Are you Kirk Wallace?

Claim your profile

Publications (4)6.94 Total impact

  • [show abstract] [hide abstract]
    ABSTRACT: OBJECTIVES: The ability to estimate tissue perfusion (in milliliter per minute per gram) in vivo using contrast-enhanced 3-dimensional (3D) harmonic and subharmonic ultrasound imaging was investigated. MATERIALS AND METHODS: A LOGIQ™ 9 scanner (GE Healthcare, Milwaukee, WI) equipped with a 4D10L probe was modified to perform 3D harmonic imaging (HI; ftransmit, 5 MHz and freceive, 10 MHz) and subharmonic imaging (SHI; ftransmit, 5.8 MHz and freceive, 2.9 MHz). In vivo imaging was performed in the lower pole of both kidneys in 5 open-abdomen canines after injection of the ultrasound contrast agent (UCA) Definity (Lantheus Medical Imaging, N Billerica, MA). The canines received a 5-μL/kg bolus injection of Definity for HI and a 20-μL/kg bolus for SHI in triplicate for each kidney. Ultrasound data acquisition was started just before the injection of UCA (to capture the wash-in) and continued until washout. A microvascular staining technique based on stable (nonradioactive) isotope-labeled microspheres (Biophysics Assay Laboratory, Inc, Worcester, MA) was used to quantify the degree of perfusion in each kidney (the reference standard). Ligating a surgically exposed branch of the renal arteries induced lower perfusion rates. This was followed by additional contrast-enhanced imaging and microsphere injections to measure post-ligation perfusion. Slice data were extracted from the 3D ultrasound volumes and used to generate time-intensity curves offline in the regions corresponding to the tissue samples used for microvascular staining. The midline plane was also selected from the 3D volume (as a quasi-2-dimensional [2D] image) and compared with the 3D imaging modes. Perfusion was estimated from the initial slope of the fractional blood volume uptake (for both HI and SHI) and compared with the reference standard using linear regression analysis. RESULTS: Both 3D HI and SHI were able to provide visualization of flow and, thus, perfusion in the kidneys. However, SHI provided near-complete tissue suppression and improved visualization of the UCA flow. Microsphere perfusion data were available for 4 canines (1 was excluded because of an error with the reference blood sample) and showed a mean (SD) perfusion of 9.30 (6.60) and 5.15 (3.42) mL/min per gram before and after the ligation, respectively. The reference standard showed significant correlation with the overall 3D HI perfusion estimates (r = 0.38; P = 0.007), but it correlated more strongly with 3D SHI (r = 0.62; P < 0.001). In addition, these results showed an improvement over the quasi-2D HI and SHI perfusion estimates (r = -0.05 and r = 0.14) and 2D SHI perfusion estimates previously reported by our group (r = 0.57). CONCLUSIONS: In this preliminary study, 3D contrast-enhanced nonlinear ultrasound was able to quantify perfusion in vivo. Three-dimensional SHI resulted in better overall agreement with the reference standard than 3D HI did and was superior to previously reported 2D SHI results. Three-dimensional SHI outperforms the other methods for estimating blood perfusion because of the improved visualization of the complete perfused vascular networks.
    Investigative radiology 05/2013; · 4.85 Impact Factor
  • [show abstract] [hide abstract]
    ABSTRACT: Although contrast-enhanced ultrasound imaging techniques such as harmonic imaging (HI) have evolved to reduce tissue signals using the nonlinear properties of the contrast agent, levels of background suppression have been mixed. Subharmonic imaging (SHI) offers near complete tissue suppression by centering the receive bandwidth at half the transmitting frequency. The aims of this study were to demonstrate the feasibility of three-dimensional (3D) SHI and to compare it to 3D HI. Three-dimensional HI and SHI were implemented on a Logiq 9 ultrasound scanner with a 4D10L probe. Four-cycle SHI was implemented to transmit at 5.8 MHz and receive at 2.9 MHz, while two-cycle HI was implemented to transmit at 5 MHz and receive at 10 MHz. The ultrasound contrast agent Definity was imaged within a flow phantom and the lower pole of two canine kidneys in both HI and SHI modes. Contrast-to-tissue ratios and rendered images were compared offline. SHI resulted in significant improvement in contrast-to-tissue ratios relative to HI both in vitro (12.11 ± 0.52 vs 2.67 ± 0.77, P< .001) and in vivo (5.74 ± 1.92 vs 2.40 ± 0.48, P = .04). Rendered 3D subharmonic images provided better tissue suppression and a greater overall view of vessels in a flow phantom and canine renal vasculature. The successful implementation of SHI in 3D allows imaging of vascular networks over a heterogeneous sample volume and should improve future diagnostic accuracy. Additionally, 3D SHI provides improved contrast-to-tissue ratios relative to 3D HI.
