Renal Scintigraphy Techniques

• Scintigraphy assists in diagnosing renal diseases
• Nuclear medicine uses radiotracers for diagnosing and treating pathologies
• Theranostics combines diagnostics and therapy in nuclear medicine at a molecular level
• Scanners and radiopharmaceuticals (radioactive substances) are necessary for nuclear medicine

Scanners

• Gamma-cameras, Single-photon Emission Tomography (SPECT), and Positron Emission Tomography (PET) are three types of scanners used
• Gamma-cameras are older and allow only planar acquisition in bone scans (2D)
• SPECT cameras rotate 360 degrees and are coupled with CT for anatomical localisation (SPECT/CT)
• PET scanners can be coupled with CT (PET/CT) or MRI (PET/MRI).
• Gamma-cameras emit gamma rays for image formation
• PET images are based on annihilation

Radiopharmaceuticals

• Radiopharmaceuticals are drugs with radioisotopes that give compounds characteristic radioactivity
• Radiopharmaceuticals are used for diagnostic and therapeutic purposes, observing physiological processes or treating oncological diseases
• Drugs need specific features:
• Short half-life for diagnostic purposes for immediate scanning
• Longer half-life for therapeutic use, acting on cancer cells
• High specific activity allows using a small amount of radiotracer
• Localisation largely and quickly
• Good stability
• Affordable, available and safe
• Alpha and Beta decay are used in therapy, while Gamma decay is used in GC/SPECT imaging and positron emission in PET scanning
• Radiopharmaceuticals undergo production, testing in vitro and in vivo, clinical trials, and end up as medicinal products
• Radiotracers are used in GC/SPECT for bone metabolism, perfusion, renal function, and tumour and inflammation detection
• Radiotracers like choline, fluorodeoxyglucose, and fluoride are primarily used in PET imaging for oncological purposes, protein metabolism, glucose metabolism, and bone scans respectively

Therapeutic radiopharmaceuticals

• Composed of a linker that connects the radioactive component to the cancer cell receptor for cell destruction
• Beta particles, like Lutathera, are used for neuroendocrine tumours
• Xofigo targets bone metastasis from prostate cancer
• Features vary per radiopharmaceutical like range, linear energy transfer (LET), etc
• Can be injected, inhaled (for lung ventilation studies), etc
• Scans are performed 3-10 hours after administration using PET or SPECT/CT
• Kidney location is important for patient positioning
• Transplanted kidneys are commonly located in, and require an anterior view with the gamma-camera
• Anatomical kidneys are located posteriorly, acquisitions done in the posterior view
• Glomerular filtration rate is approximately 120 ml/min in a healthy individual
• Vascularization is from the renal arteries
• Renin-angiotensin system regulates renal vascular resistance
• Glomerular filtration uses DTPA (radiolabelled with Technetium-99)
• Tubular secretion uses MAG3 (labelled with Technetium-99)
• Tubular fixation uses DSMA
• DTPA, DMSA, and MAG3 are commonly used radiopharmaceuticals for glomerular filtration, active tubular secretion
• MAG3 is mostly used in children, those with severely impaired renal function, has higher renal extraction
• MAG3 is more useful compared to DTPA, in kidneys that are not developed or impaired

Scintigraphy Protocol

• Good hydration helps in the process
• IV injected radiotracer
• Images are acquired, dynamic usually, posterior view
• Images are processed, findings are reported
• DTPA and MAG3 acquisition lasts 30 minutes after injection
• Direct stimulation occurs when furosemide is injected, after 15 minutes
• The phases are vascular, parenchymal, and excretory
• DMSA uses static acquisition, lasting 5 minutes with projections
• Regions of interest (kidneys and aorta) are traced
• The software gives back activity-time curves
• Relative parenchymal indices are most important and indicate the split renal function
• Clinical indications for scintigraphy (with Dynamic acquisition)
• Obstructive uropathy and hydronephrosis
• Renovascular hypertension
• Post-renal transplantation
• Vesico-ureteral reflux
• Clinical indications for scintigraphy (with Static acquisition)
• Pyelonephritis and scarring
• Renal morphological abnormalities

Obstructive Uropathy & Hydronephrosis

• True obstructive uropathy is something obstructing/compressing the ureter
• Radiotracer cannot pass into ureter, remains in kidney/collecting systems
• Pseudo-obstructions are related to inadequate urinary flow.
• Dilation of the collecting system and bladder effect can occur when patient voids, generates high pressure that goes back up the ureter
• Furosemide/lasix distinguishes a simple dilation of urinary tract, from a true obstructive disease
• Dosing diuretic treatment enables a distinction between hydronephrosis, obstructive disease
• The first case is the normal situation (Group 1), in which no observable changes occur after administration of furosemide
• If an obstruction is present, there is no response to the diuretic
• In stasis (Group 3a/3b), the kidney accumulates radioactivity, then drops as soon as furosemide is administered

