Metal artifact reduction in 68Ga-PSMA-11 PET/MRI for prostate cancer patients with hip joint replacement using multiacquisition variable-resonance image combination

Multiparametric-magnetic resonance imaging (mp-MRI) of the prostate and Urolift: Identifying artefact size, location and clinical implications

Objectives

We sought to define the degree of artefact caused by prostatic urethral lift (PUL) on multiparametric-magnetic resonance imaging (mp-MRI) to determine the location, size of artefact and if the device could potentially obscure a diagnosis of prostate cancer.

Methods

Ten patients were prospectively enrolled to undergo PUL for treatment of benign prostatic hyperplasia and follow-up imaging. A standard mp-MRI protocol using a 3.0 Tesla scanner was performed prior to and following Urolift insertion. Pre- and post-PUL images were compared to measure maximum artefact diameter around each implant in each MRI parameter. A transverse relaxation time weighted (T2) artefact reduction protocol was also evaluated. The location of each artefact was then compared to a separate database of 225 consecutive patients who underwent magnetic resonance guided prostate biopsies.

Results

Artefact occurred around the stainless steel urethral implant component only. Mean T2 artefact maximum diameter was 7.7 mm (sd = 1.71 mm), with an artefact reduction protocol reducing this to 5.4 mm (sd = 1.43). Mean dynamic-contrast-enhancement artefact was 10 mm (sd = 2.5 mm), and mean diffusion-weighted-imaging artefact was 28.2 mm (sd = 7.8 mm). All artefacts were confined to the posterior transition zone only. In the 225 consecutive patients who had undergone magnetic resonance guided prostate biopsies, there were 55 positive biopsies with prostate cancer, with 13 cases found in the transition zones and no cancer identified solely in the posterior transitional zone.

Conclusions

The stainless steel urethral component of the PUL does cause artefact, which is confined to the posterior transition zone only. PUL artefact occurs in an area of the prostate that has a very low incidence of a single focus of prostate cancer. If there is concern for prostate cancer in the posterior TZ (e.g. if every other area is clear with a high PSA), this area can undergo targeted biopsy.

Recent Advances in Positron Emission Tomography/Magnetic Resonance Imaging Technology

More than a decade has passed since the clinical deployment of the first commercial whole-body hybrid PET/MR scanner in the clinic. The major advantages and limitations of this technology have been investigated from technical and medical perspectives. Despite the remarkable advantages associated with hybrid PET/MR imaging, such as reduced radiation dose and fully simultaneous functional and structural imaging, this technology faced major challenges in terms of mutual interference between MRI and PET components, in addition to the complexity of achieving quantitative imaging owing to the intricate MRI-guided attenuation correction in PET/MRI. In this review, the latest technical developments in PET/MRI technology as well as the state-of-the-art solutions to the major challenges of quantitative PET/MR imaging are discussed.

MR safety considerations for patients undergoing prostate MRI

Over the past decade, there has been a dramatic increase in the number of patients undergoing prostate MRI scans. Patients presenting for prostate MRI are an ageing population and may present with a variety of passive or active implants and devices. These implants and devices can be MR safe or MR conditional or MR unsafe. Patients with certain MR-conditional active implants and devices can safely obtain prostate MRI in a specified MR environment within specific MR imaging parameters. Prostate MRI and PET-MRI in patients with passive implants such as hip prostheses, fiducial markers for SBRT, brachytherapy seeds and prostatectomy bed clips have unique concerns for image optimization that can cause geometric distortion of the diffusion-weighted imaging (DWI) sequence. We discuss strategies to overcome these susceptibility artifacts. Prostate MRI in patients with MR conditional active implants such as cardiac implantable electronic devices (CIED) also require modification of imaging parameters and magnet strength. In this setting, a diagnostic quality prostate MRI can be performed at a lower magnet strength (1.5 T) along with modification of imaging parameters to ensure patient safety. Imaging strategies to minimize susceptibility artifact and decrease the specific absorption rate (SAR) in both settings are described. Knowledge of MR safety considerations and imaging strategies specific to prostate MRI and PET-MRI in patients with implants and devices is essential to ensure diagnostic-quality MR images and patient safety.