Clinical Radiology xxx (2013) 1e8 Contents lists available at SciVerse ScienceDirect Clinical Radiology journal homepage: www.clinicalradiologyonline.net Prostate MRI: Who, when, and how? Report from a UK consensus meeting A.P.S. Kirkham a, *, P. Haslam b, J.Y. Keanie c, I. McCafferty d, A.R. Padhani e, S. Punwani a, J. Richenberg f, G. Rottenberg g, A. Sohaib h, P. Thompson f, L.W. Turnbull i, L. Kurban j, A. Sahdev k, R. Clements l, B.M. Carey m, C. Allen a a Department of Imaging, University College Hospital, London, UK Department of Radiology, Freeman Hospital, Newcastle, UK c Department of Radiology, Western General Hospital, Edinburgh, UK d Department of Imaging, Queen Elizabeth Hospital, Birmingham, UK e Paul Strickland Scanner Center, Mount Vernon Cancer Centre, London, UK f Department of Imaging, Royal Sussex County Hospital, Brighton, UK g Department of Imaging, Guy’s and St Thomas Hospital, London, UK h Department of Imaging, Royal Marsden Hospital, London, UK i Hull York Medical School at the University of Hull, Hull, UK j Department of Radiology, Aberdeen Royal Infirmary, Aberdeen, UK k Department of Imaging, Barts and the London NHS Trust, London, UK l Department of Radiology, Royal Gwent Hospital, Newport, UK m Department of Radiology, St James Hospital, Leeds, UK b art icl e i nformat ion Article history: Received 22 January 2013 Received in revised form 16 March 2013 Accepted 20 March 2013 The current pathway for men suspected of having prostate cancer [transrectal biopsy, followed in some cases by magnetic resonance imaging (MRI) for staging] results in over-diagnosis of insignificant tumours, and systematically misses disease in the anterior prostate. Multiparametric MRI has the potential to change this pathway, and if performed before biopsy, might enable the exclusion of significant disease in some men without biopsy, targeted biopsy in others, and improvements in the performance of active surveillance. For the potential benefits to be realized, the setting of standards is vital. This article summarizes the outcome of a meeting of UK radiologists, at which a consensus was achieved on (1) the indications for MRI, (2) the conduct of the scan, (3) a method and template for reporting, and (4) minimum standards for radiologists. ! 2013 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved. Introduction The standard pathway for men suspected of having prostate cancer is resulting in over-diagnosis and over* Guarantor and correspondent: A.P.S. Kirkham, Department of Imaging, University College Hospital, 235 Euston Road, London NW1 2BU, UK. E-mail address: [email protected] (A.P.S. Kirkham). treatment,1 as well as systematically missing significant tumours, particularly in the anterior and apical parts of the gland.2 Many of those who routinely request and perform magnetic resonance imaging (MRI) of the prostate know that it has the potential to solve many of these problems and enable effective active surveillance. However, we recognize that the technique is at a crossroads, and that the initial experience in many centres is disappointing because of why and how it is being performed. For MRI to live up to 0009-9260/$ e see front matter ! 2013 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.crad.2013.03.030 Please cite this article in press as: Kirkham APS, et al., Prostate MRI: Who, when, and how? Report from a UK consensus meeting, Clinical Radiology (2013), http://dx.doi.org/10.1016/j.crad.2013.03.030 2 A.P.S. Kirkham et al. / Clinical Radiology xxx (2013) 1e8 its promise, the setting of standards is vital. This paper is an attempt to summarize the consensus opinions of a group of specialist UK radiologists, on the indications for and performance of multiparametric MRI of the prostate. It builds on two previous European consensus documents in particular: one from a meeting held in London in 20103 and the second the European Society of Uroradiology consensus document on prostate MRI published in 2012.4 Our aim is not an exhaustive summary of the data on prostate MRI or a duplication of the comprehensive European Society of Uroradiology (ESUR) guidelines: rather, we aim to (1) summarize the established and emerging indications for the technique, together with the performance characteristics of modern multi-parametric MRI; (2) describe a single protocol that is applicable to the great majority of UK MRI systems; (3) propose a structured, practical approach for reporting and a standard template; (4) suggest minimum standards for performing multiparametric MRI in the UK. Methods Uroradiologists from nine centres routinely performing large numbers of prostate MRI or with a research interest in the field met in April 2012. They addressed a set of predefined topics on prostate MRI under the following categories: indications, conduct, reporting, and minimum standards. Several other radiologists could not attend but took part in editing initial and subsequent versions of this document, or in subsequent meetings to draft the paper, and