EFSUMB Technical Review - Update 2023: Dynamic Contrast-Enhanced Ultrasound (DCE-CEUS) for the Quantification of Tumor Perfusion

Dynamic contrast-enhanced ultrasound (DCE-US) is a technique to quantify tissue perfusion based on phase-specific enhancement after the injection of microbubble contrast agents for diagnostic ultrasound. The guidelines of the European Federation of Societies for Ultrasound in Medicine and Biology (EFSUMB) published in 2004 and updated in 2008, 2011, and 2020 focused on the use of contrast-enhanced ultrasound (CEUS), including essential technical requirements, training, investigational procedures and steps, guidance regarding image interpretation, established and recommended clinical indications, and safety considerations. However, the quantification of phase-specific enhancement patterns acquired with ultrasound contrast agents (UCAs) is not discussed here. The purpose of this EFSUMB Technical Review is to further establish a basis for the standardization of DCE-US focusing on treatment monitoring in oncology. It provides some recommendations and descriptions as to how to quantify dynamic ultrasound contrast enhancement, and technical explanations for the analysis of time-intensity curves (TICs). This update of the 2012 EFSUMB introduction to DCE-US includes clinical aspects for data collection, analysis, and interpretation that have emerged from recent studies. The current study not only aims to support future work in this research field but also to facilitate a transition to clinical routine use of DCE-US.

Contrast-Enhanced Ultrasound for Musculoskeletal Applications: A World Federation for Ultrasound in Medicine and Biology Position Paper

This World Federation for Ultrasound in Medicine and Biology position paper reviews the diagnostic potential of ultrasound contrast agents for clinical decision-making and provides general advice for optimal contrast-enhanced ultrasound performance in musculoskeletal issues. In this domain, contrast-enhanced ultrasound performance has increasingly been investigated with promising results, but still lacks everyday clinical application and standardized techniques; therefore, experts summarized current knowledge according to published evidence and best personal experience. The goal was to intensify and standardize the use and administration of ultrasound contrast agents to facilitate correct diagnoses and ultimately to improve the management and outcomes of patients.

Low radiation dose in computed tomography: the role of iodine

Recent approaches to reducing radiation exposure during CT examinations typically utilize automated dose modulation strategies on the basis of lower tube voltage combined with iterative reconstruction and other dose-saving techniques. Less clearly appreciated is the potentially substantial role that iodinated contrast media (CM) can play in low-radiation-dose CT examinations. Herein we discuss the role of iodinated CM in low-radiation-dose examinations and describe approaches for the optimization of CM administration protocols to further reduce radiation dose and/or CM dose while maintaining image quality for accurate diagnosis. Similar to the higher iodine attenuation obtained at low-tube-voltage settings, high-iodine-signal protocols may permit radiation dose reduction by permitting a lowering of mAs while maintaining the signal-to-noise ratio. This is particularly feasible in first pass examinations where high iodine signal can be achieved by injecting iodine more rapidly. The combination of low kV and IR can also be used to reduce the iodine dose. Here, in optimum contrast injection protocols, the volume of CM administered rather than the iodine concentration should be reduced, since with high-iodine-concentration CM further reductions of iodine dose are achievable for modern first pass examinations. Moreover, higher concentrations of CM more readily allow reductions of both flow rate and volume, thereby improving the tolerability of contrast administration.

Dynamic contrast-enhanced ultrasound and elastography assess deltoid muscle integrity after reverse shoulder arthroplasty

BACKGROUND

The outcome after reverse shoulder arthroplasty (RSA) depends on the condition of the deltoid muscle, which we assessed with new ultrasound modalities and electromyography (EMG). Contrast-enhanced ultrasound (CEUS) and acoustic radiation force impulse (ARFI) were applied to assess perfusion and elasticity of the deltoid muscle compared with the clinical and functional outcome.

METHODS

The study recruited 64 patients (mean age, 72.9 years) treated with RSA between 2004 and 2013. The deltoid muscle was examined with EMG and ultrasound imaging. Functional scores such as Constant score and American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form score were assessed. Among other CEUS parameters, the wash-in perfusion index, time to peak, and rise time were compared between the operated-on and contralateral shoulders as well as between patients with above-average and below-average outcome. The stiffness of the deltoid muscle was analyzed with ARFI.

RESULTS

After RSA, deltoid perfusion (wash-in perfusion index, Δ = -12% ± 22%, P = .0001) and shoulder function (Constant score, Δ = -14 ± 24, P < .0001) were both inferior compared with the contralateral side. This perfusion deficit was associated with a limited range of motion (time to peak and anteversion: r = -0.290, P = .022). Deltoid perfusion was higher in patients with above-average outcome (rise time, Δ = 33% ± 13%, P = .038). The operated-on deltoid muscles showed higher stiffness than the contralateral muscles (ARFI, Δ = 0.2 ± 0.9 m/s, P = .0545). EMG excluded functionally relevant axillary nerve injuries in the study population.

CONCLUSIONS

CEUS revealed reduced mean perfusion of the deltoid muscle after RSA. Reduced perfusion was associated with limited range of motion and below-average outcome. Functional shoulder impairment after RSA might be predicted by noninvasive CEUS as a surrogate parameter for the integrity of the deltoid muscle.

Dynamic Contrast-Enhanced Sonography and Dynamic Contrast-Enhanced Magnetic Resonance Imaging for Preoperative Diagnosis of Infected Nonunions

OBJECTIVES

Bone regeneration depends on perfusion of the fracture tissue, whereby hypervascularity is associated with infection, which itself causes nonunions. To date, nonunion perfusion has not been assessed with contrast-enhanced sonography. The aim of this study was to evaluate the potential of contrast-enhanced sonography in the analysis of nonunion tissue perfusion.

METHODS

Nonunion vascularity of 31 patients before revision surgery was prospectively examined with qualitative contrast-enhanced sonography and dynamic contrast-enhanced magnetic resonance imaging (MRI). Time-intensity curves from 2-minute contrast-enhanced sonographic video clips were generated, and parameters such as wash-in rate, rise time, and peak enhancement were quantified. On dynamic contrast-enhanced MRI, the initial area under the enhancement curve was quantified. Preoperative radiographs, computed tomograms, the clinical nonunion score, laboratory infection features, as well as contrast-enhanced sonographic and dynamic contrast-enhanced MRI perfusion were correlated with microbiological results from the nonunion tissue.

RESULTS

Both qualitative and quantitative contrast-enhanced sonography showed significant differences between infected and aseptic nonunions (P = .015 and .020). The qualitative dynamic contrast-enhanced MRI analysis was not significant (P= .244), but after quantification, a strong correlation (P = .007) with microbiological results was noted. A receiver operating characteristic analysis calculated ideal cutoff values for quantitative contrast-enhanced sonography and dynamic contrast-enhanced MRI so that their combination detected infected nonunions with sensitivity and specificity of 88.9% and 77.3%, respectively. Clinical, radiologic, and laboratory examinations did not correlate with microbiological results (P > .05).

