Pulmonary perfusion: qualitative assessment with dynamic contrast-enhanced MRI using ultra-short TE and inversion recovery turbo FLASH

Co-registration of acquired MR ventilation and perfusion images--validation in a porcine model

Under controlled imaging conditions, functional, co-registered ventilation and perfusion images were obtained for quantitative MRI assessment of pulmonary function. Experiments were conducted on 25-35 kg Yorkshire pigs (N = 5) under ketamine/isoflurane anesthesia. Ventilation and perfusion MR images were obtained using laser polarized gas and gadolinium (Gd), respectively. The mutual information-based technique was used to quantify the initial misregistration between the acquired ventilation and perfusion images, to cope with different intensity characteristics. Means and standard deviations (SDs) of misregistrations for the five subjects, in terms of absolute translation and absolute rotations around each of the three coordinate axes, were computed to evaluate the hypothesis. For qualitative illustrations, plots of mutual information values under absolute translations and rotations around each of the three coordinate axes are presented. This preliminary study shows the feasibility of acquiring functional image data that are spatially co-registered. This method has potential applications in the quantitative assessment of regional alveolar ventilation and pulmonary perfusion ratio, in both normal and diseased lung.

Time-resolved three-dimensional pulmonary MR angiography and perfusion imaging with ultrashort repetition time

RATIONALE AND OBJECTIVES

The purpose of this study was to implement ultrafast, multiphase three-dimensional (3D) magnetic resonance (MR) angiography and perfusion imaging after bolus injection of contrast medium to generate preliminary validation of parameters in a pig model and to illustrate potential applications in patients with lung abnormalities.

MATERIALS AND METHODS

Five healthy volunteers, five patients, and three pigs underwent rapid, time-resolved pulmonary MR angiography and perfusion imaging on a 1.5-T MR imager. All patients had undergone correlative computed tomographic or conventional angiography. The pulse sequence was a 3D spin-warp, gradient-echo acquisition with a repetition time of 1.6 msec and an echo time of 0.6 msec. Each 3D acquisition lasted 2-3 seconds, and 8-16 sequential measurements were made in each study. Artificial pulmonary emboli were generated in pigs with gelatin sponge. All patients had diseases of the pulmonary circulation (as confirmed with other studies).

RESULTS

Multiphasic, time-resolved pulmonary parenchymal enhancement was demonstrated in all healthy subjects and animals. All segmental (n = 100) and subsegmental (n = 200) branches were identified in the healthy subjects. Perfusion deficits were clearly demonstrated in all pigs after gelatin embolization. Perfusion defects were identified in two patients with lung disease. Abnormalities of the pulmonary vasculature were clearly identified in the patient group.

CONCLUSION

Dynamic time-resolved 3D pulmonary MR angiography and perfusion imaging is feasible in humans as well as in animals. Induced perfusion deficits are identifiable after artificial embolization in pigs. Combined pulmonary MR angiography and parenchymal (perfusion) imaging may improve evaluation of the pulmonary circulation in a variety of conditions.

MR-pathologic correlation of lung specimens

The aim of this study was to assess the feasibility of a new MR-pathologic correlation method utilizing a high-resolution MR technique with a 3-inch surface coil and elimination of susceptibility by replacing air in the pulmonary alveoli of lung specimens with water. Inflated cadaver lung specimens of various lung disorders were imaged using a conventional spin echo (SE) sequence in a clinical 1.5 T MR scanner. The MR images were correlated with pathologic specimens. In six out of seven specimens, MR revealed detailed images corresponding to pathological changes. MR may provide a non-invasive and non-destructive method for examining lung specimens and for image-pathologic correlation.

Assessment of pulmonary perfusion with ultrafast projection magnetic resonance angiography in comparison with lung perfusion scintigraphy in patients with malignant stenosis

RATIONALE AND OBJECTIVE

The aim of this study was to demonstrate and measure perfusion deficits caused by central bronchogenic carcinoma and to compare magnetic resonance angiography (MRA) perfusion data with data of perfusion scintigraphy. The diagnostic value of 2D MRA in detection of malignant pulmonary artery stenosis in comparison with conventional DSA was investigated.

MATERIALS AND METHODS

Eighteen patients were included in the study. MRA, conventional pulmonary angiograms, and pulmonary perfusion scintigrams were performed. MRA and DSA were compared and MR pulmonary perfusion data were assessed and compared with scintigraphical data.

RESULTS

Perfusion defect could be demonstrated and localized in all patients. A quantitative perfusion deficit and a side dependent perfusion ratio could be evaluated. There was statistically significant correlation between MR perfusion and scintigraphically acquired data. 2D MRA showed a high correlation for detection and grading of stenosis compared with angiograms.

CONCLUSIONS

Pulmonary perfusion could be demonstrated by using an ultrafast 2D projection MR DSA sequence. This technique allows measurement and quantification of pulmonary perfusion abnormalities in patients with malignant stenosis with statistically significant correlation to perfusion scintigraphy. The diagnostic potency in the evaluation of malignant pulmonary artery stenosis compared with conventional DSA could be shown.

Comparison of first-pass Gd-DOTA and FAIRER MR perfusion imaging in a rabbit model of pulmonary embolism

PURPOSE

To compare the sensitivity of contrast-enhanced magnetic resonance imaging (MRI) and arterial spin labeling to perfusion deficits in the lung.

MATERIALS AND METHODS

A rabbit model of pulmonary embolism was imaged with both flow-sensitive alternating inversion recovery with an extra radiofrequency pulse (FAIRER) arterial spin labeling and Gd-DOTA enhanced MRI. The signal-to-noise ratio (SNR) was measured in the area of the perfusion deficit and the normal lung for both techniques.

RESULTS

The defect was readily visible in all images. The normal lung had an average of 3.8 +/- 1.2 times the SNR of the unperfused lung with the arterial spin labeling technique, and approximately 13.7 +/- 3.3 times the SNR with the contrast-enhanced technique.

CONCLUSION

Gd-DOTA enhanced MRI provides higher SNR in pulmonary perfusion imaging; however, arterial spin labeling is also adequate and may be used when repeated studies are indicated.

Solitary pulmonary nodules: potential role of dynamic MR imaging in management initial experience

PURPOSE

To evaluate the utility of dynamic magnetic resonance (MR) imaging in the management of solitary pulmonary nodules (SPNs).

