Aerated Lung Tissue Research Articles

Solitary pulmonary nodule - the role of imaging in the diagnostic process.

A solitary pulmonary nodule is a round opacity less than 30 mm in diameter surrounded by normally aerated lung tissue. Determination of the character of the lesion following its detection (particularly when the identification was incidental) may require a complex diagnostic process. In most cases, nodules are benign in character; however, the probability of malignancy increases significantly for part-solid lesions. The main features that describe the solitary pulmonary nodule in computed tomography scans include their size, shape, density, presence of calcification and rate of growth. PET-CT examination provides additional information on the metabolic activity of the lesions, and MRI is helpful in assessment of local invasion of surrounding structures. Due to limited availability and highly specialized character, these examinations are not routinely used. Therefore, despite development of other imaging modalities, computed tomography remains the most important and crucial diagnostic tool. Clinical risk factors such as age or smoking status are very important for evaluation of the likelihood of malignancy of a nodular lesion. Due to the multidisciplinary nature of data required for complex assessment of a solitary nodular lesion, management routines are needed in the diagnostic process such as those proposed by the Fleischner Society.

Ultrasound diagnostic opportunities in pulmonology

Ultrasound diagnostic methods completely respond to all current requirements for diagnostic procedures and are valuable, safe, and relatively independent on the patient's condition. As ultrasound scanners are improved and new diagnostic regimens are developed, their use in different clinical field is extended. The most common ultrasound methods in pulmonology are echocardiography and ultrasonography of pleural cavities. Ultrasound investigation of the lung parenchyma is limited due to full reflection of ultra-sound from the aerated lung tissue. The lung density is increased in respiratory diseases; this gives an opportunity to use ultrasonography together with radiological methods for diagnosis and, therefore, to decrease radiation dose for the patient.

Research progress of biomarkers of acute respiratory distress syndrome

ARDS is a type of acute diffuse lung injury, characterized by inflammation leading to increased pulmonary vascular permeability and loss of aerated lung tissue, the clinical manifestations are refractory hypoxia, progressive respiratory distress and non cardiac pulmonary edema.ARDS mortality rate is very high, especially in patients with severe ARDS, about 27%-45%. In order to improve diagnostic specificity, a revised definition was published in JAMA in 2012, but no new biomarkers or parameters were adopted.Along with the progress in understanding the pathophysiology of ARDS, a variety of humoral factors by inflammation and molecules derived from injured tissues or activated cells may be potential biomarkers for clinical.

Optimal support techniques when providing mechanical ventilation to patients with acute respiratory distress syndrome.

Adult respiratory distress syndrome (ARDS) is a type of acute diffuse lung injury characterized by severe inflammation, increased pulmonary vascular permeability and a loss of aerated lung tissue. The effects of high fraction of inspired oxygen (FiO2 ) include oxygen toxicity manifested by damage to the lung parenchyma in the acute phase of lung injury. There is still a high mortality rate among this group of patients, so clinically sensitive evidence-based interventions are paramount to maximize survival chances during critical care. The aim of this article is to explore the current opinion concerning optimal mechanical ventilation support techniques for patients with acute respiratory distress syndrome. A literature search of clinical trials and observation studies, reviews, discussion papers, meta-analyses and clinical guidelines written in English up to 2015, derived from the databases of Scopus, CINAHL, Cochrane Library databases and PubMed was conducted. Low tidal volume, pressure limitation and prone positioning in severe ARDS patients appear to be of some benefit. More research is required and further development and use of standardized protocols is an important strategy for reducing practice variations across disciplines, as well as giving clear guidelines to nurses practising in critical care. There is also evidence that this syndrome is under-diagnosed and the utilization of lung protective ventilation is still variable. It is important that nurses have underlying knowledge of both aetiology of ARDS and ventilation management, and that they monitor patients very closely. The adoption of a low tidal ventilation protocol, which is based on quality evidence guidelines, the value of rescue therapies and patient observation practices in the overall patient management, and the need to place emphasis on long-term patient outcomes, all these emerge as key factors for consideration and future research. However, there is also a need for more research that would explore the unique contribution of nurses in the management of this patient group, as it is difficult to discern this in the current literature.

Prone position ameliorates lung elastance and increases functional residual capacity independently from lung recruitment.

