Multiparametric Magnetic Resonance Imaging of the Prostate




The multiparametric approach expanded the clinical applications for prostate magnetic resonance (MR) imaging to include not only staging but also a correlation with tumor aggressiveness. It can also help to guide biopsies, to achieve a higher tumor detection rate, and to better reflect the true Gleason grade. The improved accuracy provided by multiparametric MR imaging and a better understanding of the clinical significance of the imaging findings can pave the way to a more direct role of MR imaging in patient management.


Key points








  • There is plenty of room for improvement in the current standard of care for prostate cancer.



  • The combined use of anatomic and functional information provided by the multiparametric approach increases the accuracy of MR imaging in detecting and staging prostate cancer.



  • Some MR imaging findings in prostate cancer correlate with tumor aggressiveness.



  • Multiparametric MR imaging–guided biopsies have a higher tumor detection rate and better correlate with final Gleason grade than random systematic ones.



  • Multiparametric MR imaging improves the risk assessment of patients with prostate cancer and can aid in the selection of patients for radical treatment or active surveillance.






Introduction


Prostate cancer (PCa) is the second most frequently diagnosed cancer worldwide and the sixth leading cause of cancer death in men. According to Globocan, PCa accounts for 13.6% of the total new cases of cancer and is responsible for 6% of the total cancer deaths per year.


The 2 most commonly used tests for the diagnosis of PCa are serum prostate specific antigen (PSA) level measurement and digital rectal examination (DRE). However, DRE has a low positive predictive value and a low interobserver agreement among urologists. PSA levels correlate with PCa risk but no threshold level provides an acceptable combination of sensitivity and specificity. Up to 32% of men with positive biopsies have PSA levels lower than 4.0 ng/mL and up to 79% of men with PSA serum levels higher than 4.1 ng/mL do not have PCa. When PCa is suspected on the basis of elevated serum PSA levels or abnormal DRE, the diagnosis must be confirmed with systematic transrectal ultrasound (TRUS)-guided biopsies. Systematic random TRUS-guided biopsies sample only a small fraction of the prostate and are known to give false-negative results in a significant number of patients, often requiring repeated biopsy procedures, which are associated with discomfort and potential morbidity. Magnetic resonance (MR) imaging offers an alternative assessment technique that has been shown to be highly accurate for the detection of clinically significant PCa and can be used to identify areas of greater likelihood of cancer to be sampled during TRUS-guided biopsies.


PCa mortality has been declining since the middle 1990s and part of the decline is probably because of early diagnosis and improvements in treatments with curative intent. On the other hand, it is known that many patients die with PCa but not from PCa and between 23% and 42% of screen-detected PCa would not have been diagnosed in the absence of screening. The differentiation of patients who will benefit from treatment from those who will not is a key step in the management of PCa and the Gleason score has proven to be the most important clinical parameter in measuring the risk of mortality from PCa. Because PCa is often heterogeneous, and areas with different grades of differentiation are commonly present in one patient, systematic TRUS-guided biopsies of the prostate are known to yield a misleading Gleason score in a significant number of patients. Gleason scores obtained from MRI-guided prostate biopsies correlate better with the final Gleason score than systematic random biopsies.


Depending on local staging and risk assessment, treatment options for patients with PCa include prostatectomy, radiotherapy, hormone ablation, and active surveillance. DRE alone is not accurate enough for local staging, so clinical nomograms that combine clinical stage (determined by means of DRE), serum PSA levels, and the Gleason grade in the biopsy specimen were developed. MR imaging can detect significant extracapsular extension (ECE) of PCa and the addition of MR imaging information to clinical nomograms increases the accuracy for local staging.


Contemporary MR imaging of the prostate combines anatomic images from high-resolution T2-weighted (T2W) sequences and functional information obtained from diffusion-weighted imaging (DWI), dynamic contrast-enhanced imaging (DCEI), and MR spectroscopy (MRS), in a multiparametric approach (mpMR imaging). This article describes some aspects of each of these techniques and the clinical impact of mpMR imaging in the detection, characterization, and staging of PCa.




Introduction


Prostate cancer (PCa) is the second most frequently diagnosed cancer worldwide and the sixth leading cause of cancer death in men. According to Globocan, PCa accounts for 13.6% of the total new cases of cancer and is responsible for 6% of the total cancer deaths per year.


