Unenhanced helical CT using increased pitch for suspected renal colic: an effective technique for radiation dose reduction?

PURPOSE: To determine the accuracy and utility of unenhanced helical CT for suspected renal colic, using a pitch of either 2.5 or 3.0. METHODS: 59 consecutive patients underwent unenhanced helical CT. 5 mm contiguous images were obtained at a kVP of 120 and an mA of 260. Thirty-four patients were imaged at a pitch of 2.5, and 25 patients were imaged at a pitch of 3.0. Two radiologists, an attending (reader 1), and a second-year resident (reader 2), independently and retrospectively reviewed the CT images, blinded to the clinical outcome. The presence or absence of a ureteral stone was recorded and image quality was graded. A third radiologist determined accuracy for each reader. Average entrance exposure was estimated using a CT phantom at a variety of pitches. RESULTS: Overall sensitivity, specificity, and accuracy for reader 1 were 91, 96, and 93%. For reader 2, they were 86, 93, and 90%. There was no significant difference in accuracy using a pitch of 3.0 compared with 2.5 for either reader. Readers 1 and 2 rated image quality at 2.5 pitch as excellent for 88 and 76% of scans, respectively; at 3.0 pitch the scans were rated by both readers as excellent for 40% and acceptable for 60%. Average entrance exposures were estimated at 461, 553. and 913 mR at pitches of 3.0, 2.5, and 1.5. CONCLUSION: Increasing the pitch on unenhanced helical CT for suspected renal colic to 2.5 or 3.0 appears to be an effective method of reducing radiation dose. Although accuracy of the technique did not significantly change using a pitch of 3.0 in one group of patients, compared with a pitch of 2.5 in another group of patients, image quality did decrease.     

How accurate is helical CT volumetric assessment in renal tumors?

The aim of this study was to evaluate the accuracy of tumor size measurement on CT studies of renal tumors. Sixteen patients with tumors of the kidneys were imaged by helical CT prior to surgery. Assessment of tumor volume was made by two radiologists on the CT images with the summation of area method, then compared with the resected specimen water displacement volume. Intra- and interobserver agreement for CT measurements were also assessed. There were substantial differences between the CT volume measurement compared with the tumor post-operative volume (mean of differences 30.05+/-91.6, 95%CI: 31.45-91.55). The inter- and intraobservation agreements for tumor measurement by CT was found to be satisfactory (ANOVA: p < 0.0001; t-test: p < 0.05). The CT volumetric measurement by area summation is a method with good inter- and intraexamination reproducibility but not an accurate technique for tumor volume assessment.     

Multidetector Computed Tomography for the Assessment of Adnexal Mass: Is Unenhanced CT Scan Necessary?

Objective

To compare the diagnostic performance and radiation dose between contrast-enhanced CT (ECT) alone, and combined unenhanced and contrast-enhanced CT (UE + ECT) for the assessment of adnexal mass.

Materials and Methods

This retrospective study was approved by the Institutional Review Board. A total of 146 consecutive patients (mean age, 41.1 years) who underwent preoperative unenhanced and contrast-enhanced multidetector CT of the pelvis and had adnexal masses found at surgery were included. Two readers independently evaluated the likelihood of adnexal malignancy on a 5-point scale on two different imaging datasets (ECT alone and UE + ECT). The area under the receiver operating characteristic curve (AUC) was used to evaluate diagnostic performance. Radiation dose to patients was calculated by the volume CT dose index (CTDI_vol) and the dose length products (DLP) on each dataset.

Results

Of the total 178 adnexal masses, 133 masses were benign and 45 masses were malignant. For both readers, there is no significant difference of AUC values between ECT alone and UE + ECT for the detection of adnexal malignancy (reader 1, 0.93 vs. 0.95; reader 2, 0.92 vs. 0.91) (p > 0.05). The mean CTDI_vol (12.6 ± 2.2 mGy) and DLP (641.2 ± 137.2 mGy) of ECT alone was significantly lower than the mean CTDI_vol (21.5 ± 2.7 mGy) and DLP (923.6 ± 158.8 mGy) of UE + ECT (p < 0.0001).

Conclusion

The use of unenhanced CT scan in addition to contrast-enhanced CT scan does not improve the detection of adnexal malignancy, but increases radiation exposure.     

Does ultra-low-dose CT with a radiation dose equivalent to that of KUB suffice to detect renal and ureteral calculi?