BackgroundProne position is used to recruit collapsed dependent lung regions during severe acute respiratory distress syndrome, improving lung elastance and lung gas content. We hypothesised that, in the absence of recruitment, prone position would not result in any improvement in lung mechanical properties or gas content compared to supine position.MethodsTen healthy pigs under general anaesthesia and paralysis underwent a pressure–volume curve of the respiratory system, chest wall and lung in supine and prone positions; the respective elastances were measured. A lung computed tomography (CT) scan was performed in the two positions to compute gas content (i.e. functional residual capacity (FRC)) and the distribution of aeration. Recruitment was defined as a percentage change in non-aerated lung tissue compared to the total lung weight.ResultsNon-aerated (recruitable) lung tissue was a small percentage of the total lung tissue weight in both positions (4 ± 3 vs 1 ± 1 %, supine vs prone, p = 0.004). Lung elastance decreased (20.5 ± 1.8 vs 15.5 ± 1.6 cmH2O/l, supine vs prone, p < 0.001) and functional residual capacity increased (380 ± 82 vs 459 ± 60 ml, supine vs prone, p = 0.025) in prone position; specific lung elastance did not change (7.0 ± 0.5 vs 6.5 ± 0.5 cmH2O, supine vs prone, p = 0.24). Lung recruitment was low (3 ± 2 %) and was not correlated to increases in functional residual capacity (R2 0.2, p = 0.19). A higher amount of well-aerated and a lower amount of poorly aerated lung tissue were found in prone position.ConclusionsIn healthy pigs, prone position ameliorates lung mechanical properties and increases functional residual capacity independently from lung recruitment, through a redistribution of lung aeration.

Lung inflammation persists after 27 hours of protective Acute Respiratory Distress Syndrome Network Strategy and is concentrated in the nondependent lung.

PET with [18F]fluoro-2-deoxy-D-glucose can be used to image cellular metabolism, which during lung inflammation mainly reflects neutrophil activity, allowing the study of regional lung inflammation in vivo. We aimed at studying the location and evolution of inflammation by PET imaging, relating it to morphology (CT), during the first 27 hours of application of protective-ventilation strategy as suggested by the Acute Respiratory Distress Syndrome Network, in a porcine experimental model of acute respiratory distress syndrome. Prospective laboratory investigation. University animal research laboratory. Ten piglets submitted to an experimental model of acute respiratory distress syndrome. Lung injury was induced by lung lavages and 210 minutes of injurious mechanical ventilation using low positive end-expiratory pressure and high inspiratory pressures. During 27 hours of controlled mechanical ventilation according to Acute Respiratory Distress Syndrome Network strategy, the animals were studied with dynamic PET imaging of [18F]fluoro-2-deoxy-D-glucose at two occasions with 24-hour interval between them. [18F]fluoro-2-deoxy-D-glucose uptake rate was computed for the total lung, four horizontal regions from top to bottom (nondependent to dependent regions) and for voxels grouped by similar density using standard Hounsfield units classification. The global lung uptake was elevated at 3 and 27 hours, suggesting persisting inflammation. In both PET acquisitions, nondependent regions presented the highest uptake (p = 0.002 and p = 0.006). Furthermore, from 3 to 27 hours, there was a change in the distribution of regional uptake (p = 0.003), with more pronounced concentration of inflammation in nondependent regions. Additionally, the poorly aerated tissue presented the largest uptake concentration after 27 hours. Protective Acute Respiratory Distress Syndrome Network strategy did not attenuate global pulmonary inflammation during the first 27 hours after severe lung insult. The strategy led to a concentration of inflammatory activity in the upper lung regions and in the poorly aerated lung regions. The present findings suggest that the poorly aerated lung tissue is an important target of the perpetuation of the inflammatory process occurring during ventilation according to the Acute Respiratory Distress Syndrome Network strategy.

Determination of 'recruited volume' following a PEEP step is not a measure of lung recruitability.

