Feasibility of Single Scan for Simultaneous Evaluation of Regional Krypton and Iodine Concentrations with Dual-Energy CT: An Experimental Study.

Purpose To evaluate the feasibility of a simultaneous single scan of regional krypton and iodine concentrations by using dual-energy computed tomography (CT). Materials and Methods The study was approved by the institutional animal experimental committee. An airway obstruction model was first made in 10 beagle dogs, and a pulmonary arterial occlusion was induced in each animal after 1 week. For each model, three sessions of dual-energy CT (80% krypton ventilation [krypton CT], 80% krypton ventilation with iodine enhancement [mixed-contrast agent CT], and iodine enhancement [iodine CT]) were performed. Krypton maps were made from krypton and mixed-contrast agent CT, and iodine maps were made from iodine and mixed-contrast agent CT. Observers measured overlay Hounsfield units of the diseased and contralateral segments on each map. Values were compared by using the Wilcoxon signed-rank test. Results In krypton maps of airway obstruction, overlay Hounsfield units of diseased segments were significantly decreased compared with those of contralateral segments in both krypton and mixed-contrast agent CT (P = .005 for both). However, the values of mixed-contrast agent CT were significantly higher than those of krypton CT for both segments (P = .005 and .007, respectively). In iodine maps of pulmonary arterial occlusion, values were significantly lower in diseased segments than in contralateral segments for both iodine and mixed-contrast agent CT (P = .005 for both), without significant difference between iodine and mixed-contrast agent CT for both segments (P = .126 and .307, respectively). Conclusion Although some limitations may exist, it might be feasible to analyze regional krypton and iodine concentrations simultaneously by using dual-energy CT. © RSNA, 2016.

Krypton for computed tomography lung ventilation imaging: preliminary animal data.

OBJECTIVES: The objective of this study was to assess the feasibility and safety of krypton ventilation imaging with intraindividual comparison to xenon ventilation computed tomography (CT). MATERIALS AND METHODS: In a first step, attenuation of different concentrations of xenon and krypton was analyzed in a phantom setting. Thereafter, 7 male New Zealand white rabbits (4.4-6.0 kg) were included in an animal study. After orotracheal intubation, an unenhanced CT scan was obtained in end-inspiratory breath-hold. Thereafter, xenon- (30%) and krypton-enhanced (70%) ventilation CT was performed in random order. After a 2-minute wash-in of gas A, CT imaging was performed. After a 45-minute wash-out period and another 2-minute wash-in of gas B, another CT scan was performed using the same scan protocol. Heart rate and oxygen saturation were measured. Unenhanced and krypton or xenon data were registered and subtracted using a nonrigid image registration tool. Enhancement was quantified and statistically analyzed. RESULTS: One animal had to be excluded from data analysis owing to problems during intubation. The CT scans in the remaining 6 animals were completed without complications. There were no relevant differences in oxygen saturation or heart rate between the scans. Xenon resulted in a mean increase of enhancement of 35.3 ± 5.5 HU, whereas krypton achieved a mean increase of 21.9 ± 1.8 HU in enhancement (P = 0.0055). CONCLUSIONS: The use of krypton for lung ventilation imaging appears to be feasible and safe. Despite the use of a markedly higher concentration of krypton, enhancement is significantly worse when compared with xenon CT ventilation imaging, but sufficiently high for CT ventilation imaging studies.

Krypton-enhanced ventilation CT with dual energy technique: experimental study for optimal krypton concentration.

PURPOSE/AIM OF THE STUDY: To assess the feasibility of krypton-enhanced ventilation CT using dual energy (DE) technique for various krypton concentrations and to determine the appropriate krypton concentration for DE ventilation CT through an animal study. MATERIALS AND METHODS: Baseline DECT was first performed on seven New Zealand white rabbits. The animals were then ventilated using 20%, 30%, 40%, 50%, 60%, to 70% krypton concentration, and DECT was performed for each concentration. Krypton extraction was performed through a workstation, and results were displayed on a color map. Overlay Hounsfield unit (HU) values were obtained by two observers in consensus readings. A linear mixed model was used to correlate overlay HU values and krypton concentrations. Visual assessments of the homogeneity of krypton maps were also performed. RESULTS: Mean overlay HU values according to krypton concentration were as follows; 20% krypton, 1.68 ± 5.15; 30% krypton, 3.73 ± 5.93; 40% krypton, 6.92 ± 5.51; 50% krypton, 10.88 ± 5.17; 60% krypton, 14.54 ± 4.23; and 70% krypton, 18.79 ± 3.63. We observed a significant correlation between overlay HU values on krypton maps and krypton concentrations (P < .001). For the krypton color maps, all observers determined universal enhancement on the 70% krypton map for all animals. CONCLUSION: It is feasible to evaluate lung ventilation function using DECT with a krypton concentration of at least 70%.

