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Single cell tumour suspensions were prepared from biopsy and urine samples from 28 patients with muscle invasive transitional cell carcinoma of the bladder. Nuclear extracts (nucleoids) containing intact chromatin were isolated from these cells and the condensation of DNA supercoils measured by the light scattered from individual nucleoids within a flow cytometer. Exposure of these nucleoids to 10 micrograms ml-1 ethidium bromide produced 78.9% increase in light scatter compared to those treated with 50 micrograms ml-1. This finding is consistent with the known effect of ethidium bromide on DNA supercoiling and confirms that the light scatter signal is responding to changes at this level of DNA organisation. Cell samples were also exposed to 12 Gy of gamma radiation and the effect on nucleoid light scatter recorded. Of the patients studied prior to radiotherapy, those with persistent disease 3 months after treatment generated an increase in nucleoid light scatter of + 9.35 +/- 4.8% after 12 Gy irradiation, of these, 2/14 produced nucleoids that relaxed by more than 10% compared to controls. Those patients with no evidence of disease after radiotherapy gave an increase in nucleoid light scatter after in vitro irradiation of + 19.3 +/- 4.5% of which 10/14 (71%) relaxed by more than 10%. It is proposed that the increased relaxation within the supercoiled DNA from patients whose tumours were undetectable 3 months after therapy, is related to the inherent radiosensitivity of these tumour cells. Such a difference in nucleoid response within tumour cells from patients that responded to radiation may arise due to a decreased affinity of DNA loops for the nuclear matrix. This structural change, at a site associated with the initiation of DNA synthesis, may affect the ability of cells to continue successful cell division after radiation damage.

V79 cells grown as spheroids are more radioresistant than those grown as monolayers. Viable cells from spheroid culture contain restraints to ethidium bromide driven rewinding of DNA supercoils that are absent in monlayer cells. Spheroid cells also contain a DNA-protein matrix that is more resistant to detergent-induced degradation. The increase in structural integrity may be related to a 55–60 kD protein in the nucleoids of spheroid, but not monolayer cells. Spheroid cell radioresistance may therefore be related to a more stable chromatin platform for high fidelity repair of DNA damage.

Four patients with non-Hodgkin's lymphoma in the head and neck region were studied with positron emission tomography (PET), using the radioactive tracer 2-[F-18]-fluoro-2-deoxy-D-glucose (18FDG). This technique, which exploits the high metabolic rate of glucose in tumour tissue, enabled the extent of disease to be visualized. The localization of the tumour was improved by combining the data from the PET scan with those from CT scans or MRI. This technique (of PET-18FDG), using visual and semiquantitative analysis in the form of standardized uptake values, allowed the differentiation between reactive hyperplasia and nodal involvement with lymphoma. We believe that PET using the tracer 18FDG may play an important role in the evaluation of patients with head and neck lymphoma.

Chinese hamster V79 cells grown as spheroids in roller culture are more radioresistant than those grown as monolayers. The supercoiled structure of chromatin, as salt-extracted nucleoids, has been examined using flow cytometry. Irradiated viable cells from spheroid culture contain restraints to supercoil relaxation that are absent in monolayer cells. Further analysis of the chromatin organization from each growth form shows that the radioresistant spheroid cells contain a DNA-protein matrix that is more resistant to detergent-induced degradation. The increase in structural integrity may be due to the retention of a 55-60 kDa protein that is apparent in the nucleoids of spheroid, but not monolayer cells. The increase in structural integrity of the spheroid cells may explain their greater radioresistance by providing a more stable platform for high-fidelity DNA damage repair.

Regional cerebral blood flow (CBF), oxygen extraction ratio (OER), oxygen utilization (CMRO2) and blood volume (CBV) were measured in a group of 34 healthy volunteers (age range 22–82 yrs) using the 15O steady-state inhalation method and positron emission tomography. Between subjects CBF correlated positively with CMRO2, although the interindividual variability of the measured values was large. OER was not dependent on CMRO2, but highly negatively correlated with CBF. CBV correlated positively with CBF. When considering the values of all the regions of interest within a single subject, a strict coupling between CMRO2 and CBF, and between CBF and CBV was found, while OER was constant and independent of CBF and CMRO2. In ‘pure’ grey and white matter regions CMRO2, CBF and CBV decreased with age approximately 0.50% per year. In other regions the decline was less evident, most likely due to partial volume effects. OER did not change or showed a slight increase with age (maximum in the grey matter region 0.35%/yr). The results suggest diminished neuronal firing or decreased dendritic synaptic density with age.