are listed as authors. The aim was not to duplicate previous meetings that have applied a formal consensus method,3 but to achieve a pragmatic consensus by group discussion. Unless stated, the statements in this paper are the unanimous opinion of the group; the exception is the section on the performance of the MRI examination where, in several cases, we describe the clinical practice of a majority. Findings Indications The indications for MRI of the prostate can be broadly split into two groups: (1) the detection of prostate cancer, and (2) the local staging of prostate cancer. To some extent this division is artificial (most examinations will be performed for both indications), but it is useful for a summary of the evidence. The detection of prostate cancer Before discussing the indications for detecting prostate cancer, it is important to address the issue of significance in a disease that will affect the majority of the male population, but result in the death of few.5 This is currently a matter of great debate amongst urologists. It is likely that Gleason 3 þ 3 cancer very rarely results in death from prostate cancer,5,6 and that the great majority of tumours <0.5 cm3 will, similarly, be insignificant.7 If the definition of significance is tumour in which current treatments make a significant difference to survival, recent trial data suggest that the criterion of Gleason 3 þ 3 and <0.5 cm3 for insignificant cancer is too conservative.8 One of the key performance characteristics of prostate MRI is that it misses the majority of small (<0.1 cm3), lowgrade tumours.9 If the aim is that it will detect the majority of all cancers, that aim is likely unattainable. Wellperformed, multiparametric MRI can usually (with >80% sensitivity) detect the following in the whole prostate (including peripheral and transition zones): "0.2 cm3 (equivalent to a 7 mm sphere) of Gleason 4 þ 3 or above "0.5 cm3 (equivalent to a 10 mm sphere) of Gleason 3 þ 4 or above For Gleason 3 þ 3 tumours, we did not achieve consensus that tumours >0.5 cm3 will be detected with 80% sensitivity. Although areas of this size of “focal” or homogeneous Gleason 3 þ 3 disease will usually be detected, those with a more diffuse pattern and loose stroma on histology often will not.10 These characteristics can only be assumed for multiparametric MRI performed before biopsy, including diffusion-weighted and dynamic contrast-enhanced sequences, with certain minimum imaging parameters (described below) and reported by an experienced radiologist. They are in keeping with recent published results.9,11e14 What do they enable? (i) Avoiding biopsy: it is likely that a multiparametric MRI showing no evidence of tumour has a negative predictive value for significant disease similar to or better than a standard 12 core prostate biopsy15,16 [modelling studies suggest that 36e47% of lesions >0.5 cm3 may be missed by a 12 core transrectal approach,17 and another study showed a detection rate at transrectal ultrasound (TRUS) of 75% for significant disease18]. If the performance characteristics for MRI described above are demonstrable in the center performing the study, then an MRI performed as the first investigation in a man suspected of having prostate cancer might in some cases prevent the need for biopsy. MRI may detect some tumours missed by biopsy (especially those lying anteriorly19) and biopsy may detect some tumours missed at MRI: the combination can be especially powerful in excluding significant tumour, and may reduce the need for follow-up biopsy when the prostate-specific antigen (PSA) level remains elevated. ii) Targeting: if performed before biopsy, the samples obtained can be targeted to areas of suspicion on the MRI images. It has recently been shown that performing a mean of 3.8 targeted biopsies based on multiparametric MRI has a performance for the detection of significant disease comparable with 12 core untargeted biopsy, and that such a technique may result considerably reduce the detection of insignificant disease.20 We are not at a stage to recommend targeted samples only, but there is little doubt that targeting also produces a more representative sample, improving the estimation of tumour volume and Please cite this article in press as: Kirkham APS, et al., Prostate MRI: Who, when, and how? Report from a UK consensus meeting, Clinical Radiology (2013), http://dx.doi.org/10.1016/j.crad.2013.03.030 A.P.S. Kirkham et al. / Clinical Radiology xxx (2013) 1e8 significantly reducing the number of tumours upgraded at definitive histology.20e22 iii) Previously negative biopsies: in patients with continuing clinical suspicion of prostate cancer, but a negative previous biopsy, MRI may detect missed tumours (often anterior) in up to 40%.19,23 This is perhaps the strongest indication for pre-biopsy MRI; indeed, we would say that it is a requirement in men with a persistently raised PSA in whom a second biopsy is being considered. iv) Active surveillance: MRI has two potential roles. Firstly, to