Prostate MRI: Who, when, and how? Report from a UK consensus meeting
2013; Elsevier BV; Volume: 68; Issue: 10 Linguagem: Inglês
10.1016/j.crad.2013.03.030
ISSN1365-229X
AutoresAlex Kirkham, Philip Haslam, Julian Keanie, Ian McCafferty, Anwar R. Padhani, Shonit Punwani, Jonathan Richenberg, Giles Rottenberg, Aslam Sohaib, Pauline Thompson, Lindsay W. Turnbull, Lutfi Kurban, Anju Sahdev, R. Clements, B. Carey, Clare Allen,
Tópico(s)Prostate Cancer Treatment and Research
ResumoThe 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. 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. IntroductionThe standard pathway for men suspected of having prostate cancer is resulting in over-diagnosis and over-treatment,1Ilic D. O'Connor D. Green S. et al.Screening for prostate cancer: an updated Cochrane systematic review.BJU International. 2011; 107: 882-891Crossref PubMed Scopus (144) Google Scholar as well as systematically missing significant tumours, particularly in the anterior and apical parts of the gland.2Ouzzane A. Puech P. Lemaitre L. et al.Combined multiparametric MRI and targeted biopsies improve anterior prostate cancer detection, staging, and grading.Urology. 2011; 78: 1356-1362Abstract Full Text Full Text PDF PubMed Scopus (116) Google Scholar 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 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 20103Dickinson L. Ahmed H.U. Allen C. et al.Magnetic resonance imaging for the detection, localisation, and characterisation of prostate cancer: recommendations from a European consensus meeting.Eur Urol. 2011; 59: 477-494Abstract Full Text Full Text PDF PubMed Scopus (589) Google Scholar and the second the European Society of Uroradiology consensus document on prostate MRI published in 2012.4Barentsz J.O. Richenberg J. Clements R. et al.ESUR prostate MR guidelines 2012.Eur Radiol. 2012; 22: 746-757Crossref PubMed Scopus (1830) Google ScholarOur 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.MethodsUroradiologists 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,3Dickinson L. Ahmed H.U. Allen C. et al.Magnetic resonance imaging for the detection, localisation, and characterisation of prostate cancer: recommendations from a European consensus meeting.Eur Urol. 2011; 59: 477-494Abstract Full Text Full Text PDF PubMed Scopus (589) Google Scholar 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.FindingsIndicationsThe 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 cancerBefore 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.5Parker C. Muston D. Melia J. et al.A model of the natural history of screen-detected prostate cancer, and the effect of radical treatment on overall survival.Br J Cancer. 2006; 94: 1361-1368Crossref PubMed Scopus (118) Google Scholar This is currently a matter of great debate amongst urologists. It is likely that Gleason 3 + 3 cancer very rarely results in death from prostate cancer,5Parker C. Muston D. Melia J. et al.A model of the natural history of screen-detected prostate cancer, and the effect of radical treatment on overall survival.Br J Cancer. 2006; 94: 1361-1368Crossref PubMed Scopus (118) Google Scholar, 6Ahmed H.U. Arya M. Freeman A. et al.Do low-grade and low-volume prostate cancers bear the hallmarks of malignancy?.Lancet Oncol. 2012; 13: e509-e517Abstract Full Text Full Text PDF PubMed Scopus (130) Google Scholar and that the great majority of tumours <0.5 cm3 will, similarly, be insignificant.7Wolters T. Roobol M.J. van Leeuwen P.J. et al.A critical analysis of the tumor volume threshold for clinically insignificant prostate cancer using a data set of a randomized screening trial.J Urol. 2011; 185: 121-125Abstract Full Text Full Text PDF PubMed Scopus (225) Google Scholar 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 + 3 and <0.5 cm3 for insignificant cancer is too conservative.8Wilt T.J. Brawer M.K. Jones K.M. et al.Radical prostatectomy versus observation for localized prostate cancer.New Engl J Med. 2012; 367: 203-213Crossref PubMed Scopus (1438) Google ScholarOne of the key performance characteristics of prostate MRI is that it misses the majority of small ( 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 + 3 or above−0.5 cm3 (equivalent to a 10 mm sphere) of Gleason 3 + 4 or aboveFor Gleason 3 + 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 + 3 disease will usually be detected, those with a more diffuse pattern and loose stroma on histology often will not.10Rosenkrantz A.B. Mendrinos S. Babb J.S. et al.Prostate cancer foci detected on multiparametric magnetic resonance imaging are histologically distinct from those not detected.J Urol. 2012; 187: 2032-2038Abstract Full Text Full Text PDF PubMed Scopus (90) Google ScholarThese 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.9Puech P. Potiron E. Lemaitre L. et al.Dynamic contrast-enhanced-magnetic resonance imaging evaluation of intraprostatic prostate cancer: correlation with radical prostatectomy specimens.Urology. 