Chinese hamster V79 cells grown as spheroids in roller culture are more radioresistant than those grown as monolayers. The supercoiled structure of chromatin, as salt-extracted nucleoids, has been examined using flow cytometry. Irradiated viable cells from spheroid culture contain restraints to supercoil relaxation that are absent in monolayer cells. Further analysis of the chromatin organization from each growth form shows that the radioresistant spheroid cells contain a DNA-protein matrix that is more resistant to detergent-induced degradation. The increase in structural integrity may be due to the retention of a 55-60 kDa protein that is apparent in the nucleoids of spheroid, but not monolayer cells. The increase in structural integrity of the spheroid cells may explain their greater radioresistance by providing a more stable platform for high-fidelity DNA damage repair.

Neoplastic tissue in general shows a high rate of glucose consumption under both anaerobic and aerobic conditions. Using positron emission tomography (PET) we measured the rate of uptake of the glucose analogue 1sfluoro-2-deoxy-D-glucose ("FDG) in 12 patients with carcinoma of the lung. The tumor types were six squamous cell, two large cell, two oat cell, one adenocarcinoma, and one undifferentiated carcinoma. In each patient a transaxial plane was selected that contained the bulk of the tumor tissue. Regional density and blood volume were measured. Following the intravenous injection of "FDG, the rates of uptake in the tumor and normal lung tissue were assessed from sequential scans over 1 hour. In each patient the rate of uptake of "FDG in the tumor tissue was significantly increased relative to normal lung tissue. For the group the rate of uptake by the tumor was 211.4 +- 69.4 m1/100 g/hr (mean 2 SD) compared to 31.9 k 13.2 in the contralateral lung (P < 0.05). The tumor-to-normal tissue ratio of 6.6 (range, 2.7 to 14.6) was higher than previously reported ratios for brain and liver tumors. In contrast to brain tumors there was little correlation between tumor type and rate of "FDG uptake. Measurements of glucose metabolism taken in vivo in human pulmonary tumors may lead to advances in screening, staging, and therapy. Cancer 60:2682-2689, 1987. HlRTY YEARS AGO, Warburg demonstrated abnorT mal glucose metabolism in neoplastic tissue in vitro. I Compared to normal hepatic tissue, rapidly growing, poorly differentiated hepatic tumors showed increased glycolysis and lactate production despite the presence of abundant oxygen, resulting in high rates of glucose consumption. The mechanism of this increased glucose consumption probably depends on the type of tissue and may be due to increased glucose transport through the cell membrane2 or an enhanced capacity for glycolysis because of increased activity of the key glycolytic en~ymes.~ This differential metabolic property of neoplastic tissue has been used by several investigators to detect malignancy. Recent studies have been performed using the

Regional cerebral haematocrit has been measured in seven patients with brain tumours, and in one normal subject, using positron emission tomography (PET). Red cell and plasma volumes of distribution were assessed using 11 CO and [ methyl - 11 C]albumin, respectively. Haematocrit values were compared with values of regional cerebral blood flow (rCBF) measured using steady-state inhalation of C 15 O 2 . Only two of the seven cerebral tumours studied showed any increase in uptake of [ methyl - 11 C]albumin over 45 min. Values of r , the regional ratio of cerebral small-to-large vessel haematocrit, varied from 0.52 to 0.84 for the seven tumours studied. No correlation between r and tumour blood flow was observed. The normal subject yielded an r value of 0.69 for the mean whole brain small-to-large vessel haematocrit ratio. No significant difference between gray and white matter r values was found. The contralateral hemispheres of the seven tumour patients studied yielded an overall mean r value of 0.71 ± 0.05. We conclude that it is reasonable to assume an r value of 0.7 in tomographic calculations of regional cerebral blood volume (rCBV) from red cell or plasma volumes of distribution in normal brain. Such an assumption for tumours, however, may lead to errors of 35% in estimated rCBV.

Cancer is one of the major clinical problems we face today; it is the second biggest killer after ischemic heart disease affecting 1 in 5 of us sometime in our life. Anyone working outside the field of positron emission tomography may be forgiven for wondering why more PET work has not been done on cancer. This outsider may be slightly puzzled when he discovers that what little work has been done has dealt with brain tumors. Brain tumors after all account for no more that 9% of all human tumors. Unfortunately, very little has been done on non-cerebral tumors. The many reasons for this will not be discussed here but include: a. Many scanners can only accomodate the head. b. Many scanners are in neurological institutes. c. The greatest experience has been acquired in brain studies. d. The tracer kinetic models used are usually derived for brain tissue.

