Clinical PET-MR Imaging in Breast Cancer and Lung Cancer

Key points

PET-computed tomography in breast cancer

Breast cancer remains exceedingly prevalent in the Western world and is a leading cause of mortality in women. Once diagnosed, survival is inversely related to the extent of disease at diagnosis, currently characterized with the tumor-node-metastasis (TNM) staging system. Metastases to axillary lymph nodes have a profound influence on patient prognosis, with 10-year survival ranging from 90% without the presence of lymphatic spread down to 30% when greater than 10 lymph nodes are involved.⁴

MR imaging in breast cancer

MR imaging is a highly utilized imaging modality for the evaluation of breast lesions in conjunction with mammography and ultrasonography. MR imaging is currently used and approved for a number purposes, including screening in women considered to be at high risk for disease (ie, lifetime risk >20%), assessment of patients with prior breast augmentation surgery, evaluation of the extent of disease in newly diagnosed patients (multifocal vs multicenter disease, chest wall invasion), and

PET-MR imaging in breast cancer

The theoretical advantages of PET-MR imaging compared with PET-CT or MR imaging alone are just starting to be explored in preliminary clinical research. Much early work has focused on studies of technical feasibility and reproducibility of SUV quantification between PET-MR imaging and PET-CT. Early data are emerging that suggest a potential additive clinical value of PET-MR imaging and which may serve as the basis for larger studies. It is likely that to prove any further increase in diagnostic

Standardized uptake value: PET-MR imaging versus PET- computed tomography in breast cancer

Preliminary work has demonstrated good correlation between SUV measured on PET-MR imaging compared with PET-CT. Most studies compare values by scanning patients first on PET-CT and then on PET-MR imaging. This leads to a time delay between the 2 PET datasets and changes in physiologic concentrations of the radiotracer, which very likely affects the results independent of scanner performance. In 2014, Pace and colleagues³³ reviewed SUV measurements in patients with breast cancer scanned on

PET-MR imaging lesion detection in breast cancer

A potential advantage of PET-MR imaging compared with PET-CT is in leveraging the MR imaging data to improve lesion detectability. It remains an open question whether or not additional lesion detection with PET-MR imaging will be statistically significant, economically beneficial (in light of the cost of PET-MR imaging), and most importantly advantageous enough to improve patient management decisions and patient outcomes.

In the aforementioned study by Pace and colleagues,³³ lesion detection

Tumor staging in breast cancer

There is scant literature directly addressing the possible synergy of PET and MR imaging for T staging of breast cancer. From a technical standpoint, a focused study of the breast is now possible with the advent of PET-MR imaging-compatible breast coils.³⁹ Although FDG PET is unlikely to improve sensitivity for detection of breast lesions, previously reported improvements in specificity might help to direct biopsies towards areas of more aggressive tumor histology.⁴⁰

Additional PET-MR imaging applications in breast cancer: multiparametric datasets

There are few existing data to assess the potential synergistic effects of combining PET and MR imaging quantitative data obtained during a single examination. In a 2014 study by Baba and colleagues,⁴¹ subjects with newly diagnosed breast cancer underwent FDG PET and separate diagnostic breast MR imaging with DWI, and calculation of apparent diffusion coefficient (ADC). A weak inverse correlation between SUV and ADC was reported, and the investigators found that the ratio of SUV to ADC provided

PET-computed tomography in lung cancer

Lung cancer remains the most deadly neoplasm in the United States, affecting both men and women and causing approximately 162,000 deaths in 2015.¹ Lung neoplasms are divided into non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC). The treatment and prognosis is greatly influenced by tumor type and stage at diagnosis. Evaluation of lung neoplasms has typically been performed using CT to characterize them as malignant, as well as to assess therapeutic response based on lesion

MR imaging in lung cancer

Limitations exist for the use of MR imaging in evaluation of nodules within the lung parenchyma because of the susceptibility artifacts created by air within the lung, low signal-to-nose ratio of aerated lung, and motion artifacts from breathing during image acquisition.66, 67, 68, 69 Several solutions have been proposed to help alleviate these problems, including improved MR imaging hardware, application of novel phased-array receiver coils, the use of newer, faster imaging sequences,

PET-MR imaging in lung cancer

Lung cancer is challenging as a diagnostic application for PET-MR imaging due to the known limitations of MR imaging for detection of small and/or low attenuation lung nodules and also due to respiratory motion artifacts that occur in PET and MR imaging. Despite these challenges, potential advantages with respect to chest wall and mediastinal tumor evaluation, combined with the ability of MR imaging to detect brain, bone marrow, adrenal gland, and liver metastases not visible on PET-CT, yields

Standardized uptake value: PET-MR imaging versus PET- computed tomography in lung cancer

There are currently limited data regarding SUV quantification in lung cancer on PET-MR imaging compared with PET-CT. Given that current clinical PET-MR imaging scanners use a tissue-classification system for estimation of lung density compared with direct measurements obtained on PET-CT, some quantitative differences are expected. In a study focusing on lung nodule detection, Chandarana and colleagues⁷⁹ reported that for subjects undergoing PET-MR imaging after PET-CT, SUVmax measurements of

PET-MR imaging lesion detection in lung cancer

Primary tumor detection rates for PET-MR imaging are of interest to clinicians managing patients with lung cancer. It is hypothesized that small lung nodules may be harder to visualize on PET-MR imaging compared with PET-CT based on the known differences between CT and MR imaging. On the other hand, lung cancer has a tendency to spread to the brain, adrenal glands, and bone marrow, which are all areas where MR imaging may potentially perform better. It is, therefore, possible that MR imaging

Additional PET-MR imaging applications in lung cancer: multiparametric datasets

A potential advantage of PET-MR imaging is that it can deliver quantitatively accurately multiparametric datasets consisting of molecular information from both PET and MR imaging, and that these datasets may improve future patient care. Most of the PET-MR imaging research in this area to date has focused on comparing FDG PET data with that obtained from DWI. The ADC values provided by DWI represent a possible new way to independently or synergistically evaluate tumors during clinical PET-MR

Summary

PET-MR imaging is a promising new modality that brings together the advantages of both MR imaging and PET-CT in a single examination, with few limitations. The potential for increased lesion detection, reduced radiation exposure, improved patient convenience, and improved patient management by leveraging of multiparametric quantitative datasets are all compelling reasons to move forward with clinical PET-MR imaging. That being said, PET-CT is already a highly accurate modality, and large