It has been proposed that the analysis of positive end-expiratory pressure (PEEP)-induced volume changes can quantify alveolar recruitment. The potential of a lung to be recruited is expected to be high in acute respiratory distress syndrome (ARDS), where collapsed lung tissue is very common. The volume change that is beyond the delta volume because of the patient's compliance has been termed 'recruited volume' (RecV). However, data of patients with low and high RecV showed less severe lung disease in high 'recruiters', indicating that RecV may not equal the 'potentially recruitable lung tissue' seen in computed tomography scans. We hypothesized that RecV is higher in lung-healthy (LH) patients with little collapsed lung compared with ARDS patients. RecV and inspiratory capacity (IC) were determined in 12 LH and in 25 ARDS patients during incremental PEEP (steps of 2 cmH2 O). RecV was determined as the time-dependent increase in end-expiratory volume following the first expiration to the new PEEP level (ΔTDV). Gas distribution in LH patients was analyzed by electric impedance tomography. Cumulative RecV(ΔTDV) and IC were higher (P < 0.01) in LH compared with ARDS patients, 1739 ml vs. 832 ml and 4432 ml vs. 2020 ml, respectively. In both groups, RecV correlated excellently with IC (R(2) = 0.86). In LH, RecV emanated mainly from nondependent lung regions at PEEP below 15 cmH2O. Maximum plateau pressure was reached with fewer PEEP steps in ARDS compared with LH patients (11 vs. 14, P < 0.01). Our findings suggest that RecV predominately measures a slow fraction of inflation of already aerated lung tissue and not recruitment of collapsed alveoli.

What's new in ARDS (clinical studies).

The definition of the acute respiratory distress syndrome (ARDS) has been revised using a conceptual model of acute, diffuse, inflammatory lung injury, leading to increased pulmonary vascular permeability and lung weight, and loss of aerated lung tissue. The definition, however, was primarily based on feasibility, reliability, and validity [1]. The term “acute lung injury (ALI)” has been removed and ARDS is now categorized into mild, moderate, and severe, based on the degree of hypoxemia (P/F ratio) with a positive end-expiratory pressure (PEEP) of at least 5 cmH2O. The accuracy of the new criteria has been evaluated from autopsy in 352 patients who met clinical criteria for ARDS at time of death, by specifically looking for the presence of diffuse alveolar damage (DAD). Sensitivity and specificity of the new criteria were 89 and 63 %, respectively, and DAD was significantly related to ARDS severity [2]. A prospective study in ten ICUs in France failed to validate the new definition, since neither the stratification by severity nor the P/F ratio at baseline was associated with 28-day mortality [3]. In this study, like in others, however, the numbers studied were relatively small for testing the predictive validity. In addition, the primarily goal of the definition is not to predict mortality at an individual level. The optimal timing of P/F ratio determination to diagnose ARDS is also still debated. A prospective, multicenter study in Spain found that using P/F ratio at 24 h with standard ventilatory setting (PEEP ≥ 10 cmH2O and FiO2 ≥ 0.5) had the best correlation to ICU mortality [4]. Costa et al. [5] also suggested that P/F ratio after 24 h could be more representative of severity and outcome of ARDS than using P/F ratio at baseline. The major problem with requiring a 24-h delay for the definition, discussed by the task force of the Berlin definition, is the risk of an additional delay for enrollment into trials.

Risk Factors of Pneumothorax after CT-Guided Coaxial Cutting Needle Lung Biopsy through Aerated versus Nonaerated Lung

PurposeTo compare the risk factors of developing a pneumothorax after computed tomography–guided lung biopsy in cases in which aerated lung is traversed and in cases in which aerated lung is not traversed. Materials and MethodsThe records of 381 patients from July 2005–December 2009 were retrospectively reviewed. Multivariable analysis of patient demographic characteristics, lung lesion characteristics, and biopsy procedure details was performed with respect to the development of pneumothorax. ResultsAmong 381 patients, 249 biopsies traversed aerated lung tissue, and 132 biopsies did not traverse aerated lung tissue. Patients in whom aerated lung tissue was traversed had a significantly higher rate of pneumothorax. When aerated lung was not traversed, lesion size (≤ 2 cm vs > 2 cm; P = .025) and pleural-lesion angle (odds ratio = 1.033/degree; P = .004) were associated with pneumothorax. When aerated lung was traversed, location (middle vs upper; P = .009) and a transfissure approach (yes vs no; P = .001) were associated with pneumothorax. ConclusionsWhen aerated lung was not traversed, lesion size and pleural-lesion angle were associated with pneumothorax, and when aerated lung was traversed, location and a transfissure approach were associated with pneumothorax.

