In vivo proton magnetic resonance spectroscopy of the human kidney and kidney lesions: new protocol

Introduction

Although kidney cancer is relatively rare, accounting for only 2–3% of all cancers, kidney cancer has heterogeneous genotypes and resultant phenotypes with complex histological characteristics and often dangerous clinical sequelae. The incidence of kidney cancer is increasing, with over 400,000 new cases diagnosed worldwide annually (1). Various causes such as smoking, obesity and hypertension contribute to the increase, but a likely explanation is the rise in incidental findings of renal masses from the increased use of imaging technologies for unrelated health problems. Up to 20% of enhancing small renal masses are benign and may be managed conservatively (2), however, there are currently no diagnostic biomarkers or screening guidelines used in clinical practice for quantitative non-invasive assessment of kidney lesions that would help distinguish malignant from indolent or benign kidney masses in vivo.

Renal cell carcinomas (RCC) are the most common type of kidney cancer, comprising 80–90% of kidney neoplasms. RCC refers to a group of tumours that arise from different segments of the epithelium of the nephron and collecting duct. Within the RCC classification, there is a high degree of heterogeneity that is evident in the number of recognized histological and metabolic subtypes (3). Clear cell RCC (ccRCC) is the most common subtype (70–80%), followed by papillary RCC (10–15%), chromophobe RCC (5%) and collecting duct RCC (<1%). The heterogeneity of these cancers has made non-invasive sub-typing of the cancers difficult, and current management of RCC frequently requires their surgical excision for a histopathological diagnosis.

There exists a need for preoperative non-invasive diagnostic procedures for distinguishing ccRCC from other aggressive or indolent kidney cancers. With rapid technological advancement, in vivo magnetic resonance spectroscopy (MRS) may cater for that need, however such research in RCC is infrequent compared to other solid cancers such as ovaries, breast and brain.

A similar challenge was resolved for preoperative diagnosis of benign versus malignant ovarian lesions using MRS. The magnetic resonance (MR) visible chemicals in ovarian cells in culture (4,5) and tissue from biopsies (6) were identified and compared with the available histopathology. These data, and significant improvements in MR hardware, allowed the technology to be successfully translated to MRS for preoperative and noninvasive diagnosis of ovarian cancer in vivo (7,8).

The evaluation of kidney cancer biopsies using one- and two-dimensional (1D, 2D) MRS has demonstrated a clear separation between ccRCC, non-ccRCC and non-cancer kidney tissue from tumour-bearing patients, using chemical profiles developed from MR spectroscopy analyses (9-11). Others have also demonstrated that the tissue chemistry from MRS of kidney cancer tissue was different, using histopathology as the basis for diagnosis (12,13). While previous studies have demonstrated the feasibility of in vivo 1D kidney MRS on clinical machines, significant technical challenges remain that limit broader clinical application (14-16). These include respiratory motion, voxel placement within heterogeneous kidney lesions, and achieving a sufficient spectral quality for reliable molecular characterisation. Addressing these challenges requires optimisation of acquisition parameters and hardware configurations suitable for clinical scanners. We aimed to use state-of-the-art MR hardware, in vivo, in a 3T clinical scanner equipped with a 60-channel body coil and determine the optimal conditions to allow a comparison of the chemical signature of ccRCC and normal kidney tissue from cancer free healthy participants.

Methods

Research ethics

The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. This study was approved by the University of Queensland Medical Research Ethics Committee (approval No. 20016001215) and the Queensland Health (Australia) Metro South Health Human Research Ethics Committee (No. HREC/16/QPAH/353, HREC/2021/QMS/68585 and HREC/15/QRBQ/610). All research procedures were conducted following written informed participant consent in the presence of a study investigator.

Participant inclusion and exclusion criteria

Research participants were sourced from the Princess Alexandra Hospital.

Inclusion criteria: over 18 years of age; diagnosed with a renal mass; is donating their kidney and is considered healthy; willing and able to provide informed consent; be agreeable and available for follow-up if needed.

