2-¹⁸F-fluoro-2-deoxy-D-glucose (FDG)-positron emission tomography (PET) imaging in prostate cancer is challenging because glucose utilization in well-differentiated prostate cancer is often lower than in other tumor types. Nonetheless, FDG-PET has a high positive predictive value for untreated metastases in viscera, but not lymph nodes. A positive FDG-PET can provide useful information to aid the clinician’s decision on future management in selected patients who have low prostate-specific antigen levels and visceral changes as a result of metastases. On the other hand, FDG-PET is limited in the identification of prostate tumors, as normal urinary excretion of radioisotope can mask pathological uptake. Moreover, there is an overlap in the degree of uptake between prostate cancer, benign prostatic hyperplasia and inflammation. The tracer choice is also important. ¹¹C-choline has the advantage of reduced urinary excretion, and thus ¹¹C-choline PET may provide more accurate information on the localization of main primary prostate cancer lesions than MRI or MR spectroscopy. ¹¹C-choline PET is sensitive and accurate in the preoperative staging of pelvic lymph nodes in prostate cancer. A few studies are available but there were no PET or PET/CT studies with a large number of patients for tissue confirmation of prostate cancer; further investigations are required.

This preliminary study suggests that 11C-choline PET may provide more accurate information regarding the localisation of main primary prostate cancer lesions than MR imaging/MR spectroscopy. A further clinical study of 11C-choline PET in a large number of patients suspected of prostate cancer will be necessary to determine the clinical utility of 11C-choline PET in patients who clinically require biopsy.

Germ-cell tumors of the central nervous system generally develop in the midline, but the tumors can also occur in the basal ganglia and/or thalamus. However, MR images have rarely been documented in the early stage of the tumor in these regions. We retrospectively reviewed MR images obtained on admission and approximately 3 years earlier in two patients with germinoma in the basal ganglia, and compared them with CT. In addition to hyperdensity on CT, both hyperintensity on T1-weighted images and a small hyperintense lesion on T2-weighted images were commonly seen in the basal ganglia. These findings may be early MRI signs of germinoma in this region, and the earliest and most characteristic diagnostic feature on MRI was atrophy of the basal ganglia, which was recognizable before development of hemiparesis.

Table I. Secondary Tritium Isotope Effects in E2 Reactions of ArCLTCH2X and ArCL2CH2X (L = H or D) at 50 OC reaction kHlkT k d k T ( k~l k~L i c d ' 1" + EtONafEtOH 1.204 f 0.015 1.0314 f 0.010 1.106 f 0.033 2b + t-BuOKfr-BuOH 1.191 f 0.012 1.0274 f 0.008 1.092 f 0.026 a 2-Phenylethyltrimethylammonium bromide. 2-@-Chlorophenyl)ethyl tosylate. cFrom the relation k H / k T = (kD/kT)3,z6 (ref 8 and 9).transferred hydrogen are coupled with the stretching motion of the transferred hydrogen. The calculations also predict that the tunnel correction to the secondary tritium isotope effect should be diminished when the transferred atom is deuterium rather than protium. We report here experimental evidence that this is indeed the case.The experiments were modeled after the earlier ones by using 2-arylethyl derivatives tracer labeled with tritium in the j3-position. The resulting mixture can undergo the following elimination reactions 2 k r ArCL2CH2X + When L = H , k l / k 3 = (kH/kT)sec, and when L = D, k l / k 3 = manner previously describedZ for the reactions of 2-phenylethyltrimethylammonium ion (1) with ethoxide in ethanol and 2-(pchlorophenyl)ethyl tosylate (2) with tert-butoxide in tert-butyl alcohol, both at 50 OC. The results are given in Table I.The secondary kH/kT values are both substantial.' We pointed out earlier2 that the fractionation factors of Hartshorn and Shiner6,' predict k H / k T = 1.17 at 50 'c for complete rehybridmtion. Since proton transfer is incomplete in the transition state, it is unlikely that rehybridization would be complete, so the actual contribution of rehybridization to k H / k T is probably well below 1.17. The kD/kT are very much smaller than the kH/kT and remain smaller when converted to k H / k T (last column of Table I) by the r e l a t i~n s h i p~.~ (kD/kT)sec. We determined (kH/kT)= and (kD/kT)sec in theThis relationship is obeyed by the calculated semiclassical (without tunneling) primary (error I 3.8%) and secondary (error I 1.1%) isotope effects reported in ref 4. If masses are assumed to be in the ratio of reduced masses of C-H, C-D, and C-T instead of 1:2:3, the exponent in eq 1 becomes 3.34, but an exponent of ca. 6 is required to bring our calculated and directly measured kH/kT values into agreement. Any protium in the deuteriated substrate (<2% by NMR) would make kD/kT appear too large rather than too small. Table I are larger than predicted for rehybridization and larger than the ( k H / k T ) , values calculated from (kD/kT)sx is consistent only with model calculations that include t~n n e l i n g .~ The disagreements between columns 2 and 4 of Table I also constitute violations of the rule of the geometric mean.1° The principle behind the rule is that the isotope effect for a doubly labeled species should be very close to the product of the isotope effects for the corresponding singly labeled species. In other words, the two isotopes should exert their effects independently. This statement can be expressed alge-( 5 ) We believe our previously reported (ref 2) kH/kT f...

We found that use of an intra-abdominal FDG uptake cut-off value for SUVmax of >5.1 assists in the diagnosis of peritoneal carcinomatosis. FDG PET may play an important role in the clinical management of patients with suspected peritoneal carcinomatosis.