Characterization of Breast Cancer with Manganese-enhanced Magnetic Resonance Imaging

Highly metastatic cancer cells are more likely to escape and form metastases, and only minimal improvements in treatment can be achieved. Despite metas- tases being the primary cause of cancer-related mortality, they often proceed unnoticed. Current imaging modalities rely solely on the morphological fea- tures of the tumor for characterization, rather than cellular differences. Our goal is to develop an MR cellular imaging capability for characterizing the po- tential of breast cancer cells to metastasize and enable early cancer detection using manganese. Experiments on breast cell lines demonstrated that aggres- sive cancer cells significantly enhanced on T1 -weighted MR images as a result of a higher uptake and retention of manganese. These results suggest that dif- ferences in uptake of manganese can help the detection and characterization of breast cancers. The proposed technique can also be useful for other cancers, and could bring a critically needed dimension to cancer imaging.MAS

Ultrashort echo time for improved positive-contrast manganese-enhanced MRI of cancer

Objective: Manganese (Mn) is a positive magnetic resonance imaging (MRI) contrast agent that has been used to obtain physiological, biochemical, and molecular biological information. There is great interest to broaden its applications, but a major challenge is to increase detection sensitivity. Another challenge is distinguishing regions of Mn-related signal enhancement from background tissue with inherently similar contrast. To overcome these limitations, this study investigates the use of ultrashort echo time (UTE) and subtraction UTE (SubUTE) imaging for more sensitive and specific determination of Mn accumulation. Materials and Methods: Simulations were performed to investigate the feasibility of UTE and SubUTE for Mn-enhanced MRI and to optimize imaging parameters. Phantoms containing aqueous Mn solutions were imaged on a MRI scanner to validate simulations predictions. Breast cancer cells that are very aggressive (MDA-MB-231 and a more aggressive variant LM2) and a less aggressive cell line (MCF7) were labeled with Mn and imaged on MRI. All imaging was performed on a 3 Tesla scanner and compared UTE and SubUTE against conventional T1-weighted spoiled gradient echo (SPGR) imaging. Results: Simulations and phantom imaging demonstrated that UTE and SubUTE provided sustained and linearly increasing positive contrast over a wide range of Mn concentrations, whereas conventional SPGR displayed signal plateau and eventual decrease. Higher flip angles are optimal for imaging higher Mn concentrations. Breast cancer cell imaging demonstrated that UTE and SubUTE provided high sensitivity, with SubUTE providing background suppression for improved specificity and eliminating the need for a pre-contrast baseline image. The SubUTE sequence allowed the best distinction of aggressive breast cancer cells. Conclusions: UTE and SubUTE allow more sensitive and specific positive-contrast detection of Mn enhancement. This imaging capability can potentially open many new doors for Mn-enhanced MRI in vascular, cellular, and molecular imaging.We thank Melanie S. Kotys-Traughber from Philips Healthcare, Cleveland, Ohio, USA, for implementing the UTE sequence

Establishment of a lung metastatic breast tumor xenograft model in nude rats.

OBJECTIVE: Larger animal models provide relevant tumor burden in the development of advanced clinical imaging methods for non-invasive cancer detection and diagnosis, and are especially valuable for studying metastatic disease. Most available experimental models, however, are based on immune-compromised mice. To lay the foundation for studying spontaneous metastasis using non-invasive magnetic resonance imaging (MRI), this study aims to establish a highly metastatic breast cancer xenograft model in nude rats. MATERIALS AND METHODS: A highly metastatic variant of human adenocarcinoma MDA-MB-231 known as LM2 was inoculated into nude rats. Orthotopic and subcutaneous (flank) sites were compared, with half of the orthotopic injections guided by ultrasound imaging. MRI with gadolinium contrast administration was performed weekly beginning on Day 6 and ending on Day 104. Excised tumors were assessed on histology using hematoxylin and eosin and CD34. Fisher's exact test was used to compare successful tumor induction amongst different inoculation methods. RESULTS: Primary LM2 tumors were established orthotopically in all cases under ultrasound-guided injection, and none otherwise (p = 0.0028). Contrast-enhanced MRI revealed rapidly progressing tumors that reached critical size (15 mm diameter) in 2 to 3 weeks after inoculation. MRI and histology findings were consistent: LM2 tumors were characterized by low vascularity confined to the tumor rim and large necrotic cores with increasing interstitial fluid pressure. CONCLUSIONS: The metastatic LM2 breast tumor model was successfully established in the mammary fat pads of nude rats, using ultrasound needle guidance as a non-invasive alternative to surgery. This platform lays the foundation for future development and application of MRI to study spontaneous metastasis and different stages throughout the metastatic cascade

