Doppler Ultrasound Applications

Abdominal Vessel Doppler Flow Patterns

• Doppler ultrasonography is used to analyze blood flow in abdominal vessels.
• Doppler techniques involve placing a sample volume "gate" in the vessel, adjusting it to encompass the vessel diameter, and ensuring the angle of the gate is 60 degrees or less for accurate measurements.
• Respiration may need to be suspended during examination of some vessels.

Doppler Technique

• The sample volume "gate" is placed within the blood vessel and adjusted to include the vessel's entire diameter.
• The angle of the gate should not exceed 60 degrees to maintain accuracy, adjusted with a knob on the control panel.
• The patient may need to hold their breath during the scan for optimal results.
• Blood flow directed towards the transducer appears above the baseline, while flow away from the transducer is below the baseline on a spectral waveform trace.

Abdominal Doppler Techniques

• Doppler ultrasonography is used to detect the presence/absence of blood flow, blood flow direction, and flow disturbance patterns.
• It's also used for tissue characterization and waveform analysis.

Presence/Absence of Flow

• Doppler ultrasonography distinguishes between vascular and nonvascular structures.
• This differentiation is illustrated by the example of the common bile duct (CBD) and hepatic artery (HA).

Direction of Flow

• Doppler ultrasonography identifies blood flow reversal, differentiating arteries from veins.
• Patients with portal hypertension exhibit hepatofugal (away from the liver) flow in the portal vein instead of the normal hepatopedal (towards the liver) flow.

Disturbance of Flow

• Faster flow is typically seen in areas with flow disturbances, often following stenosis.
• Non-smooth, turbulent flow, indicated by swirls, chaotic eddy currents, and diverse directions, can accompany abnormalities.
• Stenosis and aneurysms are possible causes of flow disturbances.

Tissue Characterization

• Doppler ultrasonography shows specific perfusion patterns diagnostic of different tissue types or conditions.
• Hepatocellular carcinoma (liver cancer) demonstrates specific Doppler patterns.
• Peripancreatic artery pseudoaneurysms exhibit turbulent flow patterns.
• Pancreatic tumors may exhibit distinct flow patterns.

Doppler Waveform Analysis

• The spectral waveform provides information about the vascular impedance of an organ and the pressure/effort required for blood flow into the organ.
• The analysis reveals the velocity and turbulence of blood flow.

Nonresistive/Low Resistance Waveform

• High diastolic flow and constant perfusion are features of a nonresistive/low resistance waveform.
• The internal carotid artery and hepatic artery provide examples of vascular structures with this type of waveform.

Resistive/High Resistance Waveform

• Little to no diastolic blood flow characterizes a resistive/high resistance waveform.
• Blood flow may even reverse during diastole.
• External carotid arteries and brachial arteries exhibit resistive/high resistance waveforms.

Low and High Resistance Images

• Ultrasound images display low and high resistance waveforms illustrating different Doppler patterns and flow characteristics respectively.

Quantifying Resistance

• The resistive index (RI) measures the ratio of peak systolic velocity to minimum diastolic velocity.
• An RI less than 0.7 signifies normal vascular resistance.

Spectral Display

• The X-axis represents time, mirroring the horizontal axis.
• The Y-axis depicts Doppler shift frequency (velocity), corresponding to the vertical axis.
• The Z-component indicates the blood flow quantity at a given velocity, with higher blood flow appearing brighter on a gray-scale image.

Velocities on Spectral Waveform

• Peak, mode, and mean velocities are reflected on a spectral waveform chart.

Plug Flow/Laminar Flow Analysis

• A uniform, clear "window" without any variations in the spectral waveform represents plug flow.
• The blood cells' velocities are identical in this vessel type.
• Spectral broadening is the opposite of plug flow.
• Vessel walls' friction or stenosis causes spectral broadening.

Abdominal Doppler Techniques

• Techniques for best Doppler information include: instructing the patient to hold their breath and matching the sample volume gate to the vessel width rather than exceeding the vessel's diameter.

Aliasing

• High acoustic frequencies can produce the aliasing artifact, which is a wave shape that appears below the baseline.
• Adjusting the transducer frequency mitigates this artifact.

