Geoffrey T. Benness

COMPARISON OF ACCURACY OF 99mTc-PYRIDOXYLIDENE GLUTAMATE SCANNING WITH ORAL CHOLECYSTOGRAPHY AND ULTRASONOGRAPHY IN DIAGNOSIS OF ACUTE CHOLECYSTITIS

A prospective study of 116 patients admitted as emergencies with a clinical diagnosis of acute cholecystitis or biliary colic has shown that the best investigation for confirming a diagnosis of acute cholecystitis is 99mTc-pyridoxylidene glutamate (PG) scanning. Its sensitivity is 99% and its specificity 86%, whereas those of oral cholecystography are 75% and 82%, respectively, and those of ultrasonography are 54% and 62%, respectively. However, estimation of plasma liver enzymes is essential to exclude acute hepatitis before proceeding to early cholecystectomy.

Hepatic kinetics and magnetic resonance imaging of gadolinium-EOB-DTPA in dogs.

RATIONALE AND OBJECTIVES To measure the hepatic uptake and biliary elimination kinetics of gadolinium (Gd)-EOB-DTPA in dogs. METHOD Two groups of four beagles each were anesthetized and given an intravenous bolus of 25 mumol/kg or 250 mumol/kg of Gd-EOB-DTPA. Blood, hepatic bile, and urine were collected over 140 minutes, and liver samples were obtained immediately after the dogs were killed. Conventional T1-weighted spin echo sequences of the liver were performed on a 1.5-Tesla (T) magnetic resonance imager during sampling. A ninth beagle received a bolus of 25 mumol/kg followed 140 minutes later with a bolus of 250 mumol/kg of Gd-EOB-DTPA. Wedge liver biopsies were obtained for Gd estimation at various times after dosing, and Gd concentration was measured by inductively coupled plasma atomic emission spectroscopy. RESULTS The plasma concentration of Gd-EOB-DTPA decreased in a biexponential manner with half-lives of approximately 4 minutes and 60 minutes for the distribution and elimination phase independent of the dose given. Gadolinium bile concentration reached peak values between 80 and 140 minutes: 6.3 +/- 1.6 mmol/L for the low dose (LD) and 11.6 +/- mmol/L for the high dose (HD). Bile Gd output was 62.0 +/- 8.8 (LD) and 78.3 +/- 30.2 (HD) nmol/minute-kg 50 to 80 minutes after injection. Gadolinium-EOB-DTPA was excreted by the biliary route to 24.8 +/- 2.6 (LD) and 3.6 +/- 1.2 (HD) percent of the dose within 140 minutes. Liver Gd concentration was 0.43 +/- 0.14 (LD) and 4.3 +/- 0.5 (HD) mmol/kg liver tissue at the conclusion of the studies. Calculated concentrations in the hepatocyte were 60 (LD) and 15 (HD) times higher than in plasma at 25 minutes after dosing. Whereas the low dose exhibited excellent contrast enhancement for the whole period, the high dose displayed a biphasic signal enhancement with a decreasing signal caused by the too-high hepatic gadolinium accumulation. CONCLUSIONS Transport of the Gd-EOB-DTPA into the hepatocyte exceeded elimination from hepatocyte to bile. The high dose defined a biliary transport maximum for Gd-EOB-DTPA of 78.3 +/- 30.2 nmol/minute-kg. The liver accumulation results from fast transport into the hepatocyte and rate-limited slower transport from hepatocyte to bile. The accumulation occurs against a strong concentration gradient, suggesting energy-dependent active transport into the hepatocyte.

Examination of the Nephrographic Potential of Iotrol by Computed Tomography

The x-ray attenuation of the renal cortex of dogs, as determined by computed tomographic (CT) scanning, was measured over a three-day period after an intravenous bolus of 600 mg I/kg of iotrol or iopamidol. A slightly higher density observed 24 hours after injection of iotrol was not considered significant, and was not considered sufficient to warrant clinical application of iotrol for specific, prolonged renal enhancement.

Ethical and financial considerations in Australia.

Benness G. Ethical and financial considerations in Australia. Invest Radiol 1988;23(Suppl 1):S93‐S94. Australian nonionic contrast media experience follows the European pattern and anticipates developments in the United States. Cost concerns and unclear safety advantages led the Royal Australian College of Radiologists to develop guidelines for contrast media usage and an adverse reaction survey.

Dr Evan Lennon and the birth of CT

Following the death of Evan Lennon in Rome in September 2007, we reflected on the paradox that this Australian-born and trained radiologist contributed so much to the initial development of CT, and yet, this fact and his career are little known in Australia and New Zealand. First, CT was born when Dr Jamie Ambrose made the first clinical examination using the prototype EMI head scanner at Atkinson Morley’s Hospital, London, on 1 October 1971. But much had happened before that study. Linear X-ray tomography was invented by Bocage in 1921. Refinements in the movements of the tube and recording film followed. However, it is muchmore difficult to show all the tissues in a cross-section slice. This requires mathematical analysis of the image and reconstruction. In a simple form, this is seen in puzzles in the daily newspapers, but a large matrix of numbers requires algorithms to reconstruct the image with a computer. Mathematicians and scientists from many disciplines developed these algorithms, and the first was recorded in 1906. The complex mathematics was assisted using Fourier transformation, and later, this was refined to fast Fourier transformation for use on a digital computer. Although Hounsfield used the now outdated iterative reconstruction, current CT uses the faster filtered back projection. In 1958, three researchers at the Kiev Polytechnical Institute described a workable CT using a TVbased analogue computer system, and in 1963 in USA, Oldendorf patented a method of reconstruction tomography using back projection, but the images were poor. Cormack, a South African physicist, developed an algorithm for reconstructing radiographic images in 1963 and 1964. In 1959, Kuhl carried out an emission transverse scan in Pennsylvania, USA, and in 1964 and 1970, Kuhl and Edwards built two emission scanners with detectors on both sides of the body. Replacing one detector with a small radioactive source (Am241), Kuhl and colleagues made the first transverse axial CT scan of a patient’s thorax, but again the images were poor. Hounsfield, a computer and research engineer at EMI in the UK, worked on radar and guided weapons, and later on an alltransistor computer. He moved to the EMI Central Laboratories to work on computer memory and then turned to image reconstruction of a matrix of numbers generated by an X-ray beam moving transversely and also rotating around a phantom. Hounsfield took his novel images to Dr Cliff Gregory, chief scientific officer, and Mr Gordon Higson at the Department of Health (DoH) who introduced him to Evan Lennon. Sir Godfrey Hounsfield, Royal Society Memorial, states, ‘it should be noted here that the involvement of the Department of Health (DoH) began in 1968. Dr Evan Lennon was radiological advisor to the DoH and he was instrumental in bringing the project to fruition’. Lennon involved Dr Frank Doyle, at the Royal Postgraduate Medical School, in bone studies, but Hounsfield’s successful images of pathological brain specimens (borrowed from the Royal Marsden Hospital) led Lennon to invite Dr Jamie Ambrose, a neuroradiologist at London’s Atkinson Morley’s hospital, to assist. When EMI considered withdrawing from the research, the progress in image quality encouraged Lennon and Gregory to arrange an unprecedented DoH subsidy (50% of the cost) for the development to continue. As stated earlier, Ambrose carried out the first clinical scan and CTwas born. It is clear that Lennon was intimately involved in the project. In 1979, the Nobel prize for medicine and physiology was shared by Cormack, who had developed the algorithm for reconstructing images and had Fig. 1. Evan Lennon in Rome, 1959.