MR Imaging of the Prostate: 1.5T versus 3T

https://doi.org/10.1016/j.mric.2007.06.004Get rights and content

Over the past several years, evidence supporting the use of MR imaging in the evaluation of prostate cancer has grown. Almost all this work has been performed at 1.5T. The gradual introduction of 3T scanners into clinical practice provides a potential opportunity to improve the quality and usefulness of prostate imaging. Increased signal to noise allows for imaging at higher resolution, higher temporal resolution, or higher bandwidth. Although this may improve the quality of conventional T2-weighted prostate imaging, which has been the standard sequence for detecting and localizing prostate cancer for years, the real potential for improvement at 3T involves more advanced techniques, such as spectroscopy, diffusion-weighted imaging, dynamic contrast imaging, and susceptibility imaging. This review presents the current data on 3T MR imaging of the prostate as well as the authors' impressions based on their experience at Yale–New Haven Hospital.

Section snippets

Current role of MR imaging and magnetic resonance spectroscopic imaging in the evaluation of prostate cancer

Once prostate cancer is diagnosed by biopsy, it is important to determine whether the cancer has spread beyond the prostate capsule or metastasized, because prognosis and treatment options differ between organ-confined and locally advanced disease (TMN stage II versus stage III and Jewett-Whitmore stage B versus stage C). Organ-confined disease or cancer with minimal ECE may be treated with radical prostatectomy, ablation therapies, brachytherapy, or watchful waiting. Once the cancer has spread

Evolving role of MR imaging and magnetic resonance spectroscopic imaging in the evaluation of prostate cancer

In response to evolving therapies for treatment of prostate cancer that are tailored for individual patients and tumors, much research is focused on using various MR imaging techniques not just for determination of ECE but for noninvasive assessment of tumor size, location, and grade [12], [13], [14]. For example, size of tumor affects radiation dose, and location of tumor is important for disease-targeted therapy. In one trial, localization of tumor by means of MR imaging altered radiotherapy

3T prostate imaging protocol

Before imaging, an endorectal coil (ERC) is inserted into the rectum (Medrad, Indianola, Pennsylvania) (Fig. 1). An adapter connects the ERC with an eight-element torso phased-array coil, and the two coils are used in conjunction.

At 1.5T, there is consensus that an ERC, usually in combination with a torso phased-array coil, is advantageous for prostate imaging compared with a torso coil alone [27], [28]. There has been some discussion about the necessity for an ERC for prostate imaging at 3T.

Coil positioning

Patients are imaged supine. Proper ERC placement involves positioning and taking steps to keep the coil from moving during the examination (see Fig. 1). When the coil moves or is in the wrong position, overall image quality is poor. The flat end of the coil is positioned flush against the posterior aspect of the prostate, centered on the prostate in the craniocaudad direction. Positioning is easily checked on the localizer images. If the coil needs to be repositioned, it should be completely

Imaging protocol

A basic prostate protocol contains axial T1W and multiplanar T2W images. MRSI, DWI, and DCE are added depending on the availability of technology and ability. The authors routinely perform DWI and DCE but do not currently have the software to perform spectroscopy at 3T.

T1-weighted imaging and T2-weighted imaging

High-resolution oblique axial and oblique coronal fast spin echo (FSE) T2W images are obtained through the prostate and seminal vesicles to evaluate for neoplasm and ECE. Some advocate also obtaining sagittal T2W images. Small field-of-view (FOV) axial FSE T1W images are acquired through the prostate to evaluate for postbiopsy hemorrhage, periprostatic nodes, and ECE. Some institutions alternatively obtain large FOV FSE T1W images through the entire pelvis to evaluate for adenopathy. Because

Magnetic resonance spectroscopic imaging

Increased magnetic field strength provides two powerful advantages for MRSI. First, the increased SNR allows smaller voxel size. MRSI voxel size at 1.5T is approximately 0.30 cm3, and it is 0.15 cm3 at 3T [40]. This reduces volume averaging effects with periprostatic fat, postbiopsy hemorrhage, seminal vesicles, BPH nodules, and periurethral tissues.

Second, separation and height of the metabolite peaks is increased at 3T. Normal prostate tissue is characterized by a high citrate-to-choline

Diffusion weighted imaging

DWI measures the Brownian motion of free water. Diffusion is decreased in areas of increased cellularity and in areas of cellular edema secondary to the loss of ATP-dependent sodium-potassium pumps. Both conditions are believed to be present within neoplasms. The authors' experience is that increased SNR at 3T improves the quality of DWI. The combination of increased field strength and an ERC allows for high-resolution DWI, which is an intrinsically low SNR technique.

