Biomedical subjects

D A Merton

Publications and source records attributed to D A Merton.

At least 19 recordsLinked to original sources

PubMed2002

Contrast enhanced vascular three-dimensional ultrasound imaging.

In other imaging modalities three-dimensional (3D) data displays are well established; not so in ultrasound. Due to the real-time requirements of ultrasound the time available to compute 3D displays is limited, particularly when flow data is acquired with Doppler techniques. Consequently, it is only recently that improvements in computer processing power have resulted in useful vascular 3D ultrasound scans. Many manufacturers have now implemented free-hand 3D power Doppler capabilities on their scanners. However, to obtain flow signals from smaller vessels associated e.g., with tumor neovascularity, may very well require the introduction of a microbubble based ultrasound contrast agent into the blood stream. Given the up to 30 dB enhancement of Doppler signals produced by the contrast microbubbles quite spectacular vascular 3D images are feasible. Moreover, new contrast imaging techniques, such as harmonic imaging, have now permitted 3D vascular information to be acquired and displayed in grayscale with the associated improvement in resolution. In this paper we will review different aspects of contrast enhanced vascular 3D ultrasound imaging including implementation, contrast specific techniques and in vivo imaging.

Animals↗

PubMed2001

Contrast-enhanced power Doppler imaging of normal and decreased blood flow in canine prostates.

The purpose of this study was to investigate if Sonazoid, a new ultrasound (US) contrast agent, can improve the delineation of areas with normal and decreased blood flow in the prostate. Sonazoid was administered in the dose range of 0.00625-0.0375 microL microbubbles/kg into five anaesthetised mongrel adult male dogs. Transrectal power Doppler imaging of the prostate was performed in 2-D and 3-D with a C9-5 end-fire probe, using an HDI 3000 scanner. An area of decreased blood flow was created by inducing tissue ablation with a CL60 laser system, to mimic an avascular lesion. A subjective assessment of the intraprostatic vessels and the prostate vascular architecture was performed, with and without Sonazoid, before and after inducing the abnormal site. Visibility of the prostate blood flow improved following Sonazoid injection (p < 0.001). A symmetric, radial vascular pattern was identified in the normal prostate prior to tissue ablation, but only on the enhanced images. After tissue ablation, a disturbance of the normal vascular pattern and identification of areas with lack of blood flow was possible, following Sonazoid injection. Furthermore, the location and size of these areas were verified in all dogs by gross histology examination. Sonazoid enhances the visibility of the prostate vascular architecture and improves, thereby the delineation of areas with normal and decreased blood flow.

Animals↗

PubMed2001

The role of contrast-enhanced sonography for radiofrequency ablation of liver tumors.

OBJECTIVE: To assess the feasibility and usefulness of contrast-enhanced sonography for tumor detection and guidance of liver VX2 tumor ablation and to evaluate post radiofrequency ablation effectiveness. METHODS: VX2 tumors were implanted into the livers of 6 rabbits. Both conventional and harmonic gray scale and power Doppler imaging were performed with a commercially available scanner to evaluate the liver tumors before and after intravenous injection of a sonographic contrast agent before and after radiofrequency ablation. Contrast-enhanced imaging was used to detect the tumors before ablation, to guide needle insertion, and to measure the ablation sites after radiofrequency ablation. Pathologic examination was performed for comparison. RESULTS: Three tumors were seen without contrast enhancement, whereas 10 tumors (<1 cm) were detected with contrast enhancement. Intentionally, 2 tumors were completely ablated and 5 tumors were partially ablated. In 3 cases, incompletely ablated tumors could only be identified on contrast-enhanced Doppler imaging by enhancing the detection of residual tumor vascularity. There was excellent concordance between sonographic imaging and gross pathologic findings. CONCLUSIONS: Contrast-enhanced sonographic imaging appears useful for detection of liver tumors and for guiding and monitoring tumor ablation therapies.

Animals↗

PubMed2000

Enhanced detection of blood flow in the normal canine prostate using an ultrasound contrast agent.