CONCLUSIONS

Contrast-enhanced sonography can visualize the vascularity of nonunions in real time, while quantification software allows for a semiobjective evaluation of bone perfusion. The correlations of both quantitative contrast-enhanced sonography and dynamic contrast-enhanced MRI with microbiological results show their high value for differentiation of infected from aseptic nonunions.

Assessment of skeletal muscle microcirculation in type 2 diabetes mellitus using dynamic contrast-enhanced ultrasound: a pilot study

PURPOSE

To investigate muscular micro-perfusion by employing dynamic contrast-enhanced ultrasound (CEUS) and performing transient arterial occlusion in patients with type 2 diabetes mellitus (DM-2).

METHODS

Twenty DM-2 patients (mean age, 58 ± 8.6 years; duration of diabetes, 15.4 ± 12.1 years) and 20 healthy volunteers (mean age, 54 ± 5.4 years) participated. CEUS was applied to the calf, while 4.8 mL of SonoVue(®) was injected intravenously. At the thigh level, arterial occlusion (60 s) was performed. CEUS parameters (tmax, max, AUCpost and m) were evaluated and Pearson-product-moment correlation coefficients were computed.

RESULTS

A moderate negative correlation of HbA1c and max was established (-0.53). Max in patients with DM-2 >10 years was 79.89 ± 37.4. Max in patients with DM-2 duration <10 years was 137.62 ± 71.72 (p = 0.04). AUCpost in patients with DM-2 duration >10 years was 3924.01 ± 1630.52. AUCpost in patients with DM-2 duration <10 years was 6453.59 ± 3206.23 (p = 0.04).

CONCLUSION

Patients with long history of DM-2 present with impaired muscular perfusion. CEUS and transient arterial occlusion may provide appropriate methods for semi-quantitative evaluation of muscular micro-perfusion in patients with DM-2.

High-contrast computed tomographic angiography better detects residual intracranial arteriovenous malformations in long-term follow-up after radiotherapy than 1.5-Tesla time-of-flight magnetic resonance angiography

BACKGROUND

Computed tomography angiography (CTA) and magnetic resonance angiography (MRA) are noninvasive alternatives for therapy monitoring of cerebral arteriovenous malformation (AVM).

PURPOSE

To evaluate if CTA is able to detect residual AVM in the long-term follow-up after radiotherapy when time-of-flight (TOF) MRA could no longer detect a remaining nidus.

MATERIAL AND METHODS

18 patients with intracranial AVM were included between November 2005 and August 2007 who were scheduled for CTA (16-slice CT, 1-mm slice thickness, 90 ml iomeprol 400 mg I/ml, 4 ml/s) in the follow-up of radiotherapy. In these patients, MRA (3D-TOF, and bolus tagging at 1.5 T) could no longer detect a remaining nidus.

RESULTS

The previously performed MRA (median time between CTA and MRA, 2.5 months) described total obliterations in 14 and subtotal obliterations in two AVM cases. Two MRA diagnoses were inconclusive due to artifacts. CTA (median time after therapy, 28 months; range, 5-66 months) could provide a diagnosis in all cases, but confirmed the MRA diagnosis only in 50% of the cases. A residual nidus was shown in an additional six cases, and subtotal obliteration in another three cases. The interval between radiotherapy and the follow-up examination was significantly different (P<0.05) between false- and true-negative MRA examinations (median, 18 vs. 30 months).

CONCLUSION

High-contrast CTA is a sensitive tool in the detection of AVM and is able to identify residual AVM after radiotherapy even if previously performed TOF MRA at 1.5 T shows total obliteration.

Comparison of transient arterial occlusion and muscle exercise provocation for assessment of perfusion reserve in skeletal muscle with real-time contrast-enhanced ultrasound

OBJECTIVE

Contrast-enhanced ultrasound (CEUS) is able to quantify muscle perfusion and changes in perfusion due to muscle exercise in real-time. However, reliable measurement of standardized muscle exercise is difficult to perform in clinical examinations. We compared perfusion reserve assessed by CEUS after transient arterial occlusion and exercise to find the most suitable measurement for clinical application.

METHODS

Contrast pulse sequencing (7 MHz) during continuous IV infusion of SonoVue(®) (4.8 mL/300 s) was used in 8 healthy volunteers to monitor muscle perfusion of the gastrocnemius muscle during transient (1 min) arterial occlusion produced by a thigh cuff of a venous occlusion plethysmograph. Isometric muscle exercise (50% of individual maximum strength for 20s) was subsequently performed during the same examination, and several CEUS parameters obtained from ultrasound-signal-intensity-time curves and its calculation errors were compared.

RESULTS

The mean maximum local blood volume after occlusion was 13.9 [∼mL] (range, 4.5-28.8 [∼mL]), and similar values were measured after sub-maximum exercise 13.8 [∼mL], (range, 4.6-22.2 [∼mL]. The areas under the curve during reperfusion vs. recovery were also similar (515.2±257.5 compared to 482.2±187.5 [∼mLs]) with a strong correlation (r=0.65), as were the times to maximum (15.3s vs. 15.9s), with a significantly smaller variation for the occlusion method (±2.1s vs. ±9.0s, p=0.03). The mean errors for all calculated CEUS parameters were lower for the occlusion method than for the exercise test.

CONCLUSIONS

CEUS muscle perfusion measurements can be easily performed after transient arterial occlusion. It delivers data which are comparable to CEUS measurements after muscle exercise but with a higher robustness. This method can be easily applied in clinical examination of patients with e.g. PAOD or diabetic microvessel diseases to assess perfusion reserve.

Real-time contrast-enhanced ultrasound for the assessment of perfusion dynamics in skeletal muscle

We developed a real-time low-MI contrast-enhanced ultrasound method (CEUS), compared it with venous occlusion plethysmography (VOP) and evaluated its robustness in the quantification of skeletal muscle perfusion during exercise. Contrast pulse sequencing (7 MHz) during continuous intravenous infusion of SonoVue (4.8 mL/300 s) was used repeatedly in eight healthy volunteers to monitor changes of the muscle perfusion before, during and after isometric exercises (10 to 50% of individual maximum strength for 20 to 30 s) of the gastrocnemius muscle in real time. CEUS was correlated with VOP at different time points, and the exactness of several CEUS parameters obtained from ultrasound-signal-intensity-time curves was evaluated. Real-time CEUS depicted a large variability of the skeletal muscle blood volume at rest (mean, 3.48; range, 0.60 to 9.92 [approximately mL]), with a significant reproducibility (r=0.72, p<0.05) and correlation with VOP (r=0.59, p<0.001). Mean blood volume during exercise was 1.58(approximately mL), increased to a mean maximum after exercise of 8.88 (approximately mL), the mean change of the local blood volume during and directly after the exercise was -0.10 and +1.57(approximately mL/s). The average CEUS signal during exercise decreased (mean area under the curve, -50.4 [approximately mL.s]) and subsequently increased post exercise (mean 118.6 [approximately mL.s]). CEUS parameters could be calculated with mean relative errors between 6 and 36%. Continuous assessment of local muscle microcirculation during exercise is possible with real-time CEUS with an acceptable robustness. Its application may be of particular interest in a better understanding of the role of perfusion during muscle training, and the monitoring of pathological vascular response, such as in diabetic microvessel diseases.