The 2 most commonly used tests for the diagnosis of PCa are serum prostate specific antigen (PSA) level measurement and digital rectal examination (DRE). However, DRE has a low positive predictive value and a low interobserver agreement among urologists. PSA levels correlate with PCa risk but no threshold level provides an acceptable combination of sensitivity and specificity. Up to 32% of men with positive biopsies have PSA levels lower than 4.0 ng/mL and up to 79% of men with PSA serum levels higher than 4.1 ng/mL do not have PCa. When PCa is suspected on the basis of elevated serum PSA levels or abnormal DRE, the diagnosis must be confirmed with systematic transrectal ultrasound (TRUS)-guided biopsies. Systematic random TRUS-guided biopsies sample only a small fraction of the prostate and are known to give false-negative results in a significant number of patients, often requiring repeated biopsy procedures, which are associated with discomfort and potential morbidity. Magnetic resonance (MR) imaging offers an alternative assessment technique that has been shown to be highly accurate for the detection of clinically significant PCa and can be used to identify areas of greater likelihood of cancer to be sampled during TRUS-guided biopsies.


PCa mortality has been declining since the middle 1990s and part of the decline is probably because of early diagnosis and improvements in treatments with curative intent. On the other hand, it is known that many patients die with PCa but not from PCa and between 23% and 42% of screen-detected PCa would not have been diagnosed in the absence of screening. The differentiation of patients who will benefit from treatment from those who will not is a key step in the management of PCa and the Gleason score has proven to be the most important clinical parameter in measuring the risk of mortality from PCa. Because PCa is often heterogeneous, and areas with different grades of differentiation are commonly present in one patient, systematic TRUS-guided biopsies of the prostate are known to yield a misleading Gleason score in a significant number of patients. Gleason scores obtained from MRI-guided prostate biopsies correlate better with the final Gleason score than systematic random biopsies.


Depending on local staging and risk assessment, treatment options for patients with PCa include prostatectomy, radiotherapy, hormone ablation, and active surveillance. DRE alone is not accurate enough for local staging, so clinical nomograms that combine clinical stage (determined by means of DRE), serum PSA levels, and the Gleason grade in the biopsy specimen were developed. MR imaging can detect significant extracapsular extension (ECE) of PCa and the addition of MR imaging information to clinical nomograms increases the accuracy for local staging.


Contemporary MR imaging of the prostate combines anatomic images from high-resolution T2-weighted (T2W) sequences and functional information obtained from diffusion-weighted imaging (DWI), dynamic contrast-enhanced imaging (DCEI), and MR spectroscopy (MRS), in a multiparametric approach (mpMR imaging). This article describes some aspects of each of these techniques and the clinical impact of mpMR imaging in the detection, characterization, and staging of PCa.




MR imaging techniques


High-Resolution T2W Sequences


In T2W images, the peripheral zone of the prostrate has hyperintense signal, whereas the central and transition zones have low signal, allowing the zonal anatomy of the prostate to be clearly delineated. The prostate capsule is also demonstrated as a thin line of low signal intensity surrounding the gland.


High-resolution T2W images are used for PCa detection, localization, and staging and should be obtained in the sagittal, axial, and coronal planes, the last 2 planes perpendicular and parallel to the line between the rectum and the prostate, respectively. A consensus meeting by European uroradiologists on MR imaging for the detection, localization, and characterization of PCa has outlined minimum and optimum slice thickness and spatial resolution parameters for MR imaging sequences ( Table 1 ).



Table 1

Minimum requirements for acquisition protocols





































Slice Thickness In-Plane Resolution Other
Technique 1.5 T 3.0 T 1.5 T 3.0 T
T2W 4 mm 3 mm 0.7 × 0.7 mm 0.5 × 0.5 mm
DWI 5 mm 4 mm 2.0 × 2.0 mm 1.5 × 1.5 mm b values of 0, 100, and 800 s/mm 2 for ADC map calculation and 1400 s/mm 2 for trace images only.
DCE 4 mm 4 mm 1.0 × 1.0 mm 0.7 × 0.7 mm Temporal resolution of at least 15 s.

Abbreviations: ADC, apparent diffusion coefficient; DCE, dynamic contrast enhanced; DWI, diffusion-weighted image; T2W, T2-weighted.


Peripheral zone PCa is typically a lesion of low signal intensity in T2W images ( Fig. 1 A ), but the growth pattern and the aggressiveness of the tumor can alter its appearance. Tumors composed of densely packed malignant glands (dense tumors) can be diagnosed using T2W images, but sparse malignant glands intermixed with normal tissue (sparse tumors) are not significantly different from the surrounding normal tissue and are not readily detected on MR imaging. Sparse tumors tend to be less aggressive than dense tumors, which indicates a correlation between tumor detectability and aggressiveness.