The objective of this study was to evaluate the diagnostic yield of multislice CT using a radiation dose equivalent to that of conventional abdominal x-ray (KUB). One hundred forty-two patients were prospectively examined with ultrasound and a radically dose-reduced CT protocol (120 kV, 6.9 eff. mAs). Number and size of calculi, presence of urinary obstruction, and alternative diagnoses were recorded and confirmed by stone removal/discharge or by clinical and imaging follow-up. The mean effective whole-body dose was 0.5 mSv in men and 0.7 mSv in women. The sensitivity and specificity in detecting patients with calculi was 97% and 95% for CT and 67% and 90% for ultrasound. Urinary obstruction was similarly assessed, whereas CT identified significantly more alternative diagnoses than ultrasound (P<0.001). With regard to published data for standard-dose CT, the present CT protocol seems to be comparable in its diagnostic yield in assessing patients with calculi, and its radiation dose is equivalent to that of KUB.     

Unenhanced Spiral CT in Acute Ureteral Colic: A Replacement for Excretory Urography?

Objective

To compare the usefulness of unenhanced spiral CT (UCT) with that of excretory urography (EU) in patients with acute flank pain.

Materials and Methods

Thirty patients presenting with acute flank pain underwent both UCT and EU. Both techniques were used to determine the presence, size, and location of urinary stone, and the presence or absence of secondary signs was also evaluated. The existence of ureteral stone was confirmed by its removal or spontaneous passage during follow-up. The absence of a stone was determined on the basis of the clinical and radiological evidence.

Results

Twenty-one of the 30 patients had one or more ureteral stones and nine had no stone. CT depicted 22 of 23 calculi in the 21 patients with a stone, and no calculus in all nine without a stone. The sensitivity and specificity of UCT were 96% and 100%, respectively. EU disclosed 14 calculi in the 21 patients with a stone and no calculus in eight of the nine without a stone. UCT and EU demonstrated secondary signs of ureterolithiasis in 15 and 17 patients, respectively.

Conclusion

For the evaluation of patients with acute flank pain, UCT is an excellent modality with high sensitivity and specificity. In near future it may replace EU.     

CT for evaluation of potential renal donors – How does iterative reconstruction influence image quality and dose?

Purpose

To assess ASIR (adaptive statistical iterative reconstruction) technique regarding dose reduction and its impact on image quality in evaluation CTs of potential kidney donors.

Materials and methods

Between May and November 2013, a prospective study of 53 assumingly healthy potential kidney donors was conducted. The subjects underwent abdominal evaluation CT prior to the planned explantation of a kidney and were randomly divided into 2 groups: Group A was examined with an ASIR 40 protocol (n = 26), group B (n = 27) was examined using a standard FBP (filtered back projection) protocol. Image quality was assessed both quantitatively (by obtaining attenuation values in different organ regions and calculating SNR and CNRs) and qualitatively (by two observers who evaluated image quality using a 5-point scale system). Applied dose was analyzed as CTDIvol (mGy), total DLP (mGy × cm) and effective dose (mSv).

Results

Applied dose in group A was about 26% lower than in group B (p < 0.05). Between both groups, dose determining parameters such as scan length and patients’ body diameter showed no significant difference. SNR (signal-to-noise ratio) was significantly higher in group A (p < 0.05). CNRs (contrast-to-noise ratios) for different tissues were not significantly different. Observer rated image quality showed no significant difference.

Conclusion

ASIR can contribute to a relevant dose reduction without any loss of image quality in CT scans for evaluating potential kidney donors.     

What are the risks from medical X-rays and other low dose radiation?

The magnitude of the risks from low doses of radiation is one of the central questions in radiological protection. It is particularly relevant when discussing the justification and optimization of diagnostic medical exposures. Medical X-rays can undoubtedly confer substantial benefits in the healthcare of patients, but not without exposing them to effective doses ranging from a few microsieverts to a few tens of millisieverts. Do we have any evidence that these levels of exposure result in significant health risks to patients? The current consensus held by national and international radiological protection organizations is that, for these comparatively low doses, the most appropriate risk model is one in which the risk of radiation-induced cancer and hereditary disease is assumed to increase linearly with increasing radiation dose, with no threshold (the so-called linear no threshold (LNT) model). However, the LNT hypothesis has been challenged both by those who believe that low doses of radiation are more damaging than the hypothesis predicts and by those who believe that they are less harmful, and possibly even beneficial (often referred to as hormesis). This article reviews the evidence for and against both the LNT hypothesis and hormesis, and explains why the general scientific consensus is currently in favour of the LNT model as the most appropriate dose-response relationship for radiation protection purposes at low doses. Finally, the impact of the LNT model on the assessment of the risks from medical X-rays and how this affects the justification and optimization of such exposures is discussed.     

