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PREFUL-MRI vs. V/Q SPECT/CT for Pulmonary Hypertension?

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Establishing an accurate CTEPH vs PAH diagnosis is fundamentally important for patient management. Specifically, Chronic Thromboembolic Pulmonary Hypertension (CTEPH) is often surgically curable through pulmonary endarterectomy, while Pulmonary Arterial Hypertension (PAH) relies on targeted medical therapies. Therefore, physicians rely heavily on diagnostic imaging to distinguish these conditions, making the performance of new, non-invasive techniques critically important for clinical practice.

The Challenge in CTEPH vs PAH Diagnosis

Ventilation/perfusion single-photon emission CT/CT (V/Q SPECT/CT) currently serves as the recommended screening tool for CTEPH, largely due to its high diagnostic accuracy. Historically, it consistently demonstrates segmental perfusion defects in CTEPH, which typically appear normal or show small, non-segmental defects in PAH patients. Conversely, Phase-Resolved Functional Lung MRI (PREFUL-MRI) offers a promising alternative because it uses no ionizing radiation or contrast agents. This non-invasive nature means that PREFUL-MRI could benefit radiation-sensitive patient populations, especially children and young adults who require serial monitoring.

Researchers recently conducted a study involving 53 pulmonary hypertension patients (27 with CTEPH, 26 with PAH) to compare PREFUL-MRI with V/Q SPECT/CT. The goal was to see if PREFUL-MRI could effectively differentiate the two conditions. Both patient groups exhibited multiple perfusion defects when assessed with PREFUL-MRI. However, the study found a significant difference in the diagnostic performance based on the type of assessment performed.

Comparing Visual and Quantitative Findings

Visual assessment of PREFUL-MRI maps yielded a poor outcome for identifying CTEPH, achieving only 70% sensitivity and 38% specificity. Consequently, this performance falls significantly short of the established standard, as V/Q SPECT/CT showed a high sensitivity of 95% and a specificity of 95% in the same cohort. However, the quantitative analysis revealed a different story. The researchers analyzed the perfusion defect percentage (QDP), a key quantitative PREFUL parameter. This parameter clearly separated the patient groups.

Specifically, patients with CTEPH demonstrated a substantially higher median perfusion defect percentage (QDP) compared to those with PAH (51.9% versus 24.4%, p < 0.001). Furthermore, the mean perfusion was significantly lower in the CTEPH group. The PREFUL-derived QDP parameter also showed a notable correlation with mean pulmonary arterial pressure and pulmonary vascular resistance, which are crucial hemodynamic measures obtained via right-heart catheterization. Conversely, the study found no significant difference in ventilation distribution between the PAH and CTEPH groups.

Clinical Takeaways for Lung Perfusion MRI

In summary, the study confirms that while visual interpretation of PREFUL-MRI for CTEPH screening is inferior to V/Q SPECT/CT, the quantitative parameters from the MRI technique offer a strong differentiating ability between CTEPH and PAH. Quantitative PREFUL-MRI parameters, such as the perfusion defect percentage (QDP), directly reflect the different pathophysiologies of the two conditions—large vessel obstruction in CTEPH versus microvascular disease in PAH. Therefore, clinicians can incorporate these specific quantitative metrics into their diagnostic algorithm to distinguish between these two PH subgroups.

Frequently Asked Questions

Q1: What is the main clinical significance of differentiating CTEPH from PAH?

A: Differentiating CTEPH from PAH is clinically significant because their treatment strategies differ fundamentally. CTEPH may be curable with surgery (pulmonary endarterectomy), whereas PAH is primarily managed with targeted vasoactive medications.

Q2: Why is V/Q SPECT/CT considered the current screening standard for CTEPH?

A: V/Q SPECT/CT is the standard because it effectively detects the mismatched segmental perfusion defects characteristic of CTEPH with high sensitivity and specificity. Conversely, a patient with PAH typically has either a normal V/Q scan or non-segmental, peripheral perfusion defects.

Q3: Does PREFUL-MRI replace V/Q SPECT/CT for CTEPH screening?

A: Based on the visual assessment in this study, PREFUL-MRI does not yet replace V/Q SPECT/CT due to lower sensitivity and specificity. However, the study confirms that quantitative PREFUL-MRI parameters like the perfusion defect percentage (QDP) offer a powerful, non-invasive tool to help differentiate CTEPH from PAH, especially in monitoring settings.

References

  1. Liu A et al. What is the difference between pulmonary arterial hypertension and chronic thromboembolic pulmonary hypertension on phase-resolved functional lung MRI? A cross-sectional observational study. Eur Radiol. 2026 Jan 13. doi: 10.1007/s00330-025-12271-z. PMID: 41528476.
  2. Phase-resolved functional lung MRI (PREFUL) magnetic resonance imaging (MRI) is an alternative technique for evaluating regional ventilation and perfusion without the use of ionizing radiation or contrast media. ResearchGate.
  3. Chronic thromboembolic pulmonary hypertension: a distinct disease entity. European Respiratory Society.
  4. Comparison of MRI and VQ-SPECT as a Screening Test for Patients With Suspected CTEPH: CHANGE-MRI Study Design and Rationale. Frontiers in Cardiovascular Medicine.