Validation of diagnostic imaging based on repeat examinations. An image interpretation model.

PURPOSE: To develop an interpretation model, based on repeatedly acquired images, aimed at improving assessments of technical efficacy and diagnostic accuracy in the detection of small lesions. MATERIAL AND METHODS: A theoretical model is proposed. The studied population consists of subjects that develop focal lesions which increase in size in organs of interest during the study period. The imaging modality produces images that can be re-interpreted with high precision, e.g. conventional radiography, computed tomography, and magnetic resonance imaging. At least four repeat examinations are carried out. RESULTS: The interpretation is performed in four or five steps: 1. Independent readers interpret the examinations chronologically without access to previous or subsequent films. 2. Lesions found on images at the last examination are included in the analysis, with interpretation in consensus. 3. By concurrent back-reading in consensus, the lesions are identified on previous images until they are so small that even in retrospect they are undetectable. The earliest examination at which included lesions appear is recorded, and the lesions are verified by their growth (imaging reference standard). Lesion size and other characteristics may be recorded. 4. Records made at step 1 are corrected to those of steps 2 and 3. False positives are recorded. 5. (Optional) Lesion type is confirmed by another diagnostic test. CONCLUSION: Applied on subjects with progressive disease, the proposed image interpretation model may improve assessments of technical efficacy and diagnostic accuracy in the detection of small focal lesions. The model may provide an accurate imaging reference standard as well as repeated detection rates and false-positive rates for tested imaging modalities. However, potential review bias necessitates a strict protocol.

Detection of small implanted tumors growing during repeated magnetic resonance imaging of the rabbit liver: application of an interpretation model.

PURPOSE: To apply experimentally and further develop a new image interpretation model based on repeated imaging and aimed at improving assessments of technical efficacy and diagnostic accuracy in the detection of small lesions. MATERIAL AND METHODS: VX2 carcinoma was implanted in the liver of 14 rabbits as two 1.1-1.7 mm3 cores. Magnetic resonance imaging was performed before and 4 days after implantation and then every second day up to the 14th to 20th day. One T2-weighted sequence (TSE T2) and three T1-weighted sequences (SE T1, GE T1, and TFL T1) were used. Interpretation was performed stepwise: three readers independently interpreted image sequences chronologically (step 1). Tumors were included at the last examination (step 2). By concurrent interpretation of repeated examinations, the earliest day at which tumors became visible and tumor size were recorded (step 3). Records were corrected (step 4) and autopsy was performed (step 5). Two procedures for use in calculating repeated detection rates of tumors with different magnetic resonance imaging sequences are presented and discussed. RESULTS: Of 40 macroscopic tumors, 34 were included. They were mainly small (size range SE T1: 1-3mm, TSE T2: 1.5-5 mm) when they became visible as determined at step 3, which was consistently earlier than observed at step 1. TSE T2, SE T1, and GE T1 did not differ significantly regarding earliest day of detection (step 3), while TFL T1 revealed the tumors later. The initial repeated detection rates were higher with TSE T2 than with the other sequences. Frequency of false positives varied over time, indicating fluctuating criteria for reporting tumors. CONCLUSION: A theoretical image interpretation model previously described proved to be applicable for detection of experimental liver tumors. The model was improved by introducing calculations of repeated detection rates for initial image interpretation using an imaging reference standard.

[Side effects after lumbal myelography. A prospective study of outpatients.].

INTRODUCTION: Since myelography was first introduced, hospitalization has been considered necessary. The incidence of side effects and their severity is considerably less since the introduction of water-soluble contrast media, and today the procedure is carried out on outpatients in many X-ray departments. The aim of this study was to examine the incidence of side effects after lumbal myelography performed at the Radiological Department of Reykjavík City Hospital. MATERIAL AND METHODS: Patients referred for lumbal myelography during a five month period from January to May 1995 were included in the study group. All data were prospectively collected. All procedures were carried out in the same way. The injection was most often between the lumbar vertebrae L3/L4. The same quantity of iodine was used in each case. After the examination, patients were permitted to sit in the waiting room and move about freely, but remained under the supervision of the department for three hours. Patients answered three questionnaires regarding their condition before the examination, after, and again two days later, to obtain a general assessment of the total discomfort and also to see whether they had followed directions. RESULTS: Ninety nine patients were included in the study. The total response rate was 89-97%. Most patients were given instructions at the end of the procedure and followed those directions. At the end of the procedure totally 44% of the patients had complaints of headache, 23% of nausea and 44% of pain at the injection site. Before the procedure 93% of the patients had complaints of pain in the back, 86% in the thighs and 77% had complaints of pain in the calves. Immediately after the procedure 54%, 71% and 66% had complaints of pain in the back, thighs or calves. Two days days later 75% had complainst of pain in the back. The large majority of the patients, or 83%, viewed the procedure as having caused little discomfort. CONCLUSIONS: The incidence of side effects from lumbal myelography performed at the X-Ray Department of Reykjavík City Hospital is within acceptable limits.