Morphology, metabolism, microcirculation, and strength of skeletal muscles in cancer-related cachexia

PURPOSE

Cancer-related cachexia is an obscure syndrome leading to muscle wasting, reduced physical fitness and quality of life. The aim of this study was to assess morphology, metabolism, and microcirculation in skeletal muscles of patients with cancer-related cachexia and to compare these data with matched healthy volunteers.

METHODS

In 19 patients with cancer-induced cachexia and 19 age-, gender-, and body-height-matched healthy volunteers body composition and aerobic capacity (VO(2max)) were analyzed. Skeletal muscle fiber size and capillarization were evaluated in biopsies of the vastus lateralis muscle. The cross-sectional area (CSA) of the quadriceps femoris muscle was measured by magnetic resonance imaging as well as its isokinetic and isometric force. The energy and lipid metabolism of the vastus lateralis muscle was quantified by (31)P and (1)H spectroscopy and parameters of its microcirculation by contrast-enhanced ultrasonography (CEUS).

RESULTS

Morphologic parameters were about 30% lower in cachexia than in volunteers (body mass index: 20 +/- 3 vs. 27 +/- 4 kg m(-2), CSA: 45 +/- 13 vs. 67 +/- 14 cm(2), total fiber size: 2854 +/- 1112 vs. 4181 +/- 1461 microm(2)). VO(2max) was reduced in cachexia (23 +/- 9 vs. 32 +/- 7 ml min(-1) kg(-1), p=0.03), whereas histologically determined capillary density and microcirculation in vivo were not different. Both concentrations of muscular energy metabolites, pH, and trimethyl-ammonium-containing compounds were comparable in both groups. Absolute strength of quadriceps muscle was reduced in cachexia (isometric: 107 +/- 40 vs. 160 +/- 40 Nm, isokinetic: 101 +/- 46 vs. 167 +/- 50 Nm; p=0.03), but identical when normalized on CSA (isometric: 2.4 +/- 0.5 vs. 2.4 +/- 0.4 Nm cm(-2), isokinetic: 2.2 +/- 0.4 vs. 2.5 +/- 0.5 Nm cm(-2)).

CONCLUSIONS

Cancer-related cachexia is associated with a loss of muscle volume but not of functionality, which can be a rationale for muscle training.

Changes in the micro-circulation of skeletal muscle due to varied isometric exercise assessed by contrast-enhanced ultrasound

PURPOSE

To quantitatively assess local muscle micro-circulation with real-time contrast-enhanced ultrasound (CEUS) during different exercises and compare the results with performed muscle work and global blood flow.

MATERIALS AND METHODS

Sixteen low mechanical index CEUS examinations of the right lower leg flexors of healthy volunteers were performed using a continuous infusion of SonoVue(®) (4.8 mL/300 s). Several muscle perfusion parameters were extracted from derived CEUS signal intensity time curves during different isometric exercises (10-50% of maximum individual strength for 20-30s) and then correlated with the performed muscle work or force, and the whole lower leg blood flow which we measured simultaneously by venous occlusion plethysmography (VOP).

RESULTS

The shapes of the CEUS curve during and after exercise differed individually depending on the performed muscle work. The maximum blood volume MAX was observed only after exercise cessation and was significantly correlated with the performed muscle force (r=0.77, p<0.0001). The blood volume over exercise time was inversely correlated with the spent muscle work (r=-0.60, p=0.006). CEUS and VOP measurements correlated only at rest and after the exercise. During exercise, mean CEUS local blood volume decreased (from 3.48 to 2.19 (∼mL)), while mean VOP global blood flow increased (mean, from 3.96 to 7.71 mL/100 mg/min).

CONCLUSION

Real-time low-MI CEUS provides complementary information about the local muscle micro-circulation compared to established blood flow measures. CEUS may be used for a better understanding of muscle perfusion physiology and in the diagnosis of micro-circulation alterations such as in peripheral arterial occlusive disease or diabetic angiopathy.

[Contrast-enhanced ultrasound for the characterization of incidental liver lesions - an economical evaluation in comparison with multi-phase computed tomography]

AIM

The aim of the study was to conduct a cost-minimization analysis of contrast-enhanced ultrasound (CEUS) compared to multi-phase computed tomography (M-CT) as the diagnostic standard for diagnosing incidental liver lesions.

METHODS

Different scenarios of a cost-covering realization of CEUS in the ambulant sector in the general health insurance system of Germany were compared to the current cost situation. The absolute savings potential was estimated using different approaches for the calculation of the incidence of liver lesions which require further characterization.

RESULTS

CEUS was the more cost-effective method in all scenarios in which CEUS examinations where performed at specialized centers (122.18-186.53 euro) compared to M-CT (223.19 euro). With about 40 000 relevant liver lesions per year, systematic implementation of CEUS would result in a cost savings of 4 m euro per year. However, the scenario of a cost-covering CEUS examination for all physicians who perform liver ultrasound would be the most cost-intensive approach (e. g., 407.87 euro at an average utilization of the ultrasound machine of 25 %, and a CEUS ratio of 5 %).

CONCLUSION

A cost-covering realization of the CEUS method can result in cost savings in the German healthcare system. A centralized approach as proposed by the DEGUM should be targeted.

Concentric resistance training increases muscle strength without affecting microcirculation

PURPOSE

While the evidence is conclusive regarding the positive effects of endurance training, there is still some controversy regarding the effects of resistance training on muscular capillarity. Thus, the purpose was to assess whether resistance strength training influences resting skeletal muscle microcirculation in vivo.

MATERIALS AND METHODS

Thirty-nine middle-aged subjects (15 female, 24 male; mean age, 54+/-9 years) were trained twice a week on an isokinetic system (altogether 16 sessions lasting 50 min, intensity 75% of maximum isokinetic and isometric force of knee flexors and extensors). To evaluate success of training, cross-sectional area (CSA) of the quadriceps femoris muscle and its isokinetic and isometric force were quantified. Muscular capillarization was measured in biopsies of the vastus lateralis muscle. In vivo, muscular energy and lipid metabolites were quantified by magnetic resonance spectroscopy and parameters of muscular microcirculation, such as local blood volume, blood flow and velocity, by contrast-enhanced ultrasound analyzing replenishment kinetics.

