renal artery doppler ns

8/3/2019 Renal Artery Doppler Ns

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Anterior Approach.The patient is lying supine and the probe is moved inferiorly

and superiorly to identify the renal arteries and any supernumery arteries.Look in

B-Mode and Colour Doppler to help idenify.

Anterior Approach


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Anterior Approach.The renal arteries are clearly imaged in B Mode from an

anterior approach however as it is perpendicular to the ultrasound beam it is not

suitable for Doppler assessment.

In most individuals, the renal arteries arise from the abdominal aorta immediately

distal to the origin of the superior mesenteric artery (SMA). The right renal artery

passes underneath the inferior vena cava (IVC) and posterior to the right renal vein


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The left renal vein passes between the aorta and SMA. The left renal artery is

located posterior to the renal vein. /

The aorta is examined for any abdominal aortic aneurysm.The velocity should be

between 50 and 100cm per second.


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This is a single renal artery posterior to the IVC

There are 2 renal arteries posterior to the IVC


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There are 3 renal arteries posterior to the IVC

Oblique Approach


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Oblique Approach.Angling 45 degrees to right renal artery or rolling the patient in

a semi left decubitus position to avoid the bowel gas and improve the Doppler angle.

Oblique Approach.Angling 45 degrees to right renal artery.In most individuals, the

renal arteries arise from the abdominal aorta immediately distal to the origin of the

SMA.By moving the probe to the right of midline and angling toward the patient's

left, an acceptable Doppler angle of 45-60 degrees is achieved


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"Coronal approach to visualise the renal artery from the aorta to the kidney.On a

tortuous vessel the mid section may not be seen."

Coronal Approach.Angling 90 degrees to left renal artery.The patient is rolled

decubitus and a coronal view through the left loin.An intercostal view through the

ribs on a deep inspiration is ideal.

Normal waveform

A normal waveform obtained from the main renal artery demonstrates a rapid


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upstroke in systole and a low resistance waveform with continuous forward flow

throughout the cardiac cycle.

The normal peak systolic velocity of the main renal artery is less than 150 cm/sec.

The resistive index is less than 0.70 .

This coronal plane gives a better appreciation of the supernumery arteries.Another

useful view to demonstrate supernumery (duplicate) renal arteries is a coronal

image of the aorta.

Aorta measurements

A Spectral analysis is made of the aorta at the level of the renal arteries. The

Velocity is taken with an angle for accurate measurement. And another


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measurement is taken with no angle so it can be compared to the renal artery at a

stenosis site to do a ratio.

Stenosis measurement

This is a spectral trace done in the stenotic site with an angle for an accurate

velocity measurement.Less than 180cm/sec is normal.

Renal artery : Aortic Ratio (RAR)

This is the same trace but the angle is taken off and the measurement is compared to

the aortic measurement (RAR)with no angle so a ratio can be determined.


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The length of the stenosis is measured and its distance from the renal artery origin.

An indirect assessment requires a good colour image to determine the position of the

interlobar and interlobular arteries, which in turn will determine the best angle to

get an accurate measurement of the RI and AT.


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This is a normal spectral trace of an interlobar (segmental) artery

Resistive Index

The Resistive Index (RI)is easily performed by placing a caliper on the early systolic

peak (ESP)and the other caliper on the lowest diastole.The RI is a ratio of peak

systolic and end diastolic velocity.


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Acceleration Time

The Acceleration Time (AT) is done by placing a caliper on the level at which the

gradient begins to rise and finished at the first peak ie the Early systolic Peak

(ESP).This should be less than 70ms

Indirect method

This is assessing the parenchymal haemodynamic changes in the waveform.

Initially there is an ESP but with a stenosis this will be lost and a tardus parvus

waveform will be the result.

With chronic renal failure the waveform becomes high resistance (RI>0.80) which

unfortunately cannot be repaired. This is also associated with high creatinine levels.