Exclusion criteria: current or suspected pregnancy; contraindicated by an MR imaging (MRI) safety questionnaire; unable to be physically accommodated within the MRI/MRS scanner; deemed unsuitable for an MRI.

Imaging protocol

The pre-spectroscopy protocol comprised a set of multiplanar T2 half-Fourier acquisition single-shot turbo spin echo (HASTE) images, T1 breath-hold volumetric interpolated breath-hold examination (VIBE) sequence with the Dixon technique designed to achieve uniform fat suppression, and diffusion-weighted imaging (DWI) (17). These parameters are summarized in Table 1. All diagnostic sequences, except DWI, were acquired with end-expiration breath suspension. Acquiring these images facilitated the choice of the region of interest (ROI) from which to acquire the spectroscopy data. All MR images were evaluated by a senior radiologist for clinical reporting and to ensure that any incidental findings were reported if necessary.

MRS

MR examinations were performed on a clinical 60 cm bore 3T MRI scanner (MAGNETOM Prisma, Siemens AG, Erlangen, Germany) using a point resolved spectroscopy (PRESS) MRS sequence. A brief procedure outline including breathing instructions was explained verbally to the participants before positioning them in the scanner in a head-first supine position. Two 30-channel radiofrequency (RF)-receiving flex arrays were placed anterior and posterior to the upper abdominal region for signal collection (Figure 1). To minimize any respiratory trigger error, the subject was instructed to maintain a regular and steady breathing pattern throughout the examination.

Figure 1 Patient positioning for in vivo magnetic resonance spectroscopy of the kidneys. The MRI machine used is a 3T 60 cm bore MAGNETOM Prisma. Patients lie supine and enter tunnel headfirst. Two 30-channel radio-frequency body arrays are placed over the patient’s abdomen, anteriorly and posteriorly. MRI, magnetic resonance imaging.

Echo time (T_E), defined as the interval between the RF excitation pulse and the peak of the detected signal, affects the signals that can be observed within an MR spectrum. For the proposed protocol, a T_E of 135 ms was selected to reduce the broad signals from macromolecules, and “simplify” the spectrum, allowing for clearer measurement of the choline (Cho), creatine and lipid peaks that we expected from RCC lesions and kidney tissue (18).

Due to its anatomical position, the kidney is susceptible to spectroscopic artefacts that can be mitigated through optimal shimming (19,20). The full width at half maximum (FWHM) of the water signal was measured and a threshold of maximum 30 Hz was set to indicate adequate shimming for the kidney.

Respiratory triggering

For this protocol, respiratory triggering was employed using a prospective acquisition correction technique (PACE) respiratory navigator. This navigator was applied to the liver dome using a 100 ms repetition time (T_R), ±0.5 mm accept window and a 5% accept window.

Post-acquisitional processing and data analysis

Spectroscopy data were analysed using MestReNova (Mestrelabs) software. Raw spectroscopy data, in the file format “.rda”, were imported into MestReNova using the “Import > Siemens Syngo” tool. No apodization was applied during post-processing. Spectra were reconstructed from the acquired free induction decay without additional line broadening using Fourier transform. 1D spectra were automatically phased in the 0^th and 1^st order and automatically baseline corrected using the in-built Whittaker smoother tool. Additional smoothing was applied to the f1 dimension using the Whittaker smoother with a factor of 3. Spectra were referenced to the lipid methylene signal at 1.33 ppm. Noise was measured for each spectrum in a signal free region. Peak heights were measured using the “Peak picking” tool and recorded. To measure signal-to-noise ratio (SNR), the Cho peak height was divided by the standard deviation of the noise. An SNR of ≥3 was acceptable.

Statistical analysis

To assess intra-individual reproducibility of the spectroscopy measurements, the coefficient of variation (% CV) was calculated for metabolite peak ratios acquired across three separate days. The % CV provides a normalised measure of variability relative to the mean and is commonly used to evaluate reproducibility in MRS studies where metabolite concentrations are expressed as ratios rather than absolute concentrations. This metric allows comparison of variability across metabolites with different signal amplitudes and provides an indication of the stability of the acquisition protocol over repeated measurements.