Doppler Beam Angle

• An angle of less than 60 degrees between the Doppler beam and blood flow is critical for accurate velocity calculations.

Color Map

• The top of the color map indicates flow towards the transducer, while the bottom of the color map indicates flow away from the transducer.

Celiac Axis

• The celiac axis is scanned transversely by the ultrasonic transducer, looking for distinctive "seagull"-shaped structures.
• Typical findings are high systolic flow and some diastolic flow patterns.

Hepatic Artery

• Scan methods for the hepatic artery include transverse scans across the porta hepatis or through the ribs.
• It is characterized by low-resistance flow showing a significant diastolic component and spectral broadening.

Splenic Artery

• The splenic artery often exhibits highly turbulent flow and a tortuous vessel appearance.
• Aneurysm formation is a potential complication in patients with chronic pancreatitis, requiring further investigation of suspicious pancreatic pseudocysts.

Superior Mesenteric Artery (SMA)

• The SMA is scanned transversely in the sagittal plane from the fasting state.
• In the postprandial state, the SMA displays low resistance flow with an enhanced diastolic component.
• The Doppler examination of the SMA helps diagnose stenosis or occlusion in mesenteric vessels.

Renal Artery

• The main renal artery has a low resistance pattern.
• Constant flow is associated with renal tissue perfusion.
• Spectral broadening is present in the waveform.

Renal Artery Stenosis

• Diagnosis in native kidneys can be challenging due to the inability to visualize the entire vessel.
• Collateral vessels may mimic the normal renal artery if obstruction is present.
• Multiple renal arteries are prevalent in a certain percentage of the population.

Renal Transplants

• Normal renal transplants typically exhibit low resistance flow patterns.
• Rejection is associated with an increased resistance and decreased diastolic flow.
• The pulsatility index (PI) or resistive index (RI) can assess vascular resistance.

Renal Veins

• Normal renal vein flow is variable, much like the flow in the inferior vena cava (IVC).
• Renal veins can be affected by tumors or blood clots requiring attention from medical professionals.

Inferior Vena Cava (IVC)

• The IVC displays a variable waveform that reflects variations in blood flow and respiration.
• IVC screening is important for identifying tumors or clots.

Hepatic Veins

• Normal hepatic veins exhibit variable flow, similar to that in the IVC.
• Budd-Chiari syndrome is associated with hepatic vein thrombosis, and its sonographic appearance is characterized by the hepatic veins appearing small and filled with echogenic material.

Portal Vein

• The portal vein typically flows toward the liver (hepatopedal).
• Thrombosis will cause thrombi to be seen in the portal vein along with dilated superior mesenteric vein (SMV) and splenic vein.
• Significant variations in portal vein flow occur in cases of portal hypertension or cirrhosis.

Cavernous Transformation of Portal Vein

• Chronic portal vein obstruction leads to collateral vessel formation around the portal vein.
• Diagnostic criteria for cavernous transformation of the portal vein include the absence of an extrahepatic portal vein and the presence of an echogenic area at the porta hepatis due to fibrosis.

Portal Hypertension

• Intrinsic liver disease (such as cirrhosis or cancer), portal vein thrombosis, and other medical conditions can lead to portal hypertension.

Portal Hypertension Doppler Findings

• Portal hypertension is characterized by a decreased velocity within the portal vein.
• The presence of patent umbilical veins is a reliable diagnostic indicator for portal hypertension.
• Fluctuations in patient flow patterns and the absence of respiratory variations are characteristic signs related to portal hypertension.

Portal Hypertension 2-D Ultrasound Findings

• Portal, splenic, and superior mesenteric veins will be dilated in patients exhibiting portal hypertension.
• A patent umbilical vein is another indicator of this condition.

Spontaneous Shunting

• Gastroesophageal anastomotic varices form in the esophagus' submucosa with the left gastric vein anastomosis with hemiazygous and azygos veins.
• Paraumbilical veins (ligamentum teres) extend downward from the left portal vein to the umbilicus, appearing as a continuation of the portal vein.
• Hemorrhoidal anastomoses arise between the superior and middle hemorrhoidal veins.
• Retroperitoneal anastomoses consist of subtle vessels seen around the pancreas.

