Gregory C. Steinbach

Lumbar spine disc height and curvature responses to an axial load generated by a compression device compatible with magnetic resonance imaging

Study Design. Axial load-dependent changes in the lumbar spine of supine healthy volunteers were examined using a compression device compatible with magnetic resonance imaging. Objective. To test two hypotheses: Axial loading of 50% body weight from shoulder to feet in supine posture 1) simulates the upright lumbar spine alignment and 2) decreases disc height significantly. Summary of Background Data. Axial compression on the lumbar spine has significantly narrowed the lumbar dural sac in patients with sciatica, neurogenic claudication or both. Methods. Using a device compatible with magnetic resonance imaging, the lumbar spine of eight young volunteers, ages 22 to 36 years, was axially compressed with a force equivalent to 50% of body weight, approximating the normal load on the lumbar spine in upright posture. Sagittal lumbar magnetic resonance imaging was performed to measure intervertebral angle and disc height before and during compression. Results. Each intervertebral angle before and during compression was as follows: T12–L1 (−0.8° ± 2.5° and −1.5° ± 2.6°), L1–L2 (0.7° ± 1.4° and 3.3° ± 2.9°), L2–L3 (4.7° ± 3.5° and 7.3° ± 6°), L3–L4 (7.9° ± 2.4° and 11.1° ± 4.6°), L4–L5 (14.3° ± 3.3° and 14.9° ± 1.7°), L5–S1 (25.8° ± 5.2° and 20.8° ± 6°), and L1–S1 (53.4° ± 11.9° and 57.3° ± 16.7°). Negative values reflect kyphosis, and positive values reflect lordosis. A significant difference between values before and during compression was obtained at L3–L4 and L5–S1. There was a significant decrease in disc height only at L4–L5 during compression. Conclusions. The axial force of 50% body weight in supine posture simulates the upright lumbar spine morphologically. No change in intervertebral angle occurred at L4–L5. However, disc height at L4–L5 decreased significantly during compression.

Lower body positive-pressure exercise after knee surgery

Lower body positive pressure allows unloading of the lower extremities during exercise in a pressurized treadmill chamber. This study assessed the preliminary feasibility of lower body positive pressure exercise as a rehabilitation technique by examining its effects on gait mechanics and pain, postoperatively. Fifteen patients who had arthroscopic meniscectomy or anterior cruciate ligament reconstruction participated in this study. Patients exercised for 5 minutes at 2.0 mph under three body weight conditions (normal body weight, 60% body weight, and 20% body weight) in random order. Bilateral ground reaction force, electromyographs, and dynamic knee range of motion were collected, and pain was assessed using a visual analog scale. Ground reaction forces for surgically treated and contralateral extremities were reduced 42% and 79% from normal body weight conditions when ambulating at 60% and 20% body weight, respectively. After meniscectomy, ambulatory knee range of motion decreased only at 20% body weight (37°), compared with normal body weight conditions (49°). Peak electromyographic activity of the biceps was maintained at all body weight conditions, whereas that of the vastus medialis was reduced at 20% body weight. Pain relief was significant with lower body positive pressure ambulation after anterior cruciate ligament reconstruction. This study showed that lower body positive pressure exercise is effective at reducing ground reaction forces, while safely facilitating gait postoperatively. Level of Evidence: Therapeutic study, Level II-1 (study of untreated controls from a previous randomized controlled trial)

Contrast-enhanced B-mode US angiography in the assessment of experimental in vivo and in vitro atherosclerotic disease

