**4. Results**

Eighteen patients showed a high uptake in the delayed IMP SPECT images (16 PCNSL, two unknown). All unknown patients were successfully treated with steroids and radiation therapy, so their clinical diagnosis was PCNSL. Other tumors or lesions did not show a high uptake on delayed IMP SPECT, so there were no false positives (Table 1). Four patients with pathologically proven PCNSL showed no uptake in the original IMP SPECT. These tumors were either too small to detect by IMP SPECT or the IMP SPECT images were taken after the administration of steroids. However, statistical mapping revealed the IMP uptake in two of these four patients. A heterogeneous IMP uptake was seen in homogenous tumors in MRI. For patients with a hot IMP uptake, statistical mapping showed clearer uptake. The sensitivity and specificity of original IMP SPECT were 80 and 100% (Chi-test p<0.01), respectively. Those of statistical mapping were 90 and 100% (Chi-test p<0.01), respectively.

The patients who had received steroid treatment showed negative of IMP SPECT findings. However, patients with glioma, MS and Burkitt's lymphoma did not show a high uptake of delayed IMP SPECT. IMP SPECT is therefore useful for the diagnosis of PCNSL, especially for the differentiation from glioma, MS and Burkitt's lymphoma. A heterogeneous IMP uptake was seen in homogenous tumors in MRI. For patients with a hot IMP uptake, statistical mapping showed an even clearer uptake. There were some artifacts on the statistical mapping, however, these artifacts did not result in diagnostic problems due to comparisons of the statistical mapping and original SPECT or MRI findings.


**Table 1**

Sensitivity 80%, specificity 100%, Chi‐test p<0.01


Sensitivity 90%, specificity 100%, Chi‐test p<0.01