Histopathology

Since the spectroscopy protocol was carried out immediately before surgery for resection, tissue samples from corresponding renal masses for histopathology were obtained from patients perioperatively, immediately following nephrectomy. Cancer tissue samples were excised from areas that best matched in vivo spectroscopic voxels, avoiding areas of central necrosis, and avoiding surgical margins needed for clinical histopathological diagnosis. Samples were formalin-fixed, processed for paraffin embedding, sectioned onto glass histology slides at 5 µm thickness, and stained with hematoxylin and eosin for routine histopathology. The histopathological diagnosis was performed at Queensland Health Pathology Services and by an internationally recognised kidney cancer pathologist (H.S.).

Results

In vivo MRS protocol developed for the kidney

• Operator selection of receiver channels ensured only the coil elements, that were close to the ROI, were enabled. On average, the number of channels enabled was 28, but this varied depending on the positioning and body habitus of the participant.
• Following a second tri-orthogonal HASTE image, covering the entire target lesion, respiratory triggered PRESS sequence was employed to optimize voxel placement. To ensure triggering at the same point in the respiratory cycle, both localizers and MRS were triggered using the identical PACE respiratory navigator.
• For shimming, high resolution three-dimensional gradient echo images were recorded to measure the B0 inhomogeneity field map, from which first- and second-order shims were used for the shimming volume. The procedure was repeated several times until the water line width could not be reduced further. FWHM ≤30 Hz was considered acceptable. There was no manual adjustment of X, Y and Z for field mapping because respiratory motion makes manual adjustment impractical.
• Voxels were placed in the kidney cortex for healthy controls or in an area of the cancer with minimal or no necrotic tissue (see below) in kidney cancer patients. Care was taken to avoid regions of perinephric or sinus fat, areas of central necrosis in the cancer, or blood vessels.
• Water suppression was achieved using the Water Suppression Enhanced through T1 effects sequence (WET) (21). After four dummy cycles, an eight-average non-water-suppressed reference spectrum was acquired, followed by 160 averages of spectroscopic acquisition with water suppression. To minimize any respiratory trigger error, the subject was instructed to maintain a regular and steady breathing pattern throughout the examination.
• The final optimal spectroscopy parameters were 135 ms TE, 2,000 ms TR, 2,000 Hz bandwidth, and 1,024 vector size. Acquisition and voxel size were patient-specific and determined by subject’s respiratory cycle and tumour size, respectively. A transmitter RF offset of 3.20 ppm was applied to mitigate the chemical-shift error.

A full description of acquisition parameters is provided in Table 2.

Healthy controls

Data recorded from the healthy kidneys came from participants with no significant adverse medical history and displaying no abnormalities. Three participants, two males aged 27 and 48 years old, and one female aged 37 years old, were scanned. The voxels were placed in the lower pole of the kidney and measured 1.5 cm × 1.5 cm × 1.5 cm. Different voxel sizes and placements were trialled and are presented in Figure 2A,2B. Multiple resonances with SNR ≥3 were observed in all spectra from healthy participants. The unsaturated lipid (C = C) at 5.20 ppm, Cho at 3.22 ppm, the methylene group (CH₂) of lipid at 1.33 ppm and the methyl group (CH₃) of lipid at 0.89 ppm were recorded in all three data sets.