A New Definition for the Acute Respiratory Distress Syndrome

Similar to other syndromes, patients are defined as having acute respiratory distress syndrome (ARDS) when they meet prespecified diagnostic criteria. These criteria have evolved over time, having gained and lost complexity, but the core principles have remained remarkably similar over the past 45 years. The specific diagnostic criteria allow clinicians and investigators to reliably identify patients with the syndrome of ARDS. ARDS is a form of acute diffuse lung injury occurring in patients with a predisposing risk factor. Lung injury is characterized by inflammation leading to increased endothelial and epithelial permeability and loss of aerated lung tissue resulting in hypoxemia and bilateral radiographic opacities on chest radiography. Additional physiological derangements include increased venous admixture and physiological dead space along with decreased respiratory system compliance. The corresponding pathological findings are lung edema, inflammation, hyaline membranes, and alveolar hemorrhage (i.e., diffuse alveolar damage). This article discusses the evolution of the definition of ARDS to the new Berlin definition of ARDS proposed in 2012 and its novel iterative refinement.

Effect of Intraparenchymal Blood Patch on Rates of Pneumothorax and Pneumothorax Requiring Chest Tube Placement After Percutaneous Lung Biopsy

The purpose of this study was to determine whether an autologous intraparenchymal blood patch reduces the rate of pneumothorax and the rate of pneumothorax requiring chest tube placement after percutaneous lung biopsy. A prospective randomized controlled trial enrolling 242 patients was conducted. Adult patients undergoing percutaneous biopsy of lung or mediastinal lesions of undetermined cause were candidates. Patients were excluded if aerated lung tissue was not crossed during the biopsy. A standard biopsy procedure was followed for all patients until an adequate tissue sample was obtained. Patients were then randomized. For patients randomized to the treatment group, an intraparenchymal blood patch was administered through the guiding needle on removal. The same postbiopsy procedures were followed for both the treatment and control groups. Data collected included development of pneumothorax and placement of a chest tube. The rate of pneumothorax was reduced from 35% to 26% (p = 0.12) with the use of the blood patch, but the reduction was not significant. The rate of pneumothorax requiring chest tube placement was significantly reduced from 18% to 9% (p = 0.048). There was a greater benefit in the blood patch group when a 19-gauge guiding needle was used: Pneumothorax requiring chest tube placement was reduced from 19% to 3% whereas an increase from 16% to 20% was seen with a 17-gauge needle (p = 0.029). The use of an autologous intraparenchymal blood patch significantly reduces the rate of pneumothorax requiring chest tube placement. It seems to be more beneficial when a 19-gauge guiding needle is used.

Proof of live birth using postmortem multislice computed tomography (pmMSCT) in cases of suspected neonaticide: advantages of diagnostic imaging compared to conventional autopsy

Proof of live birth is of major importance in suspected neonaticide cases. Although not without controversy the lung flotation test is the main method used to asses this in different jurisdictions worldwide. The present study examines the usefulness of postmortem multislice computed tomography (pmMSCT) in the detection of live birth signs. Body scans were conducted on four infants, one was stillborn, another died a day after birth and the other two were classified as neonaticides. The appearance of the lungs, gastrointestinal tract and vascular system of the liver was compared in these cases. Clear differences were discernable between the lungs of the stillborn and the 1day old infant. The aerated lungs and air in the stomach and duodenum were clearly visible in the latter case while the stillborn infant lacked these signs. The two neonaticide cases demonstrated similarly aerated lung tissue to the 1day old infant. The hepatic vessels did not show any putrefactive gas changes in any of the cases. The extent of aeration of the peripheral alveoli was easily observable on the pmMSCT, thus making it a useful tool in the possible differentiation between artificially and naturally aerated lungs. During the four autopsies the classic flotation tests were performed and similar positive aeration of the lungs in the two neonaticides was shown. The stillborn's tests, on the other hand were negative for aeration. The results of this study clearly demonstrate the advantages of using pmMSCT before commencing a conventional autopsy in cases of suspected neonaticide.

Physiological effects of an open lung ventilatory strategy titrated on elastance-derived end-inspiratory transpulmonary pressure

In the presence of increased chest wall elastance, the airway pressure does not reflect the lung-distending (transpulmonary) pressure. To compare the physiological effects of a conventional open lung approach titrated for an end-inspiratory airway opening plateau pressure (30 cm H2O) with a transpulmonary open lung approach titrated for a elastance-derived end-inspiratory plateau transpulmonary pressure (26 cm H2O), in a pig model of acute respiratory distress syndrome (HCl inhalation) and reversible chest wall mechanical impairment (chest wall and abdomen restriction). In eight pigs, physiological parameters and computed tomography were recorded under three conditions: 1) conventional open lung approach, normal chest wall; 2) conventional open lung approach, stiff chest wall; and 3) transpulmonary open lung approach, stiff chest wall. As compared with the normal chest wall condition, at end-expiration non aerated lung tissue weight was increased by 116 ± 68 % during the conventional open lung approach and by 28 ± 41 % during the transpulmonary open lung approach (p < .01), whereas cardiac output was decreased by 27 ± 19 % and 22 ± 14 %, respectively (p = not significant). In this model, the end-inspiratory transpulmonary open lung approach minimized the impact of chest wall stiffening on alveolar recruitment without causing hemodynamic impairment.