Studies at 1.5T have shown

Dynamic contrast enhancement MR imaging

DCE MR imaging techniques differentiate tumor from normal tissue by evaluating the kinetics of enhancement and de-enhancement. Enhancement depends on blood supply (large feeding vessels and local microvessel density) and capillary permeability. Increased blood supply and capillary permeability allow for increased enhancement. De-enhancement, or washout, depends on capillary permeability and the size of the local extravascular/extracellular space (ie, the space outside the vessels and cells).

T2 mapping

A final technique, but one with limited support in the current literature, is T2 mapping. A multiecho gradient echo sequence is used to obtain images at multiple values of TE. Pixel-by-pixel signal intensities plotted as a function of TE are fit to an exponential decay to create a pixel map of T2. In one study of eight patients with biopsy-proven prostate cancer, the T2 maps identified 17 of 18 tumors compared with 13 of 18 tumors identified by T2W imaging. Two central gland tumors were only

Magnetic resonance lymphography

Imaging with ultrasmall iron oxide particles, such as Ferumoxtran-10, is also a T2 technique. Ferumoxtran-10 is injected intravenously 24 to 36 hours before imaging and accumulates in normal lymph nodes. Normal nodes appear dark on T2 images secondary to susceptibility from the iron particles. Nodes infiltrated with tumor do not accumulate the iron particles and remain bright on these images. Pathologic nodes as small as 5 mm can be detected with standard sequences at 1.5T [80]. Initial

Summary

Many new techniques in prostate MR imaging are under development and refinement. Most of these techniques should benefit from the increased SNR and other features at 3T. Conventional T2W imaging can be obtained at increased spatial resolution. DWI benefits from increased signal to noise. The ability to image at increased bandwith and partial excitations without sacrificing SNR allows DCE MR imaging to be performed at higher temporal resolution. Alternatively, DCE can be performed at higher

References (81)

  • H. Hricak et al.

    Anatomy and pathology of the male pelvis by magnetic resonance imaging

    AJR Am J Roentgenol

    (1983)
  • E. Buonocore et al.

    Clinical and in vitro magnetic resonance imaging of prostatic carcinoma

    AJR Am J Roentgenol

    (1984)
  • L. Wang et al.

    Prostate cancer: incremental value of endorectal MR imaging findings for prediction of extracapsular extension

    Radiology

    (2004)
  • K. Yu et al.

    Detection of extracapsular extension of prostate carcinoma with endorectal and phased-array coil MR imaging: multivariate feature analysis

    Radiology

    (1997)
  • K. Yu et al.

    Prostate cancer: prediction of extracapsular extension with endorectal MR imaging and three-dimensional proton MR spectroscopic imaging

    Radiology

    (1999)
  • J. Zhang et al.

    Endorectal MR imaging and proton spectroscopy for preoperative evaluation of clinical T1c prostate cancer

    Proceedings of the International Society of Magnetic Resonance in Medicine

    (2007)
  • H. Hricak et al.

    The role of preoperative endorectal magnetic resonance imaging in the decision regarding whether to preserve or resect neurovascular bundles during radical retropubic prostatectomy

    Cancer

    (2004)
  • J. Futterer et al.

    Staging prostate cancer with dynamic contrast-enhanced endorectal MR imaging prior to radical prostatectomy: experienced versus less experienced readers

    Radiology

    (2005)
  • J. Scheidler et al.

    Prostate cancer: localization with three dimensional proton MR spectroscopic imaging—clinicopathologic study

    Radiology

    (1999)
  • J. Futterer et al.

    Prostate cancer localization with dynamic contrast-enhanced MR imaging and proton MR spectroscopic imaging

    Radiology

    (2006)
  • S. Reinsberg et al.

    Combined use of diffusion-weighted MRI and H MR spectroscopy to increase accuracy in prostate cancer detection

    AJR Am J Roentgenol

    (2007)
  • N. Costouros et al.

    Diagnosis of prostate cancer in patients with an elevated prostate-specific antigen level: role of endorectal MRI and MR spectroscopic imaging

    Am J Roentgenol

    (2007)
  • S. Ansellem-Ouazana et al.

    Negative prostatic biopsies in patients with a high risk of prostate cancer. Is the combination of endorectal MRI and magnetic resonance spectroscopy imaging a useful tool? A preliminary study

    Eur Urol

    (2005)
  • B. Taouli et al.

    Role of 3D 1H MR spectroscopy for prospective detection of prostate cancer in men with prior negative biopsies

    Proceedings of the International Society of Magnetic Resonance in Medicine

    (2007)
  • O. Akin et al.

    Transition zone prostate cancers: features, detection, localization, and staging at endorectal MR imaging

    Radiology

    (2006)
  • H. Li et al.

    Conventional MRI capabilities in the diagnosis of prostate cancer in the transition zone

    AJR Am J Roentgenol

    (2006)
  • K. Zakian et al.

