Potential of noncontrast electrocardiogram-gated half-fourier fast-spin-echo magnetic resonance imaging to monitor dynamically altered perfusion in regional lung

Comparison of the accuracy of 99mTc-3P4-RGD2 SPECT and CT in diagnosing solitary pulmonary nodules

The aim of the present study was to compare technetium-99m-(polyethylene glycol-4)₃-(Arg-Gly-Asp)₂ (99mTc-3P₄-RGD₂) single-photon emission computed tomography (SPECT) and computed tomography (CT) in the noninvasive differentiation of solitary pulmonary nodules (SPNs). The present study prospectively investigated a consecutive series of 24 patients with SPN, who were newly diagnosed using radiography between September 2012 and January 2014. All patients underwent 99mTc-3P₄-RGD₂ SPECT and CT scans using a dual-head variable-angle γ-camera equipped with high-resolution collimators. A blinded panel of two thoracic radiologists for CT and three nuclear physicians for SPECT analyzed the images using a 5-grade scale. The SPECT images were also semi-quantitatively evaluated using tumor to non-tumor localization ratios (T/NT). The results were verified by pathological examination of the biopsy material obtained from each patient with SPN, and receiver operating characteristic (ROC) curves were generated from these results. The present results revealed that there were 17 malignant and 7 benign SPNs among the 24 patients with SPN. The mean size of the SPN was 2.1±0.6 cm. Sensitivity of visual analysis for SPECT and CT were 100.0 and 82.4%, respectively, and specificity was 71.4% for the two methods. When the T/NT SPECT semiquantitative analysis (ratio, 1.64) was used as a cut-off, the sensitivity and specificity of SPECT were 100.0 and 71.4%, respectively. The areas under the ROC curves were 0.840 for visual analysis of SPECT [95% confidence interval (CI), 0.600–1.000], 0.849 for semiquantitative analysis of SPECT (95% CI, 0.618–1.000) and 0.815 for CT (95% CI, 0.626–1.000). In conclusion, the present results suggest that 99mTc-3P₄-RGD₂ SPECT is more accurate than CT in the detection of malignant SPN, and visual analysis appears to be sufficient for the characterization of SPN.

Thoracic magnetic resonance imaging for the evaluation of pulmonary emphysema

Pulmonary emphysema is a pathologic condition characterized by permanently enlarged airspaces distal to the terminal bronchiole with destruction of the alveolar walls. Functional information of the lungs is important to understand the pathophysiology of emphysema and that of chronic obstructive pulmonary disease. With the recent developments in magnetic resonance imaging (MRI) techniques, functional MRI with variable MR sequences can be used for the evaluation of different physiological and anatomic changes seen in cases of pulmonary emphysema. In this review article, we will focus on a brief description of each method, results of some of the most recent work, and the clinical application of such knowledge.

Oxygen-enhanced magnetic resonance imaging: influence of different gas delivery methods on the T1-changes of the lungs

OBJECTIVE

The clinical feasibility of oxygen-enhanced magnetic resonance imaging (MRI) of the lung may benefit from the use of a simple gas delivery method. In this study, the oxygen-induced T1 change of the lung obtained using a closed O(2) delivery system was compared with that obtained by a conventional nontight face mask.

MATERIAL AND METHODS

Twenty-three healthy subjects (15 men, 8 women, mean age = 25 years, age range = 20-35 years) underwent oxygen-enhanced MRI of the lung using a closed O(2) delivery system composed by a tightly fitting face mask and a 60-L reservoir bag (equipment type A: n = 13, 9 men, 4 women, mean age = 24.4 years, age range = 20-32 years), or a clinically available nontight face mask (equipment type B: n = 10; 6 men, 4 women, mean age = 25.8 years, age range = 20-35 years). The effect of 100%-oxygen inhalation was assessed using a Snapshot FLASH T1-mapping technique (repetition time/echo time = 1.5-1.6/0.56 milliseconds; matrix = 128 x 90; acquisition time = 3.3-3.7 seconds; slice thickness = 15-20 mm; number of images = 40). By nonlinear curve fitting, the mean T1 values of the left and right lung at room air and 100%-oxygen ventilation were calculated (T1(room air, right); T1(oxygen, right); T1(room air, left); T1(oxygen, left)). The average T1 differences (DeltaT1 = T1(room air) - T1(oxygen)) of the 2 volunteer groups were compared (Wilcoxon signed rank test, Mann-Whitney U test).

