Focal liver masses: differential diagnosis with pulsed Doppler US

Duplex Doppler ultrasound (US) was used in 68 consecutive patients with focal liver lesions, including 12 hepatocellular carcinomas, one cholangiocarcinoma, 37 metastases, 15 hemangiomas, one hemangioendothelioma, and two focal nodular hyperplasias. Of the hepatocellular carcinomas, six were diffusely hyperechoic, two were hypoechoic, two were single hyperechoic lesions, and two were multifocal and hyperechoic. All ten tumors with Doppler shifts of 5 kHz or above proved to be hepatocellular carcinomas. The other two hepatocellular carcinomas showed Doppler shifts of 3 kHz. In contrast, no hemangioma showed shifts above 0.7 kHz, and ten of the 15 gave no detectable signal. Of the metastases, 20 gave no signal and 17 had signals of up to 4 kHz. Three-kilohertz signals were also obtained from a cholangiocarcinoma, a hemangioendothelioma, and focal nodular hyperplasia. Correlation with angiographic findings suggested that the high-velocity Doppler signals were associated with large pressure gradients due to arteriovenous shunting. Duplex Doppler US can therefore aid in the differential diagnosis of diffuse and focal liver lesions.     

Hepatic artery pseudoaneurysm: diagnosis with real-time and pulsed Doppler US

Duplex ultrasonography (US), consisting of real-time and pulsed Doppler US, was used to identify a pseudoaneurysm in a patient with recurrent bleeding and chronic pancreatitis. The authors present a case that illustrates the limitations of real-time US in evaluating sonolucent masses in pancreatitis and the need for using pulsed Doppler technique.     

Brain death in infants: evaluation with Doppler US

In a preliminary study, nine infants with a clinically determined diagnosis of brain death were examined with duplex pulsed Doppler ultrasonography (US) through the anterior fontanelle. Flow velocity measurements were made in the intracranial internal carotid artery and anterior cerebral artery. Resistive index (RI) was calculated in each patient and used as an indicator of diastolic flow. Eight of nine infants showed markedly elevated RI (100%-191%) with reversal of diastolic flow. One infant had low RI (42%-58%) with preserved systolic and diastolic flow until death. The authors believe that the elevation of RI with diastolic flow reversal seen in these patients is a reflection of increased intracranial pressure and is a sign of poor prognosis when present on serial examinations. Cranial duplex pulsed Doppler US is a useful, noninvasive tool in the diagnosis of brain death in infants but must be carefully correlated with clinical examination and other diagnostic tests.     

New class of pulsed Doppler US ambiguity at short ranges

A form of range ambiguity in Doppler ultrasound has been identified. It occurs when a high pulse repetition frequency (prf) is used with a superficial range gate. "Phantom" range gates are then generated at depths beyond the desired range gate, and these may produce artifactual signals. Extremely high prf values should not normally be used, and duplex machines should be programmed to display phantom range gates wherever they fall within the displayed field of view.     

Absolute flow measurements using pulsed Doppler US. Work in progress

Quantitative flow measurements were assessed in both laboratory and canine models using pulsed Doppler ultrasonography (US). A hydrodynamic model consisting of a Harvard pulsatile pump, a water bath, tubing, and a variable resistance reservoir was used to obtain absolute volumetric flow measurements. Parameters including angle of incidence, size of tubing, stroke volume, stroke rate, sample volume, and transducer frequency were changed independently. The effect of varying these parameters on the determination of absolute flow was analyzed. Absolute flow measurements using duplex US were performed in the canine aorta and femoral artery with reference to the electromagnetic flow probe. These data are presented, along with methods to reduce error in flow measurements that can be directly applied to quantitative estimates of blood flow in humans.     

Renal allograft rejection: evaluation by Doppler US and MR imaging

A prospective study compared the efficacy of Doppler ultrasonography (US) and magnetic resonance (MR) imaging in evaluating 38 renal allografts, with specific attention to transplant rejection. Forty-three Doppler US and 42 MR examinations were performed and interpreted. Histologic correlation was obtained from 22 biopsy or nephrectomy specimens. Clinical correlation or a response to instituted therapy was used as confirmation in the remaining allografts. Accuracy in identifying cyclosporine toxicity or acute tubular necrosis could not be evaluated because there were few such cases, with concomitant rejection in most. The ability to predict and identify presence or absence of rejection was not affected by different serum creatinine values. Doppler US was significantly superior to MR imaging in identifying allograft rejection, demonstrating a higher sensitivity (95% vs. 70%), specificity (95% vs. 73%), and accuracy (95% vs. 71%). Because of its low cost and accessibility, Doppler US should become the primary modality for renal transplant screening.     

