocol includes the following methods:
- T2-weighted imaging (T2-weighted imaging) — anatomical evaluation, serving as the dominant sequence for the transition zone.
- Diffusion-weighted imaging (DWI) — functional evaluation, dominant for the peripheral zone (includes apparent diffusion coefficient maps and high b-value images).
- Dynamic contrast-enhanced MRI (DCE MRI) — evaluation of areas with pathological contrast enhancement.
Which anatomical zones of the prostate are distinguished when evaluating a multiparametric MRI?
When evaluating a multiparametric MRI, the prostate gland and surrounding structures are divided into several anatomical zones.
According to the PI-RADS v2 system, the following areas are distinguished:
- Peripheral Zone (Peripheral Zone) — located posteriorly and inferiorly, it is the primary site for cancer localization.
- Transition Zone (Transition Zone) — surrounds the prostatic urethra.
- Central Zone (Central Zone) — visually indistinguishable from the transition zone in young men.
- Anterior Fibromuscular Stroma (Anterior Fibromuscular Stroma) — consists of smooth muscle cells and connective tissue, contains no glandular tissue.
- Urethral Sphincter (Urethral Sphincter) — external sphincter.
Class and exam questions
What is the main difference between an in-bore biopsy and a classical TRUS biopsy?
The in-bore procedure is performed directly inside the MR scanner under direct magnetic resonance guidance, which allows for precise targeting of the clinically significant lesion. However, this method takes significantly longer than ultrasound-guided biopsy.
What are the available options for MRI-targeted biopsy?
In clinical practice, there are three main methods: in-bore biopsy, MRI/TRUS fusion registration biopsy, and cognitive registration biopsy.
Why are robotic systems used in in-bore biopsies?
Manual adjustment of the rectal needle guide for the biopsy needle inside the scanner is an extremely labor-intensive process. Robotic positioning systems are designed to speed up the procedure and ensure perfect targeting accuracy of the suspicious lesion.
What else to study on this topic
- Comparison of the diagnostic accuracy of multiparametric MRI and standard TRUS biopsy (analysis of the PROMIS study).
- The use of ultrasmall superparamagnetic iron oxide particles to detect lymph node metastases.
- Gleason Grading system according to the 2014 ISUP consensus.
- Rules for reporting studies using the PI-RADS (version 2) and MET-RADS systems.
- The role of mpMRI in assessing the prostate after treatment and in diagnosing recurrences.
- Current EAU-ESTRO-SIOG and AUA clinical guidelines for screening and diagnosis of localized PCa.
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