Surgical Porto-Systemic Shunts

• Various surgical procedures create shunts connecting the portal vein to the inferior vena cava (IVC) or other vessels(SMA, Splenic vein, left renal vein) as treatment options for portal hypertension.
• Techniques like the portacaval shunt, mesocaval shunt, and splenorenal shunt are employed for this purpose.

Abdominal Aortic Aneurysm (AAA)

• An AAA is a weakening or dilation of the abdominal aorta exceeding 1.5 times its normal diameter.
• Patients over 60, those with hypertension/smokers, and those with vascular disease (peripheral or coronary) are at higher risk.
• The procedure for detection often utilizes a technique performed by clinicians to feel for a pulsating mass in the abdomen.

Abdominal Aortic Aneurysm (AAA) - Predisposing Factors

• The most prevalent contributor to AAA formation is arteriosclerosis.
• Syphilis and trauma are also potential causes.

Abdominal Aortic Aneurysm (AAA) - Clinical Symptoms

• AAA symptoms could include impingement on adjacent tissues, the occlusion of an artery leading to embolism , if the aneurysm ruptures causing intense back pain and an accompanying drop in hematocrit.
• A majority of AAA cases are asymptomatic.

Classification of Aneurysms

• Aneurysms are classified into true and false types.

True Aneurysms

• True aneurysms are lined with all three layers of the arterial wall.

False Aneurysms (Pseudoaneurysms)

• A breakdown in the vessel wall causes blood leakage that forms an encapsulated hematoma surrounding the vessel.

Descriptions of Aneurysms-Fusiform

• A common type, fusiform aneurysms exhibit a diffuse dilation of the aorta's entire circumference.

Descriptions of Aneurysms-Saccular

• In a saccular aneurysm, the dilation develops as a sac projecting outward from the vessel wall.
• The sac is connected to the aorta by a narrow stalk.

Locations of Aortic Aneurysms

• AAA can manifest in three major locations: infrarenal (below the renal arteries), perirenal (around the renal arteries), and suprarenal (above the renal arteries).

Growth Patterns for Abdominal Aneurysms

• Aneurysms with a size measured less than 6cm generally show gradual growth patterns.

AAA Statistics

• Survival rates for AAA vary significantly based on aneurysm size and rupture status.

Ultrasound Findings for Aortic Aneurysms

• The entire aorta must be evaluated during ultrasound testing, extending from the diaphragm to include the common iliac arteries.
• Proximal, mid, and distal aorta and right and left common iliac arteries must be measured.

Ultrasound Findings for Aortic Aneurysms-Aortic Ectasia

• Aortic ectasia is a characteristic where the distal aorta does not taper normally, signifying potential aneurysm development that warrants constant monitoring.

Aneurysm-Thrombus

• Evaluation of thrombus presence is crucial in aneurysm assessment.
• Old thrombi exhibit calcifications displaying as medium-low-level gray echoes.

Aortic Aneurysm-Thoracic Aorta

• Imaging of the thoracic aorta, if aneurysm extends this high, requires specialized techniques like angling up from the xyphoid and scanning from left parasternal/through back.

The Parasternal Approach

• The parasternal approach is utilized for thoracic aortic imaging.

Transverse Abdominal Aortic Aneurysm

• Transverse imaging is used to assess AAAs for size and potential rupture.

Aortic Dissection

• Aortic dissection involves the separation of the aortic wall layers, with blood flowing into the false lumen.

Aortic Dissection-Clinical Signs/Symptoms

• Aortic dissection is often manifested by sudden excruciatiating chest pain that radiates to the back.
• Patients are typically 40-60 years of age, frequently with hypertention
• Men tend to be affected more often.

Aortic Dissection-Sites/ Causes of Hemorrhage

• In cases of aortic dissection, blood may accumulate within the middle and outer layers of the tunica media.
• Aortic dissection affecting the ascending aorta is frequently attributed to tears within the tunica intima.
• Dissecting pathologies can progress in both directions, toward the heart and downward towards the extremities.

Aortic Dissection-Types

• Aortic dissection is categorised into three types, each having distinct starting points and potential consequences.