MATERIALS AND METHODS

Fifty-eight patients with 58 pathologic analysis-proved SPNs (diameter < 30 mm) underwent dynamic 1.5-T MR imaging. The 58 SPNs were classified into three groups at pathologic analysis: malignant SPNs (n = 38), active infections (n = 10), or benign SPNs (n = 10). From signal intensity-time curves generated after the bolus injection of contrast material, the maximum relative enhancement ratio and slope of enhancement were calculated and statistically compared among the three groups. Threshold values of these two dynamic MR indexes were determined on the basis of positive differentiations.

RESULTS

The mean relative enhancement ratio and mean slope of enhancement for the malignant SPN group were significantly higher than those for the benign SPN group and significantly lower than those for the active infection group (P <.05). With 0.15 as the threshold maximum relative enhancement ratio for distinguishing the malignant SPN and active infection groups from the benign SPN group, the sensitivity, specificity, and accuracy were 100%, 70%, and 95%, respectively. With 0.025/sec as the threshold slope of enhancement, all SPNs with malignancy and active infection were clearly distinguished from benign SPNs.

CONCLUSION

Dynamic MR indexes were useful in the differentiation between SPNs that necessitated further evaluation or treatment (malignancy and active infection) and SPNs that did not necessitate further evaluation or treatment (benign nodules).

Perfusion characteristics of radiation-injured lung on Gd-DTPA-enhanced dynamic magnetic resonance imaging

RATIONALE AND OBJECTIVES

A contrast-enhanced dynamic magnetic resonance (MR) study was performed experimentally and clinically to describe perfusion characteristics of radiation-injured lung according to pathologic phases.

METHODS

The MR study was performed before and at 0.5, 1, 2, 3, 4, and 7 months after 40 Gy-dose irradiation to the right hemithorax in 8 dogs, and clinically in 12 lung lesions of 9 patients with acute or fibrotic radiation pneumonitis. Altered Gd-DTPA kinetics in the affected lungs was assessed by time-signal intensity curves. MR findings were correlated with lung histology and CT images.

RESULTS

Within 1 month after irradiation, the irradiated animal lungs showed focal and persistent contrast enhancement relative to nonirradiated lungs. This abnormality was pronounced during the next 2 months. After 4 months, irradiated lungs conversely showed lower enhancement during the Gd-DTPA first-pass but were followed by persistently greater enhancement during Gd-DTPA redistribution phase. Similar differences in enhancement abnormalities between acute and fibrotic radiation pneumonitis were clinically observed.

CONCLUSION

These findings indicate that Gd-DTPA kinetics can be altered according to the histopathologic change in early/acute radiation pneumonitis and radiation fibrosis and that the contrast-enhanced perfusion MRI may help differentiate the phases of radiation pneumonitis.

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.

Perfusion abnormalities in pulmonary embolism studied with perfusion MRI and ventilation-perfusion scintigraphy: an intra-modality and inter-modality agreement study

PURPOSE

To compare perfusion magnetic resonance imaging (MRI) and ventilation-perfusion scintigraphy (V-P scan) in the study of perfusion abnormalities in pulmonary embolism (PE) and to compare the PE results to the findings previously reported for pneumonia and chronic obstructive pulmonary disease (COPD), in terms of perfusion abnormalities.

MATERIALS AND METHODS

Dynamic contrast-enhanced MR images and V-P scans of 20 patients with PE, 11 patients with acute pneumonia, and 13 patients with exacerbation of COPD were studied. Five categories of perfusion abnormalities within each imaging modality were defined. Intra- and inter-modality agreement (kappa values) in the evaluation of perfusion abnormalities were calculated, based on the two observers of each imaging modality (all blinded to each other and true diagnosis). Finally, three categories of perfusion MRI diagnosis (PE, pneumonia, and COPD) were also defined and the inter-observer agreement (kappa value) was calculated.

RESULTS

For PE, the intra-modality agreement (kappa value) in the evaluation of perfusion abnormalities was 0.77 for MRI and 0.65 for V-P scan. The inter-modality agreement varied from 0.52 to 0.57, respectively, and was observer-dependent. For the pooled group of PE, pneumonia, and COPD, the intra-modality agreement of perfusion abnormalities was 0.76 for MRI and 0.65 for V-P scan, and the inter-modality agreement varied from 0.51 to 0.56. The kappa value for inter-observer agreement for MRI diagnosis was 0.92.

CONCLUSION

Evaluation of perfusion abnormalities in PE, pneumonia, and COPD using perfusion MRI and V-P scan showed a high intra-modality agreement that was higher than the inter-modality agreement. Further studies are now needed in patients presenting with possible PE to evaluate the sensitivity and specificity of the method.

Combined MR proton lung perfusion/angiography and helium ventilation: potential for detecting pulmonary emboli and ventilation defects

Three-dimensional (3D) perfusion imaging allows the assessment of pulmonary blood flow in parenchyma and main pulmonary arteries simultaneously. MRI using laser-polarized (3)He gas clearly shows the ventilation distribution with high signal-to-noise ratio (SNR). In this report, the feasibility of combined lung MR angiography, perfusion, and ventilation imaging is demonstrated in a porcine model. Ultrafast gradient-echo sequences have been used for 3D perfusion and angiographic imaging, in conjunction with the use of contrast agent injections. 2D multiple-section (3)He imaging was performed subsequently by inhalation of 450 ml of hyperpolarized (3)He gas. The MR techniques were examined in a series of porcine models with externally delivered pulmonary emboli and/or airway occlusions. With emboli, perfusion deficits without ventilation defects were observed; airway occlusion resulted in matched deficits in perfusion and ventilation. High-resolution MR angiography can unambiguously reveal the location and size of the blood emboli. The combination of the three imaging methods may provide complementary information on abnormal lung anatomy and function.

Contrast-enhanced MR perfusion imaging and MR angiography: utility for management of pulmonary arteriovenous malformations for embolotherapy

OBJECTIVE

The purpose of this study was to assess the capability of MR perfusion imaging and angiography (MRA) for management of pulmonary arteriovenous malformation (PAVM).