Figure 2 Voxel placement and size are important considerations for acquiring MRS data from the kidney. (A) Varying voxel sizes within the renal cortex affect SNR. Voxel sizes were 1.5 cm × 1.5 cm × 1.5 cm (green), 2.0 cm × 0.5 cm × 1.3 cm (red) and 1.8 cm × 0.5 cm × 1.1 cm (blue). 1.5 cm × 1.5 cm × 1.5 cm was the largest voxel and resulted in the greatest SNR and better shim. SNR =5.50 (1.5 cm × 1.5 cm × 1.5 cm), 1.64 (2.0 cm × 0.5 cm × 1.3 cm), 0.93 (1.8 cm × 0.5 cm × 1.1 cm). (B) Upper and lower poles are enriched with kidney cortex compared to regions between the poles. Voxels placed in the lower pole offered better SNR, possibly due to less interference from adrenal grands superior to the kidney. SNR =7.99 (lower pole), 2.03 (upper pole). (C) A voxel placed in the lower pole, measuring 1.5 cm × 1.5 cm × 1.5 cm provides consistent results in the same patient scanned on three separate days (different coloured lines). SNR =4.54 (day 1), 4.63 (day 2), 6.32 (day 3). (D) Peak height ratio for respective resonance captured on three seperate days. Mean with standard deviation are shown. (E) Individual peak heights of spectra from the same patient on three seperate days. Mean with standard deviation are shown. C = C, unsaturated lipid group; CH₂, methylene lipid group; CH₃, methyl lipid group; Cho, choline; MRS, magnetic resonance spectroscopy; SNR, signal to noise ratio.

Intra-individual variability was assessed in a single individual with spectroscopy data accrued on three separate days. With no internal standard present, metabolites were presented as ratios. Mean ratio (% CV) for C = C : Cho, CH₃ : Cho, CH₂ : Cho, CH₃ : CH₂, C = C : CH₃ and C = C : CH₂ were 1.05 (60.20), 6.57 (26.69), 1.32 (34.12), 5.05 (7.83), 0.17 (66.29) and 0.94 (78.63), respectively. This analysis is shown in Figure 2C. Voxel placement and resultant spectra are seen in Figure 3.

Figure 3 Healthy control kidneys scanned using the proposed in vivo MRS protocol. All participants were healthy with no relevant or significant medical history. Participants were aged 27 years (Healthy 1), 37 years (Healthy 2) and 48 years (Healthy 3). Voxels were placed in the lower pole of the right or left kidney. MRI images were T2 HASTE with region for voxel (yellow rectangle, 1.5 cm × 1.5 cm × 1.5 cm) displayed. Cor, Sag and Ax imaging planes are shown. 1D MRS spectrum of the region contained within the voxel. SNR =8.33 (healthy kidney 1), 3.07 (healthy kidney 2), 3.48 (healthy kidney 3). 1D, one-dimensional; Ax, axial; Cor, coronal; HASTE, T2 half Fourier single-shot turbo spin-echo; MRI, magnetic resonance imaging; MRS, magnetic resonance spectroscopy; Sag, sagittal; SNR, signal to noise ratio.

ccRCC cases

Three cases of ccRCC were examined using the protocol established with healthy kidneys.

• A 53-year-old female presented with a mid-pole exophytic grade 1 ccRCC lesion of 22 mm in diameter. The tumour was relatively small compared to other tumours scanned as part of this study. It contained a large cystic component that was avoided to avoid significant water contamination. The size of the tumour and the presence of the cyst severely limited voxel size with dimensions of 1.0 cm × 1.4 cm × 1 cm chosen. Resonances with SNR ≥3 were recorded for Cho (3.23 ppm), lipid methylene (1.33 ppm) and lipid methyl (0.89 ppm). The ratios for the lipid resonances to Cho were 18.5 and 4.0, respectively. The MRI images, spectrum and histopathology from this patient are shown in Figure 4.
• A grade 3 ccRCC was investigated in a 48-year-old female. The tumour was 160 mm in diameter and had nearly replaced the entire renal parenchyma. The clinical pathologist noted that there were various regions of the lesion with discrete separation. One of these regions, measuring 40 mm in diameter, was selected for voxel placement. Unsaturated lipid (5.2 ppm), Cho (3.23 ppm), lipid methyl (0.89 ppm) and methylene (1.33 ppm) were all present. Creatine with SNR ≥3 was observed at 3.05 ppm. The ratios to Cho were 16.99, 28.74, 6.91 and 7.27, respectively. The MRI, representative spectrum and histopathology from this patient are shown in Figure 5.
• In a 66-year-old male, a grade 4 ccRCC lesion was analysed using this protocol. This lesion featured various areas of necrosis and cysts which were taken into consideration when placing the voxel and selecting size. Similar to the previous example (example 2) of ccRCC, the spectrum featured signals with 5 major resonances. The ratios of these peaks to creatine were 1.33 for unsaturated lipid (5.2 ppm), 11.49 for Cho (3.23 ppm), 72.70 for lipid methylene (1.33 ppm) and 6.43 for lipid methyl (0.89 ppm). The MRI images, spectrum and histopathology from this patient are shown in Figure 6.