[Effects of xenon and krypton-containing breathing mixtures on clinical and biochemical blood indices in animals].

Effects of 24-hr breathing air mixtures containing xenon (XBM) and krypton (KBM) were compared in terms of hormonal status, and blood biochemical indices and morphology in laboratory animals. Some changes observed in blood and hormone indices could be a nonspecific adaptive response. Hence, we should elicit whether these effects are quickly reversible or long. For several indices krypton was a more favorable factor than xenon. However, some of its effects invite to delve into effects of different krypton concentrations on organism.

Effect of low-xenon and krypton supplementation on signal/noise of regional CT-based ventilation measurements.

Xenon computed tomography (Xe-CT) is used to estimate regional ventilation by measuring regional attenuation changes over multiple breaths while rebreathing a constant Xe concentration ([Xe]). Xe-CT has potential human applications, although anesthetic properties limit [Xe] to

Clinical comparison of a new technetium 99m DTPA aerosol delivery system with krypton 81m.

We compared the clinical performance of a new 99Tcm DTPA aerosol delivery system with steady-state 81Krm gas in the diagnosis of pulmonary embolic disease. Forty patients had aerosol and 81Krm ventilation imaging followed by perfusion scintigraphy. The combined aerosol/perfusion images were compared with 81Krm/perfusion images for diagnostic equivalence. Aerosol image quality was also compared directly with 81Krm. Three-quarters of the patients who had segmental ventilation-perfusion (V/Q) mismatch on 81Krm/perfusion images also had mismatch on aerosol/perfusion images. Of those who had no mismatch on Kr/perfusion images, it was possible to rule out mismatch on aerosol/perfusion images in 80% of cases. Fifteen per cent of aerosol images were uninterpretable due to excess deposition in large airways. This problem was significantly more frequent in smokers than in non-smokers. The average delivery efficiency of the system was 2%, in terms of the proportion of loaded activity retained in the lungs. We conclude that the new device gives accurate clinical information in most cases, but is of less value for smokers.

Continuous determination of regional myocardial blood flow with intracoronary krypton-81m in coronary artery disease.

Pacing-induced changes in regional coronary flow were studied continuously with krypton-81m by intracoronary infusion in 25 patients: 21 with 50% or greater diameter narrowing of 1 or more left coronary arteries (group I) and 4 with less than 50% diameter reduction of a left coronary artery (group II). No changes occurred in group II. In group I, krypton-81m perfusion decreased progressively in all areas with more than 70% diameter narrowing, with a simultaneous increase in normal regions. At the end of pacing during angina, krypton-81m perfusion was reduced to 81 +/- 4% of control in areas with 71 to 90% diameter reduction (n = 8) and to 69 +/- 6% in areas with more than 90% diameter narrowing (n = 15). In contrast, in regions with 50 to 70% diameter reduction changes were variable (decrease in 4 regions, increase in 2 and an unchanged distribution in 1 region). Krypton-81m perfusion decreased early, before general signs of ischemia in areas with more than 90% diameter reduction, whereas this decrease occurred later in regions with 71 to 90% diameter narrowing, concurrently with ST-segment changes but before anginal pain. Although all signs of ischemia had disappeared between 2 and 5 minutes after pacing, changes in krypton-81m distribution persisted in most areas for 5 to 15 minutes after pacing. It is concluded that the functional significance of coronary arterial narrowing can be assessed with a continuous intracoronary infusion of krypton-81m. Changes in regional distribution persisted after cessation of pacing-induced ischemia, indicating an ongoing decrease in regional myocardial blood flow.

Regional pulmonary distribution of krypton-81m gas delivered by different breathing systems.

