AJR 2004; 183:71-78
© American Roentgen Ray Society
HASTE MRI Versus Chest Radiography in the Detection of Pulmonary Nodules: Comparison with MDCT
Florian M. Vogt1,
Christoph U. Herborn,
Peter Hunold,
Thomas C. Lauenstein,
Tobias Schröder,
Jörg F. Debatin and
Jörg Barkhausen
1 All authors: Department of Diagnostic and Interventional Radiology, University
Hospital Essen, Hufelandstrasse 55, Essen 45122, Germany.
Received September 22, 2003;
accepted after revision January 14, 2004.
Address correspondence to J. Barkhausen.
Abstract
OBJECTIVE. The purpose of our study was to compare the diagnostic
accuracy of an ultrafast ECG-triggered black blood–prepared HASTE
sequence with chest radiography for the detection of pulmonary nodules.
SUBJECTS AND METHODS. Sixty-four patients with various primary
malignancies who had undergone radiography and MDCT of the chest also
underwent ECG-triggered black blood–prepared HASTE MRI of the lung. MR
images and radiographs were interpreted separately. The number, location, and
size of detected lesions were recorded, and each hemithorax was classified as
affected or not affected on the basis of a grade reflecting the conspicuity of
nodular involvement. Sensitivity, specificity, and positive and negative
predictive values for the detection of pulmonary nodules with diameters of 5
mm or larger were determined, using MDCT findings as the standard of
reference. Lesions with diameters smaller than 5 mm were not evaluated.
Additional lesion-by-lesion comparisons between MDCT and MRI findings were
performed.
RESULTS. MDCT confirmed pulmonary lesions in 32 patients, whereas
HASTE MRI revealed lesions in 30 patients and chest radiography, in 19
patients. MDCT revealed 226 nodules in 32 patients, whereas MRI HASTE revealed
227 lesions in 30 patients. Conspicuity scale–based sensitivity and
specificity for chest radiography were 55.8% and 92.4%, respectively, whereas
HASTE MRI had a sensitivity of 93.0% and a specificity of 96.2%. Positive and
negative predictive values for chest radiography were 80% and 79.3%,
respectively, and for HASTE MRI, 93.0% and 96.2%, respectively. The
sensitivity of HASTE MRI increased with lesion size, ranging from 94.9% for
nodules between 5 and 10 mm in diameter to 100% for lesions exceeding 3 cm in
diameter.
CONCLUSION. ECG-triggered black blood–prepared HASTE MRI is
reliable for detecting pulmonary nodules exceeding 5 mm and has proven
significantly more accurate than conventional chest radiography. The technique
appears useful as an adjunct to MRI of the heart, great vessels, or chest,
potentially increasing the diagnostic yield of MRI examinations.
Introduction
Substantial improvements in hardware and software have rendered scanning
times sufficiently short to allow the breath-hold acquisition of even complex
3D data sets. However, MRI of the lungs has remained clinically irrelevant.
Technical challenges include the low proton density and high susceptibility
differences between air spaces and the pulmonary interstitium inherent to the
lung, as well as the limited spatial resolution of MRI
[1–4].
Despite these difficulties, the potential advantages of pulmonary MRI have
been addressed in a number of articles describing preliminary results
[5–10].
The ability to clearly delineate vessels from soft tissue on MRI was shown to
be beneficial in the staging of bronchogenic carcinoma in hilar and
mediastinal regions [11]. The
unsurpassed soft-tissue contrast inherent to MRI has been successfully
exploited for ventilation–perfusion imaging
[12,
13]. Finally, the lack of
ionizing radiation has motivated several investigators to examine the
potential usefulness of MRI as a screening technique for detection of
pulmonary nodules. Although preliminary results have been encouraging
[5–10],
long acquisition times and limited volume coverage have prevented the
implementation of these techniques into clinical routine. New ultrafast
imaging strategies promise to overcome these limitations.
The purpose of our study was to evaluate the diagnostic accuracy of an
ultrafast pulmonary MRI protocol covering the entire chest in less than 40
sec. Using MDCT findings as the standard of reference, we determined
sensitivity and specificity for the detection of pulmonary nodules and
compared them with the sensitivity and specificity achieved with chest
radiography.
Subjects and Methods
Our study was performed in accordance with regulations of the approving
local ethics committee. Sixtyfour consecutive patients (34 men and 30 women;
age range, 23–95 years; mean age, 56 years) with various primary
malignancies (breast cancer, n = 14; bronchial carcinoma, n
= 9; colorectal cancer, n = 11; gastric cancer, n = 2;
hypernephroma, n = 1; lymphoma, n = 4; melanoma, n
= 6; prostate carcinoma, n = 2; testicular carcinoma, n = 4;
thyroid carcinoma, n = 8; and sarcoma, n = 3) were enrolled
in our study. All patients were referred to our institution to undergo
conventional chest radiography and MDCT of the lungs for evaluation of
suspected pulmonary metastases as part of clinically indicated staging
protocols. Patients with severe claustrophobia or other contraindications to
MRI such as pacemakers or metallic implants were excluded. Before undergoing
MRI of the lungs, all patients gave written confirmation of informed consent.
The range of the interval between the MDCT and MRI examinations was 0–3
days (mean, 1.6 days). The range of the interval between chest radiography and
MDCT was 0–17 days (mean, 6.8 days).
