Biomedical subjects

Kullervo Hynynen

Publications and source records attributed to Kullervo Hynynen.

At least 19 recordsLinked to original sources

PubMed2007

Focused ultrasound for blood-brain disruption and delivery of therapeutic molecules into the brain.

Noninvasive, transient and local image-guided blood-brain barrier disruption can be accomplished using focused ultrasound exposure with intravascular injection of preformed microbubbles. MRI-guided blood-brain barrier disruption has been demonstrated and has been shown to heal in within a few hours after exposure. The delivery of several marker molecules has been demonstrated in different animal models with minimal or no damage to the brain tissue. Most notably, the delivery of antibodies and liposomal doxorubicin has been shown. The method may potentially open a new era in CNS drug delivery and perhaps also aid in molecular imaging and targeting. However, effective clinical devices and methods need to be developed further and the clinical feasibility demonstrated.

Animals↗

PubMed2006

Activation of Bak in ultrasound-induced, JNK- and p38-independent apoptosis and its inhibition by Bcl-2.

The molecular mechanisms underlying ultrasound-induced apoptosis remain poorly understood. We have demonstrated that in Jurkat cells, the over-expression of the anti-apoptotic protein Bcl-2 inhibited ultrasound-induced apoptosis, but not necrosis. Inhibition of caspase activity also protected the cells from apoptosis, but not from necrosis, showing the involvement of different mechanisms in ultrasound-induced apoptosis and necrosis. Bak, a pro-apoptotic member of the Bcl-2 family proteins, was activated by ultrasound and its activation was completely inhibited by Bcl-2 over-expression, but not by caspase inhibition. Antioxidant N-acetyl cysteine did not protect the cells from ultrasound-induced apoptosis or necrosis, nor did the inhibition of either c-Jun N-terminal kinase or p38, key factors in the radical oxygen species (ROS)-mediated cell stress response, suggesting that ROS do not play a crucial role in ultrasound-induced apoptosis. Our results confirm that ultrasound induces apoptosis via a pathway that involves Bak, Bcl-2, and caspases, but not ROS.

Apoptosis↗

PubMed2006

Simulations of localized harmonic motions on a blood vessel wall induced by an acoustic radiation force used in ultrasound elastography.

Many noninvasive techniques have been developed recently to explore the mechanical properties of soft tissue. In this paper, dynamic acoustic radiation force induced vibrations on a blood vessel wall were simulated using different stimulation frequencies and stiffness parameters for the vessel wall. The stimulation frequency was varied between 20 Hz and 20 kHz and the stiffness parameter (Young's modulus) was varied between 60 kPa and 360 kPa. The vibration simulations were computed using a finite-element method in a 3D geometry that contained a vessel wall surrounded by soft tissue. The results indicate that vibrations caused by acoustic stimulation are sensitive to the changes in mechanical properties of the vessel wall and that the vibrations are highly dependent on the stimulation frequency and target structure. Therefore, measurements of absolute stiffness parameters may not be accurately achieved because this method is so dependent on the whole target structure, whereas the monitoring of changes during some process may be feasible.

Animals↗

PubMed2006

Noninvasive localized delivery of Herceptin to the mouse brain by MRI-guided focused ultrasound-induced blood-brain barrier disruption.

Antibody-based anticancer agents are promising chemotherapeutic agents. Among these agents, Herceptin (trastuzumab), a humanized anti-human epidermal growth factor receptor 2 (HER2/c-erbB2) monoclonal antibody, has been used successfully in patients with breast cancer. However, in patients with brain metastasis, the blood-brain barrier limits its use, and a different delivery method is needed to treat these patients. Here, we report that Herceptin can be delivered locally and noninvasively into the mouse central nervous system through the blood-brain barrier under image guidance by using an MRI-guided focused ultrasound blood-brain barrier disruption technique. The amount of Herceptin delivered to the target tissue was correlated with the extent of the MRI-monitored barrier opening, making it possible to estimate indirectly the amount of Herceptin delivered. Histological changes attributable to this procedure were minimal. This method may represent a powerful technique for the delivery of macromolecular agents such as antibodies to treat patients with diseases of the central nervous system.

