Advances in medicine sometimes involve hybrid technologies, often with stunning results. Just as hybrid cars produce vehicles that offer the best of two worlds in one, integrating two different medical imaging technologies can accomplish the same goal.
PET and MRI scans
Combining Positron Emitting Tomography (PET) scanning with Magnetic Resonance Imaging (MRI) boosts the accuracy of both. Here’s what each scan offers individually:
- PET scans take advantage of radiopharmaceuticals, which are specialized drugs made by binding radiation-emitting isotopes to biological molecules that have a high affinity for cancer cells. When taken up by malignant tumors, this causes the tumor tissue to “light up” on scanners designed to receive radioactive signals. Thus, PET detects cancer locations. Although radiation is involved, the levels are very safe because they are low and quickly fade away.
- MRI scans utilize a magnetic field and radio waves to generate detailed, 3-dimensional pictures of anatomy and tissue characteristics. These images are the result of the radio waves’ influence on the magnetic position of the body’s atoms. As the positions change and quickly return to normal, an antenna registers the changes and transmits them to a computer, which translates them into images. MRI is completely safe because there is no radiation.
Integrating PET with MRI has been commercially available since 2010, when technological advances allowed the merger of their respective imaging results. This now means that the sensitivity of PET for picking up cancer cells as they metabolized the biologic molecules (functional imaging) can be immediately combined with the precise anatomic details and tissue characterization of MRI.
Could imaging replace needle biopsies?
A definitive diagnosis of a tumor cancer depends on collecting tissue samples from the body. Cells and their genetic components can then be analyzed in the lab. Harvesting tissue means invading the body. We’ve come a long way from exploratory surgery to minimally invasive image-guided needle biopsies, and that’s a good thing. However, needle biopsies can be unpleasant, even painful, and may have risks of side effects such as infection or bleeding.
This is especially true for suspected prostate cancer (PCa). Conventional needle biopsies for prostate cancer (PCa) are guided by transrectal ultrasound (TRUS) that is blind to tissue differences. As a result, at least 12 needles are used to sample the gland. Although in-bore MRI-guided biopsies target the tumor with only a minimum number of needles, making the biopsy safer, more comfortable and precise, tissue must still be sampled. I don’t know a single patient who doesn’t wish imaging alone could diagnose PCa.
A new imaging study out of Germany suggests the day is fast approaching when metastatic breast cancer (BCa) can be diagnosed without a needle biopsy. As with PCa, BCa must be staged to assess the extent of the cancer before treatment decisions are made. It’s important to know if the cancer has invaded normal breast tissue, nearby lymph nodes, or beyond.
Breast cancer commonly spreads to the lymph nodes in the armpit (axillary nodal metastatic disease); in fact, “up to 40% of early breast cancer patients show axillary nodal metastatic disease at the time of diagnosis.”[i] If this could be accomplished by imaging, it would reduce the need for an invasive biopsy.
The 2021 German study by Morawitz, et al.[ii] involved 112 women newly diagnosed with BCa. The study compared four imaging modalities that can be used to detect axillary nodal disease:
- Sonography (ultrasound)
- Breast MRI
- MRI of the chest and armpit
- Hybrid FDG-PET/MRI of the chest and armpit (FDG refers to fluorodeoxyglucose, the most widely available PET radiopharmaceutical tracer)
The authors found that the hybrid FDG-PET/MRI “…outperforms axillary sonography, breast MRI and [thoracic] MRI in determining the axillary lymph node status.” They suggested that in clinical use, ultrasound of the armpit might be performed as well, and correlated with FDG-PET/MRI “to provide even more accuracy in diagnosis” in a sort of two-heads-are-better-than-one double-check of results.
More research needs to be done before ditching a needle biopsy, but hybrid imaging is a step closer to noninvasive diagnosis. A different type of hybrid has the potential to do the same for PCa. Integrating multiparametric MRI (mpMRI) with multiplatform artificial intelligence utilizing quantitative analytics for image analysis more precise than the human eye and more accurate than the human reader will be an important step toward eliminating unnecessary needle biopsies. Perhaps the day will come when they will altogether be no longer useful.
NOTE: This content is solely for purposes of information and does not substitute for diagnostic or medical advice. Talk to your doctor if you are experiencing pelvic pain, or have any other health concerns or questions of a personal medical nature.
[i] Will Morton. “PET/MRI advances efforts for virtual biopsy in breast cancer.” AuntMinnie.com, May 26, 2021. https://www.auntminnie.com/index.aspx?sec=ser&sub=def&pag=dis&ItemID=132511
[ii] Morawitz J, Bruckmann NM, Dietzel F, Ullrich T et al. Determining the axillary nodal status with four current imaging modalities including 18 F-FDG PET/MRI in newly diagnosed breast cancer: A comparative study using histopathology as reference standard. J Nucl Med. 2021 May 20;jnumed.121.262009.