Fig. 1


High-resolution axial T2W MR images (3 mm) of PCa at 3 T (phased-array coil). ( A ) There is a low–signal intensity lesion on the right peripheral zone ( white arrows ) at the mid-third of the prostate, with no signs of capsular invasion. At prostatectomy, the lesion was classified as Gleason grade 7 (4 + 3) prostate adenocarcinoma. ( B ) An ill-defined homogeneous low–signal intensity area in the left transition zone ( white arrows ) at mid-third of the prostate in another patient. TRUS-guided biopsy (MR imaging oriented) showed a Gleason grade 8 (4 + 4) prostate adenocarcinoma on the corresponding position.


Certain benign conditions of the prostate, including chronic prostatitis, scars, and postbiopsy hemorrhage can result in low signal intensity areas on the T2W images, and can be misdiagnosed as cancer. Although postbiopsy hemorrhage may be a source of confusion, sometimes the hemorrhage can support detection of a suspect lesion because of what is called the “hemorrhage exclusion sign,” when the tumor presents as an isointense area on the T1W images, surrounded by hyperintense hemorrhage. For lesions presenting as low signal intensity on the T2W images, wedge shape and diffuse extension without mass effect are the best predictors of benignity, whereas diffuse extension with mass effect and irregular shape and size are associated with malignancy.


The detection of tumors located in the transition zone is more challenging. Because the signal intensities of benign prostatic hyperplasia (BPH) and PCa usually overlap on the T2W images, other imaging features have to be used to make the diagnosis, namely homogeneous low T2W signal intensity, ill-defined margins, lack of capsule, lenticular shape, and extension into the fibromuscular stroma (see Fig. 1 B).


The acquisition of high-resolution T2W images of the prostate is the first and most important step in the mpMR imaging protocol. These sequences are the basis of PCa MR imaging evaluation and play an important role in both location and staging of PCa ( Box 1 ).



Box 1





  • Peripheral zone



  • Predictors of malignancy




    • Mass effect



    • Round or oval



    • Irregular contours




  • Predictors of benignity




    • No mass effect



    • Linear or wedge shaped




  • Transition zone



  • Predictors of malignancy




    • Homogeneous low T2W signal intensity



    • Ill-defined margins,



    • Lack of capsule



    • Lenticular shape



    • Extension into the fibromuscular stroma




T2W hypointense lesions


DWI


Recently, the technological developments of echo-planar imaging (EPI), high-amplitude gradients, multichannel coils, and the introduction of parallel imaging have extended the applications of DWI to the abdomen and pelvis. DWI measures the microscopic random motion of molecules in a fluid, termed Brownian motion. In a simple solution, the diffusion depends on the temperature and the viscosity of the fluid. Biologic components, mainly cell membranes, form barriers to the free motion of water, thus restricting diffusion. Diffusion tends to be more restricted in tissues with a high cellular density and a narrow extracellular space, such as neoplastic tissue, so DWI is currently an important imaging technique in oncology.


The sensitivity of the DWI sequence to molecular motion can be adjusted by modifying the “b value” parameter (the b value depends on the amplitude, duration, and time interval between the paired gradients used to generate the DWI sequence). Two separate image sets are generated in DWI acquisition: the trace image and an apparent diffusion coefficient (ADC) map. Signal intensity on the DWI trace images reflects the amount of restriction to diffusion but also the T2W characteristics of the tissue (“T2 shine through” effect). The ADC map is obtained by using data from DWI trace images with at least 2 different b values and does not reflect T2W characteristics.


ADC levels are significantly lower in PCa tissue than in noncancerous prostate, allowing the detection of PCa. PCa demonstrates high signal intensity on the DWI trace images obtained at high b values and has low signal intensity on the ADC maps ( Fig. 2 ). Both the trace images and the ADC map should be assessed when detecting PCa using DWI because some tumors are diagnosed only on the ADC maps and others are visible only on the trace images. Recent studies have shown a correlation between the ADC and the Gleason score, with lower ADCs corresponding to increasing Gleason scores. Because ADC values are lower in BPH than in the peripheral zone, the accuracy for detection of PCa in the transition zone is significantly lower and even lower in the prostate base.




