Understanding Doppler and its Current Uses in OB

Diana M. Strickland, BSBA, RDMS, RDCS

Continuous vs. Pulsed

Doppler – Moving structures-Red Blood Cells-

Scattered waves-low level NOISE!

Wall motion – high level NOISE!

ƒd = 2(ƒt • v • cosθ)/c

Doppler – Moving structures-Red Blood Cells-

ft ft

fr fr

f

Time

Positive shift

Negative shift

ft

f

time

Doppler – Moving structures-Red Blood Cells-

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ft

f

time

ft

Doppler – Moving structures-Red Blood Cells-

<20o

Optimal

Doppler modes are differentiated by the way the signal is processed

FFT – Fast Fourier Transform• Algorithm to display multiple frequencies in a single

time frame – Spectral Doppler• Think of a single note versus a chord• Color Doppler is an average of the spectral doppler

– it can’t show each frequency in a specific time unit• Standard display is BART – Blue away, Red towards

• Density of blood cells displayed as an intensity of gray • High density (power) – bright• Low density (power) – less bright

• Is power useful in Spectral Doppler – NO, but it is in Power Doppler• Color tone determined by density (#) of cells

Plug Flow - Systole

Diastole

Consider spread through sample volume

Broadening / Narrowing

Time

Frequency

S D

Envelope

Adjusting Parameters

• Gain• Scale• Baseline• Filter• Gate• Sweep

Adjusting Parameters

• Gain• Scale• Baseline• Filter• Gate• Sweep

Adjusting Parameters

• Gain• Scale• Baseline• Filter• Gate• Sweep

Adjusting Parameters

• Gain• Scale• Baseline• Filter• Gate• Sweep

Adjusting Parameters

• Gain• Scale• Baseline• Filter• Gate• Sweep

Adjusting Parameters

• Gain• Scale• Baseline• Filter• Gate• Sweep

Adjusting Parameters

• Gain• Scale• Baseline• Filter• Gate• Sweep

Adjusting Parameters

• Gain• Scale• Baseline• Filter• Gate• Sweep

Adjusting Parameters

•Gain

•Scale

•Baseline

•Filter

•Gate

•Sweep

Size

Invert

Other causes for poor Doppler signal…

• Frequency of transducer too high for vessel depth• Lower frequency

• Receiver gain too low• Increase gain

• Focal zone not optimized to area of interest – the vessel• Move it ;-)

Fetal Well Being

• NST• BPP• Doppler

Fetal Well Being

S / D

RI (Resistance Index or Pourcelot Index)(S-D)S

PI (Pulsatilty Index)(S-D)A

TAMV Time-averaged mean velocity

Maximum Systole / Minimum Diastole

Middle Cerebral ArteryMCA

• Placental Insufficiency• Anemia (Isoimmunization / Parvo)

MCA – Circle of Willus

ACA

ACo

MCA

PCoAPCA

BA IC

MCA – Placental Insufficiency• CerebroPlacental Ratio – CPR

• Originally used the anterior cerebral artery– Wladimiroff, et al.

• RI c / RI u• >1 Normal, <1 Redistribution

• MCA RI• <70 Indicative of Redistribution

• Others• Umb Artery RI• Umb Artery PI• MCA PI• MCA TAMV• Thoracic Aorta PI• Thoracic artery TAMV• UA/MCA PI ratio• MCA/Thoracic Aorta PI ratio• MCA PI x Thoracic TAMV

MCA – Placental Insufficiency

• Valuable when fetus is reacting to hypoxia• When physiological responses to hypoxia

become exhausted, fetus cannot adapt further• Decline of forward cardiac function (increase

venous doppler indices)• Deregulation of cardiovascular homeostasis

may be seen and arterial circulation indices become less reliable.

MCA – Placental InsufficiencyIncreased diastolic umbilical vein flow = GOOD

Increased diastolic cerebral flow - may signal placental problem

Viscosity = # of red blood cells

Anemia

Viscosity - Normal

Viscosity - Anemia

MCA – Anemia• Fetuses healthy and w/ anemia mild, moderate,

and severe.• Linear models fitted to data for individual fetuses

– slope was determined• Average rate of change as a function of GA• MCA-PSV – expressed as MoM

• Healthy vs. Mild anemic – NS• Healthy vs. Severely anemic (P=.01)

• Conclusion – excellent tool to predict which fetuses will become severely anemic

Detti, Mari, Moise et al, AJOG Oct 2002

MCA - Anemia

• Peak Velocity (w/fetal blood sampling)• Sensitivity for moderate or severe anemia 100%

FPR 12% fetuses w/o hydrops (Mari, et al, NEJM Jan 2000)• Fetuses w/Parvo B19 Sens /Spec 100/100% slightly less in

alloimmune group (included post transfusion follow-up) (Delle Chiaie, et al, USOG Sep 2001)

• Correlation between Hemoglobin and MCA-PSV becomes more accurate as severity of anemia increases. (Mari, et al, OG Apr 2002)

• TAMV (Abdel-Fattah, et al, BJR Sep 2002)

IVC/SVC doppler

• Influenced by heart rate, RH hemodynamics and function, and AMOUNT of blood flowing through veins

• Reciprocal shift observed between IVC and SVC velocity waveforms (Smin)

• Changes another manifestation of blood flow redistribution toward the brain

• May be good to use prior to 30 weeks when doppler findings more difficult to interpret

Fetal Echo• Critical to evaluate flow an GV anomalies

• Quantitate flow – Artery size, volume, VTI• Direction of flow• Presence of flow• Quality of flow – turbulence• Tei Index – (TI) MV & LV flow in one

waveform• Tissue Doppler

MVLV

Uterine Artery Doppler

• Continuous Wave Doppler / Intraplacental• IUGR (Chronic Hypertension) and

Preeclampsia• High AFP

• Little change seen in doppler indices after 26 weeks

• More difficult to assess when they are abnormal

Ovarian Artery Doppler

• Tumor Angiogenesis – limited vascular tone due to absence of the muscular tunica media

• CD screening optimal in PM women• No cyclic change in ovarian volume

• RI < .40• 96.4% Sens., 98.8% Spec., 98.2 PPV in 14,317

patients• Kurjak, Fleischer, and Bourne

Ovarian Artery Doppler

• Impedance values in benign vs. malignant lesions overlap

• Studies now looking at arrangement and density of vessels

• Neural Networks and Baysian networks are being developed and tested