Challenges in radiological evaluation of brain metastases, beyond progression

MRI is the cornerstone in the evaluation of brain metastases. The clinical challenges lie in discriminating metastases from mimickers such as infections or primary tumors and in evaluating the response to treatment. The latter sometimes leads to growth, which must be framed as pseudo-progression or radionecrosis, both inflammatory phenomena attributable to treatment, or be considered as recurrence. To meet these needs, imaging techniques are the subject of constant research. However, an exponential growth after radiotherapy must be interpreted with caution, even in the presence of results suspicious of tumor progression by advanced techniques, because it may be due to inflammatory changes. The aim of this paper is to familiarize the reader with inflammatory phenomena of brain metastases treated with radiotherapy and to describe two related radiological signs: "the inflammatory cloud" and "incomplete ring enhancement", in order to adopt a conservative management with close follow-up.

18F-choline PET/MRI in suspected recurrence of prostate carcinoma

OBJECTIVE

To evaluate the usefulness of simultaneous ¹⁸F-choline PET/MRI in the suspicion of prostate cancer recurrence and to relate ¹⁸F-choline PET/MRI detection rate with analytical and pathological variables.

MATERIAL AND METHODS

27 patients with prostate cancer who received local therapy as primary treatment underwent a ¹⁸F-choline PET/MRI due to suspicion of recurrence (persistently rising serum PSA level). ¹⁸F-choline PET/MRI findings were validated by anatomopathological analysis, other imaging tests or by biochemical response to oncological treatment.

RESULTS

¹⁸F-choline PET/MRI detected disease in 15 of 27 patients (detection rate 55.56%). 4 (15%) presented exclusively local recurrence, 5 (18%) lymph node metastases and 7 (26%) bone metastases. Mean PSA (PSA_med) at study time was 2.94ng/mL (range 0.18-10ng/mL). PSA_med in patients with positive PET/MRI was 3.70ng/mL (range 0.24-10ng/mL), higher than in patients with negative PET/MRI, PSA_med 1.97ng/mL (range 0.18-4.38ng/mL), although without statistically significant differences. Gleason score at diagnosis in patients with a positive study was 7.33 (range 6-9) and in patients with a negative study was 7 (range 6-9), without statistically significant differences.

CONCLUSION

¹⁸F-choline PET/MRI detection rate was considerable despite the relatively low PSA values in our sample. The influence of Gleason score and PSA level on ¹⁸F-choline PET/MRI detection rate was not statistically significant.

PET/MRI: A luxury or a necessity?

PET/MRI is a new multimodality technique with a promising future in diagnostic imaging. Technical limitations are being overcome. Interference between the two systems (PET and MRI) seems to have been resolved. MRI-based PET attenuation correction can be performed safely. Scan time is acceptable and the study is tolerable, with claustrophobia prevalence similar to that of MRI. Quantification with common parameters, such as Standardized Uptake Value (SUV), shows a fairly good correlation between both systems. However, PET/CT currently provides better results in scan time, scan costs, and patient comfort. Less patient radiation exposure is a big advantage of PET/MRI over PET/CT, which makes it particularly recommended in paediatric and adolescent patients requiring one or more studies. PET/MRI indications are the same as those of PET/CT, given that in cases where MRI is superior to CT, PET/MRI is superior to PET/CT. This superiority is clear in many soft tissue tumours. Moreover, it is common to perform both PET/CT and MRI in neurological diseases, as well as in some tumours, such as breast cancer. A single PET/MRI study replaces both with obvious benefit. MRI also allows other MRI-based PET corrections, such as motion or partial volume effect corrections. The better spatial resolution of MRI allows the transfer of well-defined MRI areas or small volumes of interest to PET image, in order to measure PET biomarkers in these areas. The richness of information of both techniques opens up immense possibilities of synergistic correlation between them.

[Helical CT and perfusion scintigraphy: diagnosis of pulmonary embolus in the clinical practice]

The purpose of this study was to compare helical CT with lung perfusion scintigraphy (LPS) as the initial investigations of patients with suspected pulmonary embolism (PE).

PATIENTS AND METHOD

A total of 54 patients with clinically suspected acute PE were studied retrospectively. Each patient was assigned a pretest clinical probability of acute PE (very likely, 90%; possible, 50%; unlikely, 10%). Within 72 hours of presentation, patients underwent LPS and contrast material-enhanced helical CT. Perfusion LS was classified following the PISAPED criteria as normal or near normal; abnormal consistent with PE or abnormal not consistent with PE. Helical CT studies were categorized as positive for PE, negative for PE or non-diagnostic. The standard reference was a consensus based on LS, helical CT and clinical outcome.

RESULTS

In 38 of the 54 patients, the results of LS a hCT were concordant, 13 with PE and 25 without. There were 4 indeterminate hCT. In 12 patients LS and hCT were discordant. There were 4 LS false negative; 2 with parenchyma damage and 2 chronic PE. There were 5 LS false negative; 3 extrinsic vascular compressions and one low clinical probability. There was 1 hCT false positive because of breathing artifact and 2 false negatives because of subsegmental emboli.

CONCLUSION

Accurate diagnosis of acute PE is possible combining perfusion scanning and clinical probability. Helical CT has added information in patients with discordant clinical probability and perfusion lung scan results. Helical CT demonstrated lesions other than PE considered responsible for the patient's symptoms, but it was insensitive to embolism of subsegmental branches.