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ORIGINAL ARTICLE
:
:
DIAGNOSTIC ACCURACY OF TWINKLING ARTIFACT OF DOPPLER ULTRASOUND IN
PREDICTING URINARY TRACT CALCULI TAKING CT SCAN AS GOLD STANDARD
Munazza Kainat Shuja
1
, Ghazala Wahid
2
, Faryal Bashir
3
, Ayesha Jawaid
4
, Shaista Khan
5
, Ayesha Amjad
6
ABSTRACT
OBJECTIVES
This study aims to determine the diagnostic accuracy of the twinkling artifact
of Doppler ultrasound in predicting urinary tract calculi by taking a CT scan
as the gold standard in the patients presenting to the radiology department at
Hayatabad Medical Complex Peshawar.
METHODOLOGY
A cross-sectional study was conducted in the Radiology Department of
Hayatabad Medical Complex Peshawar in the duration of 22nd April 2021 to
22nd October 2021
A total of 206 suspected of having urinary tract calculi were included in the
study consecutively and subjected to Doppler ultrasound followed by CT
KUB.
RESULTS
The mean age of the sample was 42.3 + 9.1 years. 67% of the sample was
male, and 33% were female. The mean duration of symptoms in our group of
samples was 4.1 + 1.3 weeks. On twinkling artifacts with Doppler US,
urinary tract calculi were observed in 53.4% of patients. In contrast, on
follow-up CT KUB scans, urinary tract calculi were recorded in 73.3% of
patients. The sensitivity of twinkling artifacts with Doppler US was found to
be 71.5%, and the specicity was found to be 96.4%. The positive predictive
value of the twinkling artifacts with Doppler US is 98.2%, and the negative
predictive value is 55.2%.
CONCLUSION
Twinkling artifact on Doppler US has an acceptable sensitivity and specicity
for detecting urinary tract calculi. As such, it is a useful radiological tool for
diagnosing urinary tract stones in adults, and further studies are
recommended to conrm its usefulness, particularly considering other
explanatory eect modiers.
KEYWORDS: Urinary Tract Calculi, Doppler Ultrasound, Computed
Tomography, Twinkling Artifacts
How to cite this article
Shuja MK, Wahid G, Bashir F, Jawaid
A, Khan S, Amjad A. Diagnostic
Accuracy of Twinkling Artifact of
Doppler Ultrasound in Predicting
Urinary Tract Calculi Taking Ct Scan
As Gold Standard. J Gandhara Med
Dent Sci. 2025;12(2):34-38. http://doi.org
Date of Submission: 29-11-2024
Date Revised: 15-03-2025
Date Acceptance: 18-03-2025
1
Trainee Medical Ofcer, Department of
Radiology, Hayatabad Medical Complex,
Peshawar
3
Specialist Registrar, Department of
Radiology, Hayatabad Medical Complex,
Peshawar
4
Trainee Medical Ocer, Department of
Radiology, Hayatabad Medical Complex,
Peshawar
5
Associate Professor, Department of
Radiology, Hayatabad Medical Complex,
Peshawar
6
Trainee Medical Ofcer, Department of
Radiology, Hayatabad Medical Complex,
Peshawar
Correspondence
2
Ghazala Wahid, Associate Professor,
Department of Radiology, Hayatabad
Medical Complex, Peshawar
+92-321-9861864
ghazalawahid3@gmail.com
INTRODUCTION
Flank pain due to urinary tract stones is one of the
leading causes of emergency department visits. Renal
colic is the acute onset of ank pain, often radiating to
the groin. The prevalence of renal colic varies, ranging
from 5% to 15% across dierent regions.
1
The
prevalence of urolithiasis in the Pakistani population is
12%.
2
Various environmental and genetic factors
contribute to the formation of renal stones.
Ultrasonography is the most commonly used imaging
method for identifying urinary tract stones, as it is
widely accessible and free of ionizing radiation. The
sensitivity and specicity of ultrasound for detecting
renal stones are 84% and 53%, respectively.
3
Ultrasonography operates in B mode (grayscale) and
Doppler mode, which uses color ow imaging. The
twinkling artifact, rst identied in 1996, is primarily
associated with renal stones and occurs due to a highly
4
reective surface on Doppler ultrasonography. The
twinkling artifact refers to rapidly uctuating Doppler
signals observed behind particular strongly reective,
irregular objects. It demonstrates high sensitivity and
positive predictive value in diagnosing renal stones.
5
A
study reported that the Doppler twinkling artifact has a
sensitivity of 54.33% and a specicity of 90.39%.
