RENAL ARTERY DOPPLER

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RENAL ARTERY DOPPLER
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Objectives

• Upon completion of the presentation
• the viewer should be able to
• Identify a normal renal artery signal.
• Describe Tardus-Parvus, RAR and Acceleration
  index.
• List causes for hypertension
• Outline a normal Renal Doppler exam

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Table of Contents

• Indications for a Renal Doppler Exam
• Renal Artery Stenosis
• Hypertension
• Anatomy Variants
• Diagnostic Criteria
• Doppler waveform
• Exam Protocol
• Case Examples

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Clinical Indications for Doppler

• Evaluate a hypertensive patient for renal artery
  stenosis (RAS).
• Hypertensive patients not controlled with medical
  treatment.
• Patients with abdominal aortic dissection.
• Evaluation of renal transplant.
• Audible Bruit
• Patients with AAA

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Renal Artery StenosisCauses

• Atherosclerosis Plaque deposits cause
  narrowing/blockage.
• Affects men gt women
• Typically effects age gt40 years
• Involves proximal aspect renal artery
• Fibromuscular Fibrous tissue growth in arterial
  walls.
• Affects women gt men ( approx.. 4 1).
• Typically affects ages lt 50 years
• Involves mid to distal aspects of renal artery
• Acute Traumatic injury causing obstruction.

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Hypertension and RAS

• Relationship
• Renal Artery Stenosis causes hypertension.
• Hypertension is the symptom that indicates RAS
  Doppler needed

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Hypertension and RAS
Adrenal Gland
Kidney
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Hypertension and RAS

• RAS
• Increased PR
• Decrease renal blood flow
• Production of rennin

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Hypertension and RAS

• Rennin converts angiotensinogen to angiotensin.
• Angiotensin is a potent vasonstrictor.

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Hypertension and RAS

• Angiotensin also acts on the adrenal cortex to
  produce aldosterone.
• Aldosterone causes the kidney to absorbed more
  sodium and water.

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Hypertension and RAS

• This leads to increased in blood volume and also
  the BP.

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Renal Artery Stenosis

• Anatomy Variants
• Diagnostic Criteria
• Doppler waveform
• Exam Protocol
• Case Examples

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Renal Anatomy

• Kidneys
• Vessels
• Accessory Vessels
• Doppler Waveform

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Normal Anatomy of the Kidneys

• Size 9-11cm
• Difference between Lt. Rt. Renal Length lt 2 cm

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Normal Anatomy of the Kidneys
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Normal Anatomy of the Kidneys
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Celiac Axis
Rt Renal Artery
Lt Renal Artery
Superior Mesenteric Artery
Aorta
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Segmental arteries
Interlobar arteries
Main Renal artery
Arcuate arteries
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Normal Right and Left Renal Artery
Coronal View
Transverse
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Normal Right Renal Artery
Transverse
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Normal Left Renal Artery
Transverse
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Renal Artery Stenosis

• Normal Variants Accessory Vessels

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Normal Variants of Renal Arteries

• Most common anatomy is single right and left
  renal artery (approx. 55 population)

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Normal Variants of Renal Arteries

• Second most common an is accessory renal artery
  branching off a main renal artery (14)

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Accessory Renal Arteries

• Branch off a main renal artery or aorta.
• Supply small portions of the renal parenchyma.
• Can be
• 1) single or multiple
• 2) unilateral or bilateral

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Accessory Renal Arteries
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Accessory Renal Arteries

• Can extend to upper, mid,or lower poles of
  kidney.
• Stenosis in an accessory can result in
  hypertension.
• Best evaluated in coronal plane with color
  Doppler.

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Accessory Renal Arteries
Two Left Renal Arteries
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The Normal Renal Waveform

• Low resistant waveform.
• Rapid and steep upstroke during systole.
• Dicrotic notch.
• Low resistant runoff during diastole.

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The Normal Renal Waveform
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RAS Exam

• Diagnostic Criteria
• Protocol
• Example of normal Exam

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Diagnostic Criteria

• Color Doppler non-visualization
• Peak Systolic Velocity
• RAR
• Acceleration time
• Acceleration Index
• End Diastolic Ratios
• Tardus Parvus

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Diagnostic Criteria
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Peak Systolic Velocity

• Normal gt1.8 m/sec
• Low grade(1-59)gt1.8 m/sec
• No post-stenotic disturbance
• High grade(60-99)gt1.8 m/sec
• Post-stenotic turbulence
• Total occlusion - no flow

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Peak Systolic Velocity
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Remember all angles MUST be 60 degrees or less!
Peak Systolic Velocity
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Renal-Aortic Ratio

• RAR PSV renal artery
• PSV aorta

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Renal-Aortic Ratio

• PSV alone may be inaccurate due to
  difficulty with Doppler angle insonation
• RAR angle independent
• Obtain aortic signal 2cm distal to SMA
• Use highest main renal artery signal

