Radioaerosol lung imaging in chronic obstructive airway disease

Inhalation radioaerosol lung imaging was performed in 22 patients with chronic obstructive lung disease (COLD) and in 8 healthy subjects. Aerosol deposition pattern within the right lung, as recorded by a gamma camera, was expressed by means of the aerosol distribution index (ADI). The degree of airway obstruction as measured by airways resistance (Raw) was significantly correlated with ADI. Differing stages of COLD are characterized by differing radioaerosol images, which may resemble each other in end-stage disease. The readily available radioaerosol technique can disclose the location and magnitude of bronchitic airway alterations and be useful for clinical inhalation lung imaging in multiple views.     

Technegas for inhalation lung imaging.

Technegas, an aerosol generator recently devised in Australia, produces aerosol particulates called 'technegas' which have characteristics of both an aerosol and a gas. The majority of the particulate is below 200 nm in size as measured by electron microscopy. Four normal subjects and 31 patients with various lung diseases were studied by imaging the lungs following inhalation of technegas. The penetration of inhaled technegas to the lung periphery was excellent; the average alveolar deposition ratio (ALDR) was 85%. Comparative studies with lung images obtained either with an ultrasonic nebulizer or jet nebulizers also confirmed better penetration of inhaled technegas to the lung periphery. There was no significant statistical difference in the ALDRs between normals and patients. Aerosol studies were comparable to perfusion counterparts, and evaluation of regional ventilatory status was greatly facilitated. Because of the large ALDR and the low airway deposition ratio (ADR), actual imaging could be done not only immediately after aerosol inhalation but also some time later without losing too much radioactivity from the lungs. One disadvantage was that technegas immediately after generation was anoxic.     

Radioaerosol ventilation imaging in ventilator-dependent patients. Technical considerations

The differentiation of pulmonary embolism (PE) from regional ventilatory abnormalities accompanied by reduced perfusion requires contemporary perfusion and ventilation studies. Distinguishing these conditions in ventilator-dependent patients is aided by administering a Tc-99m aerosol to characterize regional ventilation, and by performing a conventional Tc-99m MAA perfusion study. The technique uses a simple "in-house" constructed apparatus. Simple photographic techniques suffice, but computer subtraction of perfusion from the combined perfusion-ventilation image renders interpretation easier if aerosol administration follows perfusion imaging. Multiple defects can be examined in a single study. Excluding normal or near-normal perfusion studies, PE was thought to be present in eight of 16 patients after perfusion imaging alone, but in only one of eight after added aerosol imaging. Angiography confirmed the diagnosis in that patient. Of the eight patients who had abnormal perfusion but were thought unlikely to have PE from the perfusion study alone, two had normal ventilation, and subsequently were shown to have PE by angiography. Because angiography was only performed on patients who were thought to have a high probability of PE on sequential perfusion-ventilation imaging, the true incidence of PE may have been higher. Aerosol ventilation imaging is a useful adjunct to perfusion imaging in patients on ventilators. It requires an efficient delivery system, particularly if aerosol administration follows perfusion imaging, as it does in this study. The major disadvantage of aerosol imaging compared to a gas in intubated patients is the significant bronchial deposition due to retained mucus secretions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Improved radioaerosol administration system for routine inhalation lung imaging.

An improved radioaerosol administration system has been developed to reduce the number of droplets larger than 2.0 micron in diameter which have caused abnormal hyperdeposition of inhaled aerosols in the large airways. The new system has achieved this goal by interposing a reservoir-setting bag in the aerosol delivery line between the nebulizer and the patient. The components are inexpensive, commercially available and easily assembled in any nuclear medicine service.     

The particle size distribution of technegas and its influence on regional lung deposition

The size distribution of the aerosol produced by a technegas generator has been measured with a screen diffusion battery. The median diameter of the active aerosol was found to be of the order 140 nm and not to vary with the delay between generation and use. The measurements indicate that about 20% of the aerosol should be deposited in deep lung with about 5% deposited in the upper airways.     

Functional lung imaging using hyperpolarized gas MRI

The noninvasive assessment of lung function using imaging is increasingly of interest for the study of lung diseases, including chronic obstructive pulmonary disease (COPD) and asthma. Hyperpolarized gas MRI (HP MRI) has demonstrated the ability to detect changes in ventilation, perfusion, and lung microstructure that appear to be associated with both normal lung development and disease progression. The physical characteristics of HP gases and their application to MRI are presented with an emphasis on current applications. Clinical investigations using HP MRI to study asthma, COPD, cystic fibrosis, pediatric chronic lung disease, and lung transplant are reviewed. Recent advances in polarization, pulse sequence development for imaging with Xe-129, and prototype low magnetic field systems dedicated to lung imaging are highlighted as areas of future development for this rapidly evolving technology.     

99mTc technegas ventilation and perfusion lung scintigraphy for the diagnosis of pulmonary embolus.

