By: Dan Sperling, MD

Author’s note: Magnetic resonance imaging (MRI) is based on physics. Explaining how MRI stimulates and captures signals from hydrogen nuclei in the body, then translates them into images on a computer monitor, is complicated. It involves both a magnetic field and radio frequency waves. If you have an extra 10 minutes or so, there is a fun and user-friendly website at http://www.howequipmentworks.com/mri_basics/ that can easily acquaint you with an understanding that sets the context for this article.

The majority of MRI scans use 2 dimensional (2D) images captured as of “slices” of the part of the body being scanned. According to MRI technician John Gentile, 2D MRI is “a sequence in which a slice (or set of slices) is excited and read at different times throughout the total scan. You may have little-to-no slice gap, but you run the risk of getting less quality due to crosstalk between the slices.” 3D MRI captures volumetric images because all the signals are collected from a whole entity within the body, giving a higher signal to noise ratio (SNR) which makes the ultimate images sharper due to the diminished background noise being picked up from the body.[i] Because a block of tissue is scanned, the resulting images are called isovolumetric or isotropic, which means that three different imaging orientations (axial, coronal and sagittal sections) are equal in terms of spatial resolution. This eliminates “partial volume averaging errors due to the slice thickness.”[ii] According to Mr. Gentile, acquiring isovolumetric thin slices with high spatial resolution “allows you to post-process and reconstruct the images in other planes without distortion. That way you can run one volume scan of a particular area and reconstruct the other planes without having to take the time to acquire them conventionally. Time saver. The real question is:  is a 3D T1 weighted scan sufficient by itself to give you a confident diagnosis?” Good question.

A new European research team tested the ability of 3D T1 weighted MRI to detect metastatic prostate cancer[iii] (prostate cancer that has spread beyond the gland, either locally, regionally, or distantly). The study involved 30 prostate cancer patients who were at high risk for metastases based on their clinical factors. All patients underwent a standard MRI screening protocol for lymph node and/or bone lesions; the protocol utilized 2D whole-body T1 weighted MRI, sagittal proton-density fat-saturated imaging of the spine, and whole-body diffusion weighted MRI. In addition. All patients had a whole-body 3D T1 weighted scan.

Two observers, independent of each other and blinded to patient information, each read the 2D and 3D images separately and in random order. The agreement between their assessments, and diagnostic performance of each sequence were assessed per patient and per lesion.

Based on the results, the authors reported that the SNR and contrast-to-noise ratio (CNR) were significantly higher with whole-body 3D T1 weighted imaging than with 2D imaging “regardless of the reference region (bone or fat) and lesion location (bone or node). The 3D imaging offered better diagnostic performance “regardless of the reference region (bone or fat) and lesion location.” For node metastasis, diagnostic performance was higher, as was sensitivity. They concluded that whole-body 3D T1 weighted imaging is not only feasible, but also gives “a diagnostic performance that is as good or better for the detection of bone metastases and better for the detection of lymph node metastases.” Thus, it is valuable for physicians working with prostate cancer patients to obtain the information offered by 3D T1 weighted MRI, a non-invasive and accurate technology that can assist in tailoring treatment to the patient’s needs, especially if there is risk of cancer spread.

Special thanks to John Gentile, Dr. Sperling’s MRI technician, for the excellent patient care he provides. Mr. Gentile adds reassurance that 3D MRI is strategically used by the Sperling Prostate Center: “The imaging that we run are all 2D scans except for the DCE [dynamic contrast enhanced MRI] which is a 3D T1 weighted scan.”

[i] http://www.mr-tip.com/serv1.php?type=db1&dbs=3D%20isotropic%20MRI

[ii] http://www.fujita-hu.ac.jp/~kkatada/clinical%20folder/Aq_clin_03.html

[iii] Pasoglou V, Michoux N, Peeters F et al. Whole-Body 3D T1-weighted MR Imaging in Patients with Prostate Cancer: Feasibility and Evaluation in Screening for Metastatic Disease. Radiology. 2014 Dec 15:141242. [Epub ahead of print]