METHODS AND PATIENTS

Eight patients, having 15 PAVMs underwent pulmonary angiography (PAG), CT, MR perfusion imaging and MRA. For the pretherapeutic management, MRA was compared with PAG and CT regarding detectability and diameter of vasculature. For post-therapeutic management, the change in size of aneurysmal sac, any residual contrast-enhancement and the blood supply within the sac were evaluated.

RESULTS

All PAVMs with aneurysmal sac, feeding artery and draining vein diameters of equal to or more than 3 mm, were identified and measured with similar results by all modalities. On follow-up studies, 7 (58.4%) out of 12 treated PAVMs showed a decrease in size and residual contrast-enhancement. The residual contrast-enhancement was considered as bronchial artery-to-pulmonary artery collateral flow by MR perfusion imaging.

CONCLUSION

MR perfusion imaging and MRangiography are useful for management of PAVMs over 3 mm in diameter.

Effect of the rate of gadolinium injection on magnetic resonance pulmonary perfusion imaging

PURPOSE

To determine whether the injection rate of contrast agent affects the dynamics of enhancement of the pulmonary parenchyma on magnetic resonance (MR) pulmonary perfusion imaging.

MATERIALS AND METHODS

Fifteen healthy volunteers underwent enhanced MR pulmonary perfusion imaging to evaluate the effects of different injection rates. Injection rates were 1, 3, or 5 mL/second. Regions of interest (ROIs) were chosen in the lung and aorta to analyze the change in signal intensity over time.

RESULTS

As the injection rate increased, the peak enhancement occurred significantly earlier (P = 0.0012), but the peak enhancement signal-to-noise ratio (SNR) value was not affected (P = 0.25). With the 3- and 5-mL/second injection rates, images of both the pulmonary circulation and systemic circulation were obtained separately. However, with 1 mL/second, higher enhancement of the aorta was overlapped with peak enhancement of the lung tissue.

CONCLUSION

The injection rate affects the enhancement profiles of the pulmonary parenchyma.

Detectability of pulmonary perfusion defect and influence of breath holding on contrast-enhanced thick-slice 2D and on 3D MR pulmonary perfusion images

The present study assesses the detectability of perfusion defect and the influence of breathhold on pulmonary magnetic resonance (MR) perfusion imaging using contrast-enhanced thick-slice two-dimensional (2D) fast gradient-echo sequence compared with three-dimensional (3D) fast spoiled gradient-recalled sequence. Dynamic studies were performed in 16 patients. MR perfusion images were interpreted by two independent observers using perfusion scintigraphy as the reference standard. The patients were divided into two groups according to the duration of holding the breath measured during MR imaging. The sensitivity and specificity of 2D MR perfusion imaging in detecting perfusion defects were 93% and 94%, respectively, while those of 3D MR perfusion imaging were 89% and 85%, respectively. The diagnostic accuracy of 2D MR perfusion imaging was significantly higher than that of 3D MR perfusion imaging (P < 0.05) among those who could not hold their breath. Therefore, 2D MR perfusion imaging offers promise for evaluating pulmonary perfusion even among patients who cannot hold their breath.

Gravity-dependent perfusion of the lung demonstrated with the FAIRER arterial spin tagging method

Magnetic resonance imaging of lung perfusion using an arterial spin tagging (AST) sequence called flow sensitive alternating inversion recovery with an extra RF pulse (FAIRER) was performed in the left and right lateral positions in five volunteers. Coronal slices were obtained and the average intensity of each lung was measured. In both positions, an increase in the intensity of the dependent lung was found (229% for left lateral, 40% for right lateral). No change was seen along an isogravitational plane. Lung volumes were measured in each position to account for the compression of the lungs by the heart. This effect was found to be symmetric and did not contribute to the perfusion gradient. This demonstrates that AST is sensitive to gravity-dependent perfusion gradients in the lung.

Dynamic observation of pulmonary perfusion using continuous arterial spin-labeling in a pig model

The continuous arterial spin-labeling (CASL) method of perfusion MRI is used to observe pulmonary perfusion dynamically in an animal model. Specifically, a respiratory-triggered implementation of the CASL method is used with approximate spatial resolution of 0.9 x 1.8 x 5.0 mm (0.008 cc) and 2-minute temporal resolution. Perfusion MRI is performed dynamically during repeated balloon occlusion of a segmental pulmonary artery, as well as during pharmacological stimulation. A total of three Yorkshire pigs were studied. The results demonstrate the ability of the endogenous spin-labeling method to characterize the dynamic changes in pulmonary perfusion that occur during important physiological alterations.

Perfusion characteristics of oleic acid--injured canine lung on Gd-DTPA--enhanced dynamic magnetic resonance imaging

RATIONALE AND OBJECTIVES

We conducted an animal study to describe and interpret the perfusion characteristics of oleic acid (OA)-injured lungs on gadopentetate dimeglumine (Gd-DTPA)-enhanced dynamic perfusion magnetic resonance (MR) imaging.

METHODS

Fourteen dogs received an intravenous OA infusion in the supine (n = 4), prone (n = 4), and right lateral decubitus (n = 6) positions, and 10 minutes later these animals in the same postures underwent the dynamic MR study. Regional Gd-DTPA kinetics was analyzed by the time-signal intensity (SI) curves and by qualitative functional map images of the mean transit time that was representative of the mean circulation time in the vascular bed and the average cumulative sum of the relative increases in SI representative of Gd-DTPA distribution volume during Gd-DTPA first pass. The results were compared with those in six control animals and in another six animals that underwent the MR study 3 minutes (n = 3) and 60 minutes (n = 3) after OA infusion. The MR findings were correlated with the distribution of lung damage and the infused OA particles as assessed by histology.

RESULTS

The dynamic MR study showed postural shifts on the gravity-dependent perfusion map of normal lungs. Contrast enhancement during Gd-DTPA first pass in the lung was lower and more heterogeneous in the OA-injured lung models than in controls but was followed by conversely greater and persistent enhancement during the Gd-DTPA redistribution phase. Regardless of the postures for OA infusion, these abnormalities were predominant in the dependent lungs and became more pronounced with time after OA infusion, where more prominent capillary obstruction with OA droplets and alveolar/interstitial edema were histologically observed. On the functional map images, greater mean transit time and the average cumulative sum of the relative increases in SI values were also predominantly distributed in the dependent lungs.

