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Imaging

UROLOGICAL SURVEY

Eikefjord EN, Thorsen F, Rorvik J

Department of Radiology, Haukeland University Hospital, Bergen, Norway

AJR Am J Roentgenol. 2007; 188:934–9

OBJECTIVE: The purpose of this study was to measure and compare the effective radiation dose in patients undergoing unenhanced MDCT and excretory urography for acute flank pain, and to explore technical and practical factors affecting the effective dose.

SUBJECTS AND METHODS: One hundred nineteen patients with acute flank pain were included. All patients were examined using both MDCT and excretory urography. CT involved one acquisition from the upper kidney margin to the symphysis pubis. The only protocol variation was in the tube current (mAs), which was made according to patient body mass. The excretory urography protocol consisted of three images, with more when supplementary images were needed. Effective radiation doses were computer–simulated using dosimetry programs for CT and conventional radiography, based on Norwegian Radiological Protection Board dose data sets. Mean and SDs of measured patient doses were calculated and compared. Further analyses of dose variations in body mass categories (body mass index) were conducted, as were analyses concerning the number of images taken.

RESULTS: The mean effective doses were 7.7 mSv with MDCT and 3.63 mSv with excretory urography. The effective dose varied both in and between techniques but could be predicted. Radiation risk decreased significantly with increased patient weight.

CONCLUSION: The average effective dose with MDCT was more than double that with excretory urography. However, the appropriate dose could be strongly predicted by the patient's body mass index and by procedure. An optimum low–dose protocol should be considered before initiating unenhanced MDCT for ureteral colic in order to minimize the radiation–induced cancer risk and to secure adequate image quality.

Editorial Comment

In many institutions, nonenhanced computed tomography has largely supplanted intravenous urography as the primary modality for evaluation of patients suspected of having urolithiasis. As we know, nonenhanced multidetector CT (MDCT) examination, on average, doubled the effective radiation dose to the patient when compared with intravenous urography (if a total of 5 films are obtained). This is particularly important to the young female patients due the direct radiation exposure to the gonads. Some young female patients might present with chronic episodes of urolithiasis, and therefore will be submitted to multiple radiologic examinations during their lifetime The aim of this study was to use commercially available software to evaluate effective radiation doses between different radiologic examination procedures and to explore the relationship between technical and practical factors that could affect the effective radiation dose, both during and between the chosen imaging procedures.

The authors presents an interesting observation; they found that a significantly wide dose range of effective doses with both MDCT and excretory urography, mainly influenced by body size (BMI). Patients of normal weight were exposed to a significantly higher radiation risk with MDCT than with excretory urography when compared with the other weight categories. The mAs with both excretory urography and CT varied considerably according to BMI. With excretory urography, an exponential variation in BMI might be expected from the automatic exposure control system (photo timing). However, with MDCT, the mAs varied as a consequence of subjective considerations. This was possibly caused by operator attempts to avoid an increased noise level for patients with high BMI. Recently, several studies has been show that low–dose MDCT protocols, which delivers radiation dose comparable to those of excretory urography are appropriate for the diagnosis of ureteral stones, and that it provides excellent intraobserver and interobserver agreement and does not obscure alternative diagnosis. Nowadays it is imperative to adapt technical parameters of MDCT on the basis of clinical indication. It is not acceptable to use protocols based on subjective considerations and thus delivering increased radiation risk for patients of normal weight. Based on the authors' conclusion we should keep in mind that BMI should also be taken into consideration because it is too a risk predictor. As a rule, unenhanced optimized low–dose CT should be used routinely in clinical practice and we must pursue in the development of optimized low–dose MDCT protocols.