Animals↗

PubMed2006

Pre-clinical testing of a phased array ultrasound system for MRI-guided noninvasive surgery of the brain--a primate study.

MRI-guided and monitored focused ultrasound thermal surgery of brain through intact skull was tested in three rhesus monkeys. The aim of this study was to determine the amount of skull heating in an animal model with a head shape similar to that of a human. The ultrasound beam was generated by a 512 channel phased array system (Exablate 3000, InSightec, Haifa, Israel) that was integrated within a 1.5-T MR-scanner. The skin was pre-cooled by degassed temperature controlled water circulating between the array surface and the skin. Skull surface temperature was measured with invasive thermocouple probes. The results showed that by applying surface cooling the skin and skull surface can be protected, and that the brain surface temperature becomes the limiting factor. The MRI thermometry was shown to be useful in detecting the tissue temperature distribution next to the bone, and it should be used to monitor the brain surface temperature. The acoustic intensity values during the 20 s sonications were adequate for thermal ablation in the human brain provided that surface cooling is used.

Animals↗

PubMed2006

Multiphoton imaging of ultrasound/Optison mediated cerebrovascular effects in vivo.

Ultrasound (US) enhanced with microbubble contrast agents may transiently disrupt the blood-brain barrier (BBB) with minimal damage, providing a technique for noninvasive, localized drug-delivery deep within the brain. The mechanism and temporal profile of disruption are not understood, owing to the limitations of imaging modalities used previously. In this study, we monitored US-induced BBB disruption with multiphoton microscopy, providing high-resolution temporal and spatial information about the permeabilization mechanism and immediate effects of US exposure. Anesthetized C57 mice were prepared with a craniotomy and injected intravenously with fluorescent dyes to permit visualization of the vasculature and BBB integrity. The animals were imaged through a cranial window while exposed to low-intensity US (f=1.029 MHz, power=0.2 W) with a coincident intravenous injection of Optison (a microbubble contrast agent). We observed arteriolar vasoconstriction on US exposure that disrupted blood flow and lasted up to 5 mins; BBB disruption occurred via two characteristically distinct processes-perivascular fluorescence gradually increased (over minutes) along the length of the affected vessel without apparent rupture of the vessel wall or rapidly (seconds) increased in select, focal regions. These data corroborated previous studies suggesting increased endothelial transcytosis and breached tight junctions and demonstrated vasoconstriction, which might alter BBB permeability by modifying cerebral blood flow.

Albumins↗

PubMed2006

Does the phase of menstrual cycle affect MR-guided focused ultrasound surgery of uterine leiomyomas?

PURPOSE: To determine whether the phase of menstrual cycle at the time of MR-guided focused ultrasound surgery (MRgFUS) treatment for uterine leiomyomas affects treatment outcome. METHODS: We enrolled all patients participating in a prospective phase III clinical trial from our center who completed 6 months of clinical and imaging follow-up. Patients with irregular cycles and those on oral contraceptives were excluded. Data prospectively documenting the date of the last menstrual period (LMP) at the time of treatment, length and duration of cycle, and raw symptom severity score (SSS) from the Uterine Fibroid Symptom and Quality of Life questionnaire, at baseline and 6 months were collected. Proliferative phase patients were determined retrospectively as those who were treated within less than 14 days from LMP; secretory phase patients were classified as those who were treated greater than 14 days from LMP. RESULTS: A total of 58 patients were enrolled. There was no significant difference in the mean SSS at baseline and mean SSS at 6 months between patients treated in the proliferative versus secretory phase of the cycle. No significant difference in the SSS change from baseline to 6 months was seen between the two groups. CONCLUSIONS: Menstrual cycle phase does not influence MRgFUS treatment outcome. Symptomatic improvement occurs with treatment during either phase of the menstrual cycle. Thus, the scheduling of MRgFUS treatment need not be based upon the phase of the menstrual cycle.

