| Objective Multi-slice spiral CT pulmonary angiography (CTPA) has gradually become the primary method for diagnosis of pulmonary embolism because of non-invasive, fast speed and high spatial and temporal resolution. Howerer, its inherent weaknesses such as iodine-radiation damage, allergic reactions, kidney damage and cancer risk limited its application partly. Therefore, the purpose of our study was to assess the value of three dimensional (3D) contrast-enhanced (CE)magnetic resonance pulmonary angiography (MRPA) with liver acceleration volume acquisition (LAVA) in the detection of acute pulmonary embolism (PE).Material and MethodsInclusion criteriaThis prospective study was approved by the local ethics committee, and informed written consent was obtained from all patients. A total of 32 consecutive patients (21 males and 11 females,age range 30?74 years,mean age, 55 years) were included in this study. The patients were inpatients (from the emergency department, respiratory internal medicine department, cardiovascular medicine department, department of wound or thopedics and the chest surgery department). APE was suspected if there was a combination of clinical symptoms (e.g., chest pain, sudden shortness of breath,hydrothorax, hemoptysis and hydroncus in both lower limbs), and the D-dimer level was >500 ?ig/l on an ELISA-based test (VIDAS, BioMerieux, Lyon France).Exclusion criteriaThe exclusion criteria were the following: age (below 18 years old); reported contraindication to iodinated contrast material; pregnancy; right heart strain;contraindication for MRI, including claustrophobia, a metallic ocular implant or a pace maker; reported contraindication to iodinated or gadolinium-based contrast agents; a glomerular filtration rate under 30 ml min-1. 1.73 m-2; and the inability to breath hold over 13 seconds. A patient body mass index above 30 kg/m2 was added as exclusion criteria due to difficulties encountered in performing MRI with obese patients. Contraindications also included dependency on a continuous connection to an external electrical device or pump.Imaging methodThe imaging protocol of CT pulmonary angiography used in the study was the standard PE protocol. Axial section images were examined. All patients underwent CTPA on a 256-slice CT scanner (Brilliance CT scanner, Philips Health-care). All patients were placed in a supine position for scanning with their hands over their heads. The lungs were scanned from 2cm above the aorta to the dome of right diaphragm. The scanning parameters included a 128 x 0.625 mm collimation.0.625mm thickness, iDose 4 reconstruction, a tube voltage of 80 kV. a rotation time of 0.5 seconds, a field of view (FOV) of 350 × 350 mm, and a matrix of 512 × 512.Automated tube current modulation was used in all CT studies (CARE Dose 4D.Siemens). Contrast-enhanced CT was routinely performed for all subjects in the mode and was obtained after the injection of a bolus of 50 ml of Ultravist (370 mg I/ml.Bayer Schering Pharma, Berlin, Germany) followed by 50 ml of saline solution into an antecubital vein (left first) via a 20 gauge injector (CT Injector Mis-souri. Ulrich Medical) with injection rate 5.0 ml/sec. Using a bolus technique. a region of interest was placed into the superior vena cava, and image acquisition began after the region of interest reached the predefined threshold of 100 Hounsfield Units (HU). The scan took approximately 2.5 seconds.Three-dimensional contrast-enhanced MRPA: MRPA was performed within 4 hours of CTPA on a 3-T unit (Signa HDxt system, GE Healthcare, Chalfont St Giles, UK)without any delay in medical treatment. Before undergoing MRPA, the patients were carefully instructed on breath-holding and practiced the technique to produce precisely the same degree of inspiration for each scanning series. The patient was positioned in a supine position with their hands on their head. An ECG signal was continuously monitored during the -MR image acquisition. A specialized multichannel phased array surface coil (8 channels) was placed over the chest to receive the pulmonary MRI data. First, an unenhanced coronal MRPA was obtained with the LAVA sequence in the axial plane with the following parameters: TR 3.3 ms, TE 1.5 ms, flip angle 12°, matrix 288 × 224, FOV 350 × 350 mm, acceleration factor 0.72,bandwidth 83.3 kHz pixel-1, slice thick ness 4 mm, and overlap 2.0 mm. Optimal pul-monary arterial