6
Non-contrast CT is regarded as the gold standard for
diagnosing renal stones, with its use increasing in
recent years. It is highly eective in identifying both
renal and ureteric calculi.
7
Non-contrast CT has a
sensitivity of 96.6% and a specicity of 94.9% for
detecting urolithiasis.
8
However, increased exposure to
ionizing radiation is a concern with non-contrast CT.
Therefore, this study aims to assess the positive
predictive value of the Doppler ultrasound twinkling
artifact for diagnosing renal stones, using non-contrast
CT as the gold standard. Since limited research exists
on this topic within the local population, the ndings
/10.37762/jgmds.652
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J Gandhara Med Dent Sci
April - June 2025
will assist radiologists and clinicians in selecting
appropriate imaging techniques for detecting urinary
tract stones while minimizing exposure to harmful
ionizing radiation.
METHODOLOGY
A cross-sectional study was conducted in the Radiology
Department of Hayatabad Medical Complex Peshawar
in the duration of 22nd April 2021 to 22nd October
2021. A total of 206 suspected of having urinary tract
calculi were included in the study consecutively and
subjected to Doppler ultrasound followed by CT KUB.
The hospital's ethics and research committee consented
before the study could be carried out. After obtaining
written informed permission, patients in the radiology
department of the Hayatabad Medical Complex who
met the study’s inclusion criteria were enrolled in the
research. Since the patient was recruited before having
a CT scan, it was uncertain during the sonographic
evaluation whether or not a calculus was present. The
GE Logiq S8 ultrasound machine was used for Doppler
ultrasonography and equipped with a 2-5 MHz convex
probe capable of color Doppler imaging. The 128-slice
CT scanner was used to perform the CT scan. A
radiologist, blinded to the sonographic results, analyzed
the CT scan to detect kidney, ureter, and bladder stones.
These patients underwent a restricted sonographic scan
of their kidneys, ureters, and bladder while awaiting
their CT scan. An ultrasonographer with training
conducted this test using a device capable of color
Doppler imaging. Both greyscale and color Doppler
ultrasound were used to evaluate the urinary tract.
Color Doppler ultrasonography was performed using a
red and blue color map to detect the twinkling artifact.
The Pulse Repetition Frequency (PRF) was adjusted
just above the threshold for color mapping of renal
vessels. For ureteric and bladder calculi, PRF was set
just above the threshold of the surrounding ships of the
ureter and bladder to optimize the detection of
twinkling artifacts. The sonographer, who was also
blinded to the CT scan results, described the calculus’s
location in the tract and whether or not a twinkling
artifact was present on the color Doppler scan.
Figure 1 The grayscale ultrasound image (left) reveals a
hyperechoic focus accompanied by posterior acoustic shadowing.
The middle image, utilizing color Doppler, highlights the
twinkling artifact, appearing as a color mosaic pattern over the
stone. The unenhanced CT scan (right) conrms the presence of a
small renal calculus, ensuring diagnostic accuracy.
Version 23 of the Statistical Package for Social
Sciences (SPSS) was used to enter and analyze the data.
The mean and standard deviation were addressed about
quantitative outcome factors like age and duration of
symptoms. Gender was indicated as a qualitative
outcome variable in frequency and percentage. Using
CT scan results as the gold standard, contingency tables
were used to determine the diagnostic accuracy,
including sensitivity, specicity, positive predictive
value (PPV), and negative predictive value (NPV) of
the twinkling artifact.
RESULTS
A study was conducted on 206 patients suspected of
urinary tract calculi, with a mean age of 42.3 years
(range 25-54). The sample comprised 67% males and
33% females. The average symptom duration was 4.1
weeks. Twinkling artifacts with Doppler US detected
calculi in 53.4% of patients, while follow-up CT KUB
scans conrmed calculi in 73.3%. The sensitivity of
Doppler US twinkling artifacts was 71.5%, and
specificity was 96.4%. The positive predictive value
was 98.2%, and the negative predictive value was
55.2%. Subsequent tables detail sensitivity and
specificity across dierent demographics and symptom
durations.