RATIONALE AND OBJECTIVES This study was performed to (a) test the hypothesis that filling the arterial lumen with echoes at B-mode ultrasound (US) enables the assessment of wall and luminal abnormalities and (b) compare contrast material-enhanced B-mode US with color and power Doppler US angiography. MATERIALS AND METHODS Atherosclerotic lesions were created in 14 rabbit aortas and imaged with color Doppler and B-mode US before and after the intravenous administration of 0.3 mL of AF0150, a US contrast agent. In addition, four replicas of diseased human carotid arteries were immersed in a tissue-mimicking phantom and imaged with B-mode and color and power Doppler US before and after the administration of 1 mL of AF0150 per liter of porcine blood. Radiopaque plastic casts of the rabbit aortas and contact radiographs of the plastic replicas served as standards. RESULTS Although color and power Doppler US allowed immediate localization of the lumen, precise estimation of stenoses and reliable visualization of surface irregularities were not possible. After AF0150 administration, angiogram-like images of the lumen were created with B-mode US, allowing rapid assessment of the entire vessel lumen and wall. Consequently, luminal stenoses were more accurately measured than with unenhanced B-mode US (r2 = 0.94, P < .0001 vs r2 = 0.21, P = .25) or Doppler (r2 = 0.42, P < .03). In addition, plaques and ulcerations were visible only with contrast-enhanced B-mode US. CONCLUSION Microbubbles fill the arterial lumen with echoes at B-mode US, creating an angiogram-like image. The ability to visualize the inner and outer surfaces of the vascular wall improved the evaluation of luminal and wall abnormalities.

Comparison of standard and second harmonic B-mode sonography in the detection of segmental renal infarction with sonographic contrast in a rabbit model.

This study compares contrast‐enhanced fundamental and second harmonic B‐mode sonography using a rabbit renal infarct model. Segmental renal infarctions were produced in 13 rabbits by embolizing a 0.7 mm bead into the renal artery 1 day prior to imaging. An ultrasonographic unit equipped with an L10‐5 transducer and second harmonic imaging capability was used. Real‐time recordings were made during the injection of 0.5 ml of an experimental formulation of a perfluorohexane vapor‐stabilized microbubble (AF0145) given into the ear vein, and the imaging technique alternated between standard and harmonic imaging every 20 s. Each rabbit received two injections 1 h apart. To control for the effect of peak bolus enhancement, the initial imaging technique used for the first injection was randomized, and the other technique was used initially for the second injection. The videointensity difference between the infarcted and the normal cortex was then calculated and evaluated as a function of time. The infarcted segment could not be seen before administration of contrast agent with either technique. Although the infarction could be seen after injection of contrast agent with either technique, image contrast and contrast duration were nearly 75% greater for the harmonic technique than for the standard technique. AF0145 allows the visualization of segmental renal infarction on standard B‐mode imaging. The second harmonic B‐mode technique significantly increases image contrast and contrast duration.

Effect of acquisition rate on liver and portal vein enhancement with microbubble contrast

We showed that tissue enhancement with microbubbles is dependent upon transmit power. Because intermittent imaging decreases bubble exposure to ultrasound, and also decreases the ability of the sonographer to maintain anatomic orientation, we aimed to determine the optimum frame rate that maximizes enhancement and allows for continued anatomic orientation. Seven rabbits with an avascular liver lesion created by percutaneous injection of 1 mL ethyl alcohol 7 days earlier were imaged with an Acuson 128XP/10 using a 7-MHz sector transducer at fixed transmit power. Each rabbit was imaged 5 times in random order, at 1 frame/30 s, 1frame/5 s, 1frame/s, 4 frames/s, and 28 frames/s. The same plane was imaged at all frame rates from before to 15 min after the bolus injection of 0.3-mL (0.1-0.12 mL/kg) of AF0150 (Imagent, Alliance Pharmaceutical Corp., San Diego, CA). Liver and portal vein videointensity relative to the lesion were evaluated over time. In this study, liver enhancement progressively increased as the frame rate was reduced (p<0.001). Peak, duration, and area under the time-intensity curve were all greater at the lower frame rates (1 fr/30 s, 1 fr/5 s, and 1 fr/s) than at 28 fr/s (p<0.05). Anatomic orientation was maintained at 1 frame/s rate at which peak enhancement was 44% greater and duration was 100% longer than at 28 frames/s (p<.05). Portal vein enhancement was not affected by frame rate. In conclusion, with intermittent imaging, enhancement was dependent upon frame rate and the ability of the region being imaged to replenish its bubbles between consecutive acquisitions. The 1 frame/s allowed for anatomic orientation and adequate tissue contrast.

Enhancement of the echogenicity of flowing blood by the contrast agent perflubron.