CT radiation dose: what can you do right now in your practice?

OBJECTIVE: The purpose of this article is to review reasonable measures that community radiologists can realistically implement as a response to the current increased public concern regarding CT radiation risk. CONCLUSION: Potential measures include provision of patient information material, review of CT protocols and indications, promotion of alternative studies, use of decision support software, automatic tube current modulation, bismuth shields, improved image reconstruction algorithms, empowerment of technologists to adjust protocols, and calculation of radiation dose for possible reporting.     

Differences of renal parenchymal attenuation for acutely obstructed and unobstructed kidneys on unenhanced helical CT: a useful secondary sign?

OBJECTIVE: The purpose of this study was to ascertain whether the difference in attenuation frequently noted on unenhanced helical CT scans between a patient's acutely obstructed kidney and the unobstructed kidney is a reliable secondary sign of acute renal obstruction. CONCLUSION: In 95% of patients with acute renal obstruction, the affected kidney was less dense than the unobstructed kidney. When visually detected by radiologists using CT, this difference in density was at least two standard deviations above normal, making it a reliable secondary sign for acute obstruction.     

Nonobstructing renal stones on unenhanced CT: a real cause for renal colic?

OBJECTIVE: The purpose of this study was to evaluate the incidence of nonobstructing renal stones on unenhanced CT in patients presenting to the emergency department with renal colic and to determine whether this finding might be the cause of patients' symptoms. CONCLUSION: Nonobstructing renal stones on unenhanced CT are a frequent finding in patients evaluated in the emergency department for suspected renal colic. These stones are usually not recognized as the cause of pain by physicians and may be responsible for multiple clinical and radiologic evaluations. In the absence of other clinical or CT evidence of a separate cause, these stones are likely to be the cause of a patient's acute pain.     

Can the anode heel effect be used to optimise radiation dose and image quality for AP pelvis radiography?

IntroductionA study was conducted to determine whether the anode heel effect can be used to influence optimisation of radiation dose and image quality (IQ) for AP pelvis radiography.MethodsATOM dosimetry phantom and an anthropomorphic phantom were positioned for AP pelvis. Using a CR system, images were acquired and doses were measured with phantom feet toward anode and then feet toward cathode. Exposure factors (kVp, mAs and SID) were systematically generated using a factorial design. Images were scored visually for quality using relative visual grading together with a 3 point Likert scale. Signal to noise ratio was also calculated as a physical measure of image quality. Dosimetry data were collected for the ovaries and testes.ResultsThe optimum technique for male, which resulted in lower dose and suitable image quality, was with feet positioned toward the anode (0.80 ± 0.03 mGy; SNR of 38 ± 2.9; visual IQ score 3.13 ± 0.35). The optimum technique for female was with feet toward anode (0.23 ± 0.02 mGy; SNR of 34.7 ± 2.6; visual IQ score 3.15 ± 0.26). kVp had the biggest effect on both visual and physical image quality metrics (p < 0.001) for both tube orientations, whereas SID had the lowest effect on both visual and physical image quality metrics compared with mAs and kVp (p < 0.001). The effect of SID on the SNR was not significant (p > 0.05) with feet toward anode.ConclusionPositioning the patient with feet toward the anode, as opposed to the cathode, has no adverse effect on visual image quality assessment but it does have an effect on physical image quality.Implications for practiceThis study would add a new clinical concept in positioning of AP pelvis radiography especially for male positioning.     

Multiphase renal CT in the evaluation of renal masses: is the nephrographic phase necessary?

The aim of this study is to investigate the feasibility of eliminating the nephrographic phase from the four-phase renal computed tomography (CT) imaging to a three-phase protocol without affecting its diagnostic value. Thirty patients undergoing four-phase renal CT scans for assessment of renal lesions (> 10 mm) were included in the study. A three-phase renal CT, without nephrographic phase, had similar diagnostic ability to a four-phase renal CT in the detection and characterization of renal lesions. A three-phase CT (plain, corticomedullary, and excretory phase) is therefore adequate in the clinical diagnosis of renal lesions.