Aortic Dissections-Type I

• Aortic dissection type I is considered most dangerous, originating at the aortic root and potentially extending through the entire length of the aortic arch, potentially affecting critical branches.

• Aortic dissection-Type II

• Aortic dissection type II originates from the aortic root and typically does not extend beyond the aortic arch; this type is less dangerous compared to dissection or type I.

• Aortic dissection-Type III

• Aortic dissection type III starts at the descending aorta's distal area and often extends into the abdominal aorta, potentially restricting blood flow to vital regions.

Aortic Dissection-Causes

• Cystic medial necrosis, a weakening of the arterial wall, is considered a chief causative factor for aortic dissection.
• Marfan's syndrome, characterized by connective tissue abnormalities, is another contributor to the development of aortic dissection.
• Hypertension is a frequently associated risk factor.

Aortic Dissection-Images

• Illustrative diagrams depicting various stages of aortic dissection may aid comprehension.

Rupture of Aortic Aneurysm

• Intense abdominal pain and potential shock, along with an expanding abdominal mass, point to a ruptured abdominal aortic aneurysm (AAA).

Rupture of Aortic Aneurysm-Sites

• Rupture of AAA predominantly occurs on the lateral wall, situated below the renal artery origins.
• Potential for significant hemorrhage into surrounding tissues, such as the pararenal and perirenal spaces, displacing kidneys/obliterating psoas muscles, is a common complication.

Rupture-Aortic Compresssions

• AAA rupture can compress adjacent structures (such as the biliary system, renal arteries, and ureter) causing complications.

Aortic Graft

• Abdominal aortic aneurysms (AAAs) are frequently addressed by surgical repair involving the use of an echogenic prosthetic graft material.
• Post-operative complications, including the appearance of new aneurysms or pseudoaneurysms, at the graft interface, may necessitate further interventions.

Aorta Graft Techniques

• Techniques for endovascular graft implantation for AAA, involves insertion via the femoral artery to reach the injured site for repair.
• Endovascular procedures allow for less invasive approaches compared to traditional open surgical repairs.

Complications of Endovascular Graft

• Endoleaks, which are graft-related complications where blood leaks into tissues surrounding the graft, can arise.
• Factors including the implanted graft type, implantation method, and aortic anatomy are contributors.

Various Pulsating Tissues

• Conditions such as lymphadenopathy, pancreatic tumors, and retroperitoneal sarcomas present as pulsatile masses in the abdominal area.

Lymphadenopathy

• Lymphadenopathy, characterized by swollen lymph nodes, demonstrates pulsations synchronized with the aorta.
• Lymphoma is frequently linked to the condition.

Pancreatic Tumor

• While less common, pancreatic tumors can present as well-defined hypoechoic masses in the abdomen with pulsatile features..

Retroperitoneal Sarcomas

• Retroperitoneal sarcomas manifest as homogeneous echogenic masses surrounding the aorta.
• Tumor type, which may vary in characteristics from fatty sarcomas to fibrous/myomatous sarcomas, influence ultrasound appearances.

Arteriovenous Fistulas

• Arteriovenous fistulas refer to abnormal connections between arteries and veins.
• These connections are uncommon, primarily caused by trauma and less frequently by arteriosclerotic aneurysms.

Arteriovenous Fistulas- Clinical Signs

• Patients with arteriovenous fistulas generally experience lower back/abdominal pain, progressive cardiac decompensation, and a palpable abdominal mass with an audible bruit.
• Significant lower extremity edema and enlarged inferior vena cava (IVC) may also be observed.

Arteriovenous Fistulas-- Types and Diagnostic Findings

• Renal AV fistulas can manifest as congenital (e.g., cirsoid, aneurysmal) or acquired injuries.
• Congenital fistulas show as clusters of tubular, anechoic structures evident within the kidney. These are supplied by the enlarged renal artery and drained by the enlarged renal vein.
• Acquired fistulas tend to result from trauma, surgical intervention, inflammatory processes or tumors, and are a complication of aortic aneurysms.
• Ultrasound findings include multiple anechoic tubular structures, enlarged renal vessels, and potential overlap with hydronephrosis or para-pelvic cysts.