RATIONALE AND OBJECTIVES Perflubron, or perfluorooctylbromide, is an effective ultrasound and computed tomography contrast agent in a lecithin emulsion form. The authors studied acoustical properties of perflubron emulsion in static human and flowing porcine blood for concentrations from 0% to 30% weight per volume. METHODS Propagation velocity (c), the intensity attenuation coefficient (mu), density (rho), and particle size were measured directly. Because the backscatter of flowing blood is dependent on shear rate, relative echogenicity was measured as a function of perflubron concentration in whole porcine blood, in a laminar flow system, at shear rates of 16.0 to 68.5 sec-1 for realtime sector scanner images obtained at 7.5 MHz. RESULTS Neat perflubron is a colorless liquid with density of 1.93 g.mL-1 and velocity of 630 m.sec-1. The following values were obtained at 4.7 MHz in static human blood (hematocrit 44%) at expected human in vivo blood concentrations of 3.1% perflubron versus pure human blood: rho = 1.11 versus 1.05 g.mL-1, c = 1,480 versus 1,576 m.sec-1, mu = 1.00 versus 0.36 dB.cm-1. The mean echogenicity of whole porcine blood increased substantially with perflubron concentration and was inversely proportional to blood shear rate. CONCLUSION Adding 3.1% concentration of perflubron increased image echogenicity at all shear rates studied, ranging from 70% at 68.5 sec-1 (16.3 cm.sec-1) up to 180% at 16.0 sec-1 (3.8 cm.sec-1). Perflubron enhancement of blood is marked and demonstrates shear rate dependence like that of whole blood.

Ultrasound contrast agents. State of the art.

In the development of sonographic contrast agents it is clear that the material properties of the contrast have a profound effect on the resulting effectiveness of the product requiring careful manipulations of its properties. The important parameters are particle size, imaging frequency, density, compressibility, particle behavior (surface tension, internal pressure, bubble-like qualities), and equally important biodistribution characteristics and tolerance. Particulate agents appear to be the most likely materials, and gas filled particles are by far the most effective reflectors. However, the gas-based agents reported to date appear to have a short blood half-life. The fluorocarbon emulsions and the solid particles with entrapped air appear to be the most promising agents for abdominal imaging.

Assessment of liver and kidney enhancement with a perfluorocarbon vapor-stabilized US contrast agent

RATIONALE AND OBJECTIVES The authors evaluated the time-echogenicity response of liver, kidney, and implanted VX2 tumor after injection of a microbubble contrast medium and assessed use of an avascular lesion as an internal standard. MATERIALS AND METHODS Twenty-one New Zealand White rabbits were studied. To evaluate use of an internal standard and the dose-response relationship, nine rabbits with 7-day-old avascular liver lesions created by alcohol ablation received 0.1, 0.25, 0.5, and 1.0 mL of AF0145, a microbubble contrast agent. To evaluate tumor echogenicity, 12 rabbits implanted with VX2 tumor in the liver (six also underwent alcohol ablation) received 0.5 mL of AF0145. Videodensitometry was used to analyze echogenicity changes over 10 minutes. RESULTS Echogenicity of the alcohol-ablated liver was not affected by contrast material administration. Liver and kidney echogenicity relative to ablation increased linearly with dose, peaking 1 minute after injection and decaying to baseline over 9 minutes. Contrast material administration defined the size and margins of VX2 lesions more clearly. In the arterial phase, the tumor rim was hyperechoic relative to surrounding liver, becoming isoechoic during the portal venous phase then hypoechoic during the late phase parenchymal phase. CONCLUSIONS Lesions created by alcohol ablation can be used as an internal standard for quantitative analysis of adjacent tissues. AF0145 enhances perfused tissues, including vascular tumors, at gray-scale, real-time ultrasonography and enhances the liver.

Effect of ultrasound transmit power on liver enhancement with Imagent® US, a PFC‐stabilized microbubble contrast agent