[Double blinded prospective study of usefulness of bowel preparation on outpatients before intravenous urography.].

OBJECTIVE: The aim of this study was to examine whether or not a bowel preparation should be administered prior to intravenous urography (IVU) on outpatients at the Reykjavik Hospital. MATERIAL AND METHODS: In a period of seven months 89 outpatients remitted to IVU were randomly divided into two groups, A and B. Patients in group A went through bowel preparation before the investigation but patients in group B did not. The patients in group B were asked to consume only fluids, beginning the evening before the investigation. Five patients were excluded from the study. The remaining 84 patients were equally divided between groups A and B. Before the investigation all patients in both groups were asked to fill out a questionnaire giving their reactions to the preparation procedure. Three experienced radiologists performed image interpretation. Delineation of the urinary system, diagnostic ability and quality of cleansing were judged. The study was prospective and double blinded. The same type of contrast media, the same dose and the same type of film were used each time. A comparison of results between the two groups was carried out. RESULTS: The age distribution was the same for both groups. Most of the patients in group A (76%) experienced the cleansing procedure as uncomfortable and 12% as awful. In group B most of the patients felt the preparation was comfortable. No one in group B said that the preparation was uncomfortable. There was no difference between the groups according to delineation of the urinary system except for the urinary bladder, where the delineation was judged to be worse in group B. Air in the bowel was the main disturbing factor in group A, but both air and faeces in group B. The quality of cleansing was judged to be better in group A. There was no difference between the groups in terms of diagnostic ability. CONCLUSIONS: Bowel preparation on outpatients before IVU causes discomfort to the patients and does not improve the quality of the results.

MnDPDP enhancement in rabbit liver after intravenous bolus injection and slow infusion.

PURPOSE: To investigate the MR-enhancing effect of mangafodipir trisodium (MnDPDP, Teslascan) in the rabbit liver in relation to dose, mode of administration and imaging window. MATERIAL AND METHODS: MnDPDP was administered to 18 rabbits at a dose of 10 mumol/kg or 20 mumol/kg, as a bolus injection or infusion. MR imaging of the liver was performed at different time intervals. RESULTS: Peak liver enhancement was typically observed 10-30 min after administration and the enhancement declined with a half-time of about 5 h. This pattern was observed in all sequences (SE 400/15, FLASH, and SE 132/10), with both doses and with both rates of administration. The peak enhancement was greater, though not significantly so after 20 mumol/kg than after 10 mumol/kg. A higher relative peak signal was observed with SE 132/10 than with FLASH or SE 400/15. CONCLUSION: A good liver imaging result was obtained after a dose of 10 mumol/kg, either bolus or infusion, 10-30 min post-contrast with heavily T1-weighted sequences.

Contrast enhancement of the upper abdomen evaluated by CT. A comparison between iohexol 350 mg I/ml and iopamidol 370 mg I/ml.

The non-ionic monomeric contrast media iopamidol and iohexol were compared concerning enhancement in the organs of the upper abdomen in CT. The average peak enhancement above the base line for the 2 contrast media in the liver, vena cava, aorta and spleen was calculated. No difference between the contrast media was found with regard to increase in contrast enhancement. No correlation between the peak enhancement and body weight and body surface was found with either of the 2 contrast media.

Iodixanol in femoral arteriography. A randomized, double-blind, phase III, parallel study with iodixanol 270 mg I/ml and iohexol 300 mg I/ml.

Two contrast media, iodixanol (Visipaque, Nycomed) 270 mg I/ml and iohexol (Omnipaque, Nycomed) 300 mg I/ml, were compared in femoral arteriography, in 147 patients. Both contrast media were diagnostically effective for use in femoral arteriography, without any significant difference. Pain was reported in connection with injection of iohexol by 36% of the patients, after injection of iodixanol none reported pain. Seventy-two percent of the patients in the iodixanol group reported a sensation of warmth in connection with contrast injection versus 90% in the iohexol group. The average intensity of the warmth was greater with iohexol than with iodixanol. Fourteen percent of patients in the iodixanol group and 1% in the iohexol group reported one or more subjective adverse events.

Experimental tissue transplantation using a biopsy instrument and radiologic methods.

RATIONALE AND OBJECTIVES: The liver is the most common site for metastases from gastrointestinal tumors, malignant melanoma, and primary liver tumors. Early detection or exclusion of a neoplasm is important for appropriate treatment. The authors introduce a method for tumor transplantation into the rabbit liver for experimental purposes. METHODS: VX2 tumor cells initially were grown intraperitoneally in a New Zealand white rabbit. Using an automated biopsy instrument with an ultrathin-wall biopsy needle, standardized tumor samples were taken from the peritoneal tumor. Using the same technique, a tumor sample was transplanted into the left liver lobe in a series of seven rabbits. RESULTS: Tumor growth was achieved in all cases at the implantation site. The tumors were well delineated from the surrounding liver parenchyma. Metastases occurred only at later stages. CONCLUSION: The method is almost nontraumatic to the animals, and the technical procedure is simple, time-saving, and provides well-localized tumor growth.