Regional pulmonary distribution of 81mKr gas delivered by three breathing systems was determined. Data from 18 patients were analyzed. Posterior images were obtained using each breathing system in turn. Distribution of Kr gas was determined in terms of penetration and zonal indices. For penetration indices each lung was divided into a central, intermediate, and peripheral region and these indices, defined as the ratio of counts/cell in the intermediate or the peripheral region over those in the central region, were calculated. For the zonal indices each lung was divided equally into upper and lower zones and the percentage ratio of the counts in each zone to the total counts in both lungs was calculated. For all patients, in addition, the size, height, and width of each lung were determined from computer images. These parameters were compared between the breathing systems using a paired t-test. It was found that there were no statistical differences among the three breathing systems, either in the regional pulmonary distribution of the 81mKr gas or in the overall shapes of the lungs.

Clinical ventilation imaging with In-113m aerosol: a comparison with Kr-81m.

Following routine ventilation (Kr-81m)/perfusion (Tc-99m) scanning, we obtained aerosol ventilation scans using a solution of In-113m albumin and a settling-bag system. The large-volume settling bag reduces deposition of particles in the large airway by removing large droplets. The patient inhales the aerosol with 5-10 min of tidal breathing, then lung scans are obtained on a gamma camera. The energy of In-113m allows the ventilation scanning to be performed after Tc-99m perfusion scanning. Semiquantitative scoring of regional ventilation showed a close correlation (r = 0.97) between Kr-81m and In-113m aerosol ventilation scans. The aerosol technique gave a slight underestimation of ventilation compared with Kr-81m. This is explained by a slightly reduced penetration of particles to the periphery of the lung in patients with severe obstructive airways disease. In all cases, however, the aerosol did visualize all ventilated regions. The results indicate that this readily available aerosol technique can be useful for clinical ventilation imaging in multiple views.

[Pulmonary embolism. Perfusion and ventilation pulmonary scintigraphy findings (author's transl)[]. / Résultats fournis par les scintigraphies pulmonaires de perfusion et de ventilation dans l'embolie pulmonaire.

After discussing the rather particular misadventures that the concept, diagnosis, and treatment of pulmonary embolism have been subjected to in France, the techniques for performing and analyzing results of pulmonary scintigraphy are described. Typical findings are one (or more) totally excluded areas in the biopsy specimen, easily systematized on a profile film. Though scintigraphy imaging appears to be essential, the sensitivity of the technique enabling positive exclusion of a pulmonary embolus if the image is normal, it is not specific. Results of the investigation appear to vary according to the use of a "soft approach" (repeated scintigraphy, heparinization) or a "hard approach" (pulmonary angiography, venography, fibrinolytic). Practical experience tends to show, however, that fallacies appear mainly when an attempt is made to elucidate cases other than acute emergencies, as for example in patients with lung cancer, women on the contraceptive pill, and chronic bronchopathy patients. It is strongly recommended that clinical studies be conducted to compare the "soft" and "hard" approaches, in order to obtain a consensus of opinion on the diagnosis and treatment of pulmonary embolism, a subject which remains passionate. . . and passional.

Radionuclide venography using continuous Kr-18 m infusion: preliminary note.

Continuous infusion of Kr-81m presents important advantages compared to the commonly used radionuclides for venography. High count rates can be accumulated, and a high resolution collimator can be employed to ensure good quality images. The study can be repeated immediately and multiple views can be performed until a satisfactory result is obtained. The production of radionuclide from a Rb-81--Kr-81m generator suitable for intravenous infusion is almost the same as that which is suitable for ventilation. The same generator can first be used for venography and then for ventilation imaging to complete the work-up patients suspected of having thromboembolic disease.

A Kr-81m inhalation method for detection of absence of uniform ventilation in asthma.

In an attempt to compare inhalation methods in detecting abnormal patterns of ventilation, the following four techniques were applied in 12 asthmatic patients: spontaneous respiration with a Kr-81m gas-air mixture (SP technique); serial inhalation of a Kr-81m gas-air mixture from the level of residual volume to total lung capacity (VC technique); bolus inhalation of 10 ml or Kr-81m gas from the level of residual volume, followed by air, to total lung capacity (RV technique); bolus inhalation of 10 ml of Kr-81m gas from the level of functional residual capacity, followed by air, to total lung capacity (FRC technique). Before exercise, abnormalities were detected by the RV and FRC techniques, but no abnormalities were detected by SP and VC techniques. On studies done after exercise, the abnormalities were detected by all the described techniques. However, they were best demonstrated by the RV technique and shown least well by the VC method.