RATIONALE AND OBJECTIVES: To evaluate the sonographic appearance of normal prostate vascularity in dogs before and after injection of a new ultrasound contrast agent, NC100100. METHODS: Thirty-five intravenous injections of NC100100, in doses ranging from 0.00625 to 0.05 microL microbubbles/kg, were administered to seven anesthetized mongrel male dogs. Transrectal color Doppler imaging and power Doppler imaging were used to perform the assessment. The visibility of the vascular pattern of the prostate was assessed, including dynamics of contrast inflow, blood flow symmetry, and duration times. RESULTS: Before contrast administration, the vascular pattern was poorly visualized in all cases. After contrast injection, the visibility of the vascular architecture improved significantly for both modalities. Independent of the imaging method used, higher doses tended to be more effective than lower doses. Contrast kinetics in the prostate vessels was demonstrated with a mean time from injection of the ultrasound contrast agent to enhancement of the Doppler signals in the subcapsular arteries (+/-1 SD) of 13+/-3 seconds, and the ultrasound contrast agent reached the central periurethral veins 3 to 6 seconds later. A spokelike radial pattern of internal prostatic vessels observed with enhanced ultrasound could also be seen on silicone microfil x-ray images. The Doppler enhancement persisted for a mean time ( +/-1 SD) of 904 seconds (approximately 15 minutes) +/- 225 seconds and tended to increase with increasing dose. CONCLUSIONS: NC100100 significantly improves the detection of blood flow in the normal canine prostate and allows more accurate depiction of the vascular architecture of the prostate.

Animals↗

PubMed2000

Gray scale second harmonic imaging of acoustic emission signals improves detection of liver tumors in rabbits.

This study evaluates a new reticuloendothelium specific sonographic contrast agent NC100100 (Sonazoid) for detection of liver VX-2 tumors in rabbits. Gray scale imaging of five groups of three rabbits, with hepatic VX-2 tumors implanted 7, 10, 12, 14, and 18 days previously, was performed prior to injection of Sonazoid (dosages, 0.01-0.5 ml/kg). Sonazoid produces induced acoustic emission after uptake in the liver. Therefore, harmonic gray scale images were obtained immediately after injection as well as delayed (by up to 2(1/2) h). Five rabbits (one from each group) also had angiography performed, while all animals were evaluated by pathologic examination. Non-contrast enhanced sonography detected 17 of 61 tumors (29%), as well as three false-positives, while the addition of Sonazoid detected 57 tumors (93%) and one false-positive (P<0.001). Acoustic emission made 2 x 2 mm tumors (invisible in conventional B-mode sonography) clearly perceivable in harmonic gray scale. In the subgroup that received angiography, 12 of 36 tumors (33%) were detected with conventional sonography compared to 22 tumors (61%) seen with angiography (P = 0.002). After injection of Sonazoid the ultrasonographic detection rate increased to 97% (35 of 36 tumors), which was a significant improvement over angiography (P = 0.00024). Improved detection of hepatic VX-2 tumors with second harmonic gray scale imaging of Sonazoid is possible because of this agent's acoustic emission capabilities.

Animals↗

PubMed1999

Five-year follow-up of neonates with reconstructed right common carotid arteries after extracorporeal membrane oxygenation.

OBJECTIVE: Serial Doppler ultrasonography and long-term neurodevelopmental follow-up outcomes were evaluated prospectively in neonates whose right common carotid artery (RCCA) was reconstructed after extracorporeal membrane oxygenation (ECMO). METHODS: Children with RCCA reconstruction (n = 34) were monitored for 3.5 to 4.5 years by Doppler ultrasonography for arterial patency, and 28 had IQ testing by 5 years. A comparison group consisted of 35 infants who had RCCA ligation after ECMO. Neonatal electroencephalograms and computed tomography/magnetic resonance imaging scans were also compared. RESULTS: Reconstructions were successful (<50% RCCA stenosis by Doppler ultrasonography) in 26 (76%) of 34 children, 3 (9%) had >/=50% stenosis, and 5 (15%) had occlusion. No significant differences were seen between reconstructed and ligated groups in neonatal complications or ECMO courses. Occurrence of marked neonatal electroencephalographic abnormalities did not differ between groups. Abnormalities on computed tomography/magnetic resonance imaging scans (4 of 31 vs 11 of 29, P =.025) and cerebral palsy (0 of 34 vs 5 of 35, P =.054) were more common in infants with RCCA ligation. No differences were seen in developmental or IQ scores between the 2 groups, and 4 in each group had cognitive handicaps (at least 1 IQ score <70). CONCLUSIONS: Most RCCA reconstructions remained patent, with 24% showing significant stenosis or occlusion. Compared with a historical control group, patients with RCCA reconstruction had fewer brain scan abnormalities and tended to be less likely to have cerebral palsy. RCCA reconstruction after venoarterial ECMO may improve outcome.