confirm that the classification of risk status is accurate and that there is not an unexpected larger or higher-grade tumour: upgrading of apparently lowgrade tumours found at TRUS biopsy is common at more definitive histology24 and is more common when a lesion is conspicuous on MRI.25,26 More speculatively, if the tumour can be seen on MRI, imaging has the potential to contribute to follow-up. If a tumour is visible, it can be monitored for change. If it cannot be seen, it is unlikely (according to the performance criteria above) that a significant tumour has developed. Local staging of prostate cancer Staging aims to determine whether tumour is organconfined, and to detect local and distant spread. Staging of cancer following a positive biopsy is the only current indication for MRI in the latest edition (2008) of the UK National Institute for Health and Clinical Excellence (NICE) guidelines,27 which have the following three conclusions: (1) imaging is not routinely recommended for men in whom no radical treatment is intended; (2) computed tomography (CT) is not recommended in those with intermediate or low-risk disease; and (3) MRI is recommended in those with high-risk localized (defined “clinically”) and locally advanced disease being considered for radical treatment.27 The NICE guidelines are 4 years old (new guidance is due in January 2014), and before recent data on the value of targeted biopsies.17,22 They do not currently recommend targeting for patients with intermediate or low-risk disease (PSA < 20, Gleason # 7), in contrast to the more recent ESUR guidelines,4 which make the case (as we have done) for MRI in intermediate and low-risk patients. Ideally, MRI will have been performed before biopsy (with the benefits of targeting and detection of anterior disease), and thus, before the risk status is accurately known. There is little doubt that even T2 sequences alone improve staging accuracy compared to nomograms,28 and there are morphological predictors of both seminal vesicle (T3b)29 and extracapsular (T3a) spread,28 such as degree of capsular abutment, bulge, irregularity, and fat stranding. However, although selected groups have achieved moderately high accuracy, overall the detection of small-volume extracapsular disease remains challenging, with overall sensitivities of 67e91%, and specificity 67e100%.30,31 Overall, in the opinion of the group, MRI is useful (1) when biopsies are negative (to exclude anterior disease missed by a standard biopsy approach19); (2) in active surveillance where underestimation of size and grade is 3 common21,32 and MRI can detect larger or higher-grade tumours25,26; and (3) to stage disease in men being considered for radical treatment.4,27 These three scenarios encompass the great majority of men with a moderately raised PSA, and lead to the following conclusion: if MRI is ultimately useful in most men with a suspicion of prostate cancer, why not perform it before biopsy, when it will be free of artefact, may enable targeting, and will be immediately available for staging if tumour is found? The scan Post-biopsy artefact It has been known for some time that changes on T2-weighted and contrast-enhanced sequences may persist for at least 8 weeks after prostate biopsy,33,34 and that they can significantly degrade staging performance: in one study accuracy was 46% if the MRI was performed less than 21 days after biopsy and 83% if performed after.35 The period of persistence of post-biopsy changes is not known accurately, but changes on diffusion and T2 sequences can be seen in some patients for 2e3 months, with artefact on enhanced sequences lasting considerably longer in many patients. What are the implications? i) In the opinion of the group, a staging MRI should be performed at least 10 weeks after biopsy, and if possible after 20 weeks. Such a delay is often unacceptable to patients and risks breaching time to treatment guidelines, so that it may be necessary to perform MRI sooner. In such cases (MRI examinations <10 weeks after biopsy), the dynamically enhanced sequences are often considerably degraded, and a limited scan using the T1, T2, and diffusion-weighted parts of the protocol should be considered. The group consensus was that such scans are “second best” for the detection and staging of tumour. They might be termed “limited staging scans”. ii) In patients in whom the detection of tumour on MRI is important, the scan should be performed before biopsy. A standard imaging protocol There was a consensus amongst the group on many aspects of the conduct of prostate MRI, which can be generalized to most machines with a field strength of 1.5 T or greater. They are minimum standards, which with additional techniques (3 T machines and endorectal coils) may be exceeded. i) A field strength of 1.5 T is adequate, although optimized images at 3 T are superior.36 ii) Most of the benefits of MRI can be achieved with a multichannel pelvic phased-array coil. Performance for both detection of tumour and staging will