VENTILATION-PERFUSION MR IMAGING OF THE LUNG

CT and MR in pulmonary embolism: A changing role for nuclear medicine in diagnostic strategy

The goal of this article is to summarize current data on computed tomography (CT) and magnetic resonance (MR) in the diagnosis of acute pulmonary embolism (PE) in relation to the radionuclide ventilation perfusion scan. It is important for the nuclear medicine, CT, and MR communities to develop a shared approach to this disorder. Triage using chest radiographs appears to be a practical method for enhancing both nuclear medicine and CT/MR performance. The realization that there is no clinically available gold standard for the diagnosis of PE suggests that the imaging community should replace impractical and idealistic discussions with more realistic outcome-oriented approaches. A simplified one-step evaluation of the pulmonary arteries and the lower extremity veins for deep venous thrombus can provide a comprehensive examination for PE. CT is currently a more practical diagnostic tool, whereas MR offers a scientific probe for pulmonary physiology including the regional mapping of ventilation-perfusion relationships. Nuclear medicine, CT, and MR thus form an imaging triad for the diagnosis of acute PE.

Dynamic oxygen-enhanced MRI reflects diffusing capacity of the lung

The purpose of this study was to demonstrate the feasibility of dynamic oxygen-enhanced MRI in a clinical setting. We hypothesized that dynamic oxygen enhancement can reflect the regional diffusing capacity of the lung. Ten patients with pulmonary emphysema and seven healthy volunteers were examined with a respiratory-synchronized inversion recovery single-shot turbo spin-echo sequence (TR = 3200-5000 ms, TE = 16 ms, TI = 720 ms, ETS = 4 ms) following 100% oxygen inhalation, using a 1.5 T whole-body scanner. Maximum mean relative enhancement ratios calculated by averaging six defined regions of interest (ROIs) in both lungs were statistically compared between healthy volunteers and patients, and were correlated with diffusing lung capacity (%DL(CO)). In patients with pulmonary emphysema, maximum mean relative enhancement ratios were significantly decreased compared to those in healthy volunteers (P = 0.0008). Maximum mean relative enhancement ratio had excellent correlation with % DL(C0) (r(2) = 0.83). Dynamic oxygen-enhanced MRI may reflect the diffusing capacity of the lung; therefore, imaging of oxygen enhancement with MRI may provide maps of the diffusing capacity.

Pulmonary ventilation-perfusion MR imaging in clinical patients

The purpose of this study was to evaluate the feasibility of comprehensive magnetic resonance (MR) assessment of pulmonary perfusion and ventilation in patients. Both oxygen-enhanced ventilation MR images and first-pass contrast-enhanced perfusion MR images were obtained in 16 patients with lung diseases, including pulmonary embolism, lung malignancy, and bulla. Inversion recovery single-shot fast spin-echo images were acquired before and after inhalation of 100% oxygen. The overall success rate of perfusion MR imaging and oxygen-enhanced MR imaging was 94% and 80%, respectively. All patients with pulmonary embolism showed regional perfusion deficits without ventilation abnormality on ventilation-perfusion MR imaging. The results of the current study indicate that ventilation-perfusion MR imaging using oxygen inhalation and bolus injection of MR contrast medium is feasible for comprehensive assessment of pulmonary ventilation-perfusion abnormalities in patients with lung diseases.

Silicosis-induced pulmonary artery stenosis: demonstration by MR angiography and perfusion MRI

Silicosis is a common occupational disease. We present a 64-year-old male patient suffering from symptomatic silicosis due to compression of the pulmonary arteries by enlarged hilar lymph nodes. Clinical symptoms and diagnostic imaging modalities are described, with emphasis on cross-sectional imaging. MR angiography and perfusion MRI of the lung in silicosis are described, and their diagnostic value in pneumoconiosis is discussed.

Oxygen-enhanced MR ventilation imaging of the lung: preliminary clinical experience in 25 subjects

OBJECTIVE

The purpose of this study was to show the feasibility of oxygen-enhanced MR ventilation imaging in a clinical setting with correlation to standard pulmonary function tests, high-resolution CT, and (81m)Kr ventilation scintigraphy.

