CCMRI without a contrast agent has not been used widely for PFO diagnosis in clinical practice due to its insufficient spatial and temporal resolutions. Previous studies have focused on contrast-enhanced MRI to identify PFO at a high cost and risk of contrast agent allergy. Recent technical advances may have improved the imaging quality and diagnostic accuracy of CCMRI. This is the first study to evaluate the diagnostic value of 3.0T MRI without a contrast agent in detecting PFO.
Our study confirmed that CCMRI could effectively screen for suspected PFO in patients with cerebral disorders and was comparable to cTCD. When combined with pseudo-color coding, CCMRI holds great value for the evaluation and classification of PFO, including its shape, size, blood shunt, and complications such as IAS aneurysm and secondary septum thickening.
The cTCD test in our study found PFO in 88.6% of the patients. It was previously reported that the prevalence of PFO in patients younger than 55 years with cryptogenic stroke was approximately 55% . The difference in prevalence might be due to the examination flow in patients suspected of having PFO in clinical practice. Most patients with a negative cTCD result in this retrospective study were not selected to undergo a CMRI examination, which was associated with a higher prevalence of PFO.
cTEE is currently a widely accepted reference for PFO diagnosis; however, its major drawbacks are invasiveness and considerable dependence on the operator experience. Recent studies have confirmed that cTCD and cTTE, as non-invasive methods, showed a general concordance for PFO diagnosis and could be used for preliminary PFO detections . cTTE is cost-effective and readily available for PFO imaging but has relatively low sensitivity , while cTCD is a highly sensitive test and could quantify the severity of RLS. However, it cannot differentiate cardiac from pulmonary shunts or directly visualize the atrial septum . Hence, finding a non-invasive and intuitive modality for PFO diagnosis is crucial for clinical practice.
CMRI is a novel and reliable imaging modality that provides dynamic and objective information on cardiac anatomy. The cine sequence without contrast could be tolerated by most patients. Our study showed that CCMRI had a high sensitivity (94.9%) and concordance (90.9%) for PFO detection compared to cTCD. Two of our cases were found positive for PFO by cTCD, but negative by CCMRI, and were classified as Grade 1 in the cTCD test, indicating that CCMRI might fail in detecting small PFO. Moreover, we highlight that two of our patients were found positive by CCMRI but negative by cTCD, which could correspond to false-negative cases of cTCD. The cause could be an inadequate VM or a higher pressure in the left atrium than the right, resulting in no apparent flow inversion crossing the PFO from right to left.
Mohrs et al. reported that PFO was identified visually in all 15 patients using contrast-enhanced CMRI on a 1.5T scanner, and the sensitivity was 100% when compared with cTEE . In another study with a 1.5T MR system, RLS was detected by contrast-enhanced CMRI in 48 of 72 (66.6%) cases with moderate or severe shunts seen with cTEE, but only in 6 of 32 (18.8%) cases with mild shunts detected by cTEE . Similarly, Hamilton-Craig et al. found that contrast-enhanced CMRI on a 1.5T scanner had a sensitivity of 50%, a specificity of 100%, an NPV of 31%, and a PPV of 100% in detecting PFO when compared to cTEE . In comparison, our study showed that cine sequences without contrast on a 3.0T MR scanner presented an excellent diagnostic value in identifying PFO, indicating that the technical advances of the 3.0T MR scanner improved and optimized the application value of CMRI in PFO detection.
Our study had several limitations. First, the sample size was relatively small, and bias in patient selection in this retrospective study was unavoidable. Second, cTEE was not performed in our cohort. Hence, this study lacked the gold standard for PFO detection. A comparison between cTEE and CCMRI for identifying PFO deserves a prospective evaluation.
In conclusion, CCMRI and pseudo-color coding provided a novel and excellent method for PFO identification, evaluation, and classification in patients with cerebral disorders, with high sensitivity (92.85%) and concordance (90.9%) when compared to cTCD. Dynamic visualization, convenience, and noninvasiveness are important features that allow clinicians to perform a CMRI scan before other modalities when investigating the presence of PFO.