Mary A. McLean

Background: Fumarate hydratase-deficient renal cell carcinoma (FHd-RCC) is a rare and aggressive renal cancer subtype characterised by increased fumarate accumulation and upregulated lactate production. Renal tumours demonstrate significant intratumoral metabolic heterogeneity, which may contribute to treatment failure. Emerging non-invasive metabolic imaging techniques have clinical potential to more accurately phenotype tumour metabolism and its heterogeneity. Methods: In this case study we have used hyperpolarised ¹³C-pyruvate MRI (HP ¹³C-MRI) to assess ¹³C-lactate generation in a patient with an organ-confined FHd-RCC. Post-operative tissue samples were co-registered with imaging and underwent sequencing, IHC staining, and mass spectrometry imaging (MSI). Results: HP ¹³C-MRI reveals two metabolically distinct tumour regions. The ¹³C-lactate-rich region shows a high lactate/pyruvate ratio and slightly lower fumarate on MSI compared to the other tumour region, as well as increased CD8 + T cell infiltration, and genetic dedifferentiation. Compared to the normal kidney, the vascularity in the tumour is decreased, while immune cell fraction is markedly higher. Conclusions: This study shows the potential of metabolic HP ¹³C-MRI to characterise FHd-RCC and how targeting of biopsies to regions of metabolic dysregulation could be used to obtain the tumour samples of greatest clinical significance, which in turn can inform on early and successful response to treatment.

Purpose: To establish and optimize abdominal deuterium MR spectroscopic imaging in conjunction with orally administered ² H‐labeled molecules. Methods: A flexible transmit‐receive surface coil was used to image naturally abundant deuterium signal in phantoms and healthy volunteers and after orally administered ² H ₂ O in a patient with a benign renal tumor (oncocytoma). Results: Water and lipid peaks were fitted with high confidence from both unlocalized spectra and from voxels within the liver, kidney, and spleen on spectroscopic imaging. Artifacts were minimal, despite the high ² H ₂ O concentration in the stomach immediately after ingestion, which can be problematic with the use of a volume coil. Conclusion: We have shown the feasibility of abdominal deuterium MR spectroscopic imaging at 3 T using a flexible surface coil. Water measurements were obtained in healthy volunteers, and images were acquired in a patient with a renal tumor after drinking ² H ₂ O. The limited depth penetration of the surface coil may have advantages in characterizing early uptake of orally administered agents in abdominal organs, despite the high concentrations in the stomach which can pose challenges with other coil combinations.

Purpose: The detection of hyperpolarized carbon‐13 (HP ¹³C)‐fumarate conversion to ¹³C‐malate using ¹³C‐MRSI is a biomarker for early detection of cellular necrosis. Here, we describe the translation of HP ¹³C‐fumarate as a novel human imaging agent, including the evaluation of biocompatibility and scaling up of the hyperpolarization methods for clinical use.Methods: Preclinical biological validation was undertaken in fumarate hydratase‐deficient murine tumor models and controls. Safety and biocompatibility of ¹³C‐fumarate was assessed in healthy rats (N = 18) and in healthy human volunteers (N = 9). The dissolution dynamic nuclear polarization process for human doses of HP ¹³C‐fumarate was optimized in phantoms. Finally, 2D ¹³C‐MRSI following injection of HP ¹³C‐fumarate was performed in an ischemia–reperfusion porcine kidney model (N = 6).Results: Fumarate‐to‐malate conversion was reduced by 42%–71% in the knockdown murine tumor model compared to wildtype tumors. Twice‐daily injection of ¹³C‐fumarate in healthy rats at the maximum evaluated dose (120 mg/kg/day) showed no significant persistent blood or tissue effects. Healthy human volunteers injected at the maximum dose (3.84 mg/kg) and injection rate (5 mL/s) showed no statistically significant changes in vital signs or blood measurements 1 h post‐injection. Spectroscopic evidence of fumarate‐to‐malate conversion was observed in the ischemic porcine kidney (0.96 mg/kg).Conclusion: HP ¹³C‐fumarate has shown promise as a novel and safe hyperpolarized agent for monitoring cellular necrosis. This work provides the basis for future imaging of HP ¹³C‐fumarate metabolism in humans.