To increase our understanding of cancer and improve cancer treatment on a rational basis we need to identify both qualitative and quantitative differences between normal and neoplastic tissue. The multimodality approach to cancer treatment includes radiotherapy, chemotherapy, hyperthermia, and immunotherapy. Most of the data on which we base our therapeutic strategies have been derived from in vitro studies or animal tumor models. More information is required on the physiology of in vivo human tumors and their response to therapy. Positron emission tomography allows the regional tissue concentration of a positron emitting radionuclide to be measured in absolute units. If valid tracer models can be formulated that accurately describe the fate of an administered "biological" tracer then the physiological process under investigation can be measured quantitatively. The sequential inhalation of C15O2, 15O2, and 11CO allows regional tissue blood flow, oxygen utilization and blood volume to be measured in absolute units. Tissue perfusion, a measure of nutrient (eg, oxygen) supply, drug delivery, or a means of heat dissipation, is of immense importance to oncologists. The oxygen-15 technique has been used not only to study regional blood flow and oxygen utilization in both tumor and normal tissue but also their response to therapeutic intervention. In those studies were tracer models are thought to be less than complete (eg, due to insufficient biological data) then only a semiquantitative or qualitative assessment of the pathophysiological state may be possible. In this respect, tumor function has been characterized by the rate of uptake of 18F-2-deoxyglucose. This technique has provided a means of tumor grading and differentiating between radiation-induced tissue necrosis and tumor recurrence. Metabolic imaging with labeled amino acids appears particularly useful in the delineation of tumor extent. Blood brain barrier integrity and the pharmacokinetics of cytotoxic drugs have also been studied quantitatively. In the future, receptor studies are likely to play an increasing role. In this review dealing with the positron emission tomography oncologic work to date, emphasis has been placed on the physiological information obtainable and how it may further our understanding of cancer and its treatment.

The kinetics of the regional cerebral uptake of [11C]3- O-methyl-d-glucose ([11C]MeG), a competitive inhibitor of d-glucose transport, have been studied in normal human subjects and patients with cerebral tumours using positron emission tomography (PET). Concomitant measurement of regional cerebral blood volume and blood flow enabled corrections for the contribution of intravascular tracer signal in PET scans to be carried out and regional unidirectional cerebral [11C]MeG extractions to be determined. A three-compartment model containing an arterial plasma and two cerebral compartments was required to produce satisfactory fits to experimental regional cerebral [11C]MeG uptake data. Under fasting, resting conditions, normal controls had mean unidirectional whole-brain, cortical, and white matter [11C]MeG extractions of 14, 13, and 17%, respectively. Mean values of k1and k2, first-order rate constants describing forward and back transport, respectively, of tracer into the first cerebral compartment, were similar for [11C]MeG and [18F]2-fluoro-2-deoxy-d-glucose (18FDG), a second competitive inhibitor of d-glucose transport, k3, a rate constant describing FDG phosphorylation, was 20 times higher for cortical FDG uptake than the k3fitted for [11C]MeG cortical uptake. Glioma [11C]MeG extractions ranged from normal levels of 12% to raised levels of 30%. Transport of [11C]MeG in and out of contralateral cortical tissue was significantly depressed in patients with gliomas. It is concluded that under fasting, resting conditions, regional cerebral glucose extraction remains relatively uniform throughout normal brain tissue. Gliomas, however, may have raised levels of glucose extraction. The nature of the second cerebral compartment required to describe [11C]MeG uptake is unclear, but it could represent either a useless phosphorylation–dephosphorylation cycle or nonspecific tracer uptake by a cerebral sub-compartment.

Regional cerebral pH (rpH) was measured in 12 patients with cerebral tumours and in 5 normal subjects using continuous inhalation of11CO2and positron emission tomography (PET). Cerebral tumours with a disrupted blood–brain barrier (BBB) on computed tomography scanning had a similar rpH to that of equivalent regions of contralateral brain tissue (mean tumour rpH, 6.98; mean contralateral brain pH, 6.99). Cerebral tumours with an intact BBB were consistently found to be more alkaline than contralateral brain tissue (mean tumour rpH, 7.09). There was no significant difference between the mean rpH values obtained for peripheral cortical gray and central white matter in normal subjects (7.02 and 6.98, respectively). It is concluded that in spite of reports of raised levels of aerobic glycolysis in neoplastic tissue, there is no evidence that cerebral tumour rpH values are depressed.