enhancement was determined using the bolus technique. An intravenous injection of 20 ml of gadobenate dimeglumine with the flow rate of 2.0 ml/sec. was performed during dynamic scans at the level of the pulmonary trunk. A region of interest as large as the pulmonary trunk was drawn and used to generate the enhancement curve. The time to peak enhancement was regarded as the optimal delay time for MRPA. Next, a dose of contrast of 0.1 mmol kg-1 body weight was injected using an automatic injector via a 24 gauge catheter powered by a MR injection system(Spectris Solaris EP. MR Injection System, Medrad, Germany) at a rate of 2.0 ml/sec.and followed by a saline flush of 20 ml at the same rate. A breath-hold 3D high-resolution MRPA in the axial plane and one in the coronal with LAVA sequence were then acquired using the same parameters as above. The scan time for the MRPA was less than 13 seconds.Imaging analysisAll of the data including the CTPA and MRPA data were transmitted to the picture archiving and communication system (PACS) AW4.3 (GE Medical Systems. USA).The data sets from the CT and MR examinations were anonymous and were evaluated in a standardized manner with individually adapted window settings. Both lung and soft-tissue windows were used to identify the pulmonary arteries and bronchi.Reformations on sagittal and coronal slices were performed to visualize the pulmonary emboli if necessary. The diagnosis of PE was made by the consensus of the two senior-attending radiologists who have 15 and 22 years of experience,respectively, in interpreting CTPA and MRPA images. The images were selected in random order. For statistical convenience, the pulmonary emboli were recorded as being present or absent in each of the following lung lobes: right upper lobe, right middle lobe, right lower lobe, left upper lobe, lingual area, and left lower lobe.Continuous filling defects that extended into branching vessels were regarded as single PEs at the location. Subsegmental emboli were not counted on either the CTPA or MRPA.Statistical analysesThe statistical analyses were performed using the SPSS version 16.0 software. The data was analyzed by chi-square. Using the CTPA as the reference standard. the diagnostic sensitivity, specificity, the positive predictive value (PPV) and the negative predictive value (NPV) of the MRPA for PE detection were calculated on per-patient and per-vascular zone bases at different pulmonary artery levels.Results All CTPA examinations were successfully completed without any observable adverse effects. Of the 32 patients with MRPA examinations. 3 patients were excluded from the final analysis for the following reasons: contrast agent leak-age in one patient and failure of breath-hold cooperation in two patients. A total of 29 patients were included in the final analysis, of which 23 patients (79%) were diagnosed with 63 pulmonary emboli on CTPA. Among these 23 patients. pulmonary emboli were observed in 3 of 46 main arteries, 22 of 138 lobar arteries. and 38 of 414 segmental arteries on CTPA. Of 63 total pulmonary emboli detected on CTPA, 59 pulmonary emboli in 22 patients were detected on the MRPA examinations. The results of the MRPA imaging interpretations categorized by vascular distribution and the statistics of the MRA detections of the pulmonary emboli on per-patient and per-vascular bases were summarized using CTPA as the reference standard. No false-positive results were identified on MRPA. The sensitivities. specificities. and negative predictive values of MRPA were 95.7%, 100%, and 85.7% on the per-patient basis, respectively, 100%, 100%, and 100% for the main PA. respectively, 95.4%,100%, and 99.3% for the lobar PA, respectively, and 86.8%, 100%, and 98.9% for the segmental PA, respectively. The positive predictive value was 100%. One lobar and five segmental emboli were missed on MRI.Conclusion Our preliminary work suggests that contrast-enhanced 3-T MRPA with the 3D LAVA technique provides high-resolution multidirectional images of pulmonary arteries. Moreover,this technique appears to be an effective MRI sequence for diagnosing PEs in the main, lobar, and segmental pulmonary arteries on a per-patient basis and provides a potential diagnostic alternative to CTPA that does not involve the risks associated with exposure to ionizing radiation or iodinated contrast material. |
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