Lung ventilation/perfusion SPECT for diagnosing pulmonary embolism. Is the required minimal P/V count rate ratio fulfilled in routine situation? Results from a multicentre survey.

UNLABELLED: V/P-SPECT is a sensitive and specific procedure for the detection or exclusion of pulmonary embolism. It is important to conform to the guidelines in order to obtain reliable results. The sequence usually starts with the ventilation, followed by the perfusion scan. According to the current guidelines the count rate of the second study should be at least 3 times that of the first study. It is not always easy to meet this requirement, particularly since the deposed quantity of ventilation activity is not well known. The aim was therefore to analyse data from a multicentre survey to determine whether this essential precondition was strictly met. METHODS: In a multicentre survey 48 tertiary hospitals were asked to submit projections of all V/P-SPECT studies performed in January 2014. In total, 286 complete data sets from 16 institutions could be evaluated. First, the count rates of the first projections from the V-studies were subtracted from those of the P-studies. The resulting count rates in the first SPECT projections were then divided to calculate the activity ratios between the pure perfusion and ventilation scans (P/V-ratio at least 3 according to the guidelines). RESULTS: The range of the P/V ratio was 0.57-78.71, the mean P/V ratio was 6.94 ± 9.56. For 71 of the 286 external V/P studies (about 25%) the P/V ratio was < 3, in 23 studies (about 8%) the ratio failed to even reach the factor 2. CONCLUSIONS: An activity ratio of 3 between the perfusion and ventilation scan was not reached in about 25% of the 286 V/P studies (in around 8% the P/V ratio was <2), so that V/P studies were performed inadequately in a considerable number of procedures. Controlling the count rate increase during the perfusion tracer application (e. g. by handheld monitor) is therefore essential to avoid insufficient data.

Preoperative assessment of relative pulmonary lobar perfusion fraction in lung cancer patients. A rather simple three-dimensional CT-based vs. planar image-derived quantification.

UNLABELLED: Preoperative quantification of (relative) pulmonary lobar perfusion fraction using scintigraphy is established in predicting lung function after pulmonary surgery. Aim was to develop an easy and truly anatomical method for relative pulmonary lobar perfusion fraction quantification using SPECT/CT and to compare results with those from planar analyses in lung cancer patients. PATIENTS, METHODS: 36 patients with operable lung cancer, borderline lung function referred to pre-operative quantification. Perfusion SPECT-data were acquired p.i. of 163±9 MBq 99mTc-MAA, subsequent low-dose-CT (SymbiaT, Siemens). Iterative Flash3D-reconstruction, manual 3D segmentation of all lobes using PMOD. VOI transfer to coregistered perfusion SPECT-data, calculation of lobar fractions. Model-based calculation of relative lobar fractions based on planar data, analysis of planar vs. 3D results using t-test. RESULTS: Significant differences (p<0.05) between the results from 3D method and planar imaging were found for right upper and middle lobe and both lower lobes. Maximum differences ranged from 10.9% (left upper lobe) to 22.9% (right upper lobe). CONCLUSIONS: Relative pulmonary lobar perfusion fraction can easily be obtained by an anatomically driven 3D quantification. Results yielded by this method and the traditional planar approach differed greatly, possibly affecting eligibility for lung surgery in individual patients. Considering these results a 3D approach should be used whenever possible.

[Stunning in radioiodine therapy of benign thyroid disease. Quantification and therapeutic relevance]. / Stunning in der Radioiodtherapie benigner Schilddrüsenerkrankungen: Effektquantifizierung und therapeutische Relevanz.

UNLABELLED: In radioiodine therapy of benign thyroid disease, a reduction of radioiodine uptake is known for consecutive administrations of 131I, which needs to be considered in therapy planning. AIM: Analysis of uptake reduction with regard on the time interval between radioiodine administration and the delivered dose to the thyroid tissue. PATIENTS, METHODS: 200 patients were enrolled in the study and distributed into two groups (matched for diagnoses), each containing 32 patients with Graves' disease (target dose 250 Gy), 24 with focal (400 Gy), 44 with disseminated thyroid autonomy (150 Gy). In one group, a second fraction of radioiodine was given after 48 h (2d) due to an unexpected low radioiodine uptake or effective half-life, whereas in the other group the second fraction was given after 96 h (4d). RESULTS: There was no significant difference between delivered doses due to the first fraction after four days: 2d: 86+/-48 Gy (extrapolated) vs. 4d: 87+/-41 Gy, p>0.05. In 2d, delivered dose at time of second administration was significantly lower (51+/-29 Gy) than in 4d (p<0.01). The radioiodine uptake of the second fraction relative to the initial uptake was significantly lower in the 4d (4d: 63+/-25% vs. 2d: 82+/-24%, p<0.01). In addition, a correlation between uptake reduction and delivered dose and an influence of the time interval between radioiodine administrations could be shown. CONCLUSIONS: Relative uptake of subsequent radioiodine fractions decreases with time after first administration and with increasing delivered dose to the thyroid. If a second fraction of 131I is given at an earlier time, the same therapeutic effect can be reached using lower amounts of activity, minimising radiation exposure and increasing efficiency of radioiodine therapy.