2009; 74: 1094-1099Abstract Full Text Full Text PDF PubMed Scopus (185) Google Scholar, 11Villers A. Puech P. Mouton D. et al.Dynamic contrast enhanced, pelvic phased array magnetic resonance imaging of localized prostate cancer for predicting tumor volume: correlation with radical prostatectomy findings.J Urol. 2006; 176: 2432-2437Abstract Full Text Full Text PDF PubMed Scopus (322) Google Scholar, 12Tanimoto A. Nakashima J. Kohno H. et al.Prostate cancer screening: the clinical value of diffusion-weighted imaging and dynamic MR imaging in combination with T2-weighted imaging.J Magn Reson Imaging. 2007; 25: 146-152Crossref PubMed Scopus (303) Google Scholar, 13Villeirs G.M. De Meerleer G.O. De Visschere P.J. et al.Combined magnetic resonance imaging and spectroscopy in the assessment of high grade prostate carcinoma in patients with elevated PSA: a single-institution experience of 356 patients.Eur J Radiol. 2011; 77: 340-345Abstract Full Text Full Text PDF PubMed Scopus (96) Google Scholar, 14Girouin N. Mège-Lechevallier F. Tonina Senes A. et al.Prostate dynamic contrast-enhanced MRI with simple visual diagnostic criteria: is it reasonable?.Eur Radiol. 2007; 17: 1498-1509Crossref PubMed Scopus (139) Google Scholar 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 biopsy15Wefer A.E. Hricak H. Vigneron D.B. et al.Sextant localization of prostate cancer: comparison of sextant biopsy, magnetic resonance imaging and magnetic resonance spectroscopic imaging with step section histology.J Urol. 2000; 164: 400-404Abstract Full Text Full Text PDF PubMed Scopus (320) Google Scholar, 16Ahmed H.U. Kirkham A. Arya M. et al.Is it time to consider a role for MRI before prostate biopsy?.Nat Rev Clin Oncol. 2009; 6: 197-206Crossref PubMed Scopus (268) Google Scholar [modelling studies suggest that 36–47% of lesions >0.5 cm3 may be missed by a 12 core transrectal approach,17Lecornet E. Ahmed H.U. Hu Y. et al.The accuracy of different biopsy strategies for the detection of clinically important prostate cancer: a computer simulation.J Urol. 2012; 188: 974-980Abstract Full Text Full Text PDF PubMed Scopus (77) Google Scholar and another study showed a detection rate at transrectal ultrasound (TRUS) of 75% for significant disease18Rocco B. de Cobelli O. Leon M.E. et al.Sensitivity and detection rate of a 12-core trans-perineal prostate biopsy: preliminary report.Eur Urol. 2006; 49: 827-833Abstract Full Text Full Text PDF PubMed Scopus (35) Google Scholar]. 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 anteriorly19Hambrock T. Somford D.M. Hoeks C. et al.Magnetic resonance imaging guided prostate biopsy in men with repeat negative biopsies and increased prostate specific antigen.J Urol. 2010; 183: 520-527Abstract Full Text Full Text PDF PubMed Scopus (316) Google Scholar) 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.20Haffner J. Lemaitre L. Puech P. et al.Role of magnetic resonance imaging before initial biopsy: comparison of magnetic resonance imaging-targeted and systematic biopsy for significant prostate cancer detection.BJU Int. 2011; 108: E171-E178Crossref PubMed Scopus (328) Google Scholar 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 significantly reducing the number of tumours upgraded at definitive histology.20Haffner J. Lemaitre L. Puech P. et al.Role of magnetic resonance imaging before initial biopsy: comparison of magnetic resonance imaging-targeted and systematic biopsy for significant prostate cancer detection.BJU Int. 2011; 108: E171-E178Crossref PubMed Scopus (328) Google Scholar, 21Hambrock T. Hoeks C. Hulsbergen-van de Kaa C. et al.Prospective assessment of prostate cancer aggressiveness using 3-T diffusion-weighted magnetic resonance imaging-guided biopsies versus a systematic 10-core transrectal ultrasound prostate biopsy cohort.Eur Urol. 2012; 61: 177-184Abstract Full Text Full Text PDF PubMed Scopus (259) Google Scholar, 22Moore C.M. Robertson N.L. Arsanious N. et al.Image-guided prostate biopsy using magnetic resonance imaging-derived targets: a systematic review.Eur Urol. 2013; 63: 125-140Abstract Full Text Full Text PDF PubMed Scopus (435) Google Scholariii)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%.19Hambrock T. Somford D.M. Hoeks C. et al.Magnetic resonance imaging guided prostate biopsy in men with repeat negative biopsies and increased prostate specific antigen.J Urol. 2010; 183: 520-527Abstract Full Text Full Text PDF PubMed Scopus (316) Google