RESULTS

The significant (P<0.001) increase in CSA (60+/-16 before vs. 64+/-15 cm(2) after training) and in absolute muscle strength (isometric, 146+/-44 vs. 174+/-50 Nm; isokinetic, 151+/-53 vs. 174+/-62 Nm) demonstrated successful training. Neither capillary density ex vivo (351+/-75 vs. 326+/-62) nor ultrasonographic parameters of resting muscle perfusion were significantly different (blood flow, 1.2+/-1.2 vs. 1.1+/-1.1 ml/min/100g; blood flow velocity, 0.49+/-0.44 vs. 0.52+/-0.74 mms(-1)). Also, the intensities of high-energy phosphates phosphocreatine and beta-adenosintriphosphate were not different after training within the skeletal muscle at rest (beta-ATP/phosphocreatine, 0.29+/-0.06 vs. 0.28+/-0.04).

CONCLUSION

The significant increase in muscle size and strength in response to concentric isokinetic and isometric resistance training occurs without an increase in the in vivo microcirculation of the skeletal muscles at rest.

Quantification of enhancement in contrast ultrasound: a tool for monitoring of therapies in liver metastases

Ultrasound techniques are presented using the contrast agent SonoVue (Bracco, Italy) for microvascular imaging of liver metastases and for the detection of treatment-related changes in tumour perfusion. Technical requirements and examination protocols for contrast-enhanced ultrasound (CEUS) in the detection of microvascularity are described. Procedures for the quantitative analysis of perfusion in follow-up examinations are explained. Compared to contrast-enhanced computed tomography, low-MI (mechanical index) CEUS with SonoVue better reflected the arterial perfusion of liver metastases. Changes of tumour perfusion after stereotactic radiotherapy or chemotherapy of liver metastases could be sensitively detected using CEUS. In addition, possible changes of the liver perfusion after therapy could be assessed. Replenishment kinetics of the contrast agent allowed for a quantitative analysis of the arterial and portal venous perfusion in the tumour and the liver tissue. CEUS is a promising method to non-invasively monitor systemic or local-ablative therapies of liver metastases by sensitively detecting changes of tumour perfusion.

[Ultrasound contrast agents. Pharmaceutical drug safety and bioeffects]

In this overview safety aspects of ultrasound contrast agents (USCA) are described and discussed. In general USCA are very safe drugs. However, allergic adverse reactions can rarely occur, particularly due to the colloidal structure of USCA. In addition, the use of USCA could reduce the threshold for acoustically induced bioeffects and has the potential to increase these effects. In in vitro studies and animal trials USCA caused petechial hemorrhages, vascular damage, and the formation of free radicals. Even DNA damage with single strand breaks could be demonstrated. In human studies and clinical practice none of these bioeffects could be observed. In contrast-enhanced echocardiography a higher rate of premature ventricular contractions has been reported when imaging was triggered at the end systole. Compared with other contrast agents contrast-enhanced ultrasound showed no nephrotoxic effects and could prove to be an alternative diagnostic method for patients with renal failure.

Assessment of Metabolism and Microcirculation of Healthy Skeletal Muscles by Magnetic Resonance and Ultrasound Techniques

PURPOSE

To assess metabolism and microcirculation of healthy skeletal muscle by magnetic resonance (MR) and ultrasound techniques and to compare these data with muscle histology, and anthropometric and blood parameters.

METHODS

Thirty-four healthy volunteers were selected such that their measured aerobic capacity (VO2max) per body weight ranged between 23 and 66 mL/minute/kg to render a large variability of skeletal muscle capillarization as a result of their different physical activity. We analyzed body composition, blood parameters, and skeletal muscle fiber size and capillarization in biopsies of the vastus lateralis muscle. These data were compared with knee extensor cross-sectional area (CSA) obtained by MR imaging, microcirculation of the vastus lateralis muscle by contrast-enhanced ultrasound (CEUS), and its energy and lipid metabolism measured with 31P and 1H MR spectroscopy. Statistical analysis was performed using Pearson's correlation coefficient and significance was tested at a level of .5%.

RESULTS

The variable physical activity was reflected in a large variability of vastus lateralis muscle perfusion and metabolism at rest with highest histologic capillarization and CEUS-perfusion values observed in the best-trained volunteers. Levels of high-energy phosphates, such as phosphocreatine, were positively correlated with CSA (r= .5) and histologic fiber size (r= .6 for type IIA and IIX fibers), while phosphocreatine concentration was significantly negatively correlated to myocellular lipids (r=-.6) and trimethyl ammonium containing compounds (r=-.8). Local blood volume measured in vivo with CEUS was positively correlated with several histologic capillarization parameters.

CONCLUSIONS

Dedicated MR- and CEUS-methods deliver (patho-)physiologic information about capillarization and fiber characteristics of skeletal muscles in vivo and hence establish a useful diagnostic tool for muscular diseases.

Quantitative evaluation of muscle perfusion with CEUS and with MR

Functional imaging might increase the role of imaging in muscular diseases, since alterations of muscle morphology alone are not specific for a particular disease. Perfusion, i.e., the blood flow per tissue and time unit including capillary flow, is an important functional parameter. Pathological changes of skeletal muscle perfusion can be found in various clinical conditions, such as degenerative or inflammatory myopathies or peripheral arterial occlusive disease. This article reviews the theoretical basics of functional radiological techniques for assessing skeletal muscle perfusion and focuses on contrast-enhanced ultrasound (CEUS) and magnetic resonance imaging (MRI) techniques. Also, the applications of microvascular imaging, such as in detection of myositis and for discriminating myositis from other myopathies or evaluating peripheral arterial occlusive disease, are presented, and possible clinical indications are discussed. In conclusion, dedicated MR and CEUS methods are now available that visualize and quantify (patho-)physiologic information about microcirculation within skeletal muscles in vivo and hence establish a useful diagnostic tool for muscular diseases.

Contrast-enhanced Ultrasound in Dermatomyositis- and Polymyositis

OBJECTIVE

To evaluate prospectively contrast-enhanced ultrasound (CEUS) in patients suspected of having dermatomyositis or polymyositis.

METHODS

In 35 patients (23 women, 12 men; mean age, 51 years+/-16 years) who were suspected of having dermatomyositis or polymyositis, perfusion in clinically affected skeletal muscles was quantified with contrast-enhanced intermittent power Doppler ultrasound. By applying a modified model that analyzed the replenishment kinetics of microbubbles, the perfusion-related parameters blood flow, local blood volume and blood flow velocity were measured. Findings were compared with muscle biopsy appearances and with the results of MRI that was performed with a 1.5-Tesla unit. Receiver operating characteristic analysis was performed and optimum thresholds for diagnosis of myositis were determined.