Fig. 2


High-resolution 3-mm axial T2W, trace DWIs (b value = 1000 s/mm 2 ) and ADC map of PCa at 3 T (phased-array coil) at level of prostate mid-third to apex. ( A ) T2W image shows a hypointense lesion on the right peripheral zone ( white arrows ); note the extension of the hypointense tissue beyond the capsule and the obliteration of the recto-prostatic angle ( black arrow ), which indicates extracapsular extension. The lesion is hyperintense on the trace DWI ( B ), and hypointense on the ADC map ( C ) with a very low mean ADC (0.74 × 10 −3 mm 2 /s). The identification of a lesion on both the ADC map and trace DWI is a more specific finding than is the identification of the lesion on either image alone. The very low mean ADC suggests a more aggressive tumor. TRUS-guided biopsy (MR imaging oriented) showed a Gleason grade 9 (4 + 5) prostate adenocarcinoma on the corresponding position.


Factors including imaging hardware and choice of imaging parameters, including b values, can have a significant impact on the calculated ADC, precluding the recommendation of a universal numeric ADC threshold for the diagnosis of PCa. An optimal b value for PCa detection has not yet been established. Although some studies report better results with b values higher than 1000 s/mm 2 , others do not. Increasing b values to this “ultra-high” level (ie, b >1000 s/mm 2 ) can increase tumor visibility, especially in the transition zone ( Fig. 3 ), but also leads to an increase in the minimum allowed echo time and more pronounced image distortion artifacts that might compromise overall image quality. The recent Prostate MR Guidelines 2012 proposed by the European Society of Urogenital Radiology (ESUR) suggests the use of 3 b values of 0, 100, and 800–1000 s/mm 2 (see Table 1 ).




Fig. 3


High-resolution 3-mm axial T2W, trace DWIs (b values of 1000, 1500, and 2000 s/mm 2 ) and ADC map of PCa at 3 T (phased-array coil) at level of prostate mid-third to base. ( A ) T2W image shows an ill-defined homogeneous low–signal intensity area in the left transition zone ( white arrows ), with low signal intensity on the ADC map ( B ). Note that the lesion is slightly hyperintense on the trace DWI with b = 1000 s/mm 2 ( C ) and becomes progressively more conspicuous as the b value increases to 1500 s/mm 2 ( D ) and 2000 s/mm 2 ( E ). The imaging noise also increases with the higher b values. TRUS-guided biopsy (MR imaging oriented) showed a Gleason grade 7 (3 + 4) prostate adenocarcinoma on the corresponding position.


In conclusion, DWI is a fast and simple technique that not only increases accuracy in detection but also provides additional quantitative information that correlates with PCa aggressiveness.


DCEI


Solid tumors, including PCa, cannot grow to a significant size without neoangiogenesis. Compared with the vasculature in normal organs, these newly formed vessel networks have an increased flow and blood volume, the capillaries are more permeable, and the fractional volume of the extracellular extravascular space (EES) is proportionally larger. A simple comparison of pregadolinium and postgadolinium images is not enough to demonstrate those differences and so DCEI was developed.


When a low-molecular-weight contrast agent reaches the capillaries, initially it leaks into the EES and later, when the intravascular concentration diminishes because of renal excretion, the contrast agent diffuses back out of the EES into the intravascular space and is filtered out. DCEI uses sequential fast T1W images acquired before, during, and after intravenous injection of a gadolinium chelate to evaluate the kinetics of the uptake and clearance of the contrast agent and differentiate tumors from normal tissue. The most frequently used sequences to implement DCEI are fast 3-dimensional (3D) T1W gradient-echo sequences with or without fat suppression. Because there has to be a trade-off between temporal and spatial resolution, the ideal imaging protocol to implement DCEI is yet to be defined. To accurately assess the enhancement kinetics of PCa, a high temporal resolution is necessary, at the cost of limited spatial resolution. A higher spatial resolution can be obtained at the cost of lower temporal resolution and consequently less accurate description of the enhancement kinetics. A consensus meeting by European uroradiologists on MR imaging for the detection, localization, and characterization of PCa has outlined the minimum and optimum parameters for DCEI of the prostate (see Table 1 ).


There are several different approaches to DCEI: quantitative, semiquantitative, qualitative, and simple visual analysis.


The quantitative approach uses high temporal resolution images and pharmacokinetic modeling to derive the kinetic parameters including the transfer constant (K trans , volume transfer constant between blood plasma and EES), rate constant (K ep , rate constant between EES and blood plasma), and v e (volume of extravascular extracellular space per unit volume of tissue), all of which are increased in PCa compared with the normal peripheral zone of the prostate tissue. The signal intensity of the images must be converted into contrast agent concentration (by means of a T1 mapping) and the arterial input function must be measured to calculate the kinetic parameters from DCEI data. Because the values obtained reflect the underlying physiologic phenomena, they are reproducible and relatively independent of MR equipment and imaging parameters, allowing comparison of data from different institutions.


