Elizabeth Bailey

SPECT/CT imaging using a spiral CT scanner for anatomical localization: Impact on diagnostic accuracy and reporter confidence in clinical practice.

Purpose To evaluate the incremental benefit in routine clinical practice of computed tomography (CT) scans acquired for anatomical localization on an integrated SPECT/CT which incorporates a spiral CT scanner, in comparison with conventional planar and SPECT scanning. Methods The first 50 studies acquired on the integrated system were evaluated by two experienced nuclear medicine physicians who were aware of the patients clinical history. These included bone scans, gallium scans, octreotide scans, sestamibi parathyroid scans and MIBG scans. For each patient study, abnormalities were assessed on planar and SPECT images for location and provisional diagnosis and a quantitative scale was used to assess reporter confidence. The fused SPECT/CT images were then reviewed and the location and provisional diagnosis noted and reporter confidence was assessed using the same quantitative scale. Results There were 129 abnormalities detected in 50 patient studies. For localization of abnormalities, the inclusion of the CT resulted in a minor change in 16% of cases and a significant change in 11% over planar/SPECT imaging alone. The confidence of localization was improved moderately in 19% and improved significantly in 6%. For diagnosis, SPECT/CT resulted in a minor change in 10% and a significant change in 9% over planar/SPECT imaging. The confidence of diagnosis was improved moderately in 10% and improved significantly in a further 10% of cases. For the final scan interpretation, there would have been no change in 44% patients, a minor change in 30% and a significant change in 26% with the use of SPECT/CT. Conclusion Use of integrated SPECT/CT with a high spatial resolution, spiral CT used for anatomical localization improves accuracy and reporter confidence in clinical practice. As a result, final reports were different in 56% of the cases, including being significantly different in 26% patients compared to reporting with planar/SPECT alone.

SPECT/CT in V/Q scanning.

Combining the functional data provided by single-photon emission computed tomography (SPECT) with the anatomical information provided by CT has been shown to improve overall diagnostic accuracy in many areas of nuclear medicine. Although planar lung scans have often relied on correlation with a chest x-ray to help optimize scan interpretation, the advent of 3D lung imaging with SPECT provides the opportunity to combine lung perfusion data with CT images. This can be done by performing the study on a hybrid SPECT/CT scanner, with the CT acquisition typically performed with the use of low-dose parameters, rather than full diagnostic quality settings, or by software fusion with a fully diagnostic CT or a contrast-enhanced CT pulmonary angiogram. Such an approach has been shown to improve specificity and overall accuracy of ventilation/perfusion scintigraphy as well as facilitating more accurate clot localization. With the increased availability of hybrid SPECT/CT scanners, such an approach can be implemented in most imaging departments with little additional acquisition time or radiation dose. Misregistration caused by respiratory motion can impact combined studies, although this can be minimized with attention to patient breathing patterns during image acquisition. For patients with lung cancer, ventilation/perfusion SPECT/CT may have a role in allowing the optimal selection of radiotherapy fields and can improve the preoperative quantification of lung function before resection.

Airway closure on imaging relates to airway hyperresponsiveness and peripheral airway disease in asthma

The regional pattern and extent of airway closure measured by three-dimensional ventilation imaging may relate to airway hyperresponsiveness (AHR) and peripheral airways disease in asthmatic subjects. We hypothesized that asthmatic airways are predisposed to closure during bronchoconstriction in the presence of ventilation heterogeneity and AHR. Fourteen asthmatic subjects (6 women) underwent combined ventilation single photon emission computed tomography/computed tomography scans before and after methacholine challenge. Regional airway closure was determined by complete loss of ventilation following methacholine challenge. Peripheral airway disease was measured by multiple-breath nitrogen washout from which S(cond) (index of peripheral conductive airway abnormality) was derived. Relationships between airway closure and lung function were examined by multiple-linear regression. Forced expiratory volume in 1 s was 87.5 ± 15.8% predicted, and seven subjects had AHR. Methacholine challenge decreased forced expiratory volume in 1 s by 23 ± 5% and increased nonventilated volume from 16 ± 4 to 29 ± 13% of computed tomography lung volume. The increase in airway closure measured by nonventilated volume correlated independently with both S(cond) (partial R(2) = 0.22) and with AHR (partial R(2) = 0.38). The extent of airway closure induced by methacholine inhalation in asthmatic subjects is greater with increasing peripheral airways disease, as measured by ventilation heterogeneity, and with worse AHR.