RESULTS

Eleven patients had histologically confirmed dermatomyositis or polymyositis and showed significantly higher blood flow velocity (P=.01 for dermato- and P<.001 for polymyositis), blood flow (P<.001 for dermato- and polymyositis), and blood volume (P=.007 for dermato- and P<.001 for polymyositis) on contrast-enhanced ultrasound than those who did not have myositis. An increase in signal intensity on T2-weighted MR images was found in all patients with myositis. MRI had a sensitivity, specificity, positive (PPV), and negative predicting values (NPV) of 100%, 88%, 77%, and 100% for diagnosis of myositis, respectively. CEUS blood flow was the best ultrasound measure for diagnosis of dermato- or polymyositis with sensitivity, specificity, PPV, and NPV of 73%, 91%, 80%, and 88%, respectively.

CONCLUSIONS

Increased skeletal muscle perfusion measured by CEUS could serve as an additional measurer for the diagnosis of an inflammatory myopathy.

Contrast-enhanced ultrasound for examining tumor biology

This paper reviews the potential of ultrasound for assessing the viability and biological behavior of tumors. Unlike color Doppler sonography, modern techniques for contrast-enhanced ultrasound permit the measurement of tissue perfusion irrespective of vessel size or flow velocity. Perfusion can also be assessed quantitatively, using replenishment kinetics or derivates thereof. The perfusion of tumors is a surrogate parameter of their viability and may mirror their response to therapy. Furthermore, the degree of vascularity in a tumor may express its aggressiveness and help to predict its response to treatment. In animal models, a decrease in blood flow has been shown to precede a shrinkage of tumors treated with anti-angiogenic compounds. In liver metastases, arterial and portal blood supply can be assessed separately, and a response to stereotactic radiotherapy was found to go along with a decrease in arterial perfusion. Moreover, a relatively high arterial perfusion of liver metastases may predict a response to chemotherapy. Contrast-enhanced ultrasound may be a potent tool for assessing the effects of anti-angiogenic treatment in patients.

Relationship of skeletal muscle perfusion measured by contrast-enhanced ultrasonography to histologic microvascular density

OBJECTIVE

The purpose of this study was to compare skeletal muscle perfusion measured by contrast-enhanced ultrasonography (CEUS) with microvascular density in muscle biopsies.

METHODS

Power Doppler sonography after intravenous bolus injection of Levovist (SH U 508A; Schering AG, Berlin, Germany) was used to examine perfusion of vastus lateralis muscle in 23 healthy volunteers. Local blood volume (B), blood flow velocity (v), and blood flow (f) were calculated by analyzing replenishment kinetics. CEUS perfusion was compared with vascularization of biopsy samples from vastus lateralis muscle. Subjects were selected such that their aerobic capacity (maximal oxygen uptake [VO(2)max]) per body weight ranged between 23 and 66 mL . min(-1) . kg(-1) to render a large variability of skeletal muscle capillarization. Moreover, subjects' venous blood hematocrit (Hkt) was determined to estimate the plasmatic intravascular volume fraction (1-Hkt=PVF) in which the microbubbles can distribute.

RESULTS

Median capillary density was 331/mm(2) (range, 207-469/mm(2)), and median capillary fiber contacts (CFC) were 3.6 (range, 2.3-6.5). CFC was correlated with VO(2)max (r=0.59; P<.01). Among CEUS parameters, B showed the closest correlation to CFC (r=0.53; P<.01). When CFC was normalized for PVF, correlation of B to CFC was r=0.64 (P<.01). CEUS could depict the physiologic large variability of vastus lateralis muscle perfusion at rest (median [range]: B, 2.5 [0.1-12.3] approximately mL; v, 0.3 [0.1-3.7] mm/s; f, 0.7 [0.1-5.3] approximately mL . min(-1) . 100 g tissue(-1)).

CONCLUSIONS

B is significantly related to fiber-adjacent capillarization and may represent physiologic capillary recruitment (eg, through metabolic fiber-related signals). CEUS is feasible for skeletal muscle perfusion quantification.

[Ultrasound contrast media--principles and clinical applications]

This article reviews the technical basics and the application of contrast-enhanced ultrasonography. Ultrasound contrast agents have been evaluated in various organs and have proven to be particularly useful in the detection and characterization of liver lesions. Experiences in small parts (such as breast, or lymph nodes) are so far limited, because only since recently are the technical prerequisites available for contrast-enhanced ultrasound high-frequency transducers. Ultrasound contrast media can be used for functional studies, e. g., of organ or tumor perfusion. Mathematical models were primarily developed for measuring myocardial perfusion and have recently been adapted for studying tumors. In animal experiments as well as in clinical applications, quantitative parameters of tumor perfusion have been evaluated as surrogate parameters for response to radiotherapy, chemotherapy, or treatment with anti-angiogenic agents.

Pathologic Skeletal Muscle Perfusion in Patients with Myositis: Detection with Quantitative Contrast-enhanced US—Initial Results

PURPOSE

To prospectively determine whether contrast material-enhanced ultrasonography (US) can depict inflammation-induced changes in muscle perfusion for patients suspected of having dermatomyositis or polymyositis and to compare these findings with those of magnetic resonance (MR) imaging and muscle biopsy.

MATERIALS AND METHODS

Institutional review board approval and informed consent were obtained. Perfusion in skeletal muscles was quantified with contrast-enhanced intermittent power Doppler US by applying a modified model that analyzed the replenishment kinetics of microbubbles. In 22 patients (16 women, six men; mean age, 52 years +/- 17) who were suspected of having myositis and in 10 healthy volunteers (two women, eight men; mean age, 28 years +/- 4), contrast-enhanced US of the clinically affected right biceps muscle was performed to measure blood flow, blood volume, and blood flow velocity. Additionally, the right upper arm was examined with a 1.5-T unit by using three different MR imaging techniques. Findings were compared with the results of clinical examinations and muscle biopsy. Data for perfusion-related parameters obtained at contrast-enhanced US were analyzed by using a nonparametric Mann-Whitney U test.

RESULTS

Eight patients had histologically confirmed myositis and showed significantly higher blood flow velocity (P = .01), blood flow (P = .001), and blood volume (P = .002) at contrast-enhanced US than did patients who did not have myositis. Blood flow velocity (P = .001) and blood flow (P = .002) were significantly higher in patients with myositis than in volunteers. An increase in signal intensity on T2-weighted MR images was found in all patients with myositis, while contrast material enhancement on fat-suppressed T1-weighted MR images was found in only four of seven patients with myositis.

CONCLUSION

Initial results show that contrast-enhanced US is a feasible method for noninvasively demonstrating increased perfusion in the involved muscle groups in patients with myositis.

Vaskuläre Bildgebung mittels kontrastverstärkter Sonographie in der experimentellen Anwendung

The possibility of employing contrast-enhanced ultrasound for sensitive detection of perfusion has resulted in new forms of application in fundamental medical biological research that go far beyond mere preclinical evaluation of these techniques. This contribution explains the methods for visualization and quantification of perfusion with contrast-enhanced sonography and provides an overview of how these functional examinations have been used to date. The procedure is generally considered indicated when information on tissue perfusion using ultrasound is required. This topic is also gaining increasing clinical interest, e.g., for assessment of myocardial, cerebral, and renal perfusion or for monitoring therapy. Among the various new treatment procedures that have been investigated in animal models with ultrasound, particularly pro-angiogenic and antiangiogenic therapy approaches predict promising new fields for application of contrast-enhanced ultrasound.