Female↗

PubMed2006

Brain arterioles show more active vesicular transport of blood-borne tracer molecules than capillaries and venules after focused ultrasound-evoked opening of the blood-brain barrier.

Previously, activation of vesicular transport in the brain microvasculature was shown to be one of the mechanisms of focused ultrasound-induced blood-brain barrier (BBB) opening. In the present study, we aimed to estimate the rate of the transendothelial vesicular traffic after focused ultrasound sonication in the rabbit brain, using ultrastructural morphometry and horseradish peroxidase (HRP) as a tracer. In the capillaries, the mean endothelial pinocytotic densities (the number of HRP-containing vesicles per microm(2) of the cell cytoplasm) were 0.9 and 1.05 vesicles/microm(2) 1 h after sonication with ultrasound frequencies of 0.69 and 0.26 MHz, respectively. In the arterioles, these densities were 1.63 and 2.43 vesicles/microm(2), values 1.8 and 2.3 times higher. In control locations, the densities were 0.7 and 0.14 vesicles/microm(2) for capillaries and arterioles, respectively. A small number of HRP-positive vesicles were observed in the venules. Focal delivery of HRP tracer was also observed in light microscopy. The results indicate that the precapillary microvessels play an important role in macromolecular transcytoplasmic traffic through the ultrasound-induced BBB modulation, which should be considered in the future development of trans-BBB drug delivery strategies.

Animals↗

PubMed2006

Induction of apoptosis in vivo in the rabbit brain with focused ultrasound and Optison.

Histologic effects of focused ultrasound (FUS) exposures combined with an ultrasound contrast agent (Optison) were investigated to examine whether the lesions were dominated by apoptosis or necrosis. The rabbit brains (n = 17) were sonicated (1.5 MHz, peak rarefactional pressure amplitude: 1.4 to 8.8 MPa) after Optison was injected intravenously (IV). MRI and light microscopy were used to examine tissue effects. To detect apoptosis, TUNEL staining based on labeling of DNA strand breaks was used. The average number of apoptotic and necrotic cells in 300 x 220 microm microscopic fields were counted in 18 representative lesions. Lesions in the rabbit brains were created at lowered acoustic power levels when FUS was combined with Optison. In histology, the lesions exhibited red blood cell extravasations and destruction of blood vessels. At 4 h after sonication, the lesions lost many cells, and the remaining cells exhibited both necrotic and apoptotic features. Overall, apoptosis dominated; there were, on average, 32.3 +/- 13.2 apoptotic cells per microscopic field compared with only 5.1 +/- 3.4 necrotic cells per field. In conclusion, FUS combined with Optison could produce lesions that are dominated by apoptosis, presumably induced primarily via ischemia after cavitation-produced damage to the brain vasculature.

Albumins↗

PubMed2006

Noninvasive transesophageal cardiac thermal ablation using a 2-D focused, ultrasound phased array: a simulation study.

This simulation study proposes a noninvasive, transesophageal cardiac-thermal ablation using a planar ultrasound phased array (1 MHz, 60 x 10 mm2, 0.525 mm interelement spacing, 114 x 20 elements). Thirty-nine foci in cardiac muscle were defined at 20, 40, and 60-mm distances and at various angles from the transducer surface to simulate the accessible posterior left atrial wall through the esophageal wall window. The ultrasound pressure distribution and the resulting thermal effect in a volume of 60 x 80 x 80 mm3, including esophagus and cardiac muscle, were simulated for each focus. For 1, 10, and 20-s sonications with 60 degrees C and 70 degrees C peak temperatures in cardiac muscle and without thermal damage in esophageal wall, the transducer acoustic powers were 105-727, 28-117, 21-79 W and 151-1044, 40-167, 30-114 W, respectively. The simulated lesions (thermal dose in equivalent minutes at 43 degrees C > or = 240 minutes) at these foci had lengths of 1-6, 3-11, 3-13 mm and 3-15, 5-19, 6-23 mm, respectively, and widths of 1-4, 2-7, 3-9 mm and 3-9, 4-13, 4-17 mm, respectively. As a first step toward feasibility, controllable tissue coagulation in cardiac tissue without damage to the esophagus was demonstrated numerically.