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Renal-Aortic Ratio

• Normal lt 3.5
• Low grade (1-59) lt 3.5
• High grade (60-99) gt 3.5
• Total occlusion renal length lt 9cm

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End Diastolic Ratio

• Assess both parenchymal vascular resistance and
  disease.
• Sufficient perfusion gt 0.23
• Severe parenchymal vascular disease lt 0.23

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Acceleration Index
?V
AT
?T
AI ?V/ ?T
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Acceleration Index

• Acceleration time time for peak systolic
  velocity
• Acceleration index acceleration slope divided
  change in time
• lt 3.78 kHz/sec/MHz indicates greater than 50
  stenosis.

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Acceleration Index

• To calculate
• Place the first cursor at the beginning of
  systole.
• Place the second cursor at the peak of systole.

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Acceleration Index
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Acceleration Time

• Acceleration time gt 0.1 sec indicates greater
  than 50 stenosis.
• Measure with sweep speed of 100 mm/sec.
• Normal waveforms have steep systolic upstrokes,
  whereas waveforms distal to a stenosis have a
  more gradual upstroke and dampened systolic peak.

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Abnormal Doppler Findings

• Peak systolic velocity ( PSV) in renal artery
  ( proximal, mid, or distal ) gt 180
  cm/sec.
• Renal Artery / Aorta Ratio ( RAR), gt 3.5.
• Tardus-Parvus.

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What is Tardus-Parvus?

• Tardus delayed early systolic acceleration or
  upstroke
• Parvus diminished amplitude and rounding
  systolic peak.

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What is Tardus-Parvus?
Delayed upstroke
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What is Tardus-Parvus?
Rounded
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Tardus-Parvus

• Seen in distal segmental arteries, indicating
  high grade stenosis proximally.
• Measured using either
• Acceleration time (normal is less than 70ms)
• Acceleration Index ( normal is greater than 3/m/s
  square)
• When present, 100 indicative of RAS, but not
  ALWAYS present in RAS patients

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Tardus-Parvus
Normal
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Tardus-Parvus
Abnormal
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Tardus-Parvus
Normal renal artery notice the steep upstroke
normal acceleration index in this waveform.
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Tardus-Parvus
Notice the rounded waveform and the blunted
upstroke with tardus-parvus.
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Renal Artery Protocol

• Exam Protocol
• Normal RAS Exam

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Renal Artery Doppler Scanning

• Test usually takes 60-90 minutes.With experience
  the time can be reduced.
• Patient should be fasting (at least 8 hours).
• Patient should be well hydrated, encourage water
  intake.
• 4 to 2 MHz transducer

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Protocol

• Grey Scale
• Measure and document kidney size, and any
  abnormalities. (Normal size 9-13 cm.)
• Rule out mass, stones, hydronephrosis, etc.
• Start with the abdominal aorta midline and
  obtain and measure Doppler signal. Remember to
  look for plaque (arteriosclerosis).

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Protocol / Kidneys

• Abnormalities
• Hydronephrosis
• Stones
• Renal Failure
• Polycystic Disease

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Protocol / Kidneys
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Protocol / Kidneys
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Protocol / Kidneys
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Protocol / Kidneys
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Protocol / Aorta

• Doppler Midline
• Beware of Plaque

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Protocol / Aorta
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Protocol / Aorta
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Protocol / Aorta
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Protocol

• Doppler and Measure
• Rt. and Lt. renal arteries, Prox , mid, and
  distal aspects of each and any accessory
  arteries.
• ALL Doppler angles are 60 degrees or LESS.
• Segmental arteries (upper, mid, and lower poles)
  of each kidney.
• Acceleration index of segmental arteries. Look
  for tardus-parvus.

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A Normal Renal Artery Examination
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Proximal Right Renal Artery
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Mid Right Renal Artery
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Mid Right Renal Artery

• Transverse view

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Mid Right Renal Artery

• Transverse view

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Distal Right Renal Artery
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Segmental Renal Artery
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Segmental with Acceleration Index
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Angle lt 60
T 60
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Angle lt 60
T 78
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Overview of Renal Artery Study

• Routine US exam of the Kidneys
• evaluate size and echotexture, r/o pathology
• Doppler Aorta
• Measure PSV, for RAR calculation
• Doppler renal arteries
• Measure PSV, for RAR calculation

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Overview of Renal Artery Study

• Doppler segmental arteries
• obtain acceleration index
• look for Tardus-Parvus
• Calculate RAR
• RARPSV Renal artery/ PSV Aorta

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Renal Artery Stenosis Treatment

• Medically with ACE inhibitors
• Balloon angioplasty
• Arterial stent
• Surgically.