Assessment of skeletal muscle perfusion using contrast-enhanced ultrasonography

OBJECTIVE

The purpose of this study was to develop a clinically applicable examination method to assess perfusion of the skeletal muscle using contrast-enhanced ultrasonography (CEUS) analyzing replenishment kinetics of microbubbles.

METHODS

Power Doppler sonography (7 MHz) after intravenous bolus injection of 10 mL of a microbubble contrast agent was used to repeatedly examine the perfusion of the right biceps muscle at rest and after defined exercise in 10 healthy volunteers. Parameters of perfusion, such as local blood volume, blood flow velocity, and perfusion, were calculated by a modified analysis of replenishment kinetics. For validation, CEUS was correlated with venous occlusion plethysmography (VOP) examining the right forearm flexor muscles at rest and after defined exercise.

RESULTS

The CEUS examination was easily feasible and was able to depict the physiologic large variability of the right biceps muscle perfusion at rest (mean +/- SD, 3.0 +/- 2.3 [approximately mL/s x 100 mg]) compared with the results after exercise (22.9 +/- 11.0 [approximately mL/s x 100 mg]). The perfusion calculated with VOP significantly correlated with the CEUS parameters perfusion (r = 0.81; P < .001) and blood volume (r = 0.82; P < .001). The calculated mean blood flow velocity in the right forearm flexor muscles raised from 0.41 +/- 0.24 mm/s at rest to 0.64 +/- 0.39 mm/s after exercise, showing a significant correlation with the CEUS perfusion (r = 0.72; P < .001).

CONCLUSIONS

Muscle perfusion can be easily and quantitatively assessed with CEUS. Compared with VOP, CEUS allows for a separate analysis of different muscle groups, unaffected by skin perfusion. Its application may be of particular interest in the diagnosis and monitoring of pathologic microvascularization in myositis or diabetic obstructive disease.

Monitoring of liver metastases after stereotactic radiotherapy using low-MI contrast-enhanced ultrasound--initial results

The purpose of this study was to monitor liver metastases after radiotherapy using contrast-enhanced ultrasound (CEUS). In 15 patients, follow-up examinations after stereotactic, single-dose radiotherapy were performed using CEUS (low mechanical index (MI), 2.4-ml SonoVue) and computed tomography (CT). Besides tumor size, the enhancement of the liver and the metastases was assessed at the arterial, portal venous, and delayed phases. The sizes of the tumor and of a perifocal liver reaction after radiotherapy measured with CEUS significantly correlated with those measured at CT (r=0.93, p<0.001). CEUS found a significant reduction of the arterial vascularization in treated tumors (p<0.05). In the arterial phase, the perifocal liver tissue was hypervascularized compared to the treated tumor (p<0.001); in the late phase, it was less enhanced than the liver (p<0.001) and more than the tumor (p<0.01). The perifocal liver reaction was also seen in CT, but with a variable enhancement at the arterial (50% hyperdense compared to normal liver tissue), venous, or delayed phase (each with 70% hyperdense reactions). CEUS allows for the assessment of tumor and liver perfusion, in addition to morphological tumor examination, which was comparable with CT. Thus, changes of tumor perfusion, which may indicate tumor response, as well as the perifocal liver reaction after radiotherapy, which must be differentiated from perifocal tumor growth, can be sensitively visualized using CEUS.

Dynamic contrast-enhanced magnetic resonance imaging rapidly indicates vessel regression in human squamous cell carcinomas grown in nude mice caused by VEGF receptor 2 blockade with DC101

The purpose of our study was the investigation of early changes in tumor vascularization during antiangiogenic therapy with the vascular endothelial growth factor (VEGF) receptor 2 antibody (DC101) using dynamic contrast-enhanced magnetic resonance imaging (DCE MRI). Subcutaneous heterotransplants of human skin squamous cell carcinomas in nude mice were treated with DC101. Animals were examined before and repeatedly during 2 weeks of antiangiogenic treatment using Gd-DTPA-enhanced dynamic T1-weighted MRI. With a two-compartment model, dynamic data were parameterized in "amplitude" (increase of signal intensity relative to precontrast value) and k(ep) (exchange rate constant). Data obtained by MRI were validated by parallel examinations of histological sections immunostained for blood vessels (CD31). Already 2 days after the first DC101 application, a decrease of tumor vascularization was observed, which preceded a reduction of tumor volume. The difference between treated tumors and controls became prominent after 4 days, when amplitudes of treated tumors were decreased by 61% (P =.02). In line with change of microvessel density, the decrease in amplitudes was most pronounced in tumor centers. On day 7, the mean tumor volumes of treated (153 +/- 843 mm(3)) and control animals (596 +/- 384 mm(3)) were significantly different (P =.03). After 14 days, treated tumors showed further growth reduction (83 +/- 93 mm(3)), whereas untreated tumors (1208 +/- 822 mm(3)) continued to increase (P =.02). Our data underline the efficacy of DC101 as antiangiogenic treatment in human squamous cell carcinoma xenografts in nude mice and indicate DCE MRI as a valuable tool for early detection of treatment effects before changes in tumor volume become apparent.

Quantification of perfusion of liver tissue and metastases using a multivessel model for replenishment kinetics of ultrasound contrast agents

Low-MI (mechanical index) ultrasound allows real-time observation of replenishment kinetics after destruction ("flash") of ultrasound contrast agents (USCA). We developed an examination protocol and a mathematical model to quantify perfusion of liver tissue and hepatic metastases. Using a modified multivessel model, we attempted a consistent, physiological description of microbubble replenishment in liver tissue. Perfusion parameters were calculated, separately for the arterial and portal venous phase of liver perfusion, using an i.v. bolus injection of 2 x 2.4 mL SonoVue. The model was evaluated for 10 examinations of liver metastases using flash/low-MI imaging. In contrast to the established, exponential model, the new model consistently describes the sigmoid replenishment of USCA measured in vivo, using flash/low-MI imaging. Parameters for blood volume, blood velocity and blood flow in liver tissue and metastases can be calculated during the arterial and the portal venous phase after a CA bolus injection. The median arterial perfusion in the examined liver metastases was more than 2.5 times higher than in normal liver tissue, whereas the median perfusion during the portal venous phase was more than five times higher in the liver tissue than that in metastases. Microbubble replenishment measured with flash/low-MI US techniques can be consistently analyzed using the multivessel model, even after a bolus injection of USCA. This allows for the quantification of perfusion of liver tissue and hepatic metastases and provides promising parameters of tissue viability and tumor characterization.