Birth Weight↗

PubMed1999

Tissue-specific US contrast agent for evaluation of hepatic and splenic parenchyma.

PURPOSE: To evaluate the recently developed ultrasonographic (US) contrast agent SHU 563A, which is specifically taken up by the reticuloendothelial system (RES). MATERIALS AND METHODS: Color Doppler imaging (CDI) was performed in a gel phantom, with SHU 563A microbubbles in stationary suspension. CDI was performed in vivo in five woodchucks with natural hepatomas and in 12 rabbits before and after intravenous bolus injections of SHU 563A (0.16-0.48 mL/kg). After a 15-135-minute delay, the liver and spleen were scanned again, and the image findings were compared with pathologic analysis results. RESULTS: Phantom CDI demonstrated a random mosaic color pattern in spite of the lack of flow. This phenomenon, which is associated with bubble rupture, is termed induced acoustic emission. In vivo, delayed imaging demonstrated acoustic emission signals in normal parenchyma, whereas no mosaic color was seen in regions lacking reticuloendothelial cells (e.g., tumors). Four of 12 VX-2 tumors detected with pathologic analysis were detected with US alone; the remaining eight tumors were detected by using US with contrast agent (100%, P = .0078). Nine of 20 hepatomas were detected at baseline US, whereas 17 were detected after administration of SHU 563A (P = .0215). Acoustic emission enabled detection of hepatic tumors as small as 3 mm in diameter. CONCLUSION: CDI with SHU 563A demonstrates a random mosaic color pattern, even without flow. The characteristic appearance of acoustic emission signals provides a distinctive method of visualizing normal hepatic tissues and substantially improves the detectability of hepatic tumors.

Animals↗

PubMed1998

Clinical applications of ultrasound contrast agents.

Within the last decade safe and practical ultrasound contrast agents have been introduced. Most of these are based on gas-filled microbubbles, which markedly enhance Doppler signals and, in some cases, also gray-scale images. The clinical improvements expected from ultrasound contrast is reviewed. Tissue-specific contrast agents constitute another area of potential clinical significance. One particular agent is taken up by the reticulo-endothelial system and produces so-called acoustic emission signals when imaged. An introduction to the unique clinical applications of acoustic emission is given. Harmonic imaging is a new contrast-specific imaging modality, which utilizes the nonlinear properties of some agents in an attempt to alleviate current limitations of ultrasound contrast studies. Examples of harmonic images are presented.

Acoustics↗

PubMed1998

Conventional and hypobaric activation of an ultrasound contrast agent.

Hypobaric activation is a new injection technique for use with the contrast agent EchoGen and, in this study, the agent's ability to produce parenchymal enhancement in vivo, with and without prior hypobaric activation, was investigated. Injections, ranging in dose from 0.05 to 0.5 mL/kg, were administrated through a peripheral vein to eight woodchucks with multiple hepatomas. At the 0.10 mL/kg dose level, seven of eight injections following hypobaric activation (88%) resulted in definite parenchymal enhancement. Conversely, dosages of 0.10 mL/kg without prior hypobaric activation produced no grey-scale changes. Only at the 0.4 and 0.5 mL/kg dosage level did the conventional administration technique obtain similar results (4 of 5 injections increased the echogenicity for a 0.4 mL/kg dose). These differences were statistically significant (p = 0.031). In vitro experiments were conducted to establish the physical mechanisms behind hypobaric activation. Relative measurements of contrast microbubble sizes were performed with a phase Doppler particle analyzer after hypobaric and after conventional (bolus) activation. Hypobaric activation produced approximately 20 times more microbubbles per unit volume than the conventional method. In conclusion, this investigation has demonstrated the benefits of prior hypobaric activation when performing in vivo contrast studies with EchoGen and determined the physical mechanisms behind this new injection technique. Hypobaric activation of EchoGen increases contrast enhancement and reduces dose size.