CONCLUSIONS

Low and heterogeneous enhancement was observed during Gd-DTPA first pass but was followed by persistent enhancement during the Gd-DTPA redistribution phase, and predominant abnormalities in the dependent lungs may be characteristic features of the perfusion of OA-injured lungs. The histological correlations indicate that these abnormalities may reflect OA-induced pathophysiologies associated with capillary OA obstruction, increased vascular resistance, and capillary permeability/extravascular spaces and that lung damage may be gravity dependent.

Evaluation of regional pulmonary perfusion using ultrafast magnetic resonance imaging

An ultrafast MR sequence was used to measure changes in signal intensity during the first pass of intravascular contrast through the pulmonary circulation. From this, mean transit time, relative blood volume, and relative blood flow were calculated. Data were collected in an isogravitational plane in six healthy subjects. A slight but significant gradient in transit time was present, with faster times at the lung apex. A significant decrease in blood volume, compared with the lung base, was also seen in the apex. Significant decreases in blood volume and blood flow, compared with central portions of the lung, were seen in the lung periphery. Six additional subjects were imaged along a gravitational plane. A significant gradient in transit time was seen, with faster transit in dependent regions of the lung. MRI is able to evaluate regional differences in pulmonary perfusion with high spatial and temporal resolution. Magn Reson Med 46:166-171, 2001.

Pulmonary ventilation imaged by magnetic resonance: at the doorstep of clinical application

Over the past few years, magnetic resonance imaging (MRI) has emerged as an important instrument for functional ventilation imaging. The aim of this review is to summarize established clinical methods and emerging techniques for research and clinical arenas. Before the advent of MRI, chest radiography and computed tomography (CT) dominated morphological lung imaging, while functional ventilation imaging was accomplished with scintigraphy. Initially, MRI was not used for morphological lung imaging often, due to technical and physical limitations. However, recent developments have considerably improved anatomical MRI, as well as advanced new techniques in functional ventilation imaging, such as inhaled contrast aerosols, oxygen, hyperpolarized noble gases (Helium-3, Xenon-129), and fluorinated gases (sulphur-hexafluoride). Straightforward images demonstrating homogeneity of ventilation and determining ventilated lung volumes can be obtained. Furthermore, new image-derived functional parameters are measurable, such as airspace size, regional oxygen partial pressure, and analysis of ventilation distribution and ventilation/perfusion ratios. There are several advantages to using MRI: lack of radiation, high spatial and temporal resolution and a broad range of functional information. The MRI technique applied in patients with chronic obstructive pulmonary disease, emphysema, cystic fibrosis, asthma, and bronchiolitis obliterans, may yield a higher sensitivity in the detection of ventilation defects than ventilation scintigraphy, CT or standard pulmonary function tests. The next step will be to define the threshold between physiological variation and pathological defects. Using complementary strategies, radiologists will have the tools to characterize the impairment of lung function and to improve specificity.

Quantification of pulmonary perfusion with MR imaging: recent advances

Recent advances in magnetic resonance pulmonary perfusion imaging are reviewed, focusing on magnetic resonance perfusion imaging using gadolinium contrasts agents or spin labeling of blood using naturally flowing spins as the source of intravascular signal. These recent developments in magnetic resonance imaging have made it possible to analyze data quantitatively which holds significant potential for clinical imaging of lung perfusion and opens windows to functional MR imaging of the lung. We believe that fast magnetic resonance functional imaging will play an important role in the assessment of pulmonary function and the pulmonary disease process.

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.

Multiphase ECG-triggered 3D contrast-enhanced MR angiography: utility for evaluation of hilar and mediastinal invasion of bronchogenic carcinoma

The purpose of this study was to evaluate the usefulness of cardiac synchronized magnetic resonance angiography [electrocardiographically (ECG)-triggered MRA] for improving image quality and detection of hilar and mediastinal invasion of bronchogenic carcinoma. Fifty patients, suspected of having hilar or mediastinal invasion of bronchogenic carcinoma, underwent contrast-enhanced computed tomography and MR imaging including conventional and ECG-triggered MRA. Twenty patients subsequently also underwent surgical resection. Vascular enhancement-to-background ratio (VBR), vascular enhancement-to-tumor ratio (VTR), signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and image quality scores of thoracic vessels obtained with both MRA techniques were determined and compared. In addition, the diagnostic accuracy of tumor invasion of pulmonary vessels was compared. VBRs and VTRs of both MRA techniques were not significantly different. ECG-triggered MRA significantly improved SNRs and CNRs (P < 0.05). Two readers judged that overall image quality of ECG-triggered MRA was better than that of conventional MRA (kappa > or = 0.41). In conclusion, ECG-triggered MRA improves the image quality and the detection of hilar and mediastinal invasion of bronchogenic carcinoma.

Blood pool MR contrast agents for cardiovascular imaging

Currently available magnetic resonance (MR) contrast agents are not confined to the intravascular space because of their small molecular size. These agents produce peak vascular enhancement for only a short period. Conversely, blood pool agents have longer intravascular residence time and higher relaxivity. Therefore these agents provide MR angiography with flexibility, versatility, and accuracy. With blood pool agents, the timing of contrast injection becomes less significant because the optimal imaging window is in tens of minutes rather than seconds. In addition, larger anatomic regions can be imaged optimally. Preliminary evidence appears to support the notion that blood pool agents may play a diagnostic role in coronary, peripheral, and pulmonary angiography. Besides their ability to increase vascular contrast, blood pool agents provide physiologic information, including rate of entry, rate of accumulation, and rate of elimination. MR imaging with blood pool agents also have proven to be of significant value in the assessments of myocardial perfusion and microvascular permeability. In anticipation of broad clinical use, blood pool agents are currently being evaluated in human trails. Examples include gadolinium-chelate that binds in vivo to albumin to form blood pool agents and ultrasmall superparamagnetic iron oxide particles. This review discusses the applications of MR blood pool agents in the cardiovascular system. J. Magn. Reson. Imaging 2000;12:890-898.