RESULTS

The mean T1 values obtained using the 2 respiratory equipments at room air or oxygen ventilation were not significantly different (A vs. B at room air ventilation: P = 0.85 for the right lung, P = 0.27 for the left lung; A vs. B at oxygen ventilation: P = 0.55 for the left lung, P = 0.29 for the right lung). With both systems, the mean T1 values decreased significantly after oxygen inhalation (P = 0.03-0.0002). For both lungs, the DeltaT1 obtained using the equipment type A was statistically equivalent to that obtained using the equipment type B: DeltaT1A, right = 96 +/- 19 milliseconds versus DeltaT1B, right = 97 +/- 34 milliseconds (P = 0.82); DeltaT1A, left = 74 +/- 47 milliseconds versus DeltaT1B, left = 68 +/- 63 milliseconds (P = 0.85).

CONCLUSION

Gas delivery in oxygen-enhanced MRI of the lung can be performed with a clinically available standard face mask, without the need for closed sophisticated equipments.

Relation between lung perfusion defects and intravascular clots in acute pulmonary thromboembolism: Assessment with breath-hold SPECT–CT pulmonary angiography fusion images

PURPOSE

The relation between lung perfusion defects and intravascular clots in acute pulmonary thromboembolism (PTE) was comprehensively assessed on deep-inspiratory breath-hold (DIBrH) perfusion SPECT-computed tomographic pulmonary angiography (CTPA) fusion images.

MATERIALS AND METHODS

Subjects were 34 acute PTE patients, who had successfully performed DIBrH perfusion SPECT using a dual-headed SPECT and a respiratory tracking system. Automated DIBrH SPECT-CTPA fusion images were used to assess the relation between lung perfusion defects and intravascular clots detected by CTPA.

RESULTS

DIBrH SPECT visualized 175 lobar/segmental or subsegmental defects in 34 patients, and CTPA visualized 61 intravascular clots at variable locations in 30 (88%) patients, but no clots in four (12%) patients. In 30 patients with clots, the fusion images confirmed that 69 (41%) perfusion defects (20 segmental, 45 subsegmental and 4 lobar defects) of total 166 defects were located in lung territories without clots, although the remaining 97 (58%) defects were located in lung territories with clots. Perfusion defect was absent in lung territories with clots (one lobar branch and three segmental branches) in four (12%) of these patients. In four patients without clots, nine perfusion defects including four segmental ones were present.

CONCLUSION

Because of unexpected dissociation between intravascular clots and lung perfusion defects, the present fusion images will be a useful adjunct to CTPA in the diagnosis of acute PTE.

Evaluation of a Newly Developed Percutaneous Thrombectomy Basket Device in Sheep With Central Pulmonary Embolisms

OBJECTIVE

The authors studied the development of a thrombectomy device that is adequately steerable and quickly placeable in case of extensive pulmonary embolism.

MATERIALS AND METHODS

The device consists of a self-expandable nitinol basket mounted at a catheter-tip, which allows suction and extraction of thrombus material. Five in vitro tests were performed followed by tests in 6 sheep. In vivo thrombus material was introduced through a jugular vein to produce pulmonary embolism. After catheter insertion over the right femoral vein, the basket was placed adjacent to the pulmonary embolus and the extraction procedure was performed.

RESULTS

In in vitro tests, the extracted thrombus amount varied between 60% and 95%. In animal experiments, the extracted amount varied between 30% and 95% as determined angiographically. Limiting factors were steerability and optimal positioning of the basket in relation to the embolus.

CONCLUSIONS

Extraction of pulmonary embolism with the self-expanding suction basket is feasible. However, successful recanalization is limited by catheter maneuverability in the pulmonary arterial system.

Simultaneous Cardiac and Respiratory Synchronization in Oxygen-Enhanced Magnetic Resonance Imaging of the Lung Using a Pneumotachograph for Respiratory Monitoring

OBJECTIVES

We sought to evaluate an optimized method for oxygen-enhanced magnetic resonance imaging of the lung, using electrocardiogram-trigger and a pneumotachograph for simultaneous cardiac and respiratory synchronization.

MATERIALS AND METHODS

Five series of IR-SSFSE images (echo time = 28.2 milliseconds; inversion time = 1,200 milliseconds) were obtained in 6 volunteers during the ventilation-paradigm room-air/oxygen/room-air: series 1, respiratory-triggered; series 2, cardiac-triggered; series 3, cardiac-triggered and respiratory-synchronized using the signal of the pneumatic belt; series 4, cardiac-triggered and respiratory-synchronized using the external signal of the pneumotachograph; and series 5, not cardiac-triggered and respiratory-synchronized using the signal of the pneumotachograph. Standard deviations of the lung (SI(var)) and diaphragm mismatch (DM) were measured. The relative SI change (DeltaSI) was computed from room-air and oxygen-enhanced images. Parametric maps were obtained from cross-correlation analysis of the ventilation paradigm. Mean correlation coefficients (cc) and the percentage of activated pixels over the lung (Act%) were calculated from these maps. All 5 parameters were compared among the 5 series (Friedman-analysis of variance, Dunn's posthoc test).