Animals↗

PubMed2006

Quality assurance and system stability of a clinical MRI-guided focused ultrasound system: four-year experience.

To retrospectively evaluate the four-year experience of a quality assurance method for a MRI-guided focused ultrasound system that uses temperature maps acquired during heating in an ultrasound/MRI phantom. This quality assurance method was performed before 148 clinical uterine fibroid thermal ablation treatments. The stability of the peak temperature rise, the targeting accuracy, the shape of the heated zone, and the noise level in the imaging was evaluated. The peak temperature rise was mostly stable for the first three years. An increase in heating was observed when the system was replaced after year three. Detection of this increase was taken into account in the subsequent clinical treatments. A small secondary hotspot was detected by the temperature maps and was seen to be resolved after system calibration. The average standard deviation in unheated regions of the phantom in the temperature maps was 0.5 +/- 0.2 degrees C; it was less than 1 degrees C in all but one procedure. The average initial targeting error was 2.8 +/- 1.8 and 2.8 +/- 2.1 mm in two radial directions and 7.7 +/- 2.9 mm along the ultrasound beam direction. The width of the heating profile was consistent over the four years. This simple method to evaluate the performance appeared to be sensitive to small changes in system performance, which was adequately stable over a four-year time period.

Equipment Failure Analysis↗

PubMed2006

Uterine leiomyomas: MR imaging-based thermometry and thermal dosimetry during focused ultrasound thermal ablation.

PURPOSE: To retrospectively evaluate magnetic resonance (MR) imaging-based thermometry and thermal dosimetry during focused ultrasound treatments of uterine leiomyomas (ie, fibroids). MATERIALS AND METHODS: All patients gave written informed consent for the focused ultrasound treatments and the current HIPAA-compliant retrospective study, both of which were institutional review board approved. Thermometry performed during the treatments of 64 fibroids in 50 women (mean age, 46.6 years +/- 4.5 [standard deviation]) was used to create thermal dose maps. The areas that reached dose values of 240 and 18 equivalent minutes at 43 degrees C were compared with the nonperfused regions measured on contrast material-enhanced MR images by using the Bland-Altman method. Volume changes in treated fibroids after 6 months were compared with volume changes in nontreated fibroids and with MR-based thermal dose estimates. RESULTS: While the thermal dose estimates were shown to have a clear relationship with resulting nonperfused regions, the nonperfused areas were, on average, larger than the dose estimates (means of 1.9 +/- 0.7 and 1.2 +/- 0.4 times as large for areas that reached 240- and 18-minute threshold dose values, respectively). Good correlation was observed for smaller treatment volumes at the lower dose threshold (mean ratio, 1.0 +/- 0.3), but for larger treatment volumes, the nonperfused region extended to locations within the fibroid that clearly were not heated. Variations in peak temperature increase were as large as a factor of two, both between patients and within individual treatments. On average, the fibroid volume reduction at 6 months increased as the ablated volume estimated by using the thermal dose increased. CONCLUSION: Study results showed good correlation between thermal dose estimates and resulting nonperfused areas for smaller ablated volumes. For larger treatment volumes, nonperfused areas could extend within the fibroid to unheated areas.

Adult↗

PubMed2006

Microbubble contrast agent with focused ultrasound to create brain lesions at low power levels: MR imaging and histologic study in rabbits.

