From the Guidelines
MRI is generally superior to non-contrast CT scans for evaluating kidney conditions, particularly for patients with renal insufficiency or contrast allergies, due to its ability to provide better soft tissue contrast and detect small renal lesions without radiation exposure. When evaluating kidney conditions, the choice between MRI and non-contrast CT scans depends on the specific clinical question.
- MRI provides better soft tissue contrast, allowing for clearer visualization of kidney structures, masses, and abnormalities without radiation exposure.
- It can detect small renal lesions (down to 5mm), characterize cysts and solid masses, evaluate renal blood vessels, and assess function without iodinated contrast that might harm compromised kidneys 1.
- Non-contrast CT scans, while faster and more widely available, offer limited soft tissue differentiation and may miss subtle lesions.
- CT excels at showing kidney stones and calcifications, which MRI may miss. The most recent and highest quality study, published in 2020, supports the use of MRI for characterizing renal lesions, particularly for small renal masses <4 cm, due to its high sensitivity and specificity 1. In patients with decreased renal function, non-contrast MRI protocols are an alternative to contrast-enhanced CT angiography (CTA) and MR angiography (MRA), which have been associated with potential morbidity in the setting of impaired renal function 1. However, the risk of contrast-induced nephropathy (CIN) with iodinated contrast material for CT has been disputed, and recent data suggest a low risk of clinically relevant CIN 1. Ultimately, the choice between MRI and non-contrast CT scans should be based on the individual patient's history, associated clinical conditions, and available imaging resources.
- For patients with a high index of suspicion for renovascular disease and diminished renal function, duplex Doppler US is a preferred screening examination 1.
- For patients with relative or absolute contraindications to multi-phasic CT, MRU (without/with IV contrast) is an acceptable alternative imaging approach 1.
From the Research
Benefits of MRI in Evaluating Kidney Function
- MRI can noninvasively assess the structure and function of the kidney in a single scan session 2
- MRI techniques, such as diffusion-weighted imaging, can measure renal fibrosis and show promise in chronic kidney disease and renal transplantation 2
- Longitudinal relaxation time (T1) mapping can measure fibrosis and oedema in the kidney 2
- Blood oxygen-level-dependent MRI can measure renal oxygenation, although results can be affected by several factors 2
- Phase contrast and arterial spin labelling can measure renal artery blood flow and renal perfusion without exogenous contrast 2
Comparison with Non-Contrast CT Scan
- CT scan is the mainstay of renal imaging, but it requires the use of contrast agents, which can be nephrotoxic and cause contrast-induced nephropathy (CIN) 3, 4
- MRI, on the other hand, can provide functional information without the need for contrast agents, making it a safer option for patients with renal disease 5, 2
- Non-contrast CT scan may not provide the same level of functional information as MRI, and may not be as effective in evaluating renal function 3
Advantages of MRI in Evaluating Kidney Function
- MRI can provide detailed information on renal structure and function, including measures of renal perfusion, oxygenation, and fibrosis 5, 6, 2
- MRI can be used to monitor renal function in patients with renal disease, and can provide accurate measurements of single-kidney glomerular filtration rate and renal plasma flow 5
- MRI is a non-invasive and non-ionizing imaging modality, making it a safer option for patients with renal disease 5, 2