Noninvasive pulmonary perfusion imaging by STAR-HASTE sequence

The STAR-HASTE sequence has been shown to be useful for perfusion imaging in areas that are plagued by magnetic susceptibility artifacts. Pulmonary perfusion imaging with this technique was attempted in this study. Quantitative analysis was also conducted, using an appropriate kinetic model in one subject. In six healthy subjects, gradual enhancement was observed in pulmonary artery to distal lung parenchyma when inflow time was increased. Our initial results suggest that noninvasive evaluation of pulmonary perfusion by magnetic resonance imaging without administration of an exogenous agent is possible.

The role of magnetic resonance imaging and spectroscopy in transplantation: from animal models to man

Critical success factors in solid organ and vascular transplantation are the assessment of graft status/viability as well as stringent monitoring of transplant recipients, preferentially using noninvasive techniques. This review addresses the application of magnetic resonance imaging (MRI) and spectroscopy (MRS) in the field of transplantation. The first section is devoted to the description of the main MR techniques used for monitoring the status of the graft noninvasively. Subsequently, the role of MRI/MRS in the analysis of the viability of organs for transplantation is discussed. Since chronic rejection remains a major difficulty, development of new therapies is still ongoing. Thus, the third part is devoted to the use of MRI/MRS for monitoring graft rejection in animal models of transplantation. This is followed by a discussion of clinical studies of transplantation involving MRI/MRS. Finally, a general appraisal is made on available imaging techniques for the non-invasive characterization of grafts in situ, highlighting the role of MR methods in the field of transplantation.

Perfusion magnetic resonance imaging of the lung: characterization of pneumonia and chronic obstructive pulmonary disease. A feasibility study

Perfusion magnetic resonance (MR) imaging is a promising new method for detection of perfusion defects in the diagnosis of pulmonary embolism. In the present study we evaluated the first-pass characteristics of perfusion MR imaging in patients with pneumonia or chronic obstructive pulmonary disease (COPD), frequent differential diagnoses to pulmonary embolism. Dynamic contrast-enhanced MR images of 12 patients with acute pneumonia and 13 patients with exacerbation of COPD were acquired in both the coronal and transaxial planes (an inversion recovery prepared gradient-echo sequence using 0.05 mmol/kg gadodiamide/injection). The MR images and the signal intensity (SI) versus time curves were characterized for each disease entity and compared with normal lung and the findings in pulmonary embolism from our previous study. The perfusion MR images of pneumonia showed distinct regions of increased contrast enhancement; in COPD with signs of emphysema (11 of the 13 COPD patients), the images showed a coarse pattern of reduced contrast enhancement. The SI versus time curves of pneumonia, COPD with signs of emphysema, and normal lung were statistically different, the respective pooled SI values (+/-95% CI) being as follows: mean baseline SI, 20.7 (1.1), 7.4 (0.4), and 8.5 (0.3); mean peak SI, no peak, 12.9 (1.5), and 27 (4.6); and mean max change of SI in percent, 110 (27), 79 (22), and 205 (52). Perfusion MR imaging of pneumonia and COPD with signs of emphysema showed first-pass that were characteristics promising for diagnostic use. Both the MR images and the SI versus time curves were different from the perfusion characteristics in normal lung and pulmonary embolism shown previously.

Laser-polarized (3)He as a probe for dynamic regional measurements of lung perfusion and ventilation using magnetic resonance imaging

Magnetic resonance imaging (MRI) using laser-polarized noble gases, such as (129)Xe and (3)He, allows unparalleled noninvasive information on gas distribution in lung airways and distal spaces. In addition to pulmonary ventilation, lung perfusion assessment is crucial for proper diagnosis of pathological conditions, such as pulmonary embolism. Magnetic resonance perfusion imaging usually can be performed using techniques based on the detection of water protons in tissues. However, lung proton imaging is extremely difficult due to the low proton density and the magnetically inhomogeneous structure of the lung parenchyma. Here we show that laser-polarized (3)He can be used as a noninvasive probe to image, in a single MRI experiment, not only the ventilation but also the perfusion state of the lungs. Blood volume maps of the lungs were generated based on the (3)He signal depletion during the first pass of a superparamagnetic contrast agent bolus. The combined and simultaneous lung ventilation and perfusion assessments are demonstrated in normal rat lungs and are applied to an experimental animal model of pulmonary embolism. Magn Reson Med 44:1-4, 2000.

Three-dimensional MR imaging of pulmonary vessels and parenchyma with NC100150 injection (Clariscan)

The influence of increasing doses of NC100150 Injection (Clariscantrade mark) and echo times on visualization of pulmonary vessels and parenchyma was evaluated. The effects of 0.5, 1, 2, 4, and 8 mg Fe/kg NC100150 Injection and echo times (TE) of 1.1, 1.8, 2. 2, and 4.3 msec were determined in six dogs using breath-hold three-dimensional (3D) spoiled gradient-echo magnetic resonance (MR) sequence. At 2 mg Fe/kg and TE of 1.1 msec, the signal-to-noise ratio of the central pulmonary arteries and parenchyma was significantly increased (5.3 +/- 2.2 to 50.3 +/- 2.4) and (2.2 +/- 0. 9 to 6.4 +/- 1.1), respectively. Using the TE of 1.1 msec, signal intensity in the main arteries continued to increase with increasing dose. Moreover, the enhancement of pulmonary parenchyma and microvasculature had a positive dose response. 3D MR imaging with ultrashort echo time and 2 mg Fe/kg NC100150 Injection produces angiograms with strong vascular contrast and allows qualitative assessment of pulmonary parenchyma and microvasculature.

Contrast-enhanced MRI of the lung

The lung has long been neglected by MR imaging. This is due to unique intrinsic difficulties: (1) signal loss due to cardiac pulsation and respiration; (2) susceptibility artifacts caused by multiple air-tissue interfaces; (3) low proton density. There are many MR strategies to overcome these problems. They consist of breath-hold imaging, respiratory and cardiac gating procedures, use of short repetition and echo times, increase of the relaxivity of existing spins by administration of intravenous contrast agents, and enrichment of spin density by hyperpolarized noble gases or oxygen. Improvements in scanner performance and frequent use of contrast media have increased the interest in MR imaging and MR angiography of the lung. They can be used on a routine basis for the following indications: characterization of pulmonary nodules, staging of bronchogenic carcinoma, in particular assessment of chest wall invasion; evaluation of inflammatory activity in interstitial lung disease; acute pulmonary embolism, chronic thromboembolic pulmonary hypertension, vascular involvement in malignant disease; vascular abnormalities. Future perspectives include perfusion imaging using extracellular or intravascular (blood pool) contrast agents and ventilation imaging using inhalation of hyperpolarized noble gases, of paramagnetic oxygen or of aerosolized contrast agents. These techniques represent new approaches to functional lung imaging. The combination of visualization of morphology and functional assessment of ventilation and perfusion is unequalled by any other technique.