Renal transplant pyelocaliectasis: role of duplex Doppler US in evaluation

To distinguish the obstructed from the nonobstructed dilated collecting system of transplanted kidneys without interventional diagnostic measures, the authors prospectively evaluated duplex Doppler analysis (determination of resistive index [RI]) in 35 renal transplant patients with pyelocaliectasis. Proof of the presence or absence of obstruction was obtained at interventional procedures in 18 patients and at clinical follow-up in 17. Thirteen kidneys were obstructed (mean RI, .81 +/- .06), while 22 had nonobstructive dilatation (mean RI, .66 +/- .07). The RI difference was statistically significant (P less than or equal to .01). Of 21 kidneys with a normal RI, only two had obstruction. In both of these, the obstruction was associated with a significant peritransplant collection of fluid due to a ureteral leak. In the seven obstructed transplanted kidneys with follow-up, the mean RI was .82 +/- .06 before nephrostomy and .67 +/- .05 after nephrostomy. Obstruction was a common cause of an elevated RI (greater than or equal to .75). Other causes of transplant dysfunction can be associated with an elevated RI and nonobstructed dilatation. More important, a normal RI should strongly argue against obstruction unless a ureteral leak is also present.     

The Kimray-Greenfield filter: evaluation by duplex real-time/pulsed Doppler ultrasound

The Kimray-Greenfield filter is a wire cage which is inserted into the inferior vena cava (IVC) to prevent thrombi originating in pelvic and leg veins from embolizing to the lungs. Duplex real-time/pulsed Doppler ultrasound was used to evaluate placement and function in 38 patients (46 examinations). Real-time examination successfully identified the IVC and filter in 89% of cases. Pulsed Doppler studies demonstrated flow above and below the filter in 76%, accurately predicting normal flow in most cases. In 4 patients, Doppler scans revealed little or no flow distal to the filter; contrast cavograms confirmed obstruction secondary to thrombosis. This appears to be an accurate, noninvasive method of assessing postoperative reliability of the Kimray-Greenfield filter.     

Duplex pulsed Doppler US versus intracranial pressure in the neonate: clinical and experimental studies

This study was conducted to determine if the resistive index (RI) could be used for the examination and follow-up of neonates with increased intracranial pressure. First, in a laboratory model with four mongrel dogs, RI was found to correlate linearly with cerebral perfusion pressure. Second, RI was studied in 57 healthy neonates and 285 neonates with abnormal clinical or head ultrasound findings. Average RI for healthy newborns was 75 +/- 10 and was inversely related to gestational age. RI in newborns with abnormal findings was uniformly elevated, but these values varied considerably and were not statistically different from normal values. Third, the RI was found to decrease significantly after patent ductus arteriosus ligation, tapping of subdural effusions, ventricular tapping (later cerebrospinal fluid shunting led to a further drop in RI), and ventriculoperitoneal shunting. Elevated RI indicates possible intra- or extracranial abnormality affecting cerebral blood flow. Doppler RI is valuable in following up neonates with abnormal or unstable conditions and in assessing the effectiveness of therapies to improve cerebral perfusion.     

Renal blood flow in neonates: quantification with color flow and pulsed Doppler US.

Color flow and pulsed Doppler ultrasound measurements of renal artery blood flow were compared with cardiac output in 22 preterm and 19 full-term healthy neonates. Renal arteries were insonated 3-5 mm from the abdominal aorta at an angle of less than 15 degrees. Vessel diameter was estimated from color flow diameter. Total renal blood flow increased significantly (P less than .001) with advancing birth weight and gestational age, because of increased vessel diameter, but flow velocity did not. The mean (+/- 1 standard deviation) value for both right and left renal artery blood flow was 21 mL/min/kg +/- 5, and the mean proportion of cardiac output to the kidneys was 16.1% +/- 3.7. Seven preterm infants with a symptomatic patent ductus arteriosus had increased cardiac output values (444 mL/min/kg +/- 45) and reduced right (15 mL/min/kg +/- 7) and left (16 mL/min/kg +/- 7) renal artery blood flow, with 6.6% +/- 2.0 of cardiac output directed to the kidneys. These values normalized after closure of the ductus. This study provides normative data for renal artery blood flow in neonates during the first week of life.     

Hepatocellular carcinoma: evaluation with color Doppler US and MR imaging.

Fifteen patients with hepatocellular carcinoma underwent examination with color Doppler ultrasound (US), magnetic resonance (MR) imaging, dynamic computed tomography (CT), and angiography. Doppler signals ranging from 0.22 to 3.48 kHz could be obtained from within the tumor in 14 of 15 patients. The resistive index was 0.38-0.77. Color Doppler signals were visualized in nine of 15 lesions with a Doppler shift greater than 0.7 kHz. The Doppler signals and the resistive index of the tumor vessels became lower as the vessels progressed into the center of the lesion. The appearance of tumor vessels recognized on MR images obtained with gradient-recalled acquisition in the steady state (GRASS) in 11 of 15 lesions was compared with that on CT scans and angiograms. Tumors that were hyperintense on GRASS images obtained with a flip angle of 15 degrees transmitted Doppler signals of considerably higher amplitude compared with the isointense lesions. Both color Doppler US and MR imaging provided useful information for characterizing intratumoral blood flow.