SUBJECTS AND METHODS

Seven healthy volunteers, 10 lung cancer patients, and eight lung cancer patients with pulmonary emphysema were studied. A respiratory synchronized inversion-recovery single-shot turbo-spin-echo sequence (TE, 16; inversion time, 720 msec; interecho spacing, 4 msec) was used for data acquisition. The following paradigm of oxygen inhalation was used: 21% oxygen (room air), 100% oxygen, 21% oxygen. MR imaging data including maximum mean relative enhancement ratio and mean slope of relative enhancement were correlated with forced expiratory volume in 1 sec, diffusing lung capacity, high-resolution CT emphysema score, and mean distribution ratio of (81m)Kr ventilation scintigraphy.

RESULTS

Oxygen-enhanced MR ventilation images were obtained in all subjects. Maximum mean relative enhancement ratio and mean slope of relative enhancement of lung cancer patients were significantly decreased compared with those of the healthy volunteers (p < 0.0001, p < 0.0001). The mean slope of relative enhancement in lung cancer patients with pulmonary emphysema was significantly lower than that of lung cancer patients without pulmonary emphysema (p < 0.0001). Maximum mean relative enhancement ratio (r(2) = 0.81) was excellently correlated with diffusing lung capacity. Mean slope of relative enhancement (r(2) = 0.74) was strongly correlated with forced expiratory volume in 1 sec. Maximum mean relative enhancement had good correlation with the high-resolution CT emphysema score (r(2) = 0.38). The maximum mean relative enhancement had a strong correlation with the distribution ratio (r(2) = 0.77).

CONCLUSION

Oxygen-enhanced MR ventilation imaging in human subjects showed regional changes in ventilation, thus reflecting regional lung function.

Pulmonary ventilation: dynamic MRI with inhalation of molecular oxygen

We have recently demonstrated a non-invasive technique to visualize pulmonary ventilation in humans with inhalation of molecular oxygen as a paramagnetic contrast agent. In the current study, T1 shortening of lung tissue by inhalation of oxygen was observed (P<0.001). The T1 values of lung tissue were also correlated with arterial blood oxygen pressure (PaO(2)) in a pig, resulting in excellent correlation (r(2)=0.997). Dynamic wash-in and wash-out MR ventilation images as well as dynamic wash-in wash-out signal intensity versus time curves were obtained. The mean wash-in decay constants were 26.8+/-10.5 s in the right lung, and 26.3+/-9.5 s in the left lung. The mean wash-out decay constants were 23.3+/-11.3 s in the right lung, and 20.8+/-10.5 s in the left lung. Dynamic assessment of pulmonary ventilation is feasible using oxygen-enhanced MR imaging, which could provide dynamic MR ventilation-perfusion imaging in combination with recently developed MR perfusion imaging technique, and thus a robust tool for the study of pulmonary physiology and pathophysiology.

Assessment of pulmonary perfusion using a subtracted HASTE image between diastole and systole

The MR signal intensity change in the pulmonary parenchyma during the cardiac cycle was studied using HASTE sequence in volunteers. In addition, the potential to assess pulmonary perfusion abnormality by subtraction between diastolic and systolic HASTE images was tested in a pig model of pulmonary embolism. Signal intensity decreased in systole while it increased gradually in diastole. In a pig model with pulmonary embolism, subtracted images could identify the perfusion abnormality. Thus, subtraction of diastolic and systolic HASTE images has the potential to detect pulmonary perfusion abnormality. The technique may provide a new simple method for evaluating pulmonary perfusion.

Magnetic resonance imaging of the thorax. Past, present, and future

Magnetic resonance imaging is a valuable modality of extreme flexibility for specific problem-solving capability in the thorax. This article reviews MR applications in the imaging of great vessels, which are currently the most important applications in the thorax; other established applications in the thorax; and pulmonary functional MR imaging.

Magnetic resonance imaging of the thorax. Past, present, and future

Magnetic resonance is a valuable modality of extreme flexibility for specific problem-solving capability in the thorax. This article reviews MR applications in the imaging of great vessels, which are currently the most important applications in the thorax; other established applications in the thorax; and pulmonary functional MR imaging.