Background: Early and accurate grading of renal cell carcinoma (RCC) improves patient risk stratification and has implications for clinical management and mortality. However, current diagnostic approaches using imaging and renal mass biopsy have limited specificity and may lead to undergrading. Methods: This study explored the use of hyperpolarised [1-¹³C]pyruvate MRI (HP ¹³C-MRI) to identify the most aggressive areas within the tumour of patients with clear cell renal cell carcinoma (ccRCC) as a method to guide biopsy targeting and to reduce undergrading. Six patients with ccRCC underwent presurgical HP ¹³C-MRI and conventional contrast-enhanced MRI. From the imaging data, three k-means clusters were computed by combining the k_PL as a marker of metabolic activity, and the ¹³C-pyruvate signal-to-noise ratio (SNR_Pyr) as a perfusion surrogate. The combined clusters were compared to those derived from individual parameters and to those derived from the percentage of enhancement on the nephrographic phase (%NG). The diagnostic performance of each cluster was assessed based on its ability to predict the highest histological tumour grade in postsurgical tissue samples. The postsurgical tissue samples underwent immunohistochemical staining for the pyruvate transporter (monocarboxylate transporter 1, MCT1), as well as RNA and whole-exome sequencing. Results: The clustering approach combining SNR_Pyr and k_PL demonstrated the best performance for predicting the highest tumour grade: specificity 85%; sensitivity 64%; positive predictive value 82%; and negative predictive value 68%. Epithelial MCT1 was identified as the major determinant of the HP ¹³C-MRI signal. The perfusion/metabolism mismatch cluster showed an increased expression of metabolic genes and markers of aggressiveness. Conclusions: This study demonstrates the potential of using HP ¹³C-MRI-derived metabolic clusters to identify intratumoral variations in tumour grade with high specificity. This work supports the use of metabolic imaging to guide biopsies to the most aggressive tumour regions and could potentially reduce sampling error.

Purpose: To establish and optimize abdominal deuterium MRSI in conjunction with orally administered ² H-labelled molecules. Methods: A flexible transmit-receive surface coil was used to image naturally abundant deuterium signal in phantoms and healthy volunteers and after orally administered ² H ₂ O in a patient with a benign renal tumor (oncocytoma). Results: Water and lipid peaks were fitted with high confidence from both unlocalized spectra and from voxels within the liver, kidney, and spleen on spectroscopic imaging. Artifacts were minimal despite the high ² H ₂ O concentration in the stomach immediately after ingestion, which can be problematic with the use of a volume coil. Conclusion: We have shown the feasibility of abdominal deuterium MRSI at 3 T using a flexible surface coil. Water measurements were obtained in healthy volunteers and images were acquired in a patient with a renal tumor after drinking ² H ₂ O. The limited depth penetration of the surface coil may have advantages in characterizing early uptake of orally administered agents in abdominal organs despite the high concentrations in the stomach which can pose challenges with other coil combinations.

Introduction: Localised renal masses are an increasing burden on healthcare due to the rising number of cases. However, conventional imaging cannot reliably distinguish between benign and malignant renal masses, and renal mass biopsies are unable to characterise the entirety of the tumour due to sampling error, which may lead to delayed treatment or overtreatment. There is an unmet clinical need to develop novel imaging techniques to characterise renal masses more accurately. Renal tumours demonstrate characteristic metabolic reprogramming, and novel MRI methods have the potential to detect these metabolic perturbations, which may therefore aid accurate characterisation. Here, we present our study protocol for the investigation of the differential biology of benign and malignant renal masses using advanced MRI techniques (IBM-Renal). Methods and analysis: IBM-Renal is a multiarm, single-centre, non-randomised, feasibility study with the aim to provide preliminary evidence for the potential role of the novel MRI techniques to phenotype localised renal lesions. 30 patients with localised renal masses will be recruited to three imaging arms, with 10 patients in each: (1) hyperpolarised [1-¹³C]-pyruvate MRI, (2) deuterium metabolic imaging (DMI) and (3) sodium MRI. The diagnosis will be made on samples acquired at biopsy or at surgery. The primary objective is the technical development of the novel MRI techniques, with the ultimate aim to understand whether these can identify differences between benign and malignant tumours, while the secondary objectives aim to assess how complementary the techniques are, and if they provide additional information. The exploratory objective is to link imaging findings with clinical data and molecular analyses for the biological validation of the novel MRI techniques. Ethics and dissemination: This study was ethically approved (UK REC HRA: 22/EE/0136; current protocol version 2.1 dated 11 August 2022). The plans for dissemination include presentations at conferences, publications in scientific journals, a doctoral thesis and patient and public involvement. Trial registration number: NCT06016075.