Scholar, 23Lawrentschuk N. Fleshner N. The role of magnetic resonance imaging in targeting prostate cancer in patients with previous negative biopsies and elevated prostate-specific antigen levels.BJU Int. 2009; 103: 730-733Crossref PubMed Scopus (97) Google Scholar 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 low-grade tumours found at TRUS biopsy is common at more definitive histology24Margel D. Yap S.A. Lawrentschuk N. et al.Impact of multiparametric endorectal coil prostate magnetic resonance imaging on disease reclassification among active surveillance candidates: a prospective cohort study.J Urol. 2012; 187: 1247-1252Abstract Full Text Full Text PDF PubMed Scopus (147) Google Scholar and is more common when a lesion is conspicuous on MRI.25Vargas H.A. Akin O. Afaq A. et al.Magnetic resonance imaging for predicting prostate biopsy findings in patients considered for active surveillance of clinically low risk prostate cancer.J Urol. 2012; 188: 1732-1738Abstract Full Text Full Text PDF PubMed Scopus (186) Google Scholar, 26Borofsky M.S. Rosenkrantz A.B. Abraham N. et al.Does suspicion of prostate cancer on integrated T2 and diffusion-weighted MRI predict more adverse pathology on radical prostatectomy?.Urology. 2013 Feb 7; (pii: S0090-4295(12)01570-1)https://doi.org/10.1016/j.urology.2012.12.026Abstract Full Text Full Text PDF Scopus (28) Google Scholar 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 cancerStaging aims to determine whether tumour is organ-confined, 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,27Prostate cancer: diagnosis and treatment. National Institute for Health and Clinical Excellence, London2008http://www.nice.org.uk/cg58Google Scholar 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.27Prostate cancer: diagnosis and treatment. National Institute for Health and Clinical Excellence, London2008http://www.nice.org.uk/cg58Google ScholarThe NICE guidelines are 4 years old (new guidance is due in January 2014), and before recent data on the value of targeted biopsies.17Lecornet E. Ahmed H.U. Hu Y. et al.The accuracy of different biopsy strategies for the detection of clinically important prostate cancer: a computer simulation.J Urol. 2012; 188: 974-980Abstract Full Text Full Text PDF PubMed Scopus (77) Google Scholar, 22Moore C.M. Robertson N.L. Arsanious N. et al.Image-guided prostate biopsy using magnetic resonance imaging-derived targets: a systematic review.Eur Urol. 2013; 63: 125-140Abstract Full Text Full Text PDF PubMed Scopus (435) Google Scholar 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,4Barentsz J.O. Richenberg J. Clements R. et al.ESUR prostate MR guidelines 2012.Eur Radiol. 2012; 22: 746-757Crossref PubMed Scopus (1830) Google Scholar 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,28Wang L. Hricak H. Kattan M.W. et al.Prediction of organ-confined prostate cancer: incremental value of MR imaging and MR spectroscopic imaging to staging nomograms.Radiology. 2006; 238: 597-603Crossref PubMed Scopus (218) Google Scholar and there are morphological predictors of both seminal vesicle (T3b)29Wang L. Hricak H. Kattan M.W. et al.Prediction of seminal vesicle invasion in prostate cancer: incremental value of adding endorectal MR imaging to the Kattan nomogram.Radiology. 2007; 242: 182-188Crossref PubMed Scopus (112) Google Scholar and extracapsular (T3a) spread,28Wang L. Hricak H. Kattan M.W. et al.Prediction of organ-confined prostate cancer: incremental value of MR imaging and MR spectroscopic imaging to staging nomograms.Radiology. 2006; 238: 597-603Crossref PubMed Scopus (218) Google Scholar 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 67–91%, and specificity 67–100%.30Hoeks C.M. Barentsz J.O. Hambrock T. et al.Prostate cancer: multiparametric MR imaging for detection, localization, and staging.Radiology. 2011; 261: 46-66Crossref PubMed Scopus (533) Google Scholar, 31Cornud F. Rouanne M. Beuvon F. et al.Endorectal 3D T2-weighted 1mm-slice thickness MRI for prostate cancer staging at 1.5 Tesla: should we reconsider the indirects signs of extracapsular extension according to the D'Amico tumor risk criteria?.Eur J Radiol. 