Table 1: Demographic Parameters of the Study Population
(N=206)
Patient Variables n (%)
Age, Mean +/- SD (years) 42.3+/-9.1 (years)
Gender
Male 138 (67%)
Female 68 (33%)
Stone Site
Kidney and Proximal ureter 155(75.5%)
Mid and Distal Ureter or Urinary Tract 51(24.8%)
Stone Size
Greyscale Ultrasound (cm) Mean±SD 0.88±0.94
Computed Tomography Kidney, Ureters,
Bladder (cm) Mean±SD
0.86±0.99
Duration of symptoms
2-4 weeks 138(67%)
>4-6 weeks 68(33%)
Calculi on twinkling artifact
Yes 110 (53.4%)
No 96 (46.6%)
Frequency of urinary tract calculi on CT Scan
Yes 151(73.3%)
No 55(26.77%)
Table 2: Twinkling Artifact on Us & CT Scan 2 X2 Table
(N = 206)
Calculi on CT Total
Yes No
Calculi on twinkling
artifact
Yes 108 2 110
No 43 53 96
151 55 206
Diagnostic Accuracy of Twinking Artifact of Doppler Ultrasound
Total
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J Gandhara Med Dent Sci
April - June 2025
Table 3: Sensitivity and Specicity of Us in Dierent Age Groups
Age Groups
Sensiti
vity
Specifi
city
PPV NPV
Accura
cy
25-35 years
39.6% 100% 100% 27.5% 50.8%
>35-45 years
89.9% 100% 100% 88.9% 94%
>45-54 years 85.9% 92.9% 97.3% 68.4% 87.6%
Table 4: Sensitivity and Specicity of Us in Gender
Gender Sensitivi
ty
Specifici
ty
PPV NPV Accuracy
Male 68% 94.3% 97.2% 50% 74.6%
Female 79.2% 100% 100% 66.7% 85.3%
Table 5: Sensitivity and Specicity According to the Duration of
Symptoms
Duration of
symptoms
Sensiti
vity
Specifi
city
PPV NPV Accura
cy
2-4 weeks 70% 97.4% 98.6% 55.2% 77.5%
>4-6 weeks 74.5% 94.1% 97.4% 55.2% 79.4%
DISCUSSION
The study evaluated the sensitivity and specicity of
computed tomography (CT) and ultrasound in
diagnosing ureteral colic in 250 patients with lumbar
pain. It found CT to be the most eective for detecting
renal stones, while ultrasound oered a radiation-free
alternative but struggled with accurate identication of
ureteric stones. Ultrasound ecac y is limited by factors
like operator skill, obesity, and patient compliance,
necessitating plain CT (KUB) for patients with renal
colic.
9
Ultrasound is widely available and reliable for
assessing ank discomfort, with 100% specicity and
95% sensitivity, but its sensitivity is limited. CT should
be used as a follow-up investigation.
9
The mean age in
our study was 42.3 years, which coincided with the age
found by Maryam et al., which was 35.69 ± 5.91
years.
10
In our study, females made up 33% and males
67% of the sample. The twinkling artifact on Doppler
ultrasound showed sensitivity of 71.5%, specicity of
96.4%, PPV of 98.2%, NPV of 55.2%, and accuracy of
55.2%. Toru et al. reported sensitivity of 78.9% and
specificity of 83.7% in a similar study of 856 patients,
aligning with our ndings. Maryam et al. found a
sensitivity of 69.64%, specicity of 66.6%, PPV of
82.92%, NPV of 48.48%, and accuracy of 68.75%,
which are comparable to our results.
10
In a retrospective
investigation, Fowler et al. found renal stones with a
sensitivity of 24% and specicity of 90% during a 30 -
day interval, while the US detected only 24 of 101
stones detected by NCCT.
11
Patlas et al. compared US
and NCCT for the detection of ureteric stones in 62
patients, yielding a sensitivity of 93% and specicity of
95%.
12
The low specicity of this study may stem from
using tones near renal sinus fat, vascular calcications,
knowledge of urinary tract anatomy, and bowel gas,
which can obscure ureteral calculi. Additionally,
measuring stones in multiple planes impacts
reproducibility, and artifacts like vascular calcications
can be mistaken for rocks, reducing specicity.
2,6,13,14
Kanno et al. found that the US-detected stone sizes
were almost identical to those detected by NCCT.
15
A
prior study looked at the parameters that inuence the
accuracy of US for the diagnosis of urinary stones.
Goertz observed that the rising degree of HDN was
related to an increase in the detection of ureteric stones
by the US.
16
Kanno et al. reported that the stone size in
the US was associated with the detection rate of the
renal stone.
15
Pichler et al. reported that age and body
mass index aected the diagnosis of ureteral stones in
the US.
17
In contrast, our ndings imply that the
detection rate of urinary tract stones is unrelated to age
or BMI. Ray et al. found that greater skin-to-stone
distance was substantially linked with US and NCCT
discordance.
14
The twinkling artifact, or the color
comet-tail artifact, is a Doppler sonographic focus of
alternate colors behind a reecting item (such as
calculi) that shows turbulent blood ow. The signal
remains persistent even when the pulse repetition
frequency (PRF) is increased and no wave appears in
pulse wave mode. Gliga et al. conducted a study on 113
patients in Romania. They found that the sensitivity,
specificity, positive predictive value, and negative
predictive value of twinkling artifacts in detecting renal
stones smaller than 5 mm were 99.12%, 90.91%,
99.12%, and 90.91%, respectively, similar to our
findings.