RESULTS

In series 4, DM and SI(var) were significantly lower than in respiratory and cardiac-triggered series (DM = 4.7 vs. 14.3 and 18.4; SI(var) = 4.9 vs. 10 and 11). In the same series cc and Act% also were significantly higher than in series 1 and 2 (cc = 0.86 vs. 0.7 and 0.6; Act% = 71.3 vs. 44.7 and 41.2). DeltaSI was not significantly different among all series.

CONCLUSIONS

Effective respiratory and cardiac synchronization can be achieved in oxygen-enhanced magnetic resonance imaging of the lung, using a pneumotachograph for real-time targeting of end-expiration.

Assessment of regional lung function impairment in airway obstruction and pulmonary embolic dogs with combined noncontrast electrocardiogram-gated perfusion and gadolinium diethylenetriaminepentaacetic acid aerosol magnetic resonance images

PURPOSE

To define regional function impairment in airway obstruction (AO) and pulmonary embolic (PE) dogs with a combination study of noncontrast electrocardiogram (ECG)-gated perfusion and gadolinium diethylenetriaminepentaacetic acid (Gd-DTPA) aerosol magnetic resonance (MR) images.

METHODS

After acquisition of multiphase fast-spin-echo (FSE) MR images during cardiac cycles in 14 AO dogs and 19 PE dogs, ECG-gated perfusion-weighted (PW) images were obtained by subtraction between two-phase images of the minimum lung signal intensity (SI) during systole and maximum SI during diastole. Each dog subsequently inhaled Gd-DTPA aerosol for 20 minutes, and subtracted Gd-DTPA aerosol images were obtained from precontrast and maximally enhanced images. ECG-gated PW images were compared with intravenous Gd-DTPA-enhanced pulmonary arterial perfusion phase (PAPP) images.

RESULTS

ECG-gated PW images were consistent with Gd-DTPA-enhanced PAPP images in all dogs, with significant correlations in the affected-to-unaffected lung perfusion ratios (P < 0.005). Gd-DTPA aerosol images showed sufficient and uniform enhancement in the unaffected lungs. In all the AO areas, these combined images showed the matched perfusion and aerosol deposition defects. These images showed perfusion defects without aerosol deposition defects in the relatively small embolized areas, but showed the matched defects in the widely embolized areas probably due to hypoxic bronchial constriction.

CONCLUSION

The combination MR studies may be acceptable for noninvasively defining regionally impaired lung function in AO and PE.

Assessment of lung perfusion impairment in patients with pulmonary artery-occlusive and chronic obstructive pulmonary diseases with noncontrast electrocardiogram-gated fast-spin-echo perfusion MR imaging

PURPOSE

To evaluate the ability of noncontrast electrocardiogram (ECG)-gated fast-spin-echo (FSE) perfusion MR images for defining regional lung perfusion impairment, as compared with technetium (Tc)-99m macroaggregated albumin (MAA) single-photon emission computed tomography (SPECT) images.

MATERIALS AND METHODS

After acquisition of ECG-gated multiphase FSE MR images during cardiac cycles at selected lung levels in nine healthy volunteers, 11 patients with pulmonary artery-occlusive diseases, and 15 patients with chronic obstructive pulmonary diseases (COPD), the subtracted perfusion-weighted (PW) MR images were obtained from the two-phase images of the minimum lung signal intensity (SI) during systole and the maximum SI during diastole, and were compared with SPECT images.

RESULTS

ECG-gated PW images showed uniform but posture-dependent perfusion gradient in normal lungs and visualized the various sizes of perfusion defects in affected lungs. These defect sites were nearly consistent with those on SPECT images, with a significant correlation for the affected-to-unaffected perfusion contrast (r = 0.753; P < 0.0001). These MR images revealed that the pulmonary arterial blood flow in the affected areas of COPD was relatively preserved as compared with pulmonary artery-occlusive diseases, and also showed significant decrease in blood flow, even in the areas with homogeneous perfusion on SPECT images in patients with focal pulmonary emphysema.

CONCLUSION

This noninvasive MR technique allows qualitative and quantitative assessment of lung perfusion, and may better characterize regional perfusion impairment in pulmonary artery-occlusive diseases and COPD.