Is Cryotherapy the Optimal Technology for Ablation of Lung Tumors?

I o p c v i t s a 1 t Primary lung cancer is the leading cause of cancer death in the United States. Lobectomy is the treatment of choice for early-stage non–small-cell lung cancer. For patients who are not suitable surgical candidates, nonsurgical treatment options include radiation therapy and image-guided thermal ablation. Pulmonary metastases are present in 25%–30% of patients who die from cancer, regardless of the type of primary cancer. For patients in whom all metastases can be surgically removed from both lungs, metastasectomy improves cancer-specific survival. For patients who may not be good surgical candidates, image-guided thermal ablation may serve as a good alternative treatment option. Most investigators have focused on ablation of lung tumors with the use of commercially available radiofreqency (RF) ablation devices that were developed and marketed for ablation of liver tumors (1). There are few serious technical challenges for application of RF energy in the lung tissue. These include high electrical resistance of air, poor thermal conductivity of aerated lung, and the heat-sink effect of the blood and air flow in the well perfused and aerated lung tissue (2). There is very little experience with microwave ablation for treatment of lung tumors. Unlike RF ablation, microwave energy is not limited by the low thermal conductivity of the lung or increased impedance of charred tissues. The energy can be

Chelation of lysosomal iron protects against ionizing radiation

Ionizing radiation causes DNA damage and consequent apoptosis, mainly due to the production of hydroxyl radicals (HO•) that follows radiolytic splitting of water. However, superoxide (O2•-) and H2O2 also form and induce oxidative stress with resulting LMP (lysosomal membrane permeabilization) arising from iron-catalysed oxidative events. The latter will contribute significantly to radiation-induced cell death and its degree largely depends on the quantities of lysosomal redox-active iron present as a consequence of autophagy and endocytosis of iron-rich compounds. Therefore radiation sensitivity might be depressed by lysosome-targeted iron chelators. In the present study, we have shown that cells in culture are significantly protected from ionizing radiation damage if initially exposed to the lipophilic iron chelator SIH (salicylaldehyde isonicotinoyl hydrazone), and that this effect is based on SIH-dependent lysosomal stabilization against oxidative stress. According to its dose-response-modifying effect, SIH is a most powerful radioprotector and a promising candidate for clinical application, mainly to reduce the radiation sensitivity of normal tissue. We propose, as an example, that inhalation of SIH before each irradiation session by patients undergoing treatment for lung malignancies would protect normally aerated lung tissue against life-threatening pulmonary fibrosis, whereas the sensitivity of malignant lung tumours, which usually are non-aerated, will not be affected by inhaled SIH.

Acute Renal Failure and Mechanical Ventilation: Reality or Myth?

Acute Renal Failure and Mechanical Ventilation: Reality or Myth?

Artificial Pneumothorax With Position Adjustment for Computed Tomography-Guided Percutaneous Core Biopsy of Mediastinum Lesions

This study was designed to assess the use of artificial pneumothorax with position adjustment to gain a pleural space approach in computed tomographic-guided core biopsy of mediastinal masses. Eleven patients with mediastinal lesions who were undergoing percutaneous core biopsies received an artificial pneumothorax with a 22-gauge lumbar puncture needle. Each patient's position was adjusted to place the lesion as high as possible in the thoracic cavity. Air was injected until the lung was displaced from the path of the biopsy needle. After completion of the biopsy, a comparable volume of air was aspirated. In all patients, satisfactory displacement of the lung from the biopsy site was achieved with the artificial pneuomothorax procedure enabling the target lesion to be reached. No postoperative air leaks requiring tube drainage were encountered. Artificial pneumothorax with position adjustment is a safe and effective method that provides access for computed tomographic-guided biopsy of mediastinal lesions without the risks of traversing aerated lung tissue and with a relatively low volume of injected air.

