Limitations of MRI for monitoring prostate cancer

I was following active surveillance, and in recent years, getting an annual 3T MRI. My urologist seemed to have high confidence in the effectiveness of the 3T MRI's to spot any clinically significant lesions. My PSA was high, and rising steadily, but the urologist felt that it was probably due to imflammatory prostatitis. When the PSA continued to rise, he eventually recommented a PET/CT scan. The scan showed locally advanced prostate cancer, with seminal vesicle invasion. I found out that there some types of cancer cells that are invisible to MRI. The lesson to be taken is not to rely on negative MRI results if your PSA is rising rapidly.