A closed-chest pulmonary artery occlusion/reperfusion model in the pig: detection of experimental pulmonary embolism with MR angiography and perfusion MR imaging

RATIONALE AND OBJECTIVES

To establish a pig model suitable for imitating pulmonary emboli to facilitate research in the diagnosis of pulmonary embolism.

METHODS

Thirteen animals were anesthetized, mechanically ventilated, and subjected to pulmonary artery catheterization initiated from the right external jugular vein. With the use of a Swan-Ganz catheter, repetitive occlusion/reperfusion maneuvers were done at different locations of the pulmonary arterial tree. Conventional pulmonary angiography, MR angiography, and perfusion MR imaging were performed.

RESULTS

The model remained hemodynamically stable throughout the 13 experiments, without any significant difference between the blood pressure measurements at the start and at the end of the right-heart and pulmonary artery catheterizations. In each of the nine animal experiments that investigated MR imaging, four of four using perfusion MR imaging (proximal and distal occlusions) and five of five using MR angiography (larger pulmonary artery occlusions), all repeated pulmonary artery occlusions were successfully performed (reproducibility of 100%).

CONCLUSIONS

The closed-chest pulmonary artery occlusion/reperfusion model in the pig allowed repetitive, controlled imitations of pulmonary emboli at different levels of the pulmonary artery in the same experiment. MR angiography and perfusion MR imaging were adequate to detect the pulmonary artery occlusions and the nonperfused lung regions, respectively. The model may be a helpful tool for future research in this field.

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.

Three-dimensional contrast-enhanced MR angiography with real-time fluoroscopic triggering: design specifications and technical reliability in 330 patient studies

Technical reliability was determined for triggering three-dimensional (3D) contrast material-enhanced magnetic resonance (MR) angiography with MR fluoroscopy. Technical requirements for high reliability were also identified. Reliability was evaluated in 330 consecutive patient studies of the neck, thorax, abdomen, and pelvis. Contrast material arrival was detected fluoroscopically in 325 of the 330 studies (98.5%), and the 3D sequence was successfully triggered in 321 of 330 studies (97.3%). Fluoroscopic triggering of centrically encoded 3D MR angiographic acquisitions is a highly reliable means of obtaining 3D MR angiograms with high spatial resolution.

Vascular permeability: quantitative measurement with double-echo dynamic MR imaging--theory and clinical application

Double-echo dynamic magnetic resonance (MR) imaging was used to evaluate both vascularity and permeability of tissues simultaneously. Vascularity was evaluated on the basis of the T2*-shortening effect due to the intravascular fraction of the contrast agent and permeability on the basis of the T1-shortening effect due to the extravascular fraction. Meningioma was characterized on the basis of higher vascularity and neurinoma on the basis of higher permeability. The proposed method enables better tissue characterization.

Detection of regional pulmonary perfusion deficit of the occluded lung using arterial spin labeling in magnetic resonance imaging

Detection of regional perfusion deficit in the lung has been demonstrated using an arterial spin labeling technique called flow-sensitive alternating inversion recovery with an extra radiofrequency pulse (FAIRER). A pulmonary artery was occluded using a nondetachable balloon catheter to simulate an acute pulmonary embolism in 3 of 10 rabbits. Inflating the balloon occludes the artery, and deflating the balloon allows for reperfusion. Perfusion imaging was performed pre-occlusion, during occlusion, and after reperfusion. Signal enhancement due to perfusion of the pulmonary parenchyma was observed in the perfusion images with negligible artifacts. The perfusion deficit of the pulmonary parenchyma was detected distal to the site of occlusion in all three rabbits. Return of the pulmonary parenchymal perfusion was observed after reperfusion. Magnetic resonance imaging using FAIRER can detect signal loss due to absence of perfusion caused by pulmonary embolism.

Pulmonary disorders: ventilation-perfusion MR imaging with animal models

PURPOSE

To demonstrate the capability of magnetic resonance (MR) imaging to assess alteration in regional pulmonary ventilation and perfusion with animal models of airway obstruction and pulmonary embolism.

MATERIALS AND METHODS

Airway obstruction was created by inflating a 5-F balloon catheter into a secondary bronchus. Pulmonary emboli were created by injecting thrombi into the inferior vena cava. Regional pulmonary ventilation was assessed with 100% oxygen as a T1 contrast agent. Regional pulmonary perfusion was assessed with a two-dimensional fast low-angle shot, or FLASH, sequence with short repetition and echo times after intravenous administration of gadopentetate dimeglumine.

RESULTS

Matched ventilation and perfusion abnormalities were identified in all animals with airway obstruction. MR perfusion defects without ventilation abnormalities were seen in all animals with pulmonary emboli.

CONCLUSION

Ventilation and perfusion MR imaging are able to provide regional pulmonary functional information with high spatial and temporal resolution. The ability of MR imaging to assess both the magnitude and regional distribution of pulmonary functional impairment could have an important effect on the evaluation of lung disease.

Quantitative assessment of pulmonary perfusion with dynamic contrast-enhanced MRI

The feasibility of qualitative assessment of pulmonary perfusion using dynamic contrast enhanced MRI with ultra-short TE has recently been demonstrated. In the current study, quantitative analysis was attempted based on the indicator dilution principle using a pig model of pulmonary embolism. The results were compared with the absolute pulmonary perfusion obtained with colored microspheres. The inverse of apparent mean transit time (1/tau(app)), distribution volume (V), and V/tau(app) were correlated well with the absolute lung perfusion. This study demonstrates that MR has the potential to evaluate pulmonary perfusion quantitatively. Magn Reson Med 42:1033-1038, 1999.

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.