Figure 4 Patient with a grade 1 ccRCC scanned using the proposed in vivo MRS protocol. The tumour had a total diameter of 22 mm. This tumour was relatively small and a large cyst that was avoided for voxel placement. (A-C) Cor, Sag and Ax plane (respective) T2 HASTE MRI images with region for voxel (yellow rectangle, 1.0 cm × 1.4 cm × 1 cm) displayed. (D) 1D MRS spectrum of the ccRCC region contained within the voxel. Full 1D MRS parameters are described in Table 2. Annotated peaks: 1, Choline (3.23 ppm); 2, -CH₂- (1.33 ppm); and 3, -CH₃- (0. 89 ppm). SNR =8.31. (E) Hematoxylin and eosin staining of a histology section of the grade 1 ccRCC removed by partial nephrectomy. 1D, one-dimensional; Ax, axial; ccRCC, clear cell renal cell carcinoma; CH₂, methylene lipid group; CH₃, methyl lipid group; Cor, coronal; HASTE, T2 half Fourier single-shot turbo spin-echo; MRI, magnetic resonance imaging; MRS, magnetic resonance spectroscopy; Sag, sagittal; SNR, signal to noise ratio.

Figure 5 Patient with a grade 3 ccRCC scanned using the proposed in vivo MRS protocol. The tumour had a total diameter of 160 mm, almost completely replacing the renal parenchyma. There were also different regions of differentiated tumour, one region of approximately 40 mm diameter was selected for voxel placement. (A-C) Cor, Sag and Ax plane (respective) T2 HASTE MRI images with region for voxel (yellow rectangle, 4.0 cm × 4.0 cm × 3.0 cm) displayed. (D) 1D MRS spectrum of the ccRCC region contained within the voxel. Full 1D MRS parameters are described in Table 2. Annotated peaks: 1, -C = C- (5.20 ppm); 2, choline (3.23 ppm); 3: creatine (3.05 ppm); 4, -CH₂- (1.33 ppm); and 5, -CH₃- (0.89 ppm). SNR =15.8. (E) Hematoxylin and eosin staining of a histology section of the grade 3 ccRCC removed by radical nephrectomy. 1D, one-dimensional; Ax, axial; C = C, unsaturated lipid group; ccRCC, clear cell renal cell carcinoma; CH₂, methylene lipid group; CH₃, methyl lipid group; Cor, coronal; HASTE, T2 half Fourier single-shot turbo spin-echo; MRI, magnetic resonance imaging; MRS, magnetic resonance spectroscopy; Sag, sagittal; SNR, signal to noise ratio.

Figure 6 Patient with a grade 4 ccRCC scanned using the proposed in vivo MRS protocol. The tumour had a total diameter of 160 mm, almost completely replacing the renal parenchyma and had various areas of necrosis. There were also different regions of differentiated tumour, one region of approximately 40 mm diameter was selected for voxel placement. (A-C) Cor, Sag and Ax plane (respective) T2 HASTE MRI images with region for voxel (yellow rectangle, 4.0 cm × 3.0 cm × 3.0 cm) displayed. (D) 1D MRS spectrum of the ccRCC region contained within the voxel. Full 1D MRS parameters are described in Table 2. Annotated peaks: 1, -C = C- (5.20 ppm); 2, Choline (3.23 ppm); 3, Creatine (3.05 ppm); 4, -CH₂- (1.33 ppm); and 5, -CH₃- (0.89 ppm). SNR =34.88. (E) Hematoxylin and eosin staining of the grade 4 ccRCC removed by radical nephrectomy. 1D, one-dimensional; Ax, axial; C = C, unsaturated lipid group; ccRCC, clear cell renal cell carcinoma; CH₂, methylene lipid group; CH₃, methyl lipid group; Cor, coronal; HASTE, T2 half Fourier single-shot turbo spin-echo; MRI, magnetic resonance imaging; MRS, magnetic resonance spectroscopy; Sag, sagittal; SNR, signal to noise ratio.