likely be improved by the addition of an endorectal coil,37 but the benefit for routine use does not necessarily outweigh the costs: patient discomfort, extra time for Please cite this article in press as: Kirkham APS, et al., Prostate MRI: Who, when, and how? Report from a UK consensus meeting, Clinical Radiology (2013), http://dx.doi.org/10.1016/j.crad.2013.03.030 4 A.P.S. Kirkham et al. / Clinical Radiology xxx (2013) 1e8 placement, and field inhomogeneity. The majority of those on the consensus panel did not use endorectal coils. iii) For routine clinical use before biopsy, all of the authors used T2-weighted, diffusion-weighted and dynamically enhanced sequences, and we term this combination “multiparametric”. The relative contribution of each remains to be determined accurately, but might be summarized as follows: T2 sequences show anatomy and detect most tumours, but are not specific, diffusion sequences are of particular utility in the transition zone,38 and enhanced sequences add specificity in both peripheral and transition zones, and sometimes detect tumours missed with other techniques.39 Minimum standards for resolution and timing have been well described in the recent ESUR guidelines,4 and are summarized here with little change (Table 1): e T2 sequences: #3 mm section thickness. In-plane resolution of 0.7 mm or better. External sphincter, prostate, and seminal vesicles included. On modern machines it should be possible to achieve adequate signal-to-noise ratios using these parameters with scan times for each sequence of <5 min. Axial and coronal sequences should always be included. Sagittal sequences are performed by the majority of the group and are encouraged. The ESUR guidelines state that axial images should be orthogonal to the rectum, but the majority of the consensus group obtain them in the true axial plane, and this is recommended for the purposes of repeatability and comparison between sequences. e Diffusion-weighted sequences should be acquired with at least three b-values for calculation of apparent diffusion coefficient (ADC), with highest b ¼ 1000 s/ mm2. In-plane resolution should be 1.5e2 mm (1.5 mm is usually attainable on modern machines), and section thickness of #5 mm. A dedicated long b sequence (1400 s/mm2 at 1.5 T, 2000 s/mm2 at 3 T) is strongly recommended, and is possible on most machines. It usually requires multiple averages for adequate signal (with a scan time of 4e6 min). e Contrast-enhanced sequences: pump injection at 3 ml/s, with a standard dose of contrast medium. The time taken for each scan should be 15 s or less, and in-plane resolution 1 mm or better. The ESUR guidelines suggest a minimum slice thickness of 4 mm, but the majority of the group use 3 mm. A total scan time of at least 5 min should be used for the detection of washout. Routine use of semi-quantitative (inspection of curves) or quantitative [calculation of pharmacodynamics parameters, such as the transfer coefficient (Ktrans)] are not necessary in routine practice, but the radiologist should have access to a workstation that can plot enhancement curves. The shape of the enhancement curve may be useful in some cases40; pharmacodynamic parameters (such as Ktrans) have shown potential in several studies but have not yet been shown to convincingly improve diagnostic performance in practice.41,42 Anti-peristaltic drugs [hyoscine butylbromide (Buscopan) or glucagon], although not essential, are recommended as per the ESUR guidelines.4 Post-treatment scans Although contrast-enhanced sequences are particularly important for detecting disease after radiotherapy,43 prostatectomy,44 or ablative techniques,45 diffusion-weighted sequences are also specific for tumour45 and T2-weighted sequences are always needed for anatomy. There is no need to modify the sequences used in the standard prostate MRI protocol. Additional sequences for staging scans Nodal involvement is rare in patients with PSA < 20,46 and the pelvic nodes are involved first in the great majority,47 so that routine scanning of abdominal nodes on a pre-biopsy MRI should be reserved for men with PSA > 20. The pelvic nodes are adequately imaged on the T2 coronal sequence of the pelvis, and large field of view T1 or T2 sequences are not necessary in routine practice if the PSA is < 20. The same is true of dedicated MRI bone imaging [usually a coronal short tau inversion recovery (STIR) sequence of pelvis and lower lumbar spine]: bone metastases are rare in men with a PSA < 10,48 and men with a positive diagnosis of cancer and PSA > 10 are likely to undergo isotope bone scintigraphy. The recent ESUR guidelines recommend a full staging MRI bone examination of the cervical, thoracic, and lumbar spine with T1, diffusion, and STIR sequences,4 but this is still an area of controversy, and is not performed by the majority of those on the consensus panel. The value of a single “prostate protocol” Table 1 Minimum standards for multiparametric magnetic resonance imaging using a pelvic phased-array