Hyperpolarised magnetic resonance imaging (HP-¹³C-MRI) has shown promise as a clinical tool for detecting and characterising prostate cancer. Here we use a range of spatially resolved histological techniques to identify the biological mechanisms underpinning differential [1-¹³C]lactate labelling between benign and malignant prostate, as well as in tumours containing cribriform and non-cribriform Gleason pattern 4 disease. Here we show that elevated hyperpolarised [1-¹³C]lactate signal in prostate cancer compared to the benign prostate is primarily driven by increased tumour epithelial cell density and vascularity, rather than differences in epithelial lactate concentration between tumour and normal. We also demonstrate that some tumours of the cribriform subtype may lack [1-¹³C]lactate labelling, which is explained by lower epithelial lactate dehydrogenase expression, higher mitochondrial pyruvate carrier density, and increased lipid abundance compared to lactate-rich non-cribriform lesions. These findings highlight the potential of combining spatial metabolic imaging tools across scales to identify clinically significant metabolic phenotypes in prostate cancer.

Deuterium metabolic imaging (3 T) demonstrated a reduction in oxidative glucose metabolism at whole-brain spectroscopy, but no evidence of regional signal changes, in participants with Alzheimer disease.

Introduction: Localised renal masses are an increasing burden on healthcare due to the rising number of cases. However, conventional imaging cannot reliably distinguish between benign and malignant renal masses, and renal mass biopsies are unable to characterise the entirety of the tumour due to sampling error, which may lead to delayed treatment or overtreatment. There is an unmet clinical need to develop novel imaging techniques to characterise renal masses more accurately. Renal tumours demonstrate characteristic metabolic reprogramming, and novel MRI methods have the potential to detect these metabolic perturbations which may therefore aid accurate characterisation. Here we present our study protocol for the Investigation of the differential biology of Benign and Malignant renal masses using advanced magnetic resonance imaging techniques (IBM-Renal). Methods and analysis: IBM-Renal is a multi-arm, single-centre, non-randomised, feasibility study with the aim to provide preliminary evidence for the potential role of the novel MRI techniques to phenotype localised renal lesions. 30 patients with localised renal masses will be recruited to three imaging arms, with 10 patients in each: (1) hyperpolarised [1- ¹³ C]-pyruvate MRI (HP ¹³ C-MRI), (2) deuterium metabolic imaging (DMI), and (3) sodium MRI ( ²³ Na-MRI). The diagnosis will be made on samples acquired at biopsy or at surgery. The primary objective is to investigate whether novel MRI techniques can identify the differences between benign and malignant tumours, while the secondary objectives aim to assess how complementary the techniques are, and if they provide additional information. Exploratory objective will be to link imaging findings with clinical data and molecular analyses for biological validation of the novel MRI techniques. Ethics and dissemination: This study was ethically approved (UK REC HRA: 22/EE/0136; current protocol version 2.1 dated 11/08/2022). The plans for dissemination include presentations at conferences, publications in scientific journals, a doctoral thesis, and patient and public involvement. Registration details: ClinicalTrials.gov : NCT06016075 Strengths and limitations of this study: IBM-renal is the first prospective study to investigate the role of deuterium metabolic imaging and sodium MRI for the characterisation of indeterminate renal masses. Combining different MRI techniques in the same patient will allow a direct comparison and determining whether they provide additional data. The clinical team is multidisciplinary, enabling a multimodal assessment of these renal masses, including clinical, imaging, pathology data. Limitations of the study include potential pathological undergrading of benign renal masses, as some of these diagnoses are based on a single biopsy. As a feasibility study, the sample size is small, but the primary outcomes can be used to inform a large-scale study.

MRI with hyperpolarized (HP) ¹³C agents, also known as HP ¹³C MRI, can measure processes such as localized metabolism that is altered in numerous cancers, liver, heart, kidney diseases, and more. It has been translated into human studies during the past 10 years, with recent rapid growth in studies largely based on increasing availability of HP agent preparation methods suitable for use in humans. This paper aims to capture the current successful practices for HP MRI human studies with [1‐¹³C]pyruvate—by far the most commonly used agent, which sits at a key metabolic junction in glycolysis. The paper is divided into four major topic areas: (1) HP ¹³C‐pyruvate preparation; (2) MRI system setup and calibrations; (3) data acquisition and image reconstruction; and (4) data analysis and quantification. In each area, we identified the key components for a successful study, summarized both published studies and current practices, and discuss evidence gaps, strengths, and limitations. This paper is the output of the “HP ¹³C MRI Consensus Group” as well as the ISMRM Hyperpolarized Media MR and Hyperpolarized Methods and Equipment study groups. It further aims to provide a comprehensive reference for future consensus, building as the field continues to advance human studies with this metabolic imaging modality.