Discussion

Current clinical management of ccRCC frequently requires surgical excision of the tumour. Surgery for suspected ccRCC is routinely carried out before histopathological diagnosis, yet up to 20% of enhancing small renal masses are benign and could be managed conservatively. Differences in tissue chemistry, using MRS of human renal neoplasia biopsies, showed a clear distinction between ccRCC, non-ccRCC and healthy kidney tissue (11). The challenge here was to develop a preoperative in vivo diagnosis of renal lesions that could better inform the need for surgery or monitoring.

The resolution and reproducibility of spectra achieved using our proposed protocol at 3T using two 30-channel body coils are considerably improved compared to the literature (9). Respiratory triggering prior to the PRESS sequence, from a voxel 3 cm³ or larger, shimmed to 30 Hz or less, provided good SNR in the 1D MR spectra as seen in Figures 3-5. The total of 60-channels providing ultra-high coil density design affords superior SNR. This was achieved by ensuring only the coil elements close to the ROI are enabled. This was on average 28. As magnetic field homogeneity strongly influences spectral quality, our iterative semi-automatic shimming workflow leverages built-in shim optimization algorithms and the high order shim coils to offset the magnetic field disturbance without prolonged manual adjustment.

Peak height was chosen as the metric for signal quantification in MRS due to its simplicity and reproducibility. Furthermore, peak height avoids potential uncertainties associated with peak integration in spectra with overlapping resonances or variable baseline characteristics, which are common in renal MRS. However, peak heights may be influenced by linewidth, phase correction and baseline variation. All spectra within this study were processed using consistent and identical acquisition and post-processing parameters. As the primary aim of this work was to assess spectral quality and reproducibility rather than to investigate metabolite concentrations, peak height was deemed a pragmatic and robust measure. Future studies may incorporate peak integration approaches to enable more comprehensive quantitative analysis.

Due to the position of the kidney in the abdominal cavity, it is susceptible to movement from respiratory motion compared to other organs. With every respiratory cycle, the adult kidney can move up to 5 cm. As with most MR protocols, movement of any kind during the acquisition of data, imaging or spectroscopy, can cause image distortion, reduced SNR, spectral broadening, and poor water suppression. Moreover, the kidney is surrounded by a layer of perinephric fat, as well as containing fat within the kidney sinus. If included in the voxel this can result in lipid contamination (23). Therefore, to perform adequate MRS of the kidney, subject motion correction is essential.

The challenge is the physiological movement when the target is within the abdomen. Research shows the kidney can move up to 5 cm during respiration (24), causing significant displacement of the kidney relative to the spectroscopic voxel, complicating spectroscopic experiments through influencing shimming, water suppression, and sampling localisation (16). Respiratory motion compensation strategies including respiratory triggering (24) and breath-hold acquisitions (25,26) are effective in partially overcoming these problems. This is evident by the improvements in spectral quality in terms of linewidth from motion compensated experiments compared to those acquired with free breathing (14,27,28).

Figure 2 details how voxel placement within regions of the kidney structure, and their size, are important considerations for acquiring consistent MRS data from the healthy kidney. Upper and lower poles are enriched with kidney cortex compared to interpolar regions. Voxels placed in the lower pole offered better SNR, possibly due to less interference from adrenal grands superior to the kidney. A voxel placed in the lower pole, measuring 1.5 cm × 1.5 cm × 1.5 cm, provided generally consistent results in the same patient across three separate days, although reproducibility varied across metabolite ratios, with lower variability observed for high-SNR peaks such as CH₃ : CH_2, and greater variability for ratios involving the C = C resonance, which is more susceptible to noise and baseline effects.