    Transition zone prostate cancer: metabolic characteristics at H MR spectroscopic imaging—initial results

    Radiology

    (2003)
  • E. Sala et al.

    Endorectal MR imaging before salvage prostatectomy: tumor localization and staging

    Radiology

    (2006)
  • F. Coakley et al.

    Endorectal MR imaging and MR spectroscopic imaging for locally recurrent prostate cancer after external beam radiation therapy: preliminary experience

    Radiology

    (2004)
  • D. Pucar et al.

    Prostate cancer: correlation of MRI imaging and MR spectroscopy with pathologic findings after radiation therapy—initial experience

    Radiology

    (2005)
  • H. Hricak et al.

    Carcinoma of the prostate gland with pelvic phased array coils versus integrated endorectal-pelvic phased array-coils

    Radiology

    (1994)
  • M. Engelbrecht et al.

    Local staging of prostate cancer using magnetic resonance imaging: a meta-analysis

    Eur Radiol

    (2002)
  • P. Torricelli et al.

    Comparative evaluation between external phased array coil at 3T and endorectal coil at 1.5T

    J Comput Assist Tomogr

    (2006)
  • D. Beyersdorff et al.

    MRI of prostate cancer at 1.5 and 3T: comparison of image quality in tumor detection and staging

    AJR Am J Roentgenol

    (2005)
  • S. Heijmink et al.

    A comparison of image quality and prostate cancer localization and staging performance between body array coil and endorectal coil MR imaging at 3T

    Proceedings of the International Society of Magnetic Resonance in Medicine

    (2006)
  • J. Futterer et al.

    Initial experience of 3 tesla endorectal coil magnetic resonance imaging and H-spectroscopic imaging of the prostate

    Invest Yadiol

    (2004)
  • S. Heijmink et al.

    Prostate cancer: body-array versus endorectal coil MR imaging at 3T-comparison of image quality, localization, and staging performance

    Radiology

    (2007)
  • Y. Rosen et al.

    3T MR of the prostate: reducing susceptibility gradients by inflating the endorectal coil with a barium sulfate suspension

    Magn Reson Med

    (2007)
  • Choi H, Ma J. Use of perfluorocarbon (PFC) in magnetic resonance spectroscopy (MRS) of the prostate: a method to...
  • A. Prando et al.

    Prostatic biopsy directed with endorectal MR spectroscopic imaging findings in patients with elevated prostate specific antigen levels and prior negative biopsy findings: early experience

    Radiology

    (2005)
  • Cited by (28)

    • Assessment of the accuracy of multi-parametric MRI with PI-RADS 2.0 scoring system in the discrimination of suspicious prostatic focal lesions

      2016, Egyptian Journal of Radiology and Nuclear Medicine
      Citation Excerpt :

      Prostate cancer is the 3rd leading cause of death and is the most common genitourinary malignancy in men (1).

    • Advanced Magnetic Resonance Techniques: 3 T

      2015, Radiologic Clinics of North America
    • Prostate MRI: Who, when, and how? Report from a UK consensus meeting

      2013, Clinical Radiology
      Citation Excerpt :

      They are minimum standards, which with additional techniques (3 T machines and endorectal coils) may be exceeded. A field strength of 1.5 T is adequate, although optimized images at 3 T are superior.36 Most of the benefits of MRI can be achieved with a multichannel pelvic phased-array coil.

    • Multiparametric Magnetic Resonance Imaging of the Prostate

      2013, Magnetic Resonance Imaging Clinics of North America
      Citation Excerpt :

      The European Consensus on MRI for the Detection, Localization, and Characterization of Prostate Cancer decided that imaging should be performed at 3.0 T to reach an optimum level of detection but there was no consensus as to whether an endorectal coil should be part of the requirements for optimum imaging.17 Currently, the best signal-to-noise ratio and spatial resolution for the evaluation of the prostate can be obtained with a combination of 3.0 T and an endorectal coil.57–59 Current practices for prostate MR imaging differ between Europe and the United States; endorectal coils are used more frequently in the United States.17

    • Pelvic applications of diffusion magnetic resonance images

      2011, Magnetic Resonance Imaging Clinics of North America
      Citation Excerpt :

      Advances in MR imaging and computing technology have resulted in the ability to detect disease within the male pelvis with a high degree of accuracy. Specifically, the use of endorectal coils and pelvic phased-array coils coupled with 3-T magnetic fields has resulted in improved signal-to-noise as well as improved spatial, temporal, and spectral resolution in the evaluation of the prostate gland for malignancy.57–59 Further improvement in diagnostic accuracy in the detection of malignancy within the prostate gland can be achieved with the addition of DWI (Fig. 16).60

    View all citing articles on Scopus
    View full text