Acute Pulmonary Embolism Detected by Perfusion SPECT/CT Masquerading as an Intermediate Probability Planar V/Q Scan

To PE or Not to PE: Perfusion SPECT/CT Avoids Overdiagnosis

ABSTRACT

A 41-year-old woman with metastatic breast cancer presented with dyspnea, hypoxia, and elevated d -dimer. Perfusion planar imaging followed by SPECT/CT of the chest was performed due to the patient's iodinated contrast allergy. Planar images showed multiple pleural-based wedge-shaped defects concerning for bilateral pulmonary embolism (PE). Perfusion SPECT/CT of the chest confirmed multiple areas of perfusion defects but was considered negative for PE and attributed the perfusion defects to the compressing of pulmonary vasculature from metastatic lymph nodes and pulmonary masses. Given the high pretest probability of PE, a CT pulmonary angiogram was performed after premedication for contrast allergy confirming absence of PE.

Safe practice ventilation technique in lung scanning for pulmonary embolism

Ventilation/Perfusion scanning for suspected pulmonary embolism is undergoing a renaissance due to the advent of single-photon emission computed tomography (SPECT). The scan protocol demands the inhalation of a radioactive gas or vapour for the ventilation scan. The purpose of this article is to report the radioactive environmental contamination that can occur when Tc Technegas vapours are administered to patients for the ventilation SPECT scan. This contamination can concentrate within gamma camera heads to degrade images and is also a radiation hazard to staff. A method for sequestrating this airborne contamination was investigated using an ultra-low particulate air filter. The prevalence of radioactive contamination and the levels of contamination captured were quantified and only 36% of patients were found to have undergone the ventilation procedure without producing significant airborne contamination. Advice is given on best practice that will minimize airborne contamination and minimize the risks to staff working in the Nuclear Medicine department. The use of an extraction/filtration device may be seen as an effective additional control measure against airborne radioactive contamination for health professionals.

Software-Based Hybrid Perfusion SPECT/CT Provides Diagnostic Accuracy When Other Pulmonary Embolism Imaging Is Indeterminate

PURPOSE

To investigate the diagnostic performance of perfusion single-photon emission computed tomography/computed tomography (Q-SPECT/CT) in patients suspected to have pulmonary embolism (PE) but with indeterminate computed tomographic pulmonary angiography (CTPA) or planar ventilation/perfusion (V/Q) scans.

METHODS

This retrospective study included two groups of patients. Group I consisted of 49 patients with nondiagnostic CTPA. These 49 patients underwent subsequent V/Q scans. Further Q-SPECTs were obtained in patients with indeterminate planar images and fused with existing CTPA. Group II consisted of 182 non-CTPA patients with indeterminate V/Q scans. These 182 patients underwent further Q-SPECT and separate noncontrast low-dose CT chest. Fusion Q-SPECT/CT scans were obtained through FDA-approved software and interpreted according to published criteria as positive, negative, or indeterminate for PE. Upon retrospective analyses, the final diagnosis was made using composite reference standards including all available clinical and imaging information for at least 6-month follow-up.

RESULTS

In group I patients, 1 was positive, 24 were negative, and another 24 (49 %, 24/49) were indeterminate. In the subsequent 24 Q-SPECT/CTPAs, 4 were positive, 19 were negative, and 1 was indeterminate (4.2 %, 1/24). In group II patients, 9 (4.9 %, 9/182) were indeterminate, 33 were positive, and 140 were negative. The combined nondiagnostic rate for Q-SPECT/CT was only 4.9 % (10/206). There was six false-negative and one false-positive Q-SPECT/CT examinations. The sensitivity, specificity, and positive and negative predictive value of Q-SPECT/CT were 85.7 % (36/42), 99.4 % (153/154), 97.3 % (36/37) and 96.2 % (153/159), respectively.

CONCLUSIONS

Q-SPECT/CT improves the diagnostic rate with promising accuracy in diagnosing PE that yields a satisfactory clinical verdict, especially when the CTPA and planar V/Q scan are indeterminate.

Noncontrast perfusion single-photon emission CT/CT scanning: a new test for the expedited, high-accuracy diagnosis of acute pulmonary embolism

BACKGROUND

Standard ventilation and perfusion (V˙/Q˙) scintigraphy uses planar images for the diagnosis of pulmonary embolism (PE). To evaluate whether tomographic imaging improves the diagnostic accuracy of the procedure, we compared noncontrast perfusion single-photon emission CT (Q˙-SPECT)/CT scans with planar V˙/Q˙scans in patients at high risk for PE.

METHODS

Between 2006 and 2010, most patients referred for diagnosis of PE underwent both Q˙-SPECT/CT scan and planar V˙/Q˙scintigraphy. All scans were reviewed retrospectively by four observers; planar scans were read with modified Prospective Investigation of Pulmonary Embolism Diagnosis (PIOPED) II and Prospective Investigative Study of Pulmonary Embolism Diagnosis (PISA-PED) criteria. On Q˙-SPECT/CT scan, any wedge-shaped peripheral perfusion defect occupying > 50% of a segment without corresponding pulmonary parenchymal or pleural disease was considered to show PE. The final diagnosis was established with a composite reference standard that included ECG, ultrasound of lower-extremity veins, D-dimer levels, CT pulmonary angiography (when available), and clinical follow-up for at least 3 months.

RESULTS

One hundred six patients with cancer and mean Wells score of 4.4 had sufficient follow-up; 22 patients were given a final diagnosis of PE, and 84 patients were given a final diagnosis of no PE. According to PIOPED II, 13 studies were graded as intermediate probability. Sensitivity and specificity for PE were 50% and 98%, respectively, based on PIOPED II criteria; 86% and 93%, respectively, based on PISA-PED criteria; and 91% and 94%, respectively, based on Q˙-SPECT/CT scan. Seventy-six patients had additional relevant findings on the CT image of the Q˙-SPECT/CT scan.

CONCLUSIONS

Noncontrast Q˙-SPECT/CT imaging has a higher accuracy than planar V˙/Q˙imaging based on PIOPED II criteria in patients with cancer and a high risk for PE.