The size of the voxel affects SNR and generally a larger voxel results in increased SNR. However, the physiological motion of the kidney needs to be accounted for, and the larger the voxel, the greater the risk of lipid contamination from surrounding perinephric and internal renal sinus fat. Additionally, RCC lesions can have pronounced heterogeneous composition, containing various regions of haemorrhage or necrosis. While necrosis is typically rare in early RCC growth, a necrotic core could develop in larger lesions as the cancer outgrows its blood supply (29). These regions of necrosis need to be avoided for voxel placement since the necrotic tissue is not representative of the cancer tissue itself. The shape of the lesion also needs consideration. Since the voxel is cubic, to be fully contained it should always be smaller than the lesion in volume. It is important to maintain a constant voxel size for interpretation of spectroscopic metrics. Variable voxel dimensions may artificially influence metabolite peak heights and ratios, independent of the underlying tissue biochemistry. In the present study, efforts were made to standardise voxel dimensions and placement within lesions, but complete consistency was not always achievable due to anatomical variability, and lesion size and shape constraints.

In healthy kidneys, our protocol development indicated that SNR may be managed with voxel volumes larger than 1.4 cm³, with the smallest lesion that could be studied having a diameter of 2 cm. For non-spherical shaped lesions this may be even smaller. To estimate the maximum volume of a cubic voxel that can be fully contained within a spherical lesion, we assumed that the space diagonal of the cube equals the diameter of the lesion. For example, for a lesion with a diameter of 2 cm, this yields a maximum cube side length is l=2/3, approximately 1.15 cm, and yields a maximum voxel volume of 1.54 cm³ (l³).

Conclusions

The spectral resolution recorded using a PRISMA 3T scanner equipped with a 60-channel body coil, using respiratory triggering, prior to the PRESS sequence, a voxel 3 cm³ or larger and shimmed to 30 Hz or less, provides a high quality 1D MR spectrum of healthy kidney and kidney ccRCC. This exploratory MR protocol provides preliminary observations that suggest potential metabolic differences between kidney tumours and healthy kidney tissue, but they require validation in larger, standardised cohorts. That potential may be extended to identify ccRCC lesions of low or high grade pre-operatively. Currently, diagnoses are typically made post-operatively with tissue collected at surgery. A long-term goal of this in vivo MRS protocol is to reduce the need for unnecessary surgery, with a larger study now required.

Acknowledgments

We would like to thank Department of Diagnostic Radiology, Princess Alexandra Hospital for their evaluation of magnetic resonance imaging. We would like to thank all research participants involved in the study.

Footnote

Data Sharing Statement: Available at https://tau.amegroups.com/article/view/10.21037/tau-2025-aw-855/dss

Peer Review File: Available at https://tau.amegroups.com/article/view/10.21037/tau-2025-aw-855/prf

Funding: This research was supported by a Project Grant from the National Health and Medical Research Council of Australia (No. GNT1147077). The research was also supported by a Metro South Hospital and Health Service Research Support Scheme (Princess Alexandra Hospital SERTA Grant) and a TRI Foundation EMCR Grant.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tau.amegroups.com/article/view/10.21037/tau-2025-aw-855/coif). T.L.R.H., R.J.E., and R.S.F. report receiving a TRI Foundation EMCR grant. G.J.G., G.C.G., S.T.W., and C.M. report receiving Project Grants from the National Health and Medical Research Council of Australia and SERTA. C.M. also holds shares in DatChem Pty Ltd., a company developing MRS technology for the early assessment of breast cancer. The other authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. This study was approved by the University of Queensland Medical Research Ethics Committee (approval No. 20016001215) and the Queensland Health (Australia) Metro South Health Human Research Ethics Committee (No. HREC/16/QPAH/353, HREC/2021/QMS/68585 and HREC/15/QRBQ/610). All research procedures were conducted following written informed participant consent in the presence of a study investigator.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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