Abstract
The positron emission tomography (PET) flow tracer 82Rubidium is a known potassium analogue. During our studies of tumor blood flow in prostate cancer, we found that approximately 10% of the patients had high urinary 82Rubidium activity. In roughly half of these patients, the increased renal rubidium/potassium excretion was either causing hypokalemia or explained by Thiazide treatment. In the other half, there was no obvious explanation or clinical consequence of the renal rubidium/potassium excretion. This is the first time enhanced renal potassium excretion is visualized on 82Rubidium PET/CT.
Keywords: 82Rubidium, Hypokalemia, Potassium, Renal excretion, Prostate cancer, PET
Fig. 1.
Positron emission tomography (PET) with 82Rubidium is widely used for clinical quantification of myocardial blood flow [1]. Increased 82Rb uptake has been reported in breast cancer [2], lung cancer, lymphoma, multiple myeloma [3], metastatic renal cell carcinoma [4], and malignant pheochromocytoma [5]. Recently, we validated 82Rubidium PET/computed tomography (CT) for tumor blood flow measurement in prostate cancer [6, 7]. We have found that around 90% of patients had low urinary 82Rubidium activity. However, in thirteen out of 127 patients, we observed very high 82Rubidium activity in the urinary bladder, shown with white arrows on fused PET/CT images (a, b), and corresponding low-dose CT (c, d). The red arrow marks the prostate tumor with increased 82Rubidium uptake (a). Rubidium is a potassium analogue [8, 9], and therefore, rubidium has frequently been used as a marker of potassium in transport studies [10, 11]. It has been shown that renal excretion of 86Rubidium and potassium is parallel [8] and that renal 86Rubidium excretion can be accelerated by acetazolamide, which increases potassium excretion [8]. The increased potassium/rubidium excretion was explained in six patients as one patient had severe hypokalemia, one had mild hypokalemia, and four patients received thiazides, which is also known to increase renal potassium excretion. The remaining seven patients had normal plasma potassium and their medical records revealed no explanation for the suggested increased renal potassium excretion. To our knowledge, enhanced renal potassium excretion has not previously been visualized on 82Rubidium PET/CT. This finding may also be of relevance for the ongoing research on renal blood flow measurement with 82Rubidium PET/CT [12]. Increased renal rubidium excretion reduces the arterial rubidium concentration by a few percent at most and does not affect myocardial uptake
Funding information
This study was supported by a grant from The Danish Cancer Society, Health Research Fund of Central Denmark Region, P. Carl Petersens Fond, and Dansk Kræftforskningsfond.
Compliance with Ethical Standards
Conflict of Interest
Mads Ryø Jochumsen, Lars Poulsen Tolbod, Michael Borre, Jørgen Frøkiær, Kirsten Bouchelouche, and Jens Sörensen declare that they have no conflict of interest.
Ethical Approval
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional research committee and with the 1964 Helsinki declaration and its later amendments.
Informed Consent
Informed consent was obtained from all individual participants included in the study.
Footnotes
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Contributor Information
Mads Ryø Jochumsen, Email: madsjoch@rm.dk.
Lars Poulsen Tolbod, Email: lars.tolbod@aarhus.rm.dk.
Michael Borre, Email: borre@clin.au.dk.
Jørgen Frøkiær, Email: JF@clin.au.dk.
Kirsten Bouchelouche, Email: Kirsten.Bouchelouche@auh.rm.dk.
Jens Sörensen, Email: jens.sorensen@pet.uu.se.
References
- 1.Chatal JF, Rouzet F, Haddad F, Bourdeau C, Mathieu C, Le Guludec D. Story of Rubidium-82 and advantages for myocardial perfusion PET imaging. Front Med (Lausanne) 2015;2:65. doi: 10.3389/fmed.2015.00065. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Lu Y. FDG and (82)Rb PET/MRI features of brain metastasis of breast cancer. Clin Nucl Med. 2015;40:494–495. doi: 10.1097/RLU.0000000000000712. [DOI] [PubMed] [Google Scholar]
- 3.Mirpour S, Khandani AH. Extracardiac abnormalities on rubidium-82 cardiac positron emission tomography/computed tomography. Nucl Med Commun. 2011;32:260–264. doi: 10.1097/MNM.0b013e3283440dcb. [DOI] [PubMed] [Google Scholar]
- 4.Murthy VL, Brown RK, Corbett JR. Metastatic renal cell carcinoma avid for 82Rb but not 18F-FDG. Clin Nucl Med. 2014;39:908–909. doi: 10.1097/RLU.0000000000000311. [DOI] [PubMed] [Google Scholar]
- 5.Neumann DR, Basile KE, Bravo EL, Chen EQ, Go RT. Malignant pheochromocytoma of the anterior mediastinum: PET findings with [18F]FDG and 82Rb. J Comput Assist Tomogr. 1996;20:312–316. doi: 10.1097/00004728-199603000-00028. [DOI] [PubMed] [Google Scholar]
- 6.Jochumsen MR, Tolbod LP, Pedersen BG, Nielsen MM, Hoyer S, Frokiaer J, et al. Quantitative tumor perfusion imaging with (82)Rb PET/CT in prostate cancer: analytic and clinical validation. J Nucl Med. 2019;60:1059–1065. doi: 10.2967/jnumed.118.219188. [DOI] [PubMed] [Google Scholar]
- 7.Jochumsen MR, Bouchelouche K, Nielsen KB, Frokiaer J, Borre M, Sorensen J, et al. Repeatability of tumor blood flow quantification with (82)Rubidium PET/CT in prostate cancer - a test-retest study. EJNMMI Res. 2019;9:58. doi: 10.1186/s13550-019-0529-2. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 8.Kunin AS, Dearborn EH, Burrows BA, Relman AS. Comparison of renal excretion of rubidium and potassium. Am J Phys. 1959;197:1297–1302. doi: 10.1152/ajplegacy.1959.197.6.1297. [DOI] [PubMed] [Google Scholar]
- 9.Kilpatrick R, Renschler HE, Munro DS, Wilson GM. A comparison of the distribution of 42K and 86Rb in rabbit and man. J Physiol. 1956;133:194–201. doi: 10.1113/jphysiol.1956.sp005577. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 10.Beck FX, Giebisch G, Thurau K. Effect of K depletion on renal K and Rb excretion: evidence for activation of K reabsorption. Kidney Int. 1992;42:272–278. doi: 10.1038/ki.1992.286. [DOI] [PubMed] [Google Scholar]
- 11.Parihar AS, Coghlan MJ, Gopalakrishnan M, Shieh CC. Effects of intermediate-conductance Ca2+−activated K+ channel modulators on human prostate cancer cell proliferation. Eur J Pharmacol. 2003;471:157–164. doi: 10.1016/S0014-2999(03)01825-9. [DOI] [PubMed] [Google Scholar]
- 12.Tahari AK, Bravo PE, Rahmim A, Bengel FM, Szabo Z. Initial human experience with Rubidium-82 renal PET/CT imaging. J Med Imaging Radiat Oncol. 2014;58:25–31. doi: 10.1111/1754-9485.12079. [DOI] [PubMed] [Google Scholar]