Lung scintigraphy is used widely for diagnosis of pulmonary embolus (PE). Technegas ventilation imaging has many advantages over other methods, but little outcome data exists on this technique. The aims of this study were to better define the role of lung scintigraphy in the management of patients with suspected PE and to evaluate technegas ventilation imaging by following patient outcomes. METHODS: A group of 717 out of 834 consecutive patients, referred to a university teaching hospital for lung scintigraphy to confirm or refute the diagnosis of PE, was followed for 18-30 mo to determine clinical outcome. The follow-up endpoints were death as a result of PE, death as a result of hemorrhage after treatment for PE, uncomplicated survival, survival with subsequent PE, nonfatal hemorrhage after treatment for PE and recurrence of PE in treated patients. Ventilation imaging was performed using technegas, and perfusion imaging was performed using intravenous 99mTc macroaggregated albumin. The modified PIOPED (Prospective Investigation of Pulmonary Embolism Diagnosis) diagnostic criterion was used for interpretation of lung scintigraphy. RESULTS: Diagnostic results included 3.5% normal studies, 67.4% assessed as low probability for PE, 10% as moderate probability for PE and 19.1% as high probability for PE. A total of 231 patents received therapy with heparin, followed by warfarin, including those receiving anticoagulation therapy for other conditions. Ninety-six percent of patients with normal and low probability studies (n = 508) had good outcomes, 6 patients died as a result of PE and 12 subsequently developed PE. The odds ratio for death by PE in this group was 0.2. Of the 72 moderate probability studies, 39 patients were untreated. In this group there was 1 death due to PE, and PE subsequently developed in 2 patients. None of the remaining 33 treated patients died, but 4 patients experienced bleeding complications. The odds ratio for death by PE in the moderate probability group was 0.7. In those patients with high-probability studies, there were 8 deaths by PE, 6 deaths by hemorrhage, 11 nonfatal hemorrhages and 7 patients who experienced recurrences of PE. The odds ratios in this group were 6 and 10 for death by PE, or death by PE and the treatment of PE, respectively. CONCLUSION: The use of the modified PIOPED diagnostic classification is valid for technegas lung scintigraphy. Using technegas, normal/low-probability and high-probability results are highly predictive of respective outcomes. Technegas lung scintigraphy reduces the number of indeterminate studies.     

PET imaging of regional 18F-FDG uptake and lung function after cigarette smoke inhalation.

Cigarette smoke is thought to promote local lung inflammation that leads to lung dysfunction. Lung neutrophilic inflammation is known to result in increased pulmonary uptake of (18)F-FDG. Using a sheep model of localized exposure to cigarette smoke, in this study we tested whether PET-imaged changes in regional intrapulmonary distribution of (18)F-FDG uptake are related to changes in regional lung function as assessed with the infused (13)NN-saline method. METHODS: Five anesthetized, mechanically ventilated sheep were exposed to unilateral inhalation of smoke from 10 tobacco cigarettes while the contralateral lung was ventilated with smoke-free gas. Two hours after the exposure, regional gas content was measured from a transmission scan; regional ventilation, perfusion, and shunt were measured from the kinetics of (13)NN-saline; and regional (18)F-FDG influx constant (K(i)) was calculated with the Patlak algorithm applied at a voxel-by-voxel level. RESULTS: K(i) was higher and more heterogeneous in the smoke-exposed lungs than in the control lungs (P < 0.05). Spatial heterogeneity of K(i) and impairment in regional lung function were quite variable among animals despite similar levels of smoke exposure. However, increases in mean K(i) correlated linearly with its spatial heterogeneity (Spearman correlation, r(s) = 0.94), and the highest levels of regional K(i) in smoke-exposed lungs and control lungs correlated with regional shunt fraction (r(s) = 0.78). Also, the heterogeneity of the ventilation-perfusion (V/Q) distribution of the smoke-exposed lungs was 10 times greater than that of the control lungs but correlated strongly with that of the control lungs (r = 0.998). CONCLUSION: Substantial interanimal variability and spatial heterogeneity in lung function and (18)F-FDG uptake seem to characterize the response to smoke exposure. The highest levels of local (18)F-FDG uptake were associated with differences in V/Q matching and shunt fraction among animals. The data also suggest that preexisting heterogeneity in V/Q could have been responsible for the large interanimal variability by affecting the heterogeneity and strength of the acute response to smoke inhalation.     

Resolution enhancement in lung 1H imaging using parallel imaging methods.

Resolution in (1)H lung imaging is limited mainly by the acquisition time. Today, half-Fourier acquisition single-shot turbo spin-echo (HASTE) sequences, with short echo time (TE) and short interecho spacing (T(inter)) have found increased use in lung imaging. In this study, a HASTE sequence was used in combination with a partially parallel acquisition (PPA) strategy to increase the spatial resolution in single-shot (1)H lung imaging. To investigate the benefits of using a combination of single-shot sequences and PPA, five healthy volunteers were examined. Compared to conventional imaging methods, substantially increased resolution is obtained using the PPA approach. Representative in vivo (1)H lung images acquired with a HASTE sequence in combination with the generalized autocalibrating partially parallel acquisition (GRAPPA) method, up to an acceleration factor of three, are presented.     