coil at 1.5 T. Sequence Maximum section thickness (mm) Minimum in-plane resolution (mm) Scan time (range) T2 axial, coronal Diffusion e multi b Diffusion e long b Dynamic enhanced 3 5 5 3e4 0.7 2 2 1 3e6 min 4e7 min 4e6 min <15 s per iteration, total 5 min % % % % 0.7 2 2 1 The ESUR guidelines contain an algorithm for deciding on different protocols for prostate MRI. At the top is TRUS biopsy, and different protocols are then used at MRI depending on the biopsy results and intention to treat. All arms (no tumour, active surveillance, curative intent) end in an MRI of the prostate: in other words, an MRI is recommended in all patients who undergo biopsy. We have already described the potential benefits (in particular, the ability to target and the lack of artefact from haemorrhage) from performing the MRI before biopsy, and if pre-biopsy MRI is performed routinely, the MRI must be of a single protocol that is adequate for excluding significant tumour Please cite this article in press as: Kirkham APS, et al., Prostate MRI: Who, when, and how? Report from a UK consensus meeting, Clinical Radiology (2013), http://dx.doi.org/10.1016/j.crad.2013.03.030 A.P.S. Kirkham et al. / Clinical Radiology xxx (2013) 1e8 and staging it if detected. The other great virtue of a single protocol is simplicity. Spectroscopy and estimation of grade A well-conducted, multicentre study published in 2009 showed no benefit of using spectroscopy in addition to T2 sequences for the detection of tumour,49 and none of the group at the consensus meeting use it in routine clinical practice. Although much has been published on spectroscopy, a clear benefit has not yet been demonstrated to justify its drawbacks (the need for an endorectal coil at 1.5 T, the time for the scan, limited resolution, and the number of unusable voxels). There is little evidence that it adds significantly to the performance of the multiparametric scan we have described. There is evidence that the degree of metabolic abnormality on spectroscopy correlates with disease grade,50 although there is a similar correlation with ADC value51 and T2 signal intensity.52 In a recent study, spectroscopy differentiated high from low-grade tumours better than the ADC value,53 but the group opinion was that the estimation of tumour grade on MRI remains unreliable, and that this indication alone cannot justify its use. Reporting Grading systems The use of an ordinal scale to describe the radiologist’s suspicion of cancer is essential, and as in breast cancer54 a scale between 1 and 5 should be used: 1 ¼ tumour highly unlikely; 2 ¼ tumour unlikely; 3 ¼ equivocal; 4 ¼ tumour likely; and 5 ¼ tumour highly likely. The recent ESUR guidelines describes a scheme (prostate imaging, reporting, and data system, “PI-RADS”) for generating scores on each sequence based on semi-objective criteria, although they fall short of recommending that they be combined systematically into an overall score,4 and a recent study has validated the T2-weighted and diffusion (but not the dynamic contrast enhanced) components.55 The PI-RADS criteria may be useful for the radiologist in assessing each sequence, but what matters clinically is the final assessment of the likelihood of disease: the “overall impression” score. The unanimous opinion of the group was that MRI of the prostate should be reported to a level of significance; in particular, the radiologist’s overall impression of the likelihood of a tumour measuring >0.2 cm3 or Gleason 3 þ 4 or higher. Small, conspicuous tumours may initially be thought problematic with such a threshold, but are rarely so in practice: even if well below 0.2 cm3, conspicuous tumours have a good chance of containing a Gleason 4 component and will be scored as equivocal or greater.10,56 A score between 1 and 5 should be given for: (a) sectors of the prostate, divided into anatomical zones. There is not yet agreement on the optimum number of zones, though at least 12 are recommended (anterior and posterior, left and right, at base, mid gland and apex). Sixteen sectors may be the best balance between 5 detail and reporting burden, and such a scheme was described in the 2011 consensus.3 (b) Individual lesions, up to a maximum of three. Individual lesions should be drawn on a diagram of the prostate and each given a score for likelihood of tumour. (c) In cases where biopsy has been performed before MRI, scores of 1e5 should be given for staging parameters, as follows: (i) likelihood of involvement of bladder neck, seminal vesicles, rectum, neurovascular bundles, and external sphincter. (ii) In addition, a score should be given for the likelihood of extracapsular breach, but with an indication of whether there is visible extracapsular tumour (“direct” evidence of T3a disease, in which case the depth of extracapsular tumour should be given), or it is being inferred from “indirect” signs, such as bulge, extensive abutment, or loss of capsular definition.28 (iii) Seminal vesicle involvement should also be scored as “direct” or “indirect” evidence of involvement. The indirect signs, and the significance that should be attached to them in terms of a score of 1e5, are summarized in the ESUR guidelines.4 When the MRI is performed before biopsy, an attempt can be made to estimate the stage of the disease, but it should be emphasized that this is provisional: the radiologist should not definitively stage the disease without knowing the histology result, as the grade and size of tumour may affect the score. A revised report staging the disease should be given when the histology is known, or during discussion at an multidisciplinary team (MDT) meeting. Scans should always be reported with the clinical details, in particular, the patient’s age and PSA. Estimation of tumour size Although there are considerable errors in estimating the size of tumours at MRI,9 the tumour volume is an important factor in the estimation of clinical significance7,57 and correlates strongly with grade.58 An estimate by the radiologist of the volume of suspicious foci is important and can be performed using either a three-axis technique or planimetry; it should be given for at least the three largest visible lesions. This is not to say that further lesions should not be reported: they should be included in the diagram of the position of tumour, and in the text report. Where an estimation of volume is not possible, maximum tumour diameter correlates well with histological volume59 and is an alternative. Diagrams and scoring sheets Although in most cases the report of a prostate MRI will include a free-text element summarizing the findings, the sector scores and position of suspicious foci are much easier to convey by drawing on a diagram. The elements that should be included are summarized in Fig 1. We appreciate that it may be difficult to integrate such diagrammatic reporting into routine radiology practice and that in some centres reports will have to remain primarily text-based. In such cases, as a minimum, scores between 1 and 5 should be given for left and right lobes of the prostate, and for peripheral and transition zones. Please cite this article in press as: Kirkham APS, et al., Prostate MRI: Who, when, and how? Report from a UK consensus meeting, Clinical Radiology (2013), http://dx.doi.org/10.1016/j.crad.2013.03.030 6 A.P.S. Kirkham et al. / Clinical Radiology xxx (2013) 1e8 Figure 1 Components of a proposed scoring sheet. (a) Sixteen-sector diagram of the prostate (for tumour position), (b) 16-sector grid (for sector scoring), and (c) boxes (to be scored 1e5) for staging information and tumour volume. A practical scoring sheet would likely contain space for more demographic information and a free-text section. Minimum standards and training Like mammography, prostate MRI is challenging and requires considerable experience to reliably exclude and detect significant disease. We propose that those reporting prostate MRI should: (1) report at least 50 multiparametric scans per year; and (2) regularly attend a meeting at which the MRI and histology results are discussed. In many cases this will be part of a National Health Service (NHS) MDT meeting. The proposed scoring system simplifies audit, and all radiologists who regularly report pre-biopsy MRI of the prostate should be able to audit their performance using the results of prostate biopsy and histology at radical prostatectomy. In particular, they should be able to answer the following question: “what do your scores [between 1 and 5] mean for the likelihood of significant disease?” The group intends to set up several components that are hoped will contribute to standardized, high-quality performance of prostate MRI in the UK: (1) training courses; (2) sets of validated MRI images to enable radiologists to assess their diagnostic performance, and as a reference for the image quality that can be achieved when imaging parameters are optimized; and (3) a “sequence bank” of imaging parameters at 1.5 and 3 T for each of the manufacturers. Conclusions MRI of the prostate has the potential to fundamentally alter our approach to the investigation of men with a raised PSA, but only if performed well and reported by specialist radiologists. Most of the benefits can be achieved with a field strength of 1.5 T, a pelvic phased-array coil, and a multiparametric approach using T2-weighted, diffusionweighted, and contrast-enhanced sequences. Such machines are available at almost all UK NHS centres where prostate cancer is treated. Because MRI is useful in patients with no tumour, insignificant tumour, or disease requiring radical treatment, there is a strong case for its routine use before biopsy, which enables targeting of suspicious lesions and eliminates the problem of post-biopsy artefact. If it is necessary to perform staging scans after biopsy, a minimum period of 10 weeks is recommended to allow this artefact to settle, and scans performed before 10 weeks should be recognized as of limited resolution. 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