Renogram Report

• Normal, Partial or high grade obstruction, Renal artery stenosis or functional obstruction
• Assessed though parameters: relative renal mass, angiographic phase and clearence phase
• Orange/white indicates high values scale
• Bilateral staghorn calculi present, green line represents R kidney, red L kidney
• Plateau curve indicating radioactivity is constant over time but split function is still normal
• Right calyceal-pyelic dilation, renogram reveals the higher concentration of radioactivity in the renal pelvis of the right kidney, which accumulated then immediately dropped on administration
• Stenosis- the curve for L kidney demonstrates an upward trend, accumulating radioactivity and not responding to diuretics, can be detected in images

Renovascular hypertension

• It can be due to anatomic stenosis, dysplasia etc
• Captopril inhibits ACE, abolishes adaptations
• If there is renal artery stenosis the first graph indicates shows basal conditions, sec graph shows post-captopril
• Different renographic curves correspond to the its treatment for the renal disease

Post-transplantation indications

• Monitor events of complications
• Urinoma is a complication, an encapsulated extravasation of urine
• Alternative lateral/anterior projections can indicate the presence of abnormal urine radioactivity

Vésico-ureteral Reflux

• Most often seen in children
• Isolate the definition of ‘retrograde flow’ for later
• The ranges of its detection are between 1-2% of the population
• Nuclear medicine helps to diagnose direct radionuclide cystophraphy, patients lay on a gamma camera with a bladder catheter inserted
• Black spots in the image indicate the bladder or its function
• Some show urine reflux reaching the ureter

Static Acquisitions Tc-DMSA

• Radiotracer stays entrapped in the proximal convoluted tubule cells
• Detecting permanent renal parenchymal scarring that lasts as long as 6 months of an acute urinary tract infection
• Static scintigraphy indicates renal damage

Pyelonephritis

• Scored based on percentage impairment of the kidney, which visually indicates the degree of disease
• Detectable in both uptake indices

Horseshoe Kidney

There is the presence of a bridge between the two portions of the kidney

Characterisation of renal masses

• From 1975 to 2022 the classifications have evolved greatly
• Histotypes have their own molecular characteristics so nuclear medicine assists through radiotracers like, SPECT/CT [99mTc]Tc-Sestamibi, PET/CT or PET/MRI

SPECT/CT [99mTc]Tc-Sestamibi

• The target is the mitochondria and assist with differentiation and distinction between oncocytic tumors, and clear cell renal cell carcinoma,
• Colors goes from black, to white and orange (high indication)
• in clear cell renal cell carcinoma, the tumor has fewer mitochondria (low density) and show nearly no indication

Reviews of systematic reviews and meta analysis

• A true positive in the same class for detection of SestaMIBI SPECT/CT for renal oncocytoma and hybrid oncocytic/chromophobe tumor.
• To achieve nearly 100% one must rule out other factors.
• True positive= disorder, positive test result. False positive = no disorder, positive test result. True negative = no disorder, negative test result. False negative = disorder, negative test result
• Sensitivity measures how one who has a disorder can be detected
• Specificity = true negative

[18F]FDG

• Most commonly used for oncology in PET
• Fluorine is in the 2nd position, this traps it in the cells and keeps it from being pyrovated
• You can see the GI tract, bladder, and skeleton. The metallic implant will show
• Will show inflammations, endocarditis, etc in 34% of patients

[68Ga]Ga-DOTATOC/DOTATATE/DOTANOC

• Related to somatostatin, used as an analogue
• has high uptakes
• Used as a part of PSMA for prostate
• Kidneys have high uptake for these receptors
• Therapy is possible, but diagnosis can be damaged, so watch the salivary glands
• This PSMA is a marker PSMA-ligand rather than FDG, which leads to clearer cells on ccRCC
• Tumor behavior cant be known until its seen if its PSMA-PET or FDG-avid

Explore renal scintigraphy techniques, including the preference for MAG3 over DTPA in pediatric and renal-impaired patients. Understand patient preparation, radiopharmaceuticals used in glomerular filtration studies, and imaging phases during renography. Learn about ROI tracing and static acquisition in DMSA scans.