Animals↗

PubMed1998

Effect of distal resistance on Doppler US flow patterns.

PURPOSE: To quantify the effect of distal resistance on arterial flow patterns. MATERIALS AND METHODS: Spectral Doppler tracings were obtained from the suprarenal aorta, infrarenal aorta, and proximal renal arteries of 10 volunteers and from the common, internal, and external carotid arteries (CCA, ICA, and ECA, respectively) of 31 volunteers. Early systolic acceleration (ESA), peak systolic velocity (PSV), end diastolic velocity (EDV), and waveform morphology were evaluated. An in vitro flow model of a compliant vessel in a branched pattern was created to simulate the renal and carotid circulations. RESULTS: ESA and PSV were significantly lower in the renal artery than in the suprarenal aorta (P < .01). ESA decreased significantly from the CCA to the ICA (P < .001) but only minimally from the CCA to the ECA (P > .20). EDV increased slightly from the CCA to the ICA but decreased substantially in the ECA. As distal resistance was increased in the in vitro model, ESA was more rapid, systole was shortened, EDV was decreased, and PSV was increased. CONCLUSION: As blood flows into the low-resistance renal artery or ICA, antegrade flow is shifted into the latter portion of the cardiac cycle, resulting in apparent prolongation of systole and forward flow throughout diastole. As blood flows into the higher-resistance ECA, diastolic flow is diminished. The in vitro model reproduces these Doppler flow patterns by means of manipulation of distal resistance.

Adult↗

PubMed1998

Evaluation of bleeding sites with a tissue-specific sonographic contrast agent: preliminary experiences in an animal model.

The purpose of this study was to determine the feasibility and usefulness of using an ultrasonographic contrast agent to enhance the sonographic detection of bleeding sites in a canine model. SH U 563, an ultrasound contrast agent that elicits acoustic emission (i.e., random transient Doppler shifts produced by contrast particle rupture) even when stationary, was used. Acoustic emission is identified as a mosaic pattern on color Doppler imaging. A total of 13 active bleeding sites were created within intraabdominal organs (kidney and spleen, n = 3), the urinary tract (n = 3), and the gastrointestinal tract (n = 7) in three canine models. Gray scale and color Doppler imaging studies were performed prior to and after each of 13 individual intravenous contrast agent administrations. Imaging results were compared to gross pathologic findings. After contrast agent administration, pooling of contrast medium-containing blood in the regions adjacent to bleeding sites could be detected with color Doppler imaging as regions with the characteristic acoustic emission color display. After injection gray scale imaging failed to demonstrate the location or extent of hemorrhaging adequately. A linear relationship existed between the blood loss due to gastrointestinal tract bleeding and the amount of acoustic emission detected (r2 = 0.81). SH U 563 combined with color Doppler imaging improves the detection of bleeding sites in a variety of locations throughout the body.

Animals↗

PubMed1997

Sonographic guidance for the localization of peripheral pulmonary nodules during thoracoscopy.

OBJECTIVE: The value of sonographic guidance during video-assisted thoracoscopic surgery (VATS) was studied in 13 patients with one or more peripheral pulmonary nodules who later underwent wedge resection. SUBJECTS AND METHODS: After a review of the chest radiographs and CT scans of each patient, sonographic guidance for VATS was requested by the attending surgeon when the nodule or nodules in question were determined to be too small or too deep in the lung parenchyma from the pleural surface for location by VATS. A multifrequency (5.0-, 6.5-, or 7.5-MHz) sonographic probe was introduced through a thoracoscopic port during VATS. The nodule or nodules in question were located by intraoperative sonography or determined by inspection and confirmed by sonography before wedge resection. The size and location of each lesion and the time needed for sonographic guidance were recorded. RESULTS: Sonography revealed a peripheral pulmonary nodule in 12 of the 13 patients. Of these, it confirmed the suspected location of the pulmonary nodule in six. In the remaining six patients, the surgeon was unable to locate the nodule without the use of sonography. The additional operative time required for sonographic guidance during VATS averaged 7.5 min. However, the time commitment of radiology personnel during surgery varied and was sometimes lengthy (maximum, 150 min). CONCLUSION: Sonographic guidance during thoracoscopy helped to locate lesions and determine their size and proximity to pleural surfaces. Sonographic guidance can be done safely and can be completed expeditiously. Unlike percutaneous hookwire techniques, sonographic guidance does not require an additional invasive procedure to locate the peripheral pulmonary nodule.

