The next multiparametric MRI case of the prostate is important in consideration of image quality and our ability to recognize fact from artifact. This patient is a 67-year-old male who'd had a negative transrectal ultrasound-guided biopsy a few months before the MRI, but his PSA started to elevate and grew to 3.2. Because of the elevation of the PSA, a multiparametric MRI was ordered, which is demonstrated here, to make sure that the patient didn't have an underlying prostate cancer. The reason for showing the case is shown here on the T2 weighted sagittal images. First of all, we see that the patient does have evidence of benign prostatic hyperplasia. There's nodular enlargement within the transition zone that's inhomogeneous, and we see that there is associated median lobe hypertrophy that's protruding up into the urinary bladder lumen. Here's the median lobe hypertrophy. This actually has a pretty high correlation with obstructive symptoms due to the BPH.
Now, the reason for showing this case is this little artifact that we see. You see here, there's a little inflection zone artifact. It's dark here centrally and bright on the rim, and we see another area right here, dark with a bright signal intensity rim. If we go to the T2 weighted axial images, same thing, within the transition zone, we see a low signal intensity area with a bright signal rim. Now it turns out this artifact is actually the least significant on the T2 weighted images. Because this is actually due to metal, the artifact is significantly worse on, for example, the dynamic contrast enhanced imaging, which is shown here. These are the color overlay images. We see that centrally here we have a complete loss of the color overlay that's due to the metal artifact from this particular procedure.
Now, more significant is the effect of the metal artifact on the diffusion weighted sequence. This is the apparent diffusion coefficient image, the ADC map image, and notice that about 30 to 40% of this prostate gland, literally the entire central third to half of this gland, is covered up by this susceptibility artifact that's due to these metal clips. If we look at the high B value images in this same case on the diffusion weighted imaging, the same thing. Here's the outline of the prostate gland, so kind of the level of the prostate capsule. Here's the prostate capsule shown here, but here within the prostate capsule, this is all artifact due to these metal clips.
It turns out this is a patient who's undergone a urologic procedure called a UroLift procedure. In this procedure, stainless steel clips are placed along the uroepithelium, so kind of along where you would expect the urethra to be located within the prostate. Then titanium clips are put on the surface of the prostate gland, and there's a little string that connects these clips that helps to open up the prostatic urethra and reduce the obstructive symptoms from BPH, or benign prostatic hyperplasia. The problem with this is that these stainless steel clips, as you can see, cause a very large metallic artifact that significantly compromises the diagnostic capability of the multiparametric MRI to detect prostate cancer.
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Content reviewed: December 29, 2021