18
In another study conducted in Austria in
2009, Mitterberger et al. included 77 urinary tract
stones in 41 participants. Their ndings revealed that
twinkling artifacts on the color Doppler US are
substantially associated with urolithiasis. Interestingly,
their ndings demonstrated that the use of twinkling
artifact in color Doppler US is more accurate than the
presence of posterior shadowing for the identication
of urolithiasis (97% vs. 66%).
19
Masch et al. studied 85
patients and found that isolated sonographic twinkling
artifacts had a sensitivity of 78%, specicity of 40%,
and a positive likelihood ratio of 1.30 for detecting
renal calculi. Specicity and likelihood ratios improved
with the addition of posterior shadowing and echogenic
focus. The lower sensitivity compared to other studies
might be attributed to operator skill and imaging
protocols, with operator blinding not being addressed.
Another study by Dillman et al. examined the
diagnostic accuracy of the twinkling artifact. In this
study, twinkling artifacts' sensitivity and positive
predictive value in detecting renal stones were lower
(55% and 78%, respectively). This artifact's true-
positive and false-positive rates were 49% and 51%,
respectively.
20
The variations between the two
Diagnostic Accuracy of Twinking Artifact of Doppler Ultrasound
37
J Gandhara Med Dent Sci
April - June 2025
investigations might be attributed to imaging
procedures; Dillman et al. employed solely Doppler,
whereas our work included gray-scale imaging.
Sorensen et al. examined 32 stones in 18 kidneys and
discovered that twinkling artifacts had lower sensitivity,
specicity, and predictive values than previously
reported (56%, 74%, 62%, and 68%). This disparity
may be due to the short sample size.
21
Winkel et al.
evaluated 105 individuals with renal stones in Denmark
and discovered sparkling artifacts in 74% of the renal
stones observed in B-mode US. The combination of the
grey scale and color Doppler US for identifying
urolithiasis has a sensitivity, specicity, positive
predictive value, and negative predictive value of 55%,
99%, 67%, and 98%, respectively.
22
The variations in
studies may stem from dierences in operator skill or
stone characteristics. Our study found no factors
affecting the accuracy of the twinkling artifact,
although the limited sample size and lack of
consideration for all characteristics may have played a
role. Other studies similarly overlook anatomical
locations of stones and the eects of stone composition.
While our research highlights the diagnostic potential
of the twinkling artifact in Doppler ultrasound for
detecting urinary tract calculi, further investigation is
needed. Future studies should explore how dierent
stone compositions aect the twinkling artifact’s
presence and intensity, and assess the clinical outcomes
of patients diagnosed via ultrasound compared to CT to
better evaluate ultrasound's eectiveness as a primary
diagnostic tool.
LIMITATIONS
The twinkling artifact in Doppler ultrasound is
operator-dependent and may produce false positives
and negatives. Detection varies with stone size,
composition, and location, with mid-ureteral stones
being challenging. Interference from bowel gas,
vascular calcications, and patient factors like obesity
affects accuracy. Compared to CT, ultrasound may miss
clinically insignicant stones, leading to spectrum bias.
CONCLUSIONS
Twinkling artifact on Doppler US has an acceptable
sensitivity and specicity for detecting urinary tract
calculi. As such, it is a useful radiological tool for
diagnosing urinary tract stones in adults, and further
studies are recommended to conrm its usefulness,
particularly considering other explanatory eect
modifiers.
CONFLICT OF INTEREST: None
FUNDING SOURCES: None
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CONTRIBUTORS
1. Munazza Kainat Shuja - Concept & Design; Data Acquisition;
Data Analysis/Interpretation; Drafting Manuscript; Critical
Revision; Final Approval
2. Ghazala Wahid - Concept & Design; Data Acquisition; Data
Analysis/Interpretation; Drafting Manuscript; Critical
Revision; Supervision; Final Approval
3. Faryal Bashir - Concept & Design; Data
Analysis/Interpretation; Drafting Manuscript; Critical
Revision; Final Approval
4. Ayesha Jawaid - Data Acquisition; Data
Analysis/Interpretation; Drafting Manuscript; Critical
Revision; Final Approval
5. Shaista Khan - Data Acquisition; Data Analysis/Interpretation;
Final Approval
6. Ayesha Amjad - Data Acquisition; Data
Analysis/Interpretation; Drafting Manuscript; Critical
Revision; Final Approval