PURPOSE: To evaluate magnetic resonance (MR) imaging-based thermometry for predicting the onset and spatial extent of lesions produced by focused ultrasound combined with a microbubble contrast agent (Optison; GE Healthcare, Milwaukee, Wis) and to compare the resulting induced temperature increase and threshold for damage with those in studies performed without the agent. MATERIALS AND METHODS: The experiments were approved by the animal care committee. Fifty-three locations in the brains of 15 rabbits were sonicated with various exposure parameters by using a 1.5-MHz focused ultrasound transducer. MR imaging was used to map the temperature rise and, along with light microscopy, to examine the lesions. Diameters of isotherms created from thermometry were compared with the resulting lesions by using Bland-Altman analysis and linear regression. The minimum acoustic power necessary for lesion creation was determined, and the apparent temperature threshold for damage was calculated with probit analysis. These thresholds were compared with prior work performed without the contrast agent. The heating induced with the microbubbles was compared with that in sonications performed without them by using a t test. RESULTS: The MR imaging-mapped temperature distributions matched the shape of the lesions. The diameters of isotherms correlated well with diameters measured at contrast material-enhanced MR imaging (mean difference between measurements, 0.0 mm +/- 0.5; R = 0.93). The temperature increase with microbubbles was statistically larger (P < .01) than for sonications performed without microbubbles. In some locations (mostly continuous wave exposures), damage was observed along the ultrasound beam path. The time-averaged acoustic power damage threshold was reduced by 91% for 10-second exposures when compared with earlier studies performed without microbubbles. The probability of producing lesions was 50% at a temperature increase of 5.9 degrees C, 5.5 degrees C lower than was observed earlier without the agent. CONCLUSION: MR imaging-based temperature measurements appeared to correlate with focused ultrasound-induced lesions in the brain when microbubbles were present, even though the temperature appeared to be below the threshold for thermal damage.

Animals↗

PubMed2006

Investigation of optimal method for inducing harmonic motion in tissue using a linear ultrasound phased array--a simulation study.

Many noninvasive ultrasound techniques have been developed to explore mechanical properties of soft tissues. One of these methods, Localized Harmonic Motion Imaging (LHMI), has been proposed to be used for ultrasound surgery monitoring. In LHMI, dynamic ultrasound radiation-force stimulation induces displacements in a target that can be measured using pulse-echo imaging and used to estimate the elastic properties of the target. In this initial, simulation study, the use of a one-dimensional phased array is explored for the induction of the tissue motion. The study compares three different dual-frequency and amplitude-modulated single-frequency methods for the inducing tissue motion. Simulations were computed in a homogeneous soft-tissue volume. The Rayleigh integral was used in the simulations of the ultrasound fields and the tissue displacements were computed using a finite-element method (FEM). The simulations showed that amplitude-modulated sonication using a single frequency produced the largest vibration amplitude of the target tissue. These simulations demonstrate that the properties of the tissue motion are highly dependent on the sonication method and that it is important to consider the full three-dimensional distribution of the ultrasound field for controlling the induction of tissue motion.

Acoustics↗

PubMed2006

Mechanism of porphyrin-induced sonodynamic effect: possible role of hyperthermia.

The biological effects of ultrasound have been investigated vigorously for various applications including the thermal coagulation of tissues, the opening of tight junctions, and localized gene or drug introduction. The synergistic cell killing effect of ultrasound and porphyrin derivatives, the so-called sonodynamic effect, holds promise for cancer treatment. Although several models to explain the sonodynamic effect have been proposed, its exact mechanism, especially in vivo, remains unknown. We examined the effect of a porphyrin derivative, protoporphyrin IX, on ultrasound-induced killing of HeLa cells. In some experiments, the intracellular protoporphyrin IX concentration was increased by 5-aminolevulinic acid treatment of the cells. Although extracellular protoporphyrin IX showed an enhanced cell killing effect by microbubble-enhanced ultrasound, intracellular protoporphyrin IX did not. On the other hand, intracellular protoporphyrin IX enhanced the cell killing effect of hyperthermia, which can be produced by ultrasound exposure, in a moderately acidic environment (pH 6.6). Because porphyrin derivatives are generally imported into the intracellular component in vivo, our results suggest that hyperthermia caused by ultrasound may play an important role in the sonodynamic effect induced by porphyrin derivatives.