A clinical comparison between traditional planar V/q images and planar images generated from Spect V/q scintigraphy

PurposeTo compare interpretation of traditional planar ventilation–perfusion lung scan images with planar images reformatted from single photon emission computed tomography (SPECT) data using two different techniques. MethodsPlanar and SPECT ventilation–perfusion (V/Q) data were acquired from 50 patients referred with suspected pulmonary embolism. In addition to traditional six-view planar images, six-view planar images were also generated from SPECT data using two methodologies: an angular summing technique (angular summed planar images) and a forward projection technique (reprojected planar images). Three experienced nuclear medicine clinicians reviewed the images in a blinded, randomized fashion. Results were analysed by comparing the two reprojected techniques with the traditional true planar scans, examining for differences in the defects seen (number, type and confidence), and the impact on final clinical interpretation. ResultsCompared with true planar scintigraphy, angular summed images demonstrated fewer mismatched defects (P<0.0001), while the reprojected planar images had more matched defects (P=0.013). In addition, there was a significant change in the clinical interpretation of the angular summed planar images resulting in clinicians perceiving a decreased likelihood of pulmonary embolism (P<0.016). No such difference in interpretation was observed for the reprojected planar images. ConclusionsAngular summed planar images result in a perceived decreased likelihood of pulmonary embolism compared with true planar images. In contrast, while reprojected planar images result in an increased number of matched defects compared to true planar scans, there was no change in the clinical interpretation. Caution should be exercised when interpreting SPECT derived angular summed planar images in isolation.

Diagnosis of upper limb lymphedema: development of an evidence-based approach

Abstract Background: The diagnosis of secondary upper limb lymphedema (LE) is complicated by the lack of an agreed-upon measurement tool and diagnostic threshold. The aim of this study was to determine which of the many commonly used and normatively determined clinical diagnostic thresholds has the best diagnostic accuracy of secondary upper limb LE, when compared to diagnosis by an appropriate reference standard, lymphoscintigraphy. Material and methods: The arms of women treated for breast cancer with and without a previous diagnosis of LE, as well as healthy controls, were assessed using lymphoscintigraphy, bioimpedance spectroscopy (BIS) and perometry. Dermal backflow score determined from lymphoscintigraphy imaging assessment (reference standard) was compared with diagnosis by both commonly used and normatively determined diagnostic thresholds for volume and circumference measurements as well as BIS. Results: For those with established dermal backflow, all commonly used and normatively determined diagnostic thresholds accurately identified presence of LE compared with lymphoscintigraphy diagnosis. In participants with mild to moderate changes in dermal backflow, only a normatively determined diagnostic threshold, set at two standard deviations above the norm, for arm circumference and full arm BIS were found to have both high sensitivity (81% and 76%, respectively) and specificity (96% and 93%, respectively). For this group, strong, and clinically useful, positive (23 and 10, respectively) and negative likelihood (0.2 and 0.3) ratios were found for both the circumference and bioimpedance diagnostic thresholds. Conclusion: For the first time, evidence-based clinical diagnostic thresholds have been established for secondary LE. With mild LE, normatively determined circumference and BIS thresholds are superior to the commonly used thresholds.

Generation of planar images from lung ventilation/perfusion SPECT

ObjectiveTo develop a method of producing lung ventilation and perfusion (V/Q) planar images using forward projection of reconstructed single-photon emission computed tomography (SPECT) images through approximate attenuation (µ) maps generated from the lung emission scans alone, as transmission-based µ maps may not be routinely available.MethodsSynthetic µ maps are derived from 99mTc photopeak and “scatter” windows for the attenuation correction of the SPECT images. The attenuation-corrected SPECT images are forward projected at appropriate angles to give the equivalent of planar images. This method allows high-count planar images, as well as the SPECT images, to be produced from a single SPECT acquisition. In addition, isolated “single lung” views of lateral and medial projections without “shine-through” from the contra-lateral lung, which have not been available previously, can be formed.ResultsComparison of reprojected images produced from CT-derived or synthetic µ maps displayed similar detail and radiopharmaceutical distribution. In a blinded comparison of “true” planar images with those from reprojecting the SPECT data using the synthetic µ maps, no difference in mismatched defect detection was found, and hence it was confirmed that the reprojected planar images could replace true planar images with no loss in planar diagnostic sensitivity.ConclusionsThe reprojected planar images provide high-count, high-quality images, which are comparable with conventional 2D images.

Objective analysis of whole lung and lobar ventilation/ perfusion relationships in pulmonary embolism

Purpose:  Lung scintigraphy using single photon emission computed tomography (SPECT) allows accurate regional measurement of the ventilation/perfusion () relationship. Objective analysis has been shown to be useful in the diagnosis of pulmonary embolism (PE). By using anatomical information provided by co‐registered computed tomography, we describe methodology for determining the extent of heterogeneity at a lobar level. We investigate this methodology using simulated data, and demonstrate its potential application in the clinical setting of PE.