The semiquantitative DCEI approach uses simple descriptors derived from the signal intensity–time curve, such as the time to peak contrast enhancement, maximum relative enhancement, wash-in rate (speed of contrast uptake), and washout rate (rate of contrast clearance). Prostate cancer lesions tend to show earlier and more intense contrast enhancement compared with normal tissue and washout in later phases ( Fig. 4 ). Wash-in seems to be the most accurate discriminator between malignant and benign prostatic tissue and, on multivariate analysis, a combination of wash-in and washout provides better discriminatory capability than either parameter alone. This approach has the advantage of being simple to implement and is not subject to the assumptions of the model-based quantitative technique that may not be valid for every tissue or tumor type. On the other hand, semiquantitative descriptors are subject to variations in temporal resolution, pulse sequence parameters, rate of contrast administration, and scaling factors. These variations limit the comparison of data from different institutions and hamper the definition of universal diagnostic thresholds.




Fig. 4


mpMR image consisting of high-resolution 3-mm axial T2W, ADC map and DCE imaging of PCa at 3 T (phased-array coil) at level of the prostate apex. ( A ) T2W image shows a subtle ill-defined low–signal intensity area in the right lateral peripheral zone ( white arrows ). The lesion has low signal intensity on the ADC map ( B ). In early-phase DCE image ( C ), the lesion shows strong enhancement. Semiquantitative parametric maps superimposed on T2W images show that the lesion has intense contrast wash-in ( D ) and washout ( E ). ( F ) Signal intensity–time curve of the lesion shows a type III curve ( blue ) and the normal left peripheral zone shows a type II curve ( red ). The black lines indicate the concept of wash-in and washout. The lesion is indeterminate on the T2W image and the diagnostic confidence significantly increases with the analysis of the functional images. Random systematic biopsies showed a Gleason grade 7 (3 + 4) prostate adenocarcinoma on the right apex.


The qualitative DCEI approach is implemented by assessing the shape of the signal intensity–time curve. Signal intensity–time curves are classified as steady (type I), plateau (type II), or washout (type III) (see Fig. 4 ). Type III curves are the most indicative of PCa, especially for a focal asymmetric enhancing lesion; however, this finding is not totally specific, and types I and II curves can be seen in patients presenting with PCa as well. The assessment of the shape of the signal intensity–time curve is very simple to implement and because it does not require a very high temporal resolution, longer acquisition times can be used with higher spatial resolution. Bloch and colleagues reported a substantial increase in the accuracy of MRI in predicting ECE with the addition of high spatial resolution (low temporal resolution) DCEI and color-coded parametric maps that combined wash-in rate and the shape of the signal intensity–time curve using 1.5-T and 3.0-T magnets.


Simple visual inspection exploits the fact that PCa lesions tend to show early enhancement and can be detected as hyperintense lesions in the “arterial” phases of DCEI (see Fig. 4 ). Girouin and colleagues described a better sensitivity in the localization of malignant lesions using DCEI with simple visual inspection of images compared with the T2W images alone, although they also reported a lower specificity.


The European Consensus Meeting on MRI for the Detection, Localization, and Characterization of Prostate Cancer could not reach a consensus on the best approach to analyzing DCEI data. Quantitative or semiquantitative DCE-MR imaging were not considered minimum requirements but are recommended as optimal practice. The recent Prostate MR Guidelines 2012 proposed by the ESUR suggest using the qualitative approach based on the shape of the signal intensity–time curves.


Despite the ongoing debate on the best imaging protocol to be used in DCEI (higher spatial vs higher temporal resolution) and the best approach to analyze the data (quantitative, semiquantitative, qualitative, or simple visual analysis), DCEI adds accuracy to the detection and staging of PCa and should be used as an optimal practice.




MRS


In MRS, the position of each metabolite peak in the output graph reflects the resonant frequencies or chemical shifts of its hydrogen protons, and the area of each peak reflects the relative concentration of that metabolite. The dominant peaks observed in prostate MRS are from protons in citrate (2.60 ppm), creatine (3.04 ppm), and choline compounds (3.20 ppm). A range of smaller peaks related to polyamine protons may be observed at approximately 3.15 ppm.