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Indirect method

1. The blood travels down the aorta

2. Into the renal artery

3. Some arteriosclerotic plaque proximally causing a stenosis and high velocity

flow with a Renal to Aortic Ratio (RAR) >3.5:1 and Velocity >180cm/sec.Therefore it is >60% stenosis

4. There is post stenotic turbulent,aliasing flow

5. There is loss of the ESP and and a slow rise (increased AT)

6. The interlobar (segmental)

7. Interlobular (arcuate) assessment will reflect the earlier stenosis with

abnormal AT>0.07sec

ULTRASOUND OF THE RENAL ARTERIES

ROLE OF ULTRASOUND

PREPARATION

Fast for 6 hours. No food. Drink 2litres of water over the two hours prior to the

appointment.The bladder can be emptied as needed. Book the appointment in themorning preferably to reduce bowel gas.

TRANSDUCER:Highest frequency curved linear array probe possible. Start with 7MHz and work down to

2 or 3MHz for larger patients.Colour and Doppler capabilities . Assess the depth of

penetration required and adapt.


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A high sweep speed will improve accuracy of the measurement taken on the Spectral

Trace.INDICATIONS

Renovascular Hypertension,usually it is uncontrolled.May be caused by Renal Artery Stenosis,parenchymal disease,renal neoplasms,renal vein

thrombosis,or an adrenal mass.

It may be caused by atherosclerosis in the renal artery or less commonly fibromuscular

dysplasia(FMD) particularly in a young woman.

LIMITATIONS

This examination requires the patient to be cooperative and hold respiration in inspiration

and expiration depending where the sonographer can best see the artery. If the patient

cannot hold their breath then adequately getting an accurate Doppler signal will be

impossible.

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SCANNING TECHNIQUE

There are 2 techniques that ideally are used in conjuction with each other,however in

circumstances where the renal artery is not seen in its entirety then the indirect approach

can give an indication of vascular disease.

DIRECT

Assessing the renal artery from the aorta to the kidney and any accessory arteries for any

stenosis.A >60% stenosis is reported when there is a >3.5:1 Renal to Aortic Ratio (RAR)

or a >180 cm/sec velocity in the renal artery at any point from the origin to the kidney.

INDIRECT

Assessing the arteries within the kidney parenchyma to assess any alteration in the

waveforms.The RI should be low resistance.The Acceleration Time (AT) should be

9cm. The

RI wil be >0.8 for untreatable medical renal disease.

ANTERIOR APPROACH

The renal arteries are clearly imaged in B Mode from an anterior,subcostal approach
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however as it is perpendicular to the ultrasound beam it is not suitable for Doppler

assessment. Supernumery (duplicate) arteries can be seen looking posterior to the IVC in

B Mode and Colour in a sagittal plane.

OBLIQUE APPROACH

By moving the probe to the left of midline and angling toward the patient's right, an

acceptable Doppler angle of 60 degrees is achieved. To avoid aliasing set the colour scalehigh enough so it is minimized. If the scale is too low then it is difficult to determine

which veesel is the vein and which vessel is the artery.

CORONAL APPROACH

Roll the patient into a decubitus position to void bowel gas and improve visibility of the

renal artery,especially the mid to distal portion.

PRONE APPROACH

The patient is lying prone or decubitus and the probe is moved from the spine laterallyusing the muscles as an acoustic window to find the kidney initially and then the renal

hilum using Colour Doppler.

BASIC HARD COPY IMAGING

DIRECT METHOD

Peak Systolic Velocity in the Aorta -taken above the level of the renal arteries

origin.Taken with and without an angle for ratio with the renal artery. Renal Artery Assessment- initially with colour Doppler.

Renal Artery Spectral Analysis- Origin,Proximal,Mid and Distal Artery .If a stenosis

is suspected then a velocity with an angle and a measurement with no angle to compare

with the aorta to give a ratio (>3.5:1 is a >60% stenosis which is haemodynamicallysignificant)

Interlobar/Segmental Artery Spectral Analysis- Acceleration Time (AT) and Resistive

index (RI).(AT 0.8 for chronic renal disease)

INDIRECT METHOD

Aorta B Mode -Longitudinal and Transverse to assess for an abdominal aortic

aneurysm.

Kidney lengths-cortex assessment for reduced size. Perfusion Kidney- colour Doppler used to assess the perfusion to the edge of the renal

cortex.

Resistive Index- Spectral Doppler of kidney parenchyma at the interlobar (segmental)arteries and interlobular (arcuate)arteries.

Acceleration Time

renal artery doppler ns

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