Low mechanical index contrast-enhanced ultrasound better reflects high arterial perfusion of liver metastases than arterial phase computed tomography

RATIONALE AND OBJECTIVES

We investigated whether observing the arterial vascularization of liver metastases by contrast-enhanced ultrasound with low mechanical index (low-MI) imaging offers additional diagnostic information for the characterization of the liver lesions.

METHODS

Twenty nine patients with untreated liver metastases of different primaries were examined. Measurements were performed using a low frame rate, low-MI pulse inversion technique after injection of 2.4 mL SonoVue. The relative maximum signal intensity of the liver lesions related to the normal liver tissue was quantified. Ultrasound findings were compared with contrast-enhanced, dual-phase computed tomography (CT) using a pattern-based classification scheme.

RESULTS

Compared with contrast-enhanced CT, this modality better detects arterial perfusion. Metastases, even those usually considered hypovascularized, often showed homogeneous enhancement (66%) and higher arterial vascularization than normal liver tissue. CT did not show a comparable vascularization pattern (P < 0.001) or any similarly early signal intensity (P < 0.001).

CONCLUSIONS

Contrast-enhanced CT may not be able to visualize short-lasting but large differences of the arterial perfusion of liver metastases, as does contrast-enhanced low-MI ultrasound. This offers new methods for their characterization and for monitoring of therapeutic effects.

Dynamic Magnetic Resonance Tomography and Proton Magnetic Resonance Spectroscopy of Prostate Cancers in Rats Treated by Radiotherapy

RATIONALE AND OBJECTIVES

To establish an experimental setting for monitoring perfusion and metabolism in orthotopic prostate cancer at 1.5 T using dynamic contrast-enhanced magnetic resonance imaging (DCE MRI) and 1H-MR spectroscopy (MRS).

METHODS

Dunning rat prostate cancer cells were injected into the prostate by open surgery. Twelve tumor-bearing rats (5 of these irradiated) and 6 healthy controls were followed up using gadolinium-diethylenetriaminepentaacetic acid -enhanced dynamic MRI and 1H-MRS. Amplitude and the exchange rate constant kep were calculated (2-compartment model). From 1H-MR spectra, ratios of choline (Cho) and creatine (tCr) were calculated. All tumors were examined histologically.

RESULTS

On DCE MRI parameter maps, tumors showed increased vascularization. kep and microvessel density were correlated (r = 0.97). Tumors showed elevated Cho/tCr and an unexpected lipid fraction (2.0-2.2 parts per million). Irradiation slowed tumor growth significantly. Changes of perfusion and metabolism could be detected in all tumors during follow up.

CONCLUSION

DCE MRI and 1H-MRS has potential to characterize orthotopic Dunning prostate cancer in rats, which is a promising model similar to human prostate carcinomas.

Combined therapy with direct and indirect angiogenesis inhibition results in enhanced antiangiogenic and antitumor effects

The multifaceted nature of the angiogenic process in malignant neoplasms suggests that protocols that combine antiangiogenic agents may be more effective than single-agent therapies. However it is unclear which combination of agents would be most efficacious and will have the highest degree of synergistic activity while maintaining low overall toxicity. Here we investigate the concept of combining a "direct" angiogenesis inhibitor (endostatin) with an "indirect" antiangiogenic compound [SU5416, a vascular endothelial growth factor receptor 2 (VEGFR2) receptor tyrosine kinase (RTK) inhibitor]. These angiogenic agents were more effective in combination than when used alone in vitro (endothelial cell proliferation, survival, migration/invasion, and tube formation tests) and in vivo. The combination of SU5416 and low-dose endostatin further reduced tumor growth versus monotherapy in human prostate (PC3), lung (A459), and glioma (U87) xenograft models, and reduced functional microvessel density, tumor microcirculation, and blood perfusion as detected by intravital microscopy and contrast-enhanced Doppler ultrasound. One plausible explanation for the efficacious combination could be that, whereas SU5416 specifically inhibits vascular endothelial growth factor signaling, low-dose endostatin is able to inhibit a broader spectrum of diverse angiogenic pathways directly in the endothelium. The direct antiangiogenic agent might be able to suppress alternative angiogenic pathways up-regulated by the tumor in response to the indirect, specific pathway inhibition. For future clinical evaluation of the concept, a variety of agents with similar mechanistic properties could be tested.

Sensitive noninvasive monitoring of tumor perfusion during antiangiogenic therapy by intermittent bolus-contrast power Doppler sonography

Intermittent bolus-contrast power Doppler ultrasound was used for noninvasive, quantitative monitoring of tumor perfusion during antiangiogenic therapy. Subcutaneous heterotransplants of human squamous cell carcinoma cells in nude mice were treated with a blocking antibody to vascular endothelial growth factor receptor 2 (DC101) and repeatedly examined at weekly intervals. Using replenishment kinetics of microbubbles (Levovist) tumor vascularization, including capillary blood flow, was clearly visualized by this dynamic ultrasound method allowing the determination of a comprehensive functional status of tumor vascularization (blood volume, blood flow, perfusion, and mean blood velocity) in all examined tumors. DC101 treatment decreased tumor blood flow (-64%) and volume (-73%) compared with untreated controls (+409% and +185%, respectively). Regression of functional vessel parameters was observed early well before reduction of tumor size. The treatment-related amount of reduction in tumor volume was directly correlated for the initial tumor blood flow before start of therapy and the perfusion calculated at the preceding examination. The vessel density (immunofluorescence staining with CD31 antibody at different time points) showed an excellent correlation with the calculated relative blood volume (k = 0.84, P < 0.01), thereby validating intermittent sonography as a useful monitoring method. We conclude that intermittent sonography is a promising tool for comprehensive monitoring of antiangiogenic or proangiogenic therapies, especially during early stages of treatment, thus yielding information regarding a prospective evaluation of therapy effects beyond the follow up of tumor size.

Moderne sonographische Methoden zur Quantifizierung von Gewebeperfusion

Perfusion describes an important parameter of tissue vitality, e. g. of the myocardium, brain, or the kidney. In malign tumours, perfusion is of particular interest for characterization and prognosis. In addition, new pro- or anti-angiogenic therapies require a functional imaging which is suitable to quantify vascularity. Sonographic methods for the detection of microvascularity, particularly related smaller than those amenable to Doppler ultrasound, are reviewed. The main focus deals with the explanation of contrast-enhanced sonography using replenishment kinetics of microbubbles which provides a comprehensive quantification of tissue perfusion. Alterations of the microvascularity e. g., under anti-angiogenic therapy, can be depicted in experimental studies using this novel approach. Further clinical applications can be the quantification of the perfusion in the myocardium, the brain, or the kidney. New approaches to optimize the theoretical model to describe the replenishment, and novel technical developments are discussed.

