Interstitial fibrosis is a hallmark of progression in chronic kidney disease (CKD), yet it can presently be assessed only by kidney biopsy, which is invasive and prone to sampling error.

In recent years the advances in molecular imaging, especially high spatial and temporal resolution of the scanners and the development of radiopharmaceuticals to visualize metabolic processes or immune cells have been significant, opening promising possibilities in multiple fields. It was demonstrated that in autoimmune diseases as Crohns disease the use of fibrosis markers, as 68Ga-FAPI tracer in PET/MRI could adequately reflect the amount of fibrosis found in histologic work up of tissue specimens in the gut. Also first data in small studies including patients with chronic kidney disease showed promising results indicating that tracer uptake could reflect the degree of fibrosis.

This study aims to investigate the utility of PET/CT imaging with a [68Ga]-DOTA.SA.FAPi tracer to reflect the degree of fibrosis found in the histological work up. We hypothesize that PET/CT findings reflect histological found fibrotic changes in kidney biopsies, potentially offering a superior alternative due to its non-invasive nature and the possibility to capture the entire organ.

Background More than 10% of the general population worldwide is affected by chronic kidney disease (CKD) and approximately four million people are living on renal replacement therapy. Main causes for CKD are life style factors as hypertension and diabetes. Modern therapies improve outcome and reduce disease progression and can sustain organ function by reducing fibrosis as disease progression is mostly characterized by progressive tissue remodeling, especially including fibrosis leading to GFR reduction. To quantify the degree of fibrosis an invasive procedure as the kidney biopsy is necessary.The procedure and preparation for native kidney and graft biopsies requires detailed planning as bleeding risk and consecutive consequences of bleeding potentially leading to nephrectomy have to be minimized. Nevertheless, significant complications as erythrocyte transfusions are observed in up to 1,6 % and in 0,3% invasive interventions are needed to stop bleeding following kidney biopsies. These complications occur despite optimal preparation and in significant cases a biopsy is not feasible due to vital platelet inhibition and anticoagulation or these have to be paused for several days prior to biopsy reflecting a significant time loss.

Additionally in patients with a long known CKD and comorbidities (exg. hypertension, hyperglycemia) where a rapid decrease in kidney function also with concomitant significant proteinuria can reflect the natural slope of kidney function decline and histologic biopsy work up eventually often reveals chronic lesions and extended fibrosis as cause for progressive decline in kidney function.

In these cases and due to the mentioned difficulties and significant periprocedural risk, a non-invasive tool to bona fide visualize ongoing processes or existing damage in the kidney is preferable and due to advances in imaging techniques a promising approach.

PET Imaging In recent years the advances in molecular imaging, especially high spatial and temporal resolution of the scanners and the development of radiopharmaceuticals to visualize metabolic processes or immune cells have been significant, opening promising possibilities in multiple fields.

Nowadays widely used FDG PET/CT has proven its use in clinical practice in detecting areas of high metabolism as inflammation or cancer. By the use of alternative radiopharmaceuticals, further processes like blood flow, cell proliferation or receptor distribution in organs can be quantified at the molecular level. Fibrosis evaluation using 68Ga-FAPI tracer demonstrated that in autoimmune diseases as Crohns disease the use of fibrosis markers in PET/MRI could adequately reflect the amount of fibrosis found in histologic work up of tissue specimens in the gut and small studies have already shown promising results in fibrosis evaluation in native kidneys.

Methods We aim to prospectively include 30 patients with different degrees of fibrosis in the kidney biopsy and perform a PET/CT scan using 68Ga-DOTA.SA.FAPi tracer to evaluate a correlation between tracer uptake and the histologic findings.

Inclusion Criteria:

• Histological workup of native kidney present

Exclusion Criteria:

• Age <18
• Pregnancy

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