Noninvasive manganese-enhanced magnetic resonance imaging for early detection of breast cancer metastatic potential

Cancer cells with a high metastatic potential will more likely escape and form distant tumors. Once the cancer has spread, a cure is rarely possible. Unfortunately, metastasis often proceeds unnoticed until a secondary tumor has formed. The culprit is that current imaging-based cancer screening and diagnosis are limited to assessing gross physical changes, not the earliest cellular changes that drive cancer progression. The purpose of this study is to develop a novel noninvasive magnetic resonance (MR) cellular imaging capability for characterizing the metastatic potential of breast cancer and enable early cancer detection. This MR method relies on imaging cell uptake of manganese, an endogenous calcium analogue and an MR contrast agent, to detect aggressive cancer cells. Studies on normal breast epithelial cells and three breast cancer cell lines, from nonmetastatic to highly metastatic, demonstrated that aggressive cancer cells appeared significantly brighter on MR as a result of altered cell uptake of manganese. In vivo results in nude rats showed that aggressive tumors that are otherwise unseen on conventional gadolinium-enhanced MR imaging are detected after manganese injection. This cellular MR imaging technology brings a critically needed, unique dimension to cancer imaging by enabling us to identify and characterize metastatic cancer cells at their earliest appearance.This study was supported by funds to H-L Cheng from the Natural Sciences and Engineering Research Council of Canada (#355795), the Heart & Stroke Foundation of Canada (#000223), and the Garron Family Cancer Centre Grant through the SickKids Foundation

In-vivo gadolinium contrast-enhanced magnetic resonance imaging (MRI) of orthotopic breast tumors in nude rats at 3 Tesla.

<p><i>T</i>₁-weighted spin-echo images acquired post-contrast injection at early and late stages of tumor development are shown in two rats. (A) MRI was acquired 6 days (left) and 20 days (right) after cell inoculation in the mammary fat pad. (B) MRI was acquired 6 days (left) and 13 days (right) after cell inoculation in the mammary fat pad. Arrow points to tumor.</p

Success of establishing LM2 tumor xenografts in nude rats.

<p>*US: ultrasound image.</p

Dynamic contrast-enhanced MRI during tumor progression.

<p>(Left column) AUC₉₀ maps (mM⋅min) are overlaid on <i>T</i>₁-weighted spin-echo images acquired post-contrast injection (A) 6 days, (B) 13 days, and (C) 20 days after cell inoculation in the mammary fat pad. Arrow points to tumor. (Middle column) Corresponding signal enhancement time-course is shown for the tumor rim (solid line) and tumor core (dashed line). (Right column) Corresponding histograms of AUC₉₀ distributions show an evolution toward lower AUC₉₀ values.</p

Phantom signal-to-noise curves for UTE, SubUTE, and conventional SPGR.

<p>Signal-to-noise in MnCl₂ phantoms versus MnCl₂ concentration for UTE (dashed line) with TE = 90 µs, SubUTE (solid line) with TEs = 90 µs and 10 ms, and conventional SPGR (dotted line) with TE = 2.83 ms. Shown are mean values and standard deviations in each region-of-interest.</p

Relative contrast of SubUTE for different sequence parameters and baseline tissue properties.

<p>The relative contrast of SubUTE for different <b>A)</b> TR, <b>B)</b> UTE (i.e. shortest echo time), <b>C)</b> baseline tissue <i>T</i>_1o, and <b>D)</b> baseline tissue <i>T</i>_2o* for a Mn concentration of 1.0 mM. Where parameters are held constant, the following values were used in addition to measured relaxivities of MnCl₂: TR = 30 ms, UTE = 90 µs, <i>T</i>_1o = 1000 ms, and <i>T</i>_2o* = 47 ms. Relative contrast is expressed relative to the maximum contrast achieved on UTE. TR is seen to have the greatest influence on the optimal flip angle and TE (i.e. longer second echo).</p

Detection of aggressive breast cancer cells on UTE, SubUTE, and conventional SPGR.

<p>Highly aggressive breast cancers LM2 (top row) and MDA (middle row) and less aggressive MCF7 (bottom row) incubated with MnCl₂ at various concentrations are displayed as images (left column) and signal-to-noise (SNR) plots (right column). SNR plots present mean values and standard deviations in each region-of-interest. Cell uptake of Mn is seen as negative contrast on <i>T</i>₂-weighted FSE and positive contrast on other sequences. UTE (TE = 90 µs) provides comparatively higher signal than conventional <i>T</i>₁-weighted SPGR. SubUTE (TE = 90 µs and 10 ms) suppresses unlabeled or background tissue and also suppresses low [Mn] accumulation, and provides the best contrast between aggressive and less aggressive breast cancers.</p