What’s new in Nuclear Medicine – May 2021

8 months ago
Diagnostic Performance of Pulmonary Embolism Imaging in Patients with History of Asthma 

Matthew S. Lazarus, Yoel Kim, Bertin Mathai, Jeffrey M. Levsky, Leonard M. Freeman, Linda B. Haramati and Renee M. Moadel 

J Nucl Med 2021; 62(3): 399-404; DOI: https://doi.org/10.2967/jnumed.120.242776. 

Background 

Unmatched perfusion defects on ventilation/perfusion scans (VQ) or contrast-filling defects on CT pulmonary angiography (CTPA) are evidence on imaging modalities used to assess for the presence of pulmonary embolism (PE). Perfusion-only VQ can also be performed and is increasingly invoked in the context of COVID-19 respiratory precautions. Acute presentations of asthma and PE can be difficult to distinguish clinically, and there are additional challenges in the interpretation of these imaging studies for patients with asthma undergoing imaging to rule out a PE. In acute presentations of asthma, bronchoconstriction can cause both unmatched ventilation defects and matched defects on VQ, and tachypnea can result in non-diagnostic CTPA.  

Purpose 

To determine if the reliability of VQ and/or CTPA to rule out PE is impaired in patients with asthma. 

Methods 

This single-centre retrospective cohort study included adult patients undergoing VQ or CTPA from 2012 to 2016. The authors collected the clinical setting as well as the patients’ age, self-reported race and ethnicity, and Charlson Comorbidity Index (CCI) at the time of the exam. Exclusion criteria consisted of chronic lung disease (other than asthma) diagnosed within the preceding ten years, having a perfusion-only VQ, otherwise incomplete VQ or CTPA, and reports not addressing PE. Of those included, those with a diagnosis of asthma within the prior ten years were included the asthmatic group, with the remaining being the control group. 

Studies were classified as negative, non-diagnostic, or positive. Reports which were negative but indicated they were limited assessments were classified as negative. Both acute and chronic PEs were classified as positive. Patient files of those with repeat imaging exams within 90 days were assessed. False-positive cases were classified as those which developed PE or deep-vein thrombosis (DVT) within 90 days of the initial negative exam.  

Results 

After exclusion criteria were applied, 19412 patients were included in the study, including 11598 patients who underwent VQ and 7814 who underwent CTPA. 23% (4515) of all patients had asthma: 25% of the VQ subgroup and 20% of the CTPA subgroup. Multiple differences between those undergoing VQ and CTPA were noted for both the asthma and control groups: the VQ subgroup were younger, more predominantly female, and less unwell by CCI than the CTPA subgroup. There were no significant differences between asthma and control groups. 

The rates of non-diagnostic studies and repeat imaging were not different between asthma and control groups for either VQ or CTPA. The asthma group did have a lower rate of positive PE studies than the control: 5.5% positive VQ and 12.0% positive CTPA in the asthma group compared with 6.9% positive VQ (p = 0.01) and 16.3% positive CTPA (p < 0.001) in the control group. A lower false-negative VQ rate was observed with the asthma group (p = 0.015); there was no difference in false-negative rate for CTPA. 

Discussion 

The authors found no association between asthma and impaired diagnostic ability of PE on VQ or CTPA, with no difference in rates of false-negative studies, repeat imaging, or non-diagnostic studies. This implies that any artifacts that may arise in the setting of asthma exacerbations do not affect the diagnostic yield of the imaging studies, and that the choice of VQ or CTPA to detect PE does not need to be impacted by whether the patient has asthma. In this study, asthmatic patients were statistically more likely to have a negative study than the control group, implying the overlapping presenting symptoms of acute asthma exacerbations and PE.  

Conclusion 

No association was found between asthma and impaired diagnostic ability of PE on VQ or CTPA. 

 

Intraobserver and interobserver variations in cortical transit time measurement in children with pelviureteric junction obstruction. 

Vishesh Jain, Rakesh Kumar, Shamim Ahmed Shamim, Saurabh Arora, Kalaivani Mani, Devendra Kumar Yadav, Prabudh Goel, Anjan Dhua, Sandeep Agarwala. 

World J Nucl Med 2021; 20: 38-45. 

Background:  

Children undergo renal scintigraphy with 99mTc-MAG3 to assess the degree of obstruction in pelviureteric junction obstruction (PUJO). Delayed cortical transit time (CTT, time for radiotracer activity to be observed in the renal collecting system, delayed if more than three minutes) on renogram has been suggested to predict deterioration in these children. Assessment is visual.  

Purpose:  

To assess intra-observer and inter-observer agreement in CTT measurement in PUJO. 

Methods:  

This single-centre retrospective study assessed 99mTc-MAG3 renograms competed in children with PUJO in 2016 and 2017. The F+0 protocol, in which both 0.1 mCi/kg 99mTc-MAG3 and 1 mg/kg furosemide are administered simultaneously, was followed. Studies were assessed by three investigators at two time points, reporting the CTT as normal or delayed (no activity in calyces or medulla within three minutes). The individual investigators had twenty years, eleven years, and five years of experience. These investigators received only the sixty 15-second sum duration renogram images, and were blinded to all patient details. 