2012; 81: e591-e597Abstract Full Text Full Text PDF PubMed Scopus (49) Google ScholarOverall, in the opinion of the group, MRI is useful (1) when biopsies are negative (to exclude anterior disease missed by a standard biopsy approach19Hambrock T. Somford D.M. Hoeks C. et al.Magnetic resonance imaging guided prostate biopsy in men with repeat negative biopsies and increased prostate specific antigen.J Urol. 2010; 183: 520-527Abstract Full Text Full Text PDF PubMed Scopus (316) Google Scholar); (2) in active surveillance where underestimation of size and grade is common21Hambrock T. Hoeks C. Hulsbergen-van de Kaa C. et al.Prospective assessment of prostate cancer aggressiveness using 3-T diffusion-weighted magnetic resonance imaging-guided biopsies versus a systematic 10-core transrectal ultrasound prostate biopsy cohort.Eur Urol. 2012; 61: 177-184Abstract Full Text Full Text PDF PubMed Scopus (259) Google Scholar, 32Duffield A.S. Lee T.K. Miyamoto H. et al.Radical prostatectomy findings in patients in whom active surveillance of prostate cancer fails.J Urol. 2009; 182: 2274-2278Abstract Full Text Full Text PDF PubMed Scopus (130) Google Scholar and MRI can detect larger or higher-grade tumours25Vargas H.A. Akin O. Afaq A. et al.Magnetic resonance imaging for predicting prostate biopsy findings in patients considered for active surveillance of clinically low risk prostate cancer.J Urol. 2012; 188: 1732-1738Abstract Full Text Full Text PDF PubMed Scopus (186) Google Scholar, 26Borofsky M.S. Rosenkrantz A.B. Abraham N. et al.Does suspicion of prostate cancer on integrated T2 and diffusion-weighted MRI predict more adverse pathology on radical prostatectomy?.Urology. 2013 Feb 7; (pii: S0090-4295(12)01570-1)https://doi.org/10.1016/j.urology.2012.12.026Abstract Full Text Full Text PDF Scopus (28) Google Scholar; and (3) to stage disease in men being considered for radical treatment.4Barentsz J.O. Richenberg J. Clements R. et al.ESUR prostate MR guidelines 2012.Eur Radiol. 2012; 22: 746-757Crossref PubMed Scopus (1830) Google Scholar, 27Prostate cancer: diagnosis and treatment. National Institute for Health and Clinical Excellence, London2008http://www.nice.org.uk/cg58Google Scholar 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 scanPost-biopsy artefactIt 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,33Qayyum A. Coakley F.V. Lu Y. et al.Organ-confined prostate cancer: effect of prior transrectal biopsy on endorectal MRI and MR spectroscopic imaging.AJR Am J Roentgenol. 2004; 183: 1079-1083Crossref PubMed Scopus (147) Google Scholar, 34Tamada T. Sone T. Jo Y. et al.Prostate cancer: relationships between postbiopsy hemorrhage and tumor detectability at MR diagnosis.Radiology. 2008; 248: 531-539Crossref PubMed Scopus (127) Google Scholar 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.35White S. Hricak H. Forstner R. et al.Prostate cancer: effect of postbiopsy hemorrhage on interpretation of MR images.Radiology. 1995; 195: 385-390PubMed Google Scholar 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 2–3 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 protocolThere 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.36Cornfeld D. Weinreb J. MR imaging of the prostate: 1.5 T versus 3 T.Magn Reson Imaging Clin N Am. 2007 Aug 1; 15: 433-448Abstract Full Text Full Text PDF PubMed Scopus (28) Google Scholarii)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,37Heijmink S.W.T.P.J. Fütterer J.J. Hambrock T. et al.Prostate cancer: body-array versus endorectal coil MR imaging at 3 T—comparison of image quality, localization, and staging performance.Radiology. 2007; 244: 184-195Crossref PubMed Scopus (263) Google Scholar but the benefit for routine use does not necessarily outweigh the costs: patient discomfort, extra time for 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,38Park B.K. Lee H.M. Kim C.K. et al.Lesion localization in patients with a previous negative transrectal ultrasound biopsy and persistently elevated prostate specific antigen level using diffusion-weighted imaging at three Tesla before rebiopsy.Invest Radiol. 2008; 43: 789-793Crossref PubMed Scopus (77) Google Scholar and enhanced sequences add specificity in both peripheral and transition zones, and sometimes detect tumours missed with other techniques.39Iwazawa J. Mitani T. Sassa S. et al.Prostate cancer detection with magnetic resonance imaging: is dynamic contrast-enhanced imaging necessary in addition to diffusion-weighted imaging?.Diagn Interv Radiol. 2011; 17: 243-248PubMed Google ScholarMinimum standards for resolution and timing have been well described in the recent ESUR guidelines,4Barentsz J.O. Richenberg J. Clements R. et al.ESUR prostate MR guidelines 2012.Eur Radiol. 2012; 22: 746-757Crossref PubMed Scopus (1830) Google Scholar and are summarized here with little change (Table 1):–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.–Diffusion-weighted sequences should be acquired with at least three b-values for calculation of apparent diffusion coefficient (ADC), with highest b = 1000 s/mm2. In-plane resolution should be 1.5–2 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 4–6 min).–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
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