Measurement of preoperative lobar lung function with computed tomography ventilation imaging: progress towards rapid stratification of lung cancer lobectomy patients with abnormal lung function

OBJECTIVES In lung cancer preoperative evaluation, functional lung imaging is commonly used to assess lobar function. Computed tomography ventilation (CT-V) imaging is an emerging lung function imaging modality. We compared CT-V imaging assessment of lobar function and its prediction of postoperative lung function to that achieved by (i) positron emission tomography ventilation (PET-V) imaging and (ii) the standard anatomical segment counting (ASC) method. We hypothesized (i) that CT-V and PET-V have similar relative lobar function and (ii) that functional imaging and anatomic assessment (ASC) yield different predicted postoperative (ppo) lung function and therefore could change clinical management. METHODS In this proof-of-concept study, 11 patients were subjected to pulmonary function tests, CT-V and PET-V imaging. The Bland-Altman plot, Pearsons correlation and linear regression analysis were used to assess the agreement between the CT-V-, PET-V- and ASC-based quantification of lobar function and in the ppo lung function. RESULTS CT-V and PET-V imaging demonstrated strong correlations in quantifying relative lobar function (r = 0.96; P < 0.001). A Wilcoxon-signed rank test showed no significant difference in the lobar function estimates between the two imaging modalities (P = 0.83). The Bland-Altman plot also showed no significant differences. The correlation between ASC-based lobar function estimates with ventilation imaging was low, r < 0.45; however, the predictions of postoperative lung function correlated strongly between all three methods. CONCLUSIONS The assessment of lobar function from CT-V imaging correlated strongly with PET-V imaging, but had low correlations with ASC. CT-V imaging may be a useful alternative method in preoperative evaluation for lung cancer patients.

Pulmonary hypertension leads to a loss of gravity dependent redistribution of regional lung perfusion: a SPECT/CT study

Objective Pre-capillary pulmonary hypertension (PHT) is characterised by progressive pulmonary vascular obliteration and loss of vascular reserves. In health, regional lung perfusion redistributes under the influence of gravity due to the presence of recruitable vessels. We investigated a combined single photon emission computed tomography/CT (SPECT/CT) method for assessing the pulmonary circulation by quantifying the gravity dependent redistribution of lung perfusion. Design Characterisation of patients versus healthy controls. Patients 15 patients with pre-capillary PHT and 11 healthy controls. Setting University hospital clinic. Intervention Regional lung perfusion was measured using SPECT/CT in two different postures (supine vs upright). A perfusion redistribution index (PRI) was used to quantify the cranial–caudal shift in regional lung perfusion resulting from gravitational (postural) change. Main outcome measure PRI was compared between cases and controls, and correlated with markers of disease severity in cases. Results Patients with pre-capillary PHT had notably reduced PRI compared to controls (0.02±0.06 vs 0.28±0.15 normalised perfusion/cm, p<0.0001). PRI was significantly associated with prognostic parameters such as 6 min walk distance (r=0.60, p=0.018), functional class (p=0.008), and tricuspid annular plane systolic excursion (r=0.58, p=0.022). The receiver operating characteristic curve showed that PRI differentiated patients with pre-capillary PHT from controls with AUC=0.94 (p<0.001). Conclusions With SPECT/CT, gravity dependent redistribution of lung perfusion can be quantified using the PRI derived from supine and upright perfusion analysis. The potential utility of PRI for the non-invasive detection of PHT and assessment of disease severity warrants further study.

In vivo validation of quantitative SPECT in the heart

Background: We have previously developed and validated a method to achieve quantitative SPECT data based on CT‐derived corrections, for the radionuclide 99mTc in phantoms and in man for lung scanning. This clinical study was performed to investigate the accuracy of this method when applied to cardiac blood pool imaging. The study involves tagging the radionuclide 99mTc to erythrocytes in a sample of the subject’s blood before it is re‐injected. After a short time, the radiolabelled cells achieve an equilibrium concentration in the blood pool, such that SPECT imaging allows the radioactivity concentration of blood present in the left ventricle to be measured. Methods and results: Absolute concentration of radioactivity inside the left ventricle of the heart was compared to true concentrations measured directly from a peripheral venous blood sample taken from the subject at the time of scanning. In 12 subjects, the average difference between the measured and true concentrations was found to be within ∼1% of the true value with a range of (−6 to +5)%. Conclusions: This study demonstrates the accuracy of CT‐based quantitative SPECT in clinical cardiac blood pool imaging, and we anticipate that similar accuracy could be achieved in the myocardium.