Inhaled aerosolised recombinant human activated protein C ameliorates endotoxin-induced lung injury in anaesthetised sheep

IntroductionWe recently demonstrated that intravenously infused recombinant human activated protein C (APC) attenuates ovine lipopolysaccharide (LPS)-induced lung injury. In this study, our aim was to find out whether treatment with inhaled aerosolised APC (inhAPC) prevents formation of increased lung densities and oedema and derangement of oxygenation during exposure to LPS.MethodsSheep were anaesthetised during placement of intravascular introducers. After one to four days of recovery from instrumentation, the animals were re-anaesthetised, endotracheally intubated and mechanically ventilated throughout a six-hour experiment where the sheep underwent quantitative lung computed tomography. Sheep were randomly assigned to one of three groups: a sham-operated group (n = 8) receiving inhaled aerosolised saline from two hours after the start of the experiment; a LPS group (n = 8) receiving an intravenous infusion of LPS 20 ng/kg per hour and, after two hours, inhaled aerosolised saline over the next four hours; a LPS+inhAPC group (n = 8) receiving an intravenous infusion of LPS 20 ng/kg per hour and, after two hours, aerosolised APC 48 μg/kg per hour inhaled throughout the experiment. Data were analysed with analysis of variance; P less than 0.05 was regarded as significant.ResultsAn infusion of LPS was associated with a reduction of well-aerated lung volume and a rapid fall in arterial oxygenation that were both significantly antagonised by inhaled APC. Pulmonary vascular pressures and extravascular lung water index increased significantly during exposure to LPS, but inhaled APC had no effect on these changes.ConclusionsInhalation of aerosolised APC attenuates LPS-induced lung injury in sheep by preventing a decline in the volume of aerated lung tissue and improving oxygenation.

Ultrasound transmission at reduced frequencies in human lungs: a novelty for pulmonary diagnosis and monitoring

Conventional sonography cannot permeate the chest. Aerated lung tissue strongly scatters ultrasound and thus inhibits a significant penetration. Even thin slices of in vitro lung samples are opaque for any ultrasound from 10kHz to several MHz. As a common consensus, alternative technologies (X-ray, magnetic resonance imaging) are required for thoracic imaging. Interestingly, human lungs in vivo were never explicitly probed with ultrasound at lower frequencies below one MHz. In contrary to the expected opacity, this study reports a noticeable transparency: Apparently, ultrasound below one MHz can pervade the normal lungs and thorax. To explain this novel observation we suggest that the vascular filling, which was absent in previous in vitro studies, permits ultrasound propagation in the lungs. In normal lungs, blood filling is surprisingly high and can amount to 50% of its mass in basal parts. Ultrasound probing of healthy humans and a group of patients with various pulmonary diseases clearly demonstrate a lung-specific signal. Our observations strongly suggest efficient ultrasound propagation at moderately reduced frequencies. We propose that “transpulmonary“ ultrasound is a novel non-invasive approach for continuous real time imaging of the lungs and the thorax interior. This method appears also applicable to continuous pulmonary monitoring in mechanically ventilated patients and in patients with left heart failure (lung oedema).

Robert Apfel’s contribution to clinical diagnostic ultrasound: The mechanical index

The mechanical index, MI, resulted from theoretical considerations of the short-pulse acoustic threshold for inertial cavitation in water populated with microbubbles of all sizes [R. E. Apfel and C. K. Holland, Ultrasound Med Biol. 17, 179–185 (1991)]. In this review, the onset of cavitation will be discussed with reference to Robert Apfel’s legacy of theoretical and experimental data. The questions arise: Can the utility of the MI be extended to situations in which the threshold MI is exceeded, thereby allowing for some estimate of the quantification of a potential bioeffect due to microcavitation? Also, can the MI be extended to situations in which pulses are, unlike the original formulation, not short? Is there a theoretical or semi-empirical basis for the MI threshold below which cavitation is unlikely? Can the MI be used to predict gas contrast agent destruction? The possible consequences of gas body activation associated with aerated lung tissue, intestinal gas pockets or encapsulated gas contrast agents represent specific instances of cavitation considerations relevant to clinical practice. Monitoring the real-time display of the MI (mandated by the FDA) helps clinicians evaluate and minimize the potential risks in the use of diagnostic ultrasound instrumentation. [Research supported by National Institutes of Health Grant R29 HL58761.]