The cerebral pH of four normal human subjects has been measured using continuous inhalation of 11CO2 and positron emission tomography (PET). 11CO2 was administered to each subject at a constant rate for 15 min, during which time serial arterial plasma 11C levels were determined and serial 11C cerebral uptake PET scans were performed at a fixed axial tomographic level. 11C uptake kinetics were analysed using a three-compartment model. Rate constants have been estimated for the free exchange of 11CO2 between plasma and cerebral compartments for each subject, and their cerebral pH calculated. Whole brain pH values ranged from 6.96 to 7.05, and no significant pH difference between regions containing predominantly grey or white matter was noted. Best fits to 11C uptake data were achieved by effectively neglecting the metabolic fixation of 11C by cerebral tissue. The purpose of this study was to test the feasibility of pH measurement using the 11CO2 continuous inhalation technique. It is concluded from the results and the error analysis that continuous 11CO2 inhalation combined with PET is potentially a simple and useful method for determining regional cerebral pH.

Using positron emission tomography, regional cerebral blood flow and oxygen utilisation were measured in the contralateral cortex of 14 patients with a variety of intracranial tumours. A comparison was made with cortical values derived from 14 normal controls. Compared with normal subjects, patients with brain tumours had a significant reduction in oxygen utilisation and blood flow in their contralateral cortex. Decompression resulting from craniotomy and biopsy, led to a partial reversal of this cerebral hypofunction.

In normal brain, the blood–brain barrier (BBB) is highly impermeable to K+ cations, their transport being controlled by ATPases situated in the endothelial cell membranes. 82Rb+ is a positron-emitting analogue of K+ with a half-life of 75 s. Using a steady-state model and positron emission tomography, quantitative extraction data for 82Rb+ transport across the BBB have been obtained both in normal human subjects and in a variety of conditions of cerebral pathology. A mean cerebral Rb extraction of 2.1% was found for normal subjects, corresponding to a mean value of 1.1 × 10−6 cm s−1 for 82Rb+ cation permeability across the BBB. No increase in cerebral Rb extraction was observed for patients with diffusely raised intracranial pressure secondary to obstructive hydrocephalus and benign intracranial hypertension, or for patients with multiple sclerosis or cerebral systemic lupus erythematosus. Cerebral tumours that were enhanced on computed tomography scanning showed a significant increase in local Rb uptake. No correlation between tumour size, or grade of glioma, and tumour Rb extraction was found. Nonenhancing tumours showed no increase in local Rb extraction, and regions of perifocal tumour oedema also had Rb extraction values in the normal range. It is concluded that increased Rb extraction occurs only where tight junction integrity in the BBB breaks down locally, that is, in the microcirculation of enhancing tumours but not in that of perifocal regions of tumour oedema or nonenhancing tumours.

Positron emission tomography (PET) uses the shortlived positron-emitting radioisotopes of elements such as oxygen, nitrogen, and carbon as tracers both to image and to measure, non-invasively, normal regional tissue physiology and pathophysiology in man. This technique has been used to study the pathophysiology of brain tumours at the time they present and after therapeutic intervention.

Yttrium-90 chelated by the tetraphosphonate EDTMP achieved a high uptake in bone and a rapid clearance from all soft tissues compared with 90Y nitrilotriacetate, citrate and acetate. The biological half-life of 90Y in the bone was greater than 72 h, but the quantity, and therefore dose, could be reduced by 50% using repeated, non-toxic chelation therapy with the calcium salt of DTPA. This treatment should be able to supplement current treatments for leukaemia where the dose of external beam radiation is associated with considerable morbidity.

Neoplastic tissue in general shows a high rate of glucose consumption under both anaerobic and aerobic conditions. Using positron emission tomography (PET) we measured the rate of uptake of the glucose analogue 18fluoro-2-deoxy-D-glucose (18FDG) in 12 patients with carcinoma of the lung. The tumor types were six squamous cell, two large cell, two oat cell, one adenocarcinoma, and one undifferentiated carcinoma. In each patient a transaxial plane was selected that contained the bulk of the tumor tissue. Regional density and blood volume were measured. Following the intravenous injection of 18FDG, the rates of uptake in the tumor and normal lung tissue were assessed from sequential scans over 1 hour. In each patient the rate of uptake of 18FDG in the tumor tissue was significantly increased relative to normal lung tissue. For the group the rate of uptake by the tumor was 211.4 +/- 69.4 ml/100 g/hr (mean +/- SD) compared to 31.9 +/- 13.2 in the contralateral lung (P less than 0.05). The tumor-to-normal tissue ratio of 6.6 (range, 2.7 to 14.6) was higher than previously reported ratios for brain and liver tumors. In contrast to brain tumors there was little correlation between tumor type and rate of 18FDG uptake. Measurements of glucose metabolism taken in vivo in human pulmonary tumors may lead to advances in screening, staging, and therapy.