Recent advances in pulmonary imaging

Recent years have witnessed an explosion in imaging technology applicable to chest medicine. These include CT and magnetic resonance angiography (MRA) for the diagnosis of pulmonary embolism, and high-resolution CT for the detection and characterization of diffuse lung diseases and the quantification of emphysema. Newly developed approaches to pulmonary functional imaging using CT and MRI have been applied to the evaluation of pulmonary ventilation and perfusion and to the detection of small airways disease. Volumetric CT imaging techniques together with advanced image processing have made possible "virtual bronchoscopy." Positron emission tomography provides an important new approach to the accurate detection and staging of chest malignancies and to the evaluation of pulmonary nodules. Finally, new digital imaging techniques, which are rapidly replacing conventional x-ray film, offer the possibility of computer-aided diagnosis.

Imaging evaluation of suspected pulmonary embolism

Venous thromboembolism (VTE) is a common disorder that is difficult to diagnose clinically but carries significant morbidity and mortality if untreated. Additionally, although demonstrated to be of benefit in cases of proven deep vein thrombosis (DVT) and pulmonary embolism (PE), anticoagulation therapy is not without risk. Because the clinical exam is known to be unreliable for the detection of both DVT and PE, many imaging modalities have been used in the diagnostic imaging algorithm for the detection of VTE, including chest radiography, ventilation/perfusion (V/Q) scintigraphy, pulmonary angiography, and recently, spiral computed tomography (CT) and magnetic resonance imaging (MRI). Chest radiographic findings in acute PE include focal oligemia, vascular enlargement, atelectasis, pleural effusions, and air space opacities representing pulmonary hemorrhage or infarction. The chest radiograph can occasionally be suggestive of PE but is more often nonspecifically abnormal. The main use of the chest radiograph in the evaluation of suspected PE is to exclude entities that may simulate PE and to assist in the interpretation of V/Q scintigraphy. Lower extremity venous compression ultrasonography (CU) is both sensitive and specific for the diagnosis of femoropopliteal DVT, and the value of negative CU results has been established in outcomes studies. However, the reliability of CU for the detection of isolated calf vein thrombosis is not well established, and the clinical significance of such thrombi is debatable. Additional methods such as color and spectral Doppler analysis are also useful in the diagnostic evaluation of DVT but are best considered as adjuncts to the conventional CU examination rather than as primary diagnostic modalities themselves. Compression ultrasonography and Doppler techniques are useful in the evaluation of suspected upper extremity DVT; spectral Doppler waveform analysis is particularly useful to assess for the patency of veins that cannot be directly visualized and compressed with conventional gray-scale sonography. V/Q scintigraphy has been the initial modality obtained in patients suspected of PE for a number of years. Although many studies have investigated the role of V/Q scintigraphy in the evaluation of VTE, the Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) study has provided the most useful information regarding the utility of V/Q scintigraphy in this setting. A high probability scan interpretation is sufficient justification to institute anticoagulation, and a normal perfusion scan effectively excludes the diagnosis of PE. A normal/near normal scan interpretation also carries a sufficiently low prevalence of angiographically proven PE to withhold anticoagulation. Although the prevalence of PE in the setting of low probability scan interpretations is low and several outcomes studies have demonstrated a benign course in untreated patients with low probability scan results, patients with inadequate cardiopulmonary reserve do not necessarily have good outcomes. Such patients deserve more aggressive evaluation. Patients with intermediate probability scan results have a 20% to 40% prevalence of angiographically proven PE and thus require further investigation. The radionuclide investigation of DVT includes such techniques as radionuclide venography and thrombus-avid scintigraphy. Although these methods have not been as thoroughly evaluated as CU, studies thus far have indicated encouraging results, and further investigations are warranted. Pulmonary angiography has been the gold standard for the diagnosis of PE for decades. Studies have indicated that angiography has probably been underutilized by referring physicians for the evaluation of suspected PE, likely because of the perception of significant morbidity and mortality associated with the procedure. (ABSTRACT TRUNCATED)

Pulmonary perfusion: respiratory-triggered three-dimensional MR imaging with arterial spin tagging--preliminary results in healthy volunteers

The authors used a spin-tagging method of magnetic resonance perfusion imaging to measure pulmonary perfusion in eight healthy volunteers with use of a respiratory-triggered three-dimensional pulse sequence. The average signal intensity (SI) decrease upon arterial labeling was 24%. The perfusion SI increased by 21% after exercise (P = .02). Focal blood flow abnormalities were observed in a patient with chronic obstructive pulmonary disease.

Diagnosis of pulmonary embolism with spiral computed tomography and magnetic resonance angiography

Radiologic imaging techniques such as contrast-enhanced spiral computed tomography (CT) and magnetic resonance (MR) angiography provide noninvasive means of diagnosing pulmonary thromboembolic disease. In addition, both techniques permit direct visualization of the embolus. Although imperfect, both CT and MR angiography in various circumstances fit diagnostic pathways for pulmonary embolism detection. Recent advances in both CT (multidetector ring spiral units and electron beam) and MR technology allow not only depiction of the pulmonary arteries, but also are capable of providing information about the lower extremity deep venous system in a single examination.

Rapid imaging of hyperpolarized gas using EPI

Rapid repetitive MRI of hyperpolarized (HP) gases using echo-planar imaging (EPI) has been theoretically investigated and experimentally demonstrated for (3)He in human lung. A quantitative treatment of signal attenuation and magnetization consumption for the unique circumstance of a rapidly diffusing nonrenewable magnetization source has been performed. Rapid (compared to the human respiratory cycle) and repetitive imaging of the lung gas space with EPI and a single delivered bolus of HP-(3)He is feasible using low flip angles, provided the voxels are not too small. A coarse-grid (32 x 64) EPI pulse sequence has been developed and implemented to image the lungs of healthy volunteers during rebreathing of a HP-(3)He/N(2) gas mixture. A set of three 10-mm axial slices was imaged every 0.12 sec for the 36 sec duration of rebreathing, yielding a real-time visualization of ventilation. Despite some mild artifacts, the images are of good quality and show changes in gas density related to respiratory physiology. Magn Reson Med 42:507-514, 1999.