Aged↗

PubMed1997

Endoluminal sonographic evaluation of ureteral and renal pelvic neoplasms.

The objective of this study was to demonstrate the feasibility of endoluminal ultrasonography as an adjunct to endoscopy for the evaluation of urothelial neoplasms. An endoluminal ultrasound system using a 12.5 or 20 MHz transducer housed in a 6.2 French catheter was used intraureterally in 38 patients being evaluated endoscopically for suspected tumors in the renal pelvis or ureter. The ultrasonographic, endoscopic, and pathologic findings were evaluated. The location, size, and sonographic characteristics of the tumors in the upper urinary tract were well demonstrated. The information obtained by this technique can be used to guide endoscopic biopsy and laser ablation of the tumor. Endoluminal ultrasonography also has proved helpful in defining the location of a tumor relative to an adjacent vessel and in identifying crossing vessels that cause extrinsic filling defects in the ureter. In a few pathologically correlated cases, endoluminal ultrasonography was accurate in assessing invasion. We have evaluated successfully a variety of non-neoplastic filling defects in relatively few cases. Determination of the eventual usefulness of this technique awaits greater clinical experience and large clinical trials.

Adolescent↗

PubMed1996

Developmental changes in renal artery blood flow velocity during the first three weeks of life in preterm neonates.

Changes in color Doppler imaging measurements of renal artery blood flow velocity have been reported previously during fetal life and during the first week postnatally in term and preterm infants. This study reports longitudinal, developmental changes in renal artery and aortic blood flow velocities occurring postnatally, from birth to day 1 of life, at 1 week, and at 2 to 3 weeks of age in 14 premature babies (mean gestation, 30 +/- 4 (SD) weeks; birth weight, 1.45 +/- 0.57 kg), and identified by means of color Doppler imaging and pulsed Doppler spectral analysis. Results indicate that a significant increase in renal artery systolic blood flow velocity occurs within the first week of life (from 40 +/- 3 (SEM) cm/sec at birth or on day 1, to 53 +/- 3 cm/sec on day 7, to 51 +/- 4 cm/sec on day 14 to 21; repeated-measures analysis of variance, p = 0.004), concurrently with a significant increase in abdominal aortic blood flow velocities, both systolic (from 40 +/- 4 at birth or on day 1, to 70 +/- 8 on day 7, to 76 +/- 8 cm/sec on day 14 to 21; p <0.001) and diastolic (from 4 +/- 2 at birth or on day 1, to 11 +/- 2 on day 7, to 11 +/- 2 cm/sec on day 14 to 21; p = 0.00 1). Systemic blood pressure did not increase concomitantly during the some period. Neither the presence of respiratory distress syndrome or patent ductus arteriosus nor treatment with indomethacin altered developmental increases in observed renal artery blood flow velocities. The presence of an umbilical artery catheter in the high thoracic position in five infants, however, created turbulence at the level of the renal arteries, significantly increasing renal artery systolic flow velocity from 32 +/- 4 to 44 +/- 5 cm/sec (p = 0.009) and increasing renal resistive index from 0.90 +/- 0.03 to 0.96 +/- 0.04 (p = 0.046). These results suggest that renal artery blood flow velocity increases during the first postnatal week in preterm infants and is likely related to increases in aortic blood flow velocity and reduction in renal vascular resistance.

Analysis of Variance↗

PubMed1996

Augmenting of tumor uptake of anti-melanoma antibody MEM136: influence of interferon.