Regional values for cerebral blood flow, blood volume, oxygen extraction fraction, and oxygen utilization were measured, using PET, in 10 brain tumor patients before and after treatment with dexamethasone. Dexamethasone treatment decreased cerebral blood flow and blood volume and increased the fractional extraction of oxygen throughout the brain without affecting oxygen utilization. Dexamethasone probably causes direct vasoconstriction of cerebral blood vessels.

Two groups of patients, the first with acutely raised intracranial pressure, the second with chronic hydrocephalus have been studied with Positron Emission Tomography (PET) prior to and following decompression or c. s. f. shunting. Those with chronic hydrocephalus had pressure monitoring for 36 hours. In the acute group cerebral decompression improved cerebral blood flow but in the chronic hydrocephalic group irreversible neuronal loss had occurred and there were no metabolic consequences of c. s. f. diversion.

Dexamethasone is widely used in patients with brain tumors and perifocal edema (Weinstein 1972). It has generally been argued that the beneficial clinical influence of dexamethasone is via a direct effect on the edema itself. Possible mechanisms include diminution of edema formation and a reduction of the water content of the edematous region (Yamada 1979; Reulen 1972; Reid 1982). Some investigators have suggested that dexamethasone decreases intracranial pressure (ICP) with a concomitant immediate improvement of clinical symptoms (Brock et al. 1976; Alberti 1978). Others have found an increase in rCBF after dexamethasone therapy and suggested this is secondary to an improvement in cerebral function (Buttinger 1982; Reulen 1972). A direct action on the blood vessel wall by corticosteroids has been recognized for some time (Axelrod 1983; Altura 1966).

A method is described for measuring the regional cerebral-to-large vessel haematocrit ratio using inhalation of carbon-11-labelled carbon monoxide and the intravenous injection of carbon-11-labelled methyl-albumin in combination with positron emission tomography. The mean value in a series of nine subjects was 0.69. This is ∼20% lower than the value of 0.85 previously reported. It is concluded that previous measurements of regional cerebral blood volume using a haematocrit ratio of 0.85 will have underestimated the value of regional cerebral blood volume by 20%.

SUMMARY Cortical oxygen utilization, oxygen extraction, blood flow, and blood volume, have been measured in patients with hydrocephalus before and after surgical decompression using positron emission tomography (PET). The hydrocephalus subjects fell into two categories: patients with recent-onset obstructive hydrocephalus and symptoms of raised intracranial pressure due to obstruction of cerebrospinal fluid (CSF) drainage by posterior fossa or third ventricular cerebral tumours, and patients with hydrocephalus of more insidious onset that was associated either with congenital abnormalities, or which was idiopathic. The hydrocephalus subjects had a significantly reduced level of mean cortical oxygen utilization (rCMRO2) and mean cortical blood flow (rCBF) compared with age-matched normal controls. Patients with recent-onset obstructive hydrocephalus associated with cerebral neoplasia had inappropriately low levels of cortical blood flow compared with their levels of cortical oxygen utilization, all having elevated levels of cortical oxygen extraction (rOER). Levels of cortical blood flow in the group of patients with more insidious-onset hydrocephalus matched levels of cortical rCMRO2, all these subjects having normal levels of rOER. All those hydrocephalus subjects who had a raised cortical oxygen extraction preoperatively increased their cortical blood flow following cerebral decompression. No improvement, however, was noted in their mean cortical oxygen utilization. By contrast, those hydrocephalus subjects with normal baseline levels of cortical extraction showed no improvement in mean cortical blood flow, oxygen utilization, or cognitive function after surgical intervention. It is concluded that if cortical oxygen extraction is elevated, hydrocephalic patients are likely to improve their cortical blood flow following cerebral decompression.

Using PET, we measured regional cerebral oxygen utilization, oxygen extraction, blood flow, and blood volume in five patients with benign intracranial hypertension. No significant differences in regional cerebral function were found between the patients and 15 age-matched normal controls. Cerebral decompression with a lumboperitoneal shunt produced little, change in regional cerebral function in one patient studied serially. The raised CSF pressure of benign intracranial hypertension is therefore not associated with any significant deterioration in cerebral oxygen metabolism or hemodynamics.