Magnetic resonance imaging of lung tissue: influence of body positioning, breathing and oxygen inhalation on signal decay using multi-echo gradient-echo sequences

PURPOSE: To assess susceptibility related signal decay in lung tissue and to measure the influence of body positioning, together with inspiration and expiration, as well as oxygen inhalation. T2* maps and line shape maps of lung parenchyma were derived from datasets acquired at 0.2 T and compared with findings at 1.5 T. The line shape maps allow for a visualization of the intravoxel frequency distribution of lung parenchyma. MATERIALS AND METHODS: A multiecho spoiled gradient-echo sequence with 16 echoes was implemented both on a 0.2 T [repetition time (TR) = 100 milliseconds, echo time (TE)1 = 2.15 milliseconds, DeltaTE = 2.94 milliseconds, flip angle 30 degrees] and on a 1.5 T magnetic resonance scanner (TR = 100 milliseconds, TE1 = 1.25 milliseconds, DeltaTE = 1.65 milliseconds, flip angle 30 degrees). Sagittal datasets were recorded in 8 healthy volunteers at 0.2 T in supine position under maximal expiration and inspiration and during oxygen breathing. Additional measurements were performed after 20 minutes inside the scanner in supine position and after prone repositioning. In 2 volunteers, further datasets were acquired at 1.5 T. Color-encoded T2* maps and full-width-at-half-maximum (FWHM) maps of the frequency distribution were computed on a pixel-by-pixel basis. T2* maps were generated by mono-exponential fitting and, additionally, with an extended nonexponential fitting approach. The FWHM maps were calculated with a model-free approach using a discrete Fast Fourier Transformation. RESULTS: A notably slower T2* decay was found at 0.2 T (T2*: 5.9-11.8 milliseconds) when compared with 1.5 T (T2*: 1.0-1.4 milliseconds), allowing for the measurement of up to 6 to 8 gradient echoes above the noise level. The T2* maps and the FWHM maps computed from the datasets acquired at 0.2 T allowed regional comparison of the derived parameters. If volunteers were positioned in supine position, expiration resulted in a T2* of 10.9 +/- 1.0 milliseconds and a FWHM of 47.1 +/- 4.0 Hz in the dorsal lung. Significant changes (P < 0.05) were found, eg, in the ventral lung in expiration (T2*: 7.5 +/- 0.8, FWHM: 76.7 +/- 11.2) versus dorsal lung in expiration, in the dorsal lung in inspiration (T2*: 8.4 +/- 1.0, FWHM: 67.8 +/- 12.5) versus dorsal lung in expiration, in the dorsal lung during oxygen breathing (T2*: 8.7 +/- 1.1, FWHM: 52.2 +/- 5.2) versus dorsal lung while breathing room air, and in the dorsal lung in prone position (T2*: 8.5 +/- 0.6, FWHM: 67.0 +/- 9.2) versus dorsal lung in supine position. CONCLUSION: The proposed method allows for the computation of color-encoded T2* maps and FWHM maps of lung parenchyma in good image quality using datasets acquired at 0.2 T. The technique is robust and sensitive to physiological changes of lung magnetic resonance properties, eg, due to the type of body positioning or oxygen breathing.     

Fetal relative lung volume: quantification by using prenatal MR imaging lung volumetry

PURPOSE: To retrospectively determine a biometric algorithm for calculating relative lung volume in fetuses with normal lungs and of a wide range of gestational ages by using proved independent variables and to retrospectively investigate the use of this algorithm in fetuses with pulmonary hypoplasia. MATERIALS AND METHODS: Total lung volume (TLV) was measured by using planimetry on single-shot rapid acquisition with relaxation enhancement magnetic resonance (MR) images obtained in 91 fetuses with ultrasonographically (US) normal chests and 28 fetuses with US-determined pulmonary hypoplasia. All fetuses were aged between 18 and 38 weeks gestation. Analysis of covariance was used to identify parameters that were not different between the fetuses with US-determined normal and those with US-determined abnormal chests, and these variables were used to construct an algorithm for calculating predicted lung volume. The relative lung volume-that is, the observed lung volume expressed as a percentage of the predicted lung volume-was then calculated in fetuses with pulmonary hypoplasia. RESULTS: There was no significant difference in mean maternal or gestational age between the two fetus groups. Stepwise regression analysis was used to generate the following equation for predicting fetal lung volume on the basis of independent biometric indexes, with a correlation coefficient of 0.93: TLV = (0.52 . LV) + (0.33 . BD) - (0.06 . FL) - 13.7, with TLV and liver volume (LV) in milliliters and biparietal diameter (BD) and femoral length (FL) in centimeters. In the fetuses with normal chests, relative lung volume varied between 51% and 134%. In the fetuses with pulmonary hypoplasia, relative lung volume varied between 6% and 70%. CONCLUSION: The predicted lung volume in fetuses of a wide range of gestational ages can be calculated with a high degree of accuracy, enabling prenatal MR imaging lung volumetry in which relative lung volume is used to quantify fetal pulmonary hypoplasia.