Interferon (IFN) upregulates tumor antigenic expression and enhances tumor uptake of radiolabeled tumor-specific monoclonal antibody (MAb). IFN also increases tumor blood flow. The relationship between these phenomena was investigated. Human melanoma tumors grown in nude mice were used as the experimental tumor model, and 99mTc-MEM136 as an MAb. Tumor blood flow was monitored by ultrasound Color Doppler Imaging (CDI) and Laser Doppler Flowmetry (LDF) techniques. Tumor blood flow increased at 20 min after administration of IFN. Enhancement lasted for about 60 min before the blood flow returned to the original baseline level. Tissue distribution of 99mTc-MEM136 was studied under different experimental schemes. Tumor uptake of 99mTc-MEM136 enhanced significantly only in experimental scheme A (5.5 +/- 0.2% ID/g vs. 3.0 +/- 0.9% ID/g in control group, p = 0.04). In this scheme IFN was given 30 min prior to the administration of 99mTc-MEM136, and the animals were sacrificed 1.5 h later. No upregulation of anti-genic expression was reported at this time. The increased tumor uptake at this early period appeared to be the result of enhanced tumor blood flow.

Animals↗

PubMed1996

Fecal incontinence: transvaginal US evaluation of anatomic causes.

PURPOSE: To evaluate transvaginal ultrasonography (US) as an alternative to transanal US for determining the anatomic cause of fetal incontinence in women. MATERIALS AND METHODS: Transvaginal US of the anal canal was performed in 28 women (aged 27-74 years) with fecal incontinence. A side-fire endorectal probe was inserted into the vagina and directed toward the posterior vaginal wall. RESULTS: The internal anal sphincter (IAS) and external anal sphincter muscles were imaged as independent bands in all 28 patients. The calculated mean thickness of the IAS in patients aged younger than 55 years was not significantly different from that in patients aged older than 55 years (P=.31). Posttraumatic anterior muscle disruptions were detected in 16 women; three also had rectovaginal fistulas. A rectal fistula with abscess was detected in one of 12 patients with intact muscles. All muscle disruptions, fistulas, and abscesses were surgically confirmed. CONCLUSION: Transvaginal US enables determination of the anatomic cause of fecal incontinence, allowing the surgeon to select patients who would benefit form surgical repair.

Age Factors↗

PubMed1996

Value of sonohysterography in the diagnosis and management of abnormal uterine bleeding.

PURPOSE: To assess the value of sonohysterography in the diagnosis and management of abnormal uterine bleeding. MATERIALS AND METHODS: Sonohysterography was performed in 28 women (aged 29-55 years) in whom transvaginal sonography (TVS) suggested an abnormal endometrial echo (n = 14) or fibroids (n = 14). Its effect on diagnosis and treatment was studied. RESULTS: In the patients with an abnormal endometrial echo, sonohysterography depicted endometrial polyps (n = 9), intracavitary fibroids (n = 3), placental polyp (n = 1), and a normal cavity (n = 1). Hysteroscopic resection resolved the bleeding in 11 of 14 patients; surgery was obviated in one. In the group with fibroids, sonohysterography depicted small submucous fibroids amenable to hysteroscopic myomectomy (n = 5), a small mural fibroid with a normal cavity, which obviated surgical intervention (n = 4), and endometrial polyps, which altered the treatment plan (n = 1). Sonohysterography suggested the need for an abdominal myomectomy (n = 4) and alerted the surgeon to explore the uterine cavity in three patients. CONCLUSION: By helping elucidate the cause of bleeding, sonohysterography assisted in determining the therapeutic approach and often reduced the level of surgical intervention or obviated it altogether.

Adult↗

PubMed1996

On the feasibility of real-time, in vivo harmonic imaging with proteinaceous microspheres.

Harmonic imaging is a new contrast-specific imaging modality, which utilizes the nonlinear properties of microbubble-based sonographic contrast agents by transmitting at the fundamental frequency but receiving at the second harmonic frequency. The feasibility of improving the detection of slow, small-volume blood flow using real-time harmonic imaging has been investigated in vivo. Proteinaceous microspheres (FS069) were administrated to four dogs, two woodchucks (with multiple hepatomas), and one rabbit. Three different scanners were used to obtain real-time images of kidneys and liver (including vessels) in harmonic and conventional gray scale and color flow modes. The duration of contrast enhancement lasted significantly longer in harmonic than in conventional modes (on average 87 s; P = 0.008). Harmonic images were less susceptible to artifacts, such as acoustic shadowing, and a clear increase in the (flow) signal-to-noise ratio was observed. These preliminary in vivo results demonstrate the feasibility of performing real-time, contrast-enhanced harmonic imaging, but further studies are required to establish clinical efficacy.

Animals↗