Dr. Adilson Prando

Chief, Department of Radiology

Vera Cruz Hospital

Campinas, São Paulo, Brazil

E–mail: aprando@mpc.com.br

The utility of magnetic resonance imaging and spectroscopy for predicting insignificant prostate cancer: an initial analysis

Shukla–Dave A, Hricak H, Kattan MW, Pucar D, Kuroiwa K, Chen HN, Spector J, Koutcher JA, Zakian KL, Scardino PT

Department of Medical Physics, Memorial Sloan–Kettering Cancer Center, New York, NY, USA

BJU Int. 2007; 99:786–93

OBJECTIVE: To design new models that combine clinical variables and biopsy data with magnetic resonance imaging (MRI) and MR spectroscopic imaging (MRSI) data, and assess their value in predicting the probability of insignificant prostate cancer.

PATIENTS AND METHODS: In all, 220 patients (cT stage T1c or T2a, prostate–specific antigen level < 20 ng/mL, biopsy Gleason score 6) had MRI/MRSI before surgery and met the inclusion criteria for the study. The probability of insignificant cancer was recorded retrospectively and separately for MRI and combined MRI/MRSI on a 0–3 scale (0, definitely insignificant; – 3, definitely significant). Insignificant cancer was defined from surgical pathology as organ–confined cancer of </= 0.5 cm (3) with no poorly differentiated elements. The accuracy of predicting insignificant prostate cancer was assessed using areas under receiver operating characteristic curves (AUCs), for previously reported clinical models and for newly generated MR models combining clinical variables, and biopsy data with MRI data (MRI model) and MRI/MRSI data (MRI/MRSI model).

RESULTS: At pathology, 41% of patients had insignificant cancer; both MRI (AUC 0.803) and MRI/MRSI (AUC 0.854) models incorporating clinical, biopsy and MR data performed significantly better than the basic (AUC 0.574) and more comprehensive medium (AUC 0.726) clinical models. The P values for the differences between the models were: base vs. medium model, < 0.001; base vs. MRI model, < 0.001; base vs. MRI/MRSI model, < 0.001; medium vs. MRI model, < 0.018; medium vs. MRI/MRSI model, < 0.001.

CONCLUSIONS: The new MRI and MRI/MRSI models performed better than the clinical models for predicting the probability of insignificant prostate cancer. After appropriate validation, the new MRI and MRI/MRSI models might help in counseling patients who are considering choosing deferred therapy.

Editorial Comment

Insignificant prostate cancer defined as pathologically organ–confined cancer with a total volume of < 0.5 cm 3 and no poorly differentiated component (Gleason grade 4 or 5) on histology is not infrequent but patients with this cancer are very difficult to identify clinically. The authors presented their pioneering work emphasizing that after appropriate validation this new magnetic resonance imaging (MRI) and MRI / magnetic resonance spectroscopic imaging (MRSI) models, might improve the overall accuracy of clinical models in predicting the likelihood of insignificant prostate cancer .Information obtained with conventional MRI and with magnetic resonance spectroscopic imaging were combined with clinical variables and biopsy results in order to build this new clinical nomogram. Both MRI models and the MRI/MRSI model were more accurate than the clinical models for discriminating insignificant prostate cancer from significant prostate cancer. Since MRSI is more specific than conventional MRI for identification of prostate cancer, one could expect that the MRI/MRSI model was the most discriminating (area under the curve 0.854) and performed significantly better than MRI model alone and other clinical models. As pointed out by the authors the major limitation of the model is that they are vulnerable to upgrading of the biopsy Gleason grade after radical prostatectomy; 26% of the patients of this series had their Gleason scores upgraded. This was particularly important in 7% of the patients of this series. The authors emphasizes that their goal was not produce MRI models ready for clinical use, but rather to test the feasibility of creating such models. In our institution, we already started a prospective clinical study in order to validate this MRI/MRSI model.

Dr. Adilson Prando

Chief, Department of Radiology

Vera Cruz Hospital

Campinas, São Paulo, Brazil

E–mail: aprando@mpc.com.br

  • Imaging

    Comparison of effective radiation doses in patients undergoing unenhanced MDCT and excretory urography for acute flank pain
  • Publication Dates

    • Publication in this collection
      23 Oct 2007
    • Date of issue
      Aug 2007
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