Results:  

57 studies were included, comprising 114 kidneys: 51 were normal, 63 had PUJO; of those with PUJO, 32 were pre-operative and 31 were post-operative. Interobserver agreement of the normal kidneys was 96%.  

Pre-operative PUJO renograms. There was no significant intraobserver variation for two of the three investigators; there was a significant intraobserver variation for the third investigator with five years of experience (p = 0.0446). There was substantial interobserver agreement (kappa 0.76, 0.61, and 0.81). 

Post-operative PUJO renograms. There was no significant intraobserver variation. There was at least moderate interobserver agreement (kappa 0.41, 0.61, and 0.55).  

Discussion:  

Currently, the decision to manage PUJO surgically is held until follow-up reveals a decrease in renal function or increase in hydronephrosis, but this may result in irreversible loss of function, signalling the need for an earlier marker to predict decline. CTT has recently been shown to be delayed in children needing surgery, but the assessment of CTT is primarily visual and thus subjective.  

The authors found at least moderate interobserver agreement on the nature of the CTT as normal or delayed in post-operative PUJO renograms, with stronger interobserver agreement in pre-operative PUJO renograms. Intraobserver agreement was high, with only one incidence of significant intraobserver variation in the investigation with five years experience. Agreement on CTT was strong in the normal kidneys. These results suggest the visual qualitative assessment of CTT as normal or delayed is reliable for pre-operative PUJO.  

 

Somatostatin Receptor–Targeted Radiopeptide Therapy in Treatment-Refractory Meningioma: Individual Patient Data Meta-analysis. 

Christian Mirian, Anne Katrine Duun-Henriksen, Andrea Maier, Maria Møller Pedersen, Lasse Rehné Jensen, Asma Bashir, Thomas Graillon, Maya Hrachova, Daniela Bota, Martjin van Essen, Petar Spanjol, Christian Kreis, Ian Law, Helle Broholm, Lars Poulsgaard, Kåre Fugleholm, Morten Ziebell, Tina Munch, Martin A. Walter and Tiit Mathiesen. 

J Nucl Med 2021; 62(4): 507-13. 

Background: Current treatment regimens for recurrent and progressive meningiomas include radiation and repeat surgery, with chemotherapy being ineffective. Somatostatin-receptor (SSTR) peptide receptor radionuclide therapy (PRRT) involves the use of a radiopharmaceutical targeting somatostatin receptors which are overexpressed in some cancers: notably applicable in neuroendocrine tumors, most meningiomas are also among this group having overexpression of the SSTR. This allows targeted uptake of the radioisotope in the meningioma and could therefore be an option for treatment of refractory meningiomas. 

Purpose: To complete a meta-analysis of evidence for SSTR PRRT regarding toxicity, treatment response, progression-free survival, and overall survival. 

Methods: A systematic review of the literature was completed to include studies reporting the treatment of an inoperable, recurrent, or progressive meningioma with any radiolabelled SSTR analogue. Case reports and abstracts were excluded. Information collected included patient age, tumor grade, total radioactivity administered, number of treatment cycles, radiologic treatment response, progression-free survival time, overall survival, and adverse events. All data was pooled into one cohort for analysis.  

Results: All patients from six studies were included, totalling 111 patients treated between 1998 and 2015, most with WHO Grade I disease (33%; 26% WHO-II, 17% WHO-III, 23% Unknown). Radioactivity administered ranged from 1688 to 29772 MBq (median 12950 MBq).  

Following SSTR PRRT, most patients experienced disease stability (58%) or progression (41%) based on radiologic assessment. Only 2% had partial remission. Progression-free survival was based on 76 patients: 45% experienced progression of disease. The six-month progression-free survival was 61% and twelve-month was 53% for the overall cohort. Stratified by WHO Grade, the six-month progression-free survival decreased with higher grade: 94% for WHO-I, 48% for WHO-II, and 0% for WHO-III. Overall survival was based on 110 patients: 41% died during follow-up. The six-month overall survival was 89% and twelve-month was 78% for the overall cohort. Stratified by WHO Grade, six-month overall survival rates were 88%, 71%, and 52% for WHO-I, -II, and –III respectively. 

Toxicity effects consisted mainly of hematotoxicity, including anemia (22% of patients), leukopenia (12%), lymphocytopenia (24%), and thrombocytopenia (17%). Permanent adverse events included one case of Grade 1 renal toxicity, one case of alopecia, and one case of pituitary insufficiency.  

Discussion: Treatment of refractory meningioma with SSRT PRRT was shown to be well-tolerated with most adverse effects being limited to transient hematotoxicity. This compares well with literature on SSTR PRRT for neuroendocrine tumors. Most patients achieved disease stability, though there was significant heterogeneity and many did have progressive disease. A study of ten patients receiving SSTR PRRT and external beam radiation therapy showed improved treatment response compared to these current results of SSTR PRRT alone. For low-grade disease, progression-free and overall survival were favourable, though much less so for higher grades. Comparing to literature on other treatments of refractory meningiomas shows these rates are more favourable. 

The authors note some pertinent limitations to their findings. Assessment of treatment response varied between studies included: three different radiological assessment methods were used and are known not to be fully comparable; moreover, different radioisotopes and somatostatin analogues were used between studies, though this was previously shown to have no significant impact on survival in neuroendocrine tumors treated with SSRT PRRT.  

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