Citrate is a normal constituent of prostatic tissue and its production is dramatically reduced or lost in PCa because of changes in cellular function. Increased concentrations of choline-containing metabolites are related to an increased cell turnover and have also been associated with the presence and progression of PCa. Because it is not possible to differentiate choline peaks from creatine peaks on the spectra obtained at common clinical field strengths, the ratio of choline plus creatine to citrate is used as a metabolic biomarker for PCa.


MRS improves the detection and risk assessment of PCa, and measured peak ratios have also been shown to correlate with tumor aggressiveness ( Fig. 5 ). The ESUR Prostate MR Guidelines 2012 suggest using either a qualitative or a quantitative approach for interpreting prostate MRS. The qualitative approach is based on visual analysis of the citrate and choline/creatine peaks and a lesion is deemed suspect of significant cancer if the choline/creatine peak is higher than the citrate peak in at least 3 adjacent voxels. In the quantitative approach, the areas of the peaks are measured and choline plus creatine-to-citrate ratios higher than 0.72 in at least 2 adjacent voxels are considered to indicate malignant tissue, whereas ratios between 0.58 and 0.72 are considered ambiguous.




Fig. 5


MRS of PCa at 3 T (phased-array coil). ( A ) Axial 3-mm T2W images at level of the prostate mid-third to apex, shows a large hypointense lesion on the left peripheral zone. ( B ) A 3D MRS shows a normal spectrum on the right peripheral zone ( red box ) with normal choline plus creatine-to-citrate ratio of 0.48. In the voxel placed over the lesion on the left peripheral zone ( blue box ), the curve shows an increased choline peak and the citrate peak is markedly reduced. Random systematic biopsy showed Gleason grade 9 (4 + 5) prostate adenocarcinoma on the left apex.




mpMR imaging


One of the greatest advances in prostate MR imaging grew from the recognition that no single technique is able to adequately detect and characterize PCa. The combination of anatomic T2W images and the functional techniques described previously has been shown to increase the predictive power of MR imaging for detection and staging of PCa (see Fig. 4 ). Tanimoto and colleagues reported a significant increase in the area under the receiver operating curve (AUC) for the detection of PCa as they transitioned from a protocol with T2W images only (AUC = 0.711), to a protocol combining T2W imaging and DWI (AUC = 0.905), and finally to a more complete protocol including T2W imaging, DWI, and DCEI (AUC = 0.966). Turkbey and colleagues also reported a higher sensitivity for the combination of T2W images, MRS, and DCEI than for each sequence alone. In that study, each of the 3 MR imaging modalities provided an independent (ie, additive) predictive value for the detection of cancer. Interestingly, Riches and colleagues found that the ability to identify cancer increased significantly with the use of a combination of any 2 functional parameters over the use of individual parameters, but the addition of a third functional parameter did not cause any further improvement in sensitivity or specificity. The ideal set of techniques to be used in prostate mpMR imaging has not yet been defined but the combination of T2W images with 2 functional techniques seems to provide a reasonable compromise between accuracy and examination duration.


Accordingly, the ESUR Prostate MR Guidelines suggest the use of T2W images plus 2 functional techniques. In the European Consensus Meeting on MRI for the Detection, Localization, and Characterization of Prostate Cancer, the phrase “the data set should include T1-weighted, T2-weighted, diffusion-weighted, and contrast-enhanced MRI” was considered appropriated as a minimum and optimum imaging requirement. MRS was not considered a minimum requirement and there was not a consensus as to whether it is an optimum requirement. Because MRS is the most complex and time consuming of the functional techniques, the choice to include it in a multiparametric protocol should be based on personal experience and skill levels.


The ESUR Prostate MR Guidelines suggest a unified scoring system for mpMR imaging, named the Magnetic Resonance Prostate Imaging Reporting and Data System (MR PI-RADS), which follows the steps of the BI-RADS (Breast Imaging Reporting and Data System). In this scoring system, each lesion is scored on a 5-point scale for each sequence (T2W imaging, DWI, DCEI, MRS); the criteria for assigning scores to lesions identified by each technique are described in Table 2 . Additionally, each lesion is given an overall score that indicates its chance of being a clinically significant cancer. The maximum value depends on the number of sequences performed (2 sequences: maximum value = 10; 3 sequences: maximum value = 15; 4 sequences: maximum value = 20).


Sep 18, 2017 | Posted by in MAGNETIC RESONANCE IMAGING | Comments Off on Multiparametric Magnetic Resonance Imaging of the Prostate

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