doppler ultrasound of the kidney
TRANSCRIPT
Doppler ultrasound of the kidneys
Normal anatomy of the kidney
• :
Renal parenchymacortex
Renal sinus:arteries,veins, lymphatic, collecting systemRenal hilum: Concave, renal sinus
Anatomy of renal arteries
• RRA: Usually passes posterior to inferior vena cava
• LRA: Usually courses posterior to left renal vein
Arterial blood supply to the Kidney
Segmental artery
Apical, upper, middle, lower, posterior
Interlobular artery
Between renal pyramids
Glomerular arteriole
Main renal artery
Arcuate artery
Between cortex & medulla
Left-sided IVCNormal anatomy of
IVC
Anomalous left-sided IVC
Indications of Renal Doppler Ultrasound
1-Renal Artery Stenosis2-Renal Artery Thrombosis 3-Renal Artery Emboli4-Renal vein thrombosis5-Aneurysm & Pseudo Aneurysm6-Arterio-venous communications7-Renal mass8-Hypertension in Young age
Gray scale imaging firstKidneys
renal length Echogenicity of renal cortexThickness of renal cortexMasses hydronephrosis renal calculi
AortaPlaque – thrombus – dissection – aneurysm
Normal kidneyLongitudinal section Cross section
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Renal capsule: echogenic lineRenal parenchyma: outer cortex & inner medulla
pyramidCentral sinus complex: high echogenicity
(vessels, fat, fibrous tissue)
Renal DimensionsLength: 9 – 14 cm (longitudinal section) Width: 4 – 6 cm (cross section) Depth: 4 – 6 cm (cross section)
Appropriate renal volume231 ± 50 ml
Cortical thickness: 8 – 10 mm
Parenchymal thickness: 14 – 18 mm
Classification of renal parenchymal echogenicity
4 types based of US appearanceHypoechoic compared to liver
Isoechoic compared to liver
Hyperechoic compared to liver
Isoechoic to renal sinus
Normal
Normal
Pathological
Pathological
Grade 0Grade IGrade IIGrade III
Kidney parenchyma compared to liver parenchyma
Hypoechoic Isoechoic
Hyperechoic
Congenital Normal Variant
• Dromedary Hump
• Fetal Lobulation
• Prominent column of bertin
• Junctional Parenchymal defect
• Hypoechoic renal sinus
Dromedary hump Fetal lobulation
Common renal variation
Focal bulge on lateral border of left kidney
Result from adaptation of renal surface to adjacent spleen
Easily differentiated from renal mass by Doppler
Sites for pulsed Doppler of renal arteries
• Aorta • Ostium of main renal artery• Trunk of main renal artery• Hilum of kidney• Upper pole of kidney• Middle pole of kidney• Lower pole of kidney
Transverse scan with probe angulationsMain renal arteries
Normal right renal artery
Transverse gray scale image
Right main renal artery
Transverse color Doppler image
Right main renal artery
Normal left renal arteryGray scale image Color Doppler image
Proximal main left renal artery Proximal main left renal artery
Axial scan in left lateral decubitusUsing right kidney as acoustic window
Right main renal artery & vein
Color Doppler USSchematic drawing
Axial scan in right lateral decubitusUsing left kidney as acoustic window
Schematic drawing
Left main renal artery & vein
Color Doppler US
Zubarev AV. Eur Radiol 2001 ; 11 : 1902 – 1915.
Pulsed Doppler of renal veins Right renal vein
Resembles pulsed Doppler of IVC
Triphasic waveform
Left renal vein
Little modulation
Wall artifact due to systolic peak
Limits in visualization of main renal arteries
• Obesity• Overlying bowel gas• Dyspnea• Shadowing from arterial calcifications• Cardiac arrhythmias• Poor angle of Doppler insonation• Accessory renal arteries (small size)
Expert sonographers detect 80 – 90% of main RA
CEUS improves success rate to 95%
Angle of insonationDifficulty in case of tortuous or curved renal artery
Correct angle Incorrect angle
Adjustment of Doppler controlLow flow settings
• Lowest pulse repetition frequency without aliasing
• Small color box• Greatest gain without background noise• Lowest wall filter• High color priority
Normal segmental & interlobar renal arteries
Normal segmental renal arteries (long arrows)
Color Doppler image of the kidney
Moukaddam H et al. Ultrasound Clin 2007 ; 2 : 455 – 475.
Normal inter-lobar renal arteries (short arrows)
Normal kidneyPower Doppler
• Increases sensitivity to low flow
• Less angle-dependent
• Good visualization of the entire renal vascular tree
Zubarev AV. Eur Radiol 2001 ; 11 : 1902 – 1915.
Normal pulse Doppler waveformRenal segmental artery
• Sharp systolic upstroke
• Low resistance waveform
• Continuous forward diastolic flow
Early systolic notch
Some normal waveforms have early systolic notch
Measuring to point of PSV results in prolonged AT & AIExcellent negative predictive value of stenosis > 60%
Extrasystole
Correct RI calculated in normal sinusoidal rhythm
Spectral Doppler of renal arteriesNormal values
• PSV < 180 cm/sec• Renal Aortic Ratio (RAR) < 3• Resistive index (RI) < 0.70
• ∆ RI (right – left) < 0.05• Acceleration Time (AT) < 0.07 sec• Acceleration Index (AI) > 3.5 m/s2
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