Aminolevulinic Acid↗

PubMed2006

Focal disruption of the blood-brain barrier due to 260-kHz ultrasound bursts: a method for molecular imaging and targeted drug delivery.

OBJECT: The goal of this study was to explore the feasibility of using low-frequency magnetic resonance (MR) image-guided focused ultrasound as a noninvasive method for the temporary disruption of the blood-brain barrier (BBB) at targeted locations. METHODS: Rabbits were placed inside a clinical 1.5-tesla MR imaging unit, and sites in their brains were targeted for 20-second burst sonications (frequency 260 kHz). The peak pressure amplitude during the burst varied between 0.1 and 0.9 MPa. Each sonication was performed after an intravenous injection of an ultrasound contrast agent (Optison). The disruption of the BBB was evaluated with the aid of an injection of an MR imaging contrast agent (MAG-NEVIST). Additional tests involving the use of MION-47, a 20-nm magnetic nanoparticle contrast agent, were also performed. The animals were killed at different time points between 3 minutes and 5 weeks postsonication, after which light or electron microscopic evaluation was performed. The threshold for BBB disruption was approximately 0.2 MPa. More than 80% of the brain sites sonicated showed BBB disruption when the pressure amplitude was 0.3 MPa; at 0.4 MPa, this percentage was greater than 90%. Tissue necrosis, ischemia, and apoptosis were not found in tissue in which the pressure amplitude was less than 0.4 MPa; however, in a few areas of brain tissue erythrocytes were identified outside blood vessels following exposures of 0.4 MPa or higher. Survival experiments did not show any long-term adverse events. CONCLUSIONS: These results demonstrate that low-frequency ultrasound bursts can induce local, reversible disruption of the BBB without undesired long-term effects. This technique offers a potential noninvasive method for targeted drug delivery in the brain aided by a relatively simple low-frequency device.

Albumins↗

PubMed2005

Targeted delivery of antibodies through the blood-brain barrier by MRI-guided focused ultrasound.

The blood-brain barrier (BBB) is a persistent obstacle for the local delivery of macromolecular therapeutic agents to the central nervous system (CNS). Many drugs that show potential for treating CNS diseases cannot cross the BBB and there is a need for a non-invasive targeted drug delivery method that allows local therapy of the CNS using larger molecules. We developed a non-invasive technique that allows the image-guided delivery of antibody across the BBB into the murine CNS. Here, we demonstrate that subsequent to MRI-targeted focused ultrasound induced disruption of BBB, intravenously administered dopamine D(4) receptor-targeting antibody crossed the BBB and recognized its antigens. Using MRI, we were able to monitor the extent of BBB disruption. This novel technology should be useful in delivering macromolecular therapeutic or diagnostic agents to the CNS for the treatment of various CNS disorders.

Animals↗

PubMed2005

A novel method for the intracellular delivery of siRNA using microbubble-enhanced focused ultrasound.

Short interfering RNA (siRNA) has attracted much attention for clinical use in various diseases. However, its delivery, especially through the cell membrane, continues to present a challenge. Advances in ultrasound- and ultrasound contrast-agent technologies have made it possible to change transiently the permeability of the cell membrane and, using a focused ultrasound transducer, to narrow and focus the ultrasound energy on a small target, thereby avoiding damage to surrounding tissue. In this in vitro study, we demonstrate that it is possible to deliver siRNA intracellularly via microbubble-enhanced focused ultrasound. Although further optimization is necessary, our novel method for siRNA transduction represents a powerful tool for using siRNA in vivo and possibly in the clinical setting.

Animals↗