Inferior Vena Cava-Embryonic Development

• The inferior vena cava (IVC) is a major vessel arising from three types of cardinal veins (posterior cardinal veins, subcardinal veins, and supracardinal veins) developing through time dependent on fetal development.

Inferior Vena Cava- Abnormalities: Double IVC

• A double vena cava formation is an uncommon abnormality observed in approximately three percent of individuals.
• The size and appearance of the vessels are influenced by tissue and organ size/position.

Inferior Vena Cava-Abnormalities: Infrahepatic Interruption of IVC

• A developmental failure in the hepatic and subcardinal vein union may result in an interruption of the IVC.
• Associated variations may impact cardiac function or cause significant complications in the patient.

Inferior Vena Cava-Abnormalities: Ultrasound Findings

• The venous structures' sizes are evaluated in cases of IVC abnormalities.
• Determining the presence and location of obstruction or dilation, especially of the azygos vein, is essential..
• The direction and configuration of the vena cava's course and the presence of major vessels(e.g., azygos) within the abdomen are significant data.

IVC Dilation Causes

• Potential causes of IVC dilation include right heart failure, atherosclerosis, pulmonary hypertension, pericardial tamponade, and constrictive pericarditis.

IVC Thrombosis

• An occlusion of the IVC is life-threatening with significant consequences.
• Clinical symptoms include lower limb edema, reduced blood flow to organs/tissues of the pelvis and lower extremities, severe back pain, and gastrointestinal complications.
• Ultrasound examination should include visual identification and confirmation of the presence of a thrombus (a blood clot) within the affected vessel.

IVC Filter

• IVC filters are placed surgically or through angiographic procedures to prevent pulmonary emboli arising from lower limb thrombi.
• The filters are strategically positioned below the renal veins/above the iliac confluence and can potentially perforate vital structures like the IVC, duodenum, aorta, ureter, and hepatic veins.

Masses Affecting the IVC

• Various masses can affect the IVC, including right adrenal tumors, neurogenic masses, liver enlargement, liver masses, pancreatic masses, lumbar spine/lymphadenopathy/small bowel masses.

Renal Vein Obstruction

• Renal vein obstruction frequently affects dehydrated or septic infants.
• Adult causes may include nephrotic syndrome, shock, renal tumors, kidney transplants, or trauma.
• Tumors can either directly invade or externally compress the renal vein..

Renal Vein Obstruction- Clinical Signs/Symptoms

• Symptoms associated with renal vein obstruction may include flank pain, hematuria, a palpable flank mass, and proteinuria.
• The condition can be linked with maternal diabetes/transient hypertension..

Renal Vein Obstruction - Ultrasound Findings

• Ultrasound may identify a palpable kidney mass that requires exclusion of hydronephrosis or multicystic conditions.
• The presence of enlarged kidneys (without or with cysts) and zones of hemorrhagic/infarcted tissue are possible related findings in affected infants.

Renal Vein Obstruction - Late Clinical Findings

• Late-onset clinical symptoms of renal vein obstruction often involve elevated parenchymal echoes and loss of the corticomedullary junction and potentially a decrease in kidney size.

Renal Vein Thrombosis Criteria

• Key features of renal vein thrombosis include visible thrombi within the renal vein and IVC, dilation around the occlusion site (closer to the kidney), structural changes within the kidney, and potentially an enlargement of the affected kidney.

Renal Vein Thrombosis- Clinical Signs

• Patients with renal vein thrombosis often present with pain, nephromegaly (kidney enlargement), hematuria (blood in urine), and thromboembolic phenomena exhibiting significant variation in sonogram appearances.

References

• Hagen-Ansert, S. (2012). Textbook of diagnostic ultrasonography, vol. 1 & 2 (7th & 8th ed.s). Mosby Publishers. (This is a reference to the provided text, and not necessarily a definitive publication).

This quiz explores the fundamentals of Doppler ultrasound, including its sample volume gate, ideal angles for accuracy, and its various functions in abdominal vascular imaging. Test your knowledge on how Doppler ultrasound differentiates vascular from nonvascular structures and its capability to detect flow reversals.