    Academic radiology 03/2012; 19(6):732-9. · 2.09 Impact Factor
  • Conference Proceeding: 4D subharmonic imaging in vivo
    [show abstract] [hide abstract]
    ABSTRACT: Subharmonic imaging (SHI) improves the isolation of ultrasound contrast agent signals from the surrounding tissue signals by transmitting at f0 and receiving at f0/2. In this study we investigated the feasibility of generating real-time 3D (i.e., 4D) SHI volumes. Four-dimensional SHI (f0 = 5.8 MHz, transmitting 4 cycle pulses) was implemented on a Logiq 9 ultrasound scanner with a mechanically controlled 4D10L probe (GE Healthcare, Milwaukee, WI). Experimental software provided access to both individual slice data and rendered images. This software also allowed imaging in B-mode (at 10 MHz) and harmonic imaging (HI; f0 = 5 MHz, freceive= 10 MHz). Two canines received 5 μl/kg bolus injections of Definity (Lantheus Medical Imaging, N Billerica, MA) for HI and 20 μl/kg bolus for SHI of the lower renal pole. The contrast-to-tissue ratio was then calculated for three injections in each canine and compared between modes. Patients scheduled for biopsy of a mammographically identified breast lesion provided informed consent. Baseline scanning was performed in both B-mode and power Doppler. Patients then received a 0.25 ml bolus of Definity for HI followed by a bolus injection of 20 μl/kg for SHI. Baseline 2D cine loops, 3D slice data and rendered volumes were saved for off-line comparison. While scan volumes varied, a volume of 2.5 cm x 2.5 cm × 2.5 cm acquired at a 19° volume angle resulted in 45-50 slices per volume at an acquisition rate of 1.8 to 2.2 Hz depending on depth. In the canine model, SHI resulted in significant improvement in contrast visualization and rendered SHI images demonstrated superior tissue suppression and a greater overall view of renal vasculature. In breast lesions, enhancement varied greatly on a case by case basis. However, SHI resulted in improved tissue suppression and detection of contrast in almost all cases. Future work will explore the ability o- 4D SHI to classify breast lesions.
    Ultrasonics Symposium (IUS), 2012 IEEE International; 01/2012
  • [show abstract] [hide abstract]
    ABSTRACT: Under sufficient acoustic excitation microbubble-based ultrasound contrast agents (UCA) produce a marked subharmonic (f0/2) frequency component. By selectively receiving at the subharmonic, it is possible to perform UCA specific subharmonic imaging (SHI). We investigated the ability to quantify tissue perfusion (in ml/min/g) in 5 canines using 3D SHI. A Logiq 9 scanner (GE Healthcare, Milwaukee, WI) equipped with a 4D10L probe was modified to perform 3D harmonic imaging (HI; ftransmit=5 MHz and freceive=10 MHz) and 3D SHI (ftransmit=5.8 MHz and freceive=2.9 MHz). Imaging was performed in the lower renal pole of open-abdomen canines after injection of Definity (Lantheus Medical Imaging, N Billerica, MA). The canines received a 5 μl/kg bolus injection of Definity for HI and a 20 μl/kg for SHI in triplicate for each kidney. A microvascular staining technique based on isotope-labeled microspheres was used to quantify the degree of perfusion in each kidney. Ligation of a surgically exposed branch of the renal arteries induced low perfusion. Time-intensity curves were generated from regions-of-interest (ROIs) corresponding to the tissue samples used for microvascular staining. Perfusion was estimated from the initial slope of the fractional blood volume uptake and compared to the reference standard using linear regression analysis. Microsphere perfusion data showed an average perfusion of 9.30±6.60 and 5.15±3.42 ml/min/g pre and post ligation, respectively. The reference standard showed significant correlation with 3D HI perfusion estimates (r=0.38; p=0.007), but correlated better with 3D SHI (r=0.62; p
    Ultrasonics Symposium (IUS), 2012 IEEE International; 01/2012