The pressure of the ultrasound wave may limit the longevity of microbubble‐based contrast agents. This study evaluated liver enhancement over time as a function of transmit power after the administration of AFO145 (Imagent® US; Alliance Pharmaceutical Corp., San Diego, CA). Eight rabbits with an avascular liver lesion created by percutaneous injection of 1.0 ml of ethyl alcohol 7 days prior to scanning were imaged with an Acuson 128XP/10 at 7 MHz before and after four separate intravenous injections of 0.25 ml of AFO145 spaced at least 1 h apart. The avascular lesion served as an internal standard against which liver enhancement could be compared. After contrast injection, scanning over the same plane was either continuous at (a) maximum or (b) minimum transmit power (9 dB below maximum), or intermittent at (c) minimum power for 5 s every 15 s, or (d) for 5 s every 60 s. Each session was terminated after 15 min or when contrast was no longer visible in the hepatic parenchyma and blood vessels. Videodensitometry was used to assess liver‐to‐lesion intensity difference over time. Both the degree and duration of liver enhancement were dependent on the transmit power. Liver enhancement with imaging at minimum power for 5 s/min was nearly two times greater and persisted nearly eight times longer (P < 0.01) than at maximum power and continuous insonation. Ultrasound transmit power affects both the peak and duration of liver enhancement. A lower power and shorter insonation time after AFO145 administration dramatically lengthens the imaging window for liver lesion detection.

3:56 Axial harness loads of the cervical spine in supine posture simulates the upright loads

Abstract Purpose of study: Patients with cervical degenerative diseases often have pain or tingling in their upper extremities in upright posture. However, computed tomography or magnetic resonance imaging (MRI) is typically performed in a supine position. We reported that axial loading of 50% body weight in the lumbar spine stimulates upright loading conditions [1]. The aim of our study was to simulate upright cervical spine loads using a new compression device and to examine the change of cervical spine alignment and dural tube before and during axial compression in healthy volunteers and in patients with cervical degenerative diseases. Methods used: Eighteen healthy volunteers (9 men, 9 women) with a mean age of 44 years and 12 symptomatic patients with cervical degenerative diseases with a mean age of 53 years participated in this study. Axial compression was applied between the head and the feet, in supine posture using a MRI-compatible compression device. The compression force between the helmet and the footplate was determined with four calibrated scales, one on each of the interconnecting straps. To determine how much axial compression force is required to simulate the upright cervical spine, the lordosis angle between C2 and C6 in a lateral plain radiograph in upright posture was compared with supine posture radiographs with axial loads of 0%, 7%, 10% and 13% of the subjects body weight. To study morphological changes of the dural tube before and during axial compression both in healthy volunteers and symptomatic patients, T2-weighted axial MRI was done using a 1.5T system. The axial images were angled parallel with each disc level of C2–C3 to C7–T1. The following parameters were measured on the dural tube: anterior posterior distance (AP, mm) and cross-sectional area (CSA, mm2). of findings: The lordosis angle of the cervical spine in upright posture between C2 and C6 was 13.4 ± 2.4 degrees (mean ± SEM) in healthy volunteers. The lordosis angle in supine posture with a load of 0%, 7%, 10% and 13% of the subjects body weight relative to upright posture was −8.1 ± 1.3, −2.3 ± 1.4, 1.3 ± 1.9 and 2.8 ± 2.0 degrees, respectively. Subsequent axial force is interpolated as 8.9% of body weight to simulate the upright cervical spine. A total of 8.5% of body weight was applied to simulate the normal load experienced by the cervical spine in upright posture. There was a significant difference in healthy volunteers before and during compression regarding AP of the dural tube at C5–C6 (11.1 ± 0.4; 10.6 ± 0.4 mm). In symptomatic patients, there was a significant difference regarding AP (9.2 ± 0.4; 8.8 ± 0.3 mm), CSA (142.1 ± 8.4; 136.1 ± 8.1 mm2) of the dural tube at C6–C7. Relationship between findings and existing knowledge: A previous cadaver study has demonstrated that the weight of the head plus neck is approximately 8.4% of body weight [2]. Similarly, our results indicated that 8.9% of body weight was required to simulate the upright cervical spine. In the lumbar spine, Willen and coworker have demonstrated that axial compression of the lumbar spine narrowed the lumbar dural tube in lumbar patients [3]. Our data documented that axial compression decreased the AP diameter of the dural tube at C5–C6 in healthy volunteers, and the AP distance as well as the CSA of the dural tube at C6–C7 decreased significantly during axial compression in patients with cervical degenerative diseases. Overall significance of findings: The present results provide more understanding of the pathophysiology of cervical compression myelopathy in upright posture. Disclosures: No disclosures. Conflict of interest: Shinji Kimura, grant research support, DynaWell Inc., Sweden.