Advanced imaging concepts: a pictorial glossary of CT and MRI technology

This article serves as an illustrative glossary of concepts related to computed tomography (CT) and magnetic resonance imaging (MRI) technology. The principles of tomography, digital processing, image resolution, CT windowing, CT gray levels, contrast enhancement, and MRI spin echo pulse sequences are reviewed. Techniques not commonly described for use in animal patients are also introduced, and include gradient echo, short time of inversion recovery, fluid attenuated inversion recovery and fat saturation pulse sequences, fast imaging, MRI angiography, perfusion and diffusion imaging, brain activation, CT angiography/functional CT, interventional procedures, and three-dimensional CT.

Perfusion imaging of the human lung using flow-sensitive alternating inversion recovery with an extra radiofrequency pulse (FAIRER)

Pulmonary perfusion is an important parameter in the evaluation of lung diseases such as pulmonary embolism. A noninvasive MR perfusion imaging technique of the lung is presented in which magnetically labeled blood water is used as an endogenous, freely diffusible tracer. The perfusion imaging technique is an arterial spin tagging method called Flow sensitive Alternating Inversion Recovery with an Extra Radiofrequency pulse (FAIRER). Seven healthy human volunteers were studied. High-resolution perfusion-weighted images with negligible artifacts were acquired within a single breathhold. Different patterns of signal enhancement were observed between the pulmonary vessels and parenchyma, which persists up to TI = 1400 ms. The T1s of blood and lung parenchyma were determined to be 1.46s and 1.35 s, respectively.

Demonstration of gravity-dependent lung perfusion with contrast-enhanced magnetic resonance imaging

Imaging of lung perfusion using contrast-enhanced dynamic magnetic resonance (MR) was performed in both the supine and prone positions in six volunteers. Regions of interest (ROIs) were chosen in the dependent and non-dependent portions of the right lung. The percentage increase in signal intensity (SI) and the mean slope were calculated. In the supine position, the dorsal ROI had a greater increase in SI (236.0% vs. 156.9%, P < 0.05) and a faster rise in the slope of enhancement (55.1%/sec vs. 30.1%/sec, P < 0.05) than the ventral ROI. After changing to the prone position, higher peak enhancement (234.3% vs. 177.4%, P < 0.05) and faster slopes (59.6%/sec vs. 35.3%/sec, P < 0.05) shifted to the anterior ROI. We conclude that dynamic contrast-enhanced MR imaging is sensitive to demonstrate gravitationally dependent differences in lung perfusion.

Quantitative 3D VUSE pulmonary MRA

The purposes of this study were to quantitatively evaluate a free-breathing three-dimensional (3D) variable angle uniform signal excitation (VUSE) magnetic resonance angiography (MRA) technique in normal volunteers, to demonstrate breathold 3D VUSE MRA in a normal volunteer, and to investigate the ability of the free-breathing 3D VUSE MRA technique to quantify differential flow in lung transplant patients. A free-breathing 3D VUSE MRA pulse sequence was run on the right lungs of 15 normal volunteers and both lungs of eight single or double lung transplant patients. A breathold scan was also used on one volunteer. No contrast agents were used. Normal lung MRA images were analyzed for maximum level of branching observed and minimum distance between distal vessels seen and the pleura. In patients, differential flow was determined with a program that counted the number of MRA pixels over a threshold signal level in each lung. These values were compared to radionuclide perfusion (Q) scan results. Average observed branching order in normal lung images was 5.9 +/- 0.7. Average distance between the most peripheral vessels seen and the pleura was 0.9 cm. Differential blood flow measured by pulmonary MRA was well correlated with that measured by Q scan (R2 = 0.84, p < 0.005). In addition to providing good visualization of normal pulmonary vessels, this technique was demonstrated to provide accurate estimates of differential blood flow in lung transplant patients free of serious lung scarring.

MR perfusion imaging of pulmonary parenchyma using pulsed arterial spin labeling techniques: FAIRER and FAIR

Magnetic resonance imaging of pulmonary parenchyma perfusion using pulsed arterial spin labeling (ASL) techniques is presented. ASL uses magnetically labeled water as an endogenous, freely diffusible tracer. Presented are comparative results of ASL methods called Flow sensitive Alternating Inversion Recovery (FAIR), and FAIR with an Extra Radiofrequency pulse (FAIRER). Six healthy human volunteers were imaged. Perfusion-weighted images at different time delays, TI, were calculated from the subtraction of the control and tag images, which were acquired within a single breathhold. Detailed pulmonary structures can be visualized with negligible cardiac or respiratory motion artifacts. Different patterns of signal enhancement between the pulmonary vessels and parenchyma are shown in the perfusion images acquired at different TIs.

Diagnosis of pulmonary embolism: comparison of CT angiography and MR angiography in canines

PURPOSE

To compare the sensitivity and specificity of helical computed tomographic angiography (CTA), CTA with multiplanar reconstructions (MPR)/three-dimensional-shaded surface display (3D-SSD), and gadolinium-enhanced magnetic resonance angiography (MRA) for pulmonary embolism (PE) detection.

MATERIALS AND METHODS

Gelatin sponge emboli were introduced into the femoral veins of seven dogs and conventional digital subtraction angiography (CA), CTA, and MRA performed. Images from CTA, CTA with MPR/3D-SSD, and MRA were reviewed for the presence of PE in lobar and segmental arteries, and subsegmental zones. Postmortem angiography and CA were the gold standard.

RESULTS

There were 50 emboli in the 294 vessels/zones analyzed. The sensitivity of CTA for the two readers was 76% (95% confidence interval [CI]; 64%-88%) and 64% (95% CI; 50%-78%), and for the two MRA readers was 52% (95% CI; 38%-66%) and 48% (95% CI; 34%-62%). CTA was more sensitive than MRA when PE were subdivided by vessel caliber. Specificity was high for CTA and MRA among all readers (98.8%-99.6%). MPR/3D-SSD did not improve results of axial CT. MRA perfusion defects were 46% and 47% sensitive and 100% specific. Interobserver agreement was high for CTA and MRA (kappa 0.92 and 0.93, respectively). The average diameter of vessels with emboli was 3.7 mm +/- 1.06.

CONCLUSION

Helical CTA is more sensitive than three-dimensional gadolinium-enhanced MRA for the detection of PE. Both CTA and MRA are highly specific for PE detection and demonstrate high interobserver agreement. MPR/3D-SSD did not increase CTA performance over axial images alone.