A multivessel model describing replenishment kinetics of ultrasound contrast agent for quantification of tissue perfusion

To improve the quantification of tissue perfusion using intermittent sonography, a new model describing replenishment kinetics of microbubbles is proposed. The new approach takes into account the variability of blood flow velocities found in vivo, especially in tumors, and consistently describes the refilling process of microbubbles. Based upon this model, blood volume, blood velocity, blood flow and perfusion in 17 experimental tumors were calculated, and compared with the results obtained with the established, phenomenologically derived exponential kinetic model. In contrast to the existing model, our approach describes tissue vascularization more physiologically and allows deduction of a consistent new hyperbolic model for quantification of intermittent sonography. Blood volume and mean blood velocity did significantly correlate between both the new and the established model (k=0.99; k=0.94, both p<0.001). However, mean tumor blood velocity was lower (-19%, p<0.01) with the established model compared to the newly developed model. In addition, the range and distribution of blood flow velocities found in vivo can be estimated with the new model. Furthermore, it uses simpler mathematical fitting routines and allows easier data acquisition, which may allow a more practicable clinical application of intermittent sonography. In conclusion, a more valid, detailed and accurate calculation of perfusion parameters, especially of tumors, can be derived in vivo with the new multivessel model of intermittent sonography.

Comparing dynamic parameters of tumor vascularization in nude mice revealed by magnetic resonance imaging and contrast-enhanced intermittent power Doppler sonography

RATIONALE

Angiogenesis is essential for spread and growth of malignant tumors. Because noninvasive methods for observing tumor vascularization are limited, most of previous results were based on histologic findings alone. In this study, dynamic parameters obtained using intermittent contrast-enhanced Doppler sonography and dynamic MRI were compared and correlated with microvessel density.

METHODS

Eleven tumor-bearing nude mice were examined with dynamic T(1)-weighted sequences using Gd-DTPA in a 1.5 T magnetic resonance (MR) scanner and with intermittent power Doppler sonography after a single bolus of galactose based contrast agent. After examination 6 tumors were harvested for immunofluorescence microscopy using a CD31 stain. Using a 2-compartment model, the MR parameters amplitude (reflecting plasma volume) and k(ep) (influenced by the vessel permeability) were calculated and compared with maximal enhancement (max) and perfusion P measured with ultrasound.

RESULTS

The MR amplitude correlated with the ultrasound parameter max significantly (r = 0.61; P = 0.01). Max (r = 0.67; P = 0.01), amplitude (r = 0.72; P = 0.01), and perfusion (r = 0.62; P = 0.05) correlated with the microvessel density. k(ep) moderately correlated with max, but not with perfusion and microvessel density.

CONCLUSIONS

Dynamic MRI and contrast enhanced ultrasound are supplementing methods for examining perfusion and vascularity of experimental tumors.

Comparison of intermittent-bolus contrast imaging with conventional power Doppler sonography: quantification of tumour perfusion in small animals

Replenishment kinetics of microbubbles were adapted to a single bolus injection to investigate tumour angiogenesis in small animals with intermittent imaging, and to compare vascularisation parameters from this new approach with conventional power Doppler ultrasound (US). A reformulation of the imaging protocol and the derivation of perfusion parameters was necessary, taking into account the time-dependence of the systemic microbubble concentration after single bolus injection. Using this new method, tumour vascularisation was evaluated in 13 experimental murine tumours. Furthermore, parameters calculated with intermittent imaging after bolus injection of 100 microl Levovist were compared with parameters from the signal intensity-time curve. The results showed that quantifying tumour perfusion, blood volume and flow, as well as the assessment of the mean blood velocity (in m/s), is possible in tumours with a volume of more than 0.1 mL. In larger tumours, a lower perfusion was calculated than in smaller ones (k = -0.88; p < 0.001). Only limited correlations were found between conventional power Doppler US quantities and parameters of intermittent sonography: Perfusion correlated with the maximum signal intensity (k = 0.61, p < 0.05) and the gradient to maximum (k = 0.82, p < 0.01), full width-half maximum was associated with blood volume (k = 0.62, p < 0.05). We conclude that intermittent bolus contrast sonography allows the quantification of tumour perfusion, even in small animals, and the monitoring of basic antiangiogenic studies with perfusion parameters shows a higher significance than conventional power Doppler US.

Dynamic T1-weighted monitoring of vascularization in human carcinoma heterotransplants by magnetic resonance imaging

Studies on tumor angiogenesis and antiangiogenic therapies are commonly performed with tumor heterotransplants in nude mice. To monitor therapeutic effects, improved noninvasive analyses of functional data are required, in addition to the assessment of tumor volume and histology. Here, we report on sequential monitoring of vascularization of human squamous cell carcinomas growing as heterotransplants in nude mice using MRI. Using a custom-developed animal coil in a conventional whole-body 1.5 T MRI scanner, dynamic T1w sequences were recorded after i.v. injection of Gd-DTPA in tumors grown for 17, 21, 25, 29 and 33 days. Amplitude and the exchange rate constant (k(ep)) were calculated according to a 2-compartment model, discriminating intravascular and interstitial spaces, and correlated with tumor size and histology. High-resolution imaging of small heterotransplants from 100 to 1,000 mm(3) was achieved, clearly discriminating vital and necrotic areas. Preceding the development of necroses, which were hyperintense in T2w images and confirmed with histology, a local decrease of amplitude and k(ep) values was observed. Significantly higher amplitudes were found in tumor periphery than in central parts, correlating well with the vascular pattern obtained by immunocytochemistry. Tumor size correlated negatively with amplitude, probably as a result of increasing necrotic areas, whereas the reason for the observed increase of k(ep) value with tumor size remains unclear. These data demonstrate that dynamic MRI is an excellent method for noninvasive assessment of tumor vascularization in small animals using a clinical whole-body scanner with little technical modifications. This technique provides functional data characterizing essential features of tumor biology and is thus appropriate for monitoring antiangiogenic therapies.

Magnetic resonance imaging of nude mice with heterotransplanted high-grade squamous cell carcinomas: use of a low-loaded, covalently bound Gd-Hsa conjugate as contrast agent with high tumor affinity

RATIONALE

Malignant tumors often show an increased uptake and metabolism of plasma proteins, especially albumin.

OBJECTIVES

Determine whether the accumulation of low loaded Gd-albumin improves visualization of malignant tumors by MRI.

METHODS

Twelve nude mice with heterotransplanted squamous cell carcinomas were studied. The signal intensity of tumor, blood, liver, kidney and muscle tissue was studied in MR images after application of Gd-albumin during a period of 144 hours. MRI results were histologically correlated after simultaneously injection of Gd- and fluorescein-labeled albumins in 9 nude mice.

RESULTS

Although liver and kidney had a maximum increase in signal intensity within 30 minutes, tumors showed a delayed 51% increase in the 24 hours after application. Histologic and fluorescence evaluation demonstrated albumin localization in tumors predominantly in stroma and necroses.

CONCLUSIONS

Gd-albumin is efficiently accumulated in SCC transplants. MRI with low loaded Gd-albumin may offer relevant opportunities for recognizing tumors sensitive to a therapy with cyostic drug-labeled albumins.