Imaging
Posteroanterior and lateral radiographs were obtained in all patients. All
chest radiographs were exposed at 125 kV and printed on 35 x 43 cm film
(CR Film 100 NIF, Fuji Film Medical Systems).
MDCT scans were obtained on a 4-MDCT scanner (Volume Zoom, Siemens) with
the following parameters: 140 kVp; 100 mAs; slice thickness, 5 mm;
collimation, 2.5 mm; feed, 15 mm/sec; rotation speed, 0.5 sec; effective
reconstructed slice thickness, 5 mm; scanning time, 12–15 sec; and
inplane resolution, 0.5 x 0.5 mm2. We administered 70 mL of a
nonionic contrast agent (Ultravist 300 [iopromide], Schering) using an
automatic power injector (CT 9000, Liebel-Flarsheim) at a flow rate of 3
mL/sec through a 18- to 20-gauge IV catheter placed in an antecubital
vein.
MR images were obtained on a 1.5-T MR scanner (Magnetom Sonata, Siemens)
equipped with a high-performance gradient system characterized by an amplitude
of 40 mT/m and a slew rate of 200 mT/m per millisecond. A standard phased
array torso surface coil was used for signal reception. ECG-triggering with an
active fiberoptic ECG system was required for the black blood preparation and
for reduction of cardiac motion artifacts. On the basis of a multiplanar scout
image, ECG-triggered, breath-hold proton density–weighted black
blood–prepared HASTE images were obtained in the axial orientation. The
imaging parameters were as follows: TR/TE, 2 R-R intervals/23; flip angle,
160°; effective slice thickness, 5 mm without interslice gaps; matrix
size, 158 x 256; and spatial resolution, 2.4 x 1.5 mm2.
The phase-encoding direction was anteroposterior. Thirty-six slices covering
the entire chest were collected in two interleaved concatenations of
14–19 sec each, depending on the patient's heart rate.
Image Analysis
The standard of reference was defined by two experienced radiologists in
consensus on the basis of MDCT scans. All round or ovoid, noncalcified lesions
with diameters of 5 mm or larger within the lung parenchyma were counted as
pulmonary nodules. The number, location, and size of the detected lesions were
recorded. The nodule diameter was defined as the largest diameter on MDCT
scans as displayed on a lung window setting (window width, 2,000 H; window
level, –500 H). Particular attention was paid to the assignment of
nodules into three size categories (5–10 mm, 11–30 mm, and > 30
mm).
All chest radiographs and MR images were interpreted in consensus by two
experienced radiologists who were unaware of the results of the MDCT
examinations. The radiologists first analyzed chest radiographs and then
reviewed MR images 4 weeks later. Hard copies were used for the interpretation
of all three types of examinations. The reviewers did not know the type of
primary malignancy or the extent of the disease in the patients. To increase
the number of observations for the statistical analysis, the reviewers
reported the results for the left and the right lungs separately. The two
radiologists examined chest radiographs and MR images and used a 4-point
conspicuity scale to classify each hemithorax as affected or not affected by
pulmonary nodules. The scale ratings were as follows: 1, definitely affected;
2, probably affected; 3, probably not affected; and 4, definitely not
affected. Hemithoraces classified as grades 1 and 2 were combined and
characterized as affected, whereas hemithoraces classified as grades 3 and 4
were combined and characterized as not affected. The sensitivity and
specificity of chest radiography and MRI for nodule detection were determined
from conspicuity-scale grades. Receiver operating characteristic (ROC)
analyses were performed for chest radiography and MRI by correlating the
presence or absence of lung lesions with the degree of observer's diagnostic
certainty. Estimates of the area under the ROC curve were made with the method
described by Metz et al.
[14].
Sensitivity and specificity values for HASTE MRI and chest radiography of
the lung were determined using MDCT as the standard of reference.
Additionally, lesion-by-lesion comparisons between MDCT and MRI findings were
performed. The size and location of lung nodules detected on HASTE MRI were
compared with the size and location of lung nodules detected on the MDCT.
Sensitivity and specificity values were calculated.
One-to-one comparisons between lesions detected on chest radiography and
those detected on MDCT were performed because multiple lesions were visible in
only one plane on chest radiographs; thus, many lesions on a chest radiograph
could not have been accurately assigned to a potentially corresponding lesion
on the MDCT scan.
Results
Three patients were unable to undergo MRI because of claustrophobia and had
to be excluded from the study. Thus, data sets of 61 examinations were
analyzed. Both MDCT and MRI examinations were well tolerated; no adverse
reactions were observed with either examination. None of the data sets was
degraded by respiratory motion artifacts, and no examination had to be
repeated because of poor image quality. The mean in-room time required for the
MRI examination was 10 ± 4 min, compared with 8 ± 3 min for the
MDCT examination. Longer in-room times for MRI examinations were due to the
ECG-triggered sequence in our protocol, which required time for electrode
placement.
Lesion Detection
On the basis of MDCT findings, metastases were excluded in 29 subjects and
confirmed in 32 patients. HASTE MRI revealed pulmonary nodules in 30 of these
32 patients (Fig. 1A,
1B,
1C,
1D). In two patients, MRI
failed to show pulmonary nodules detected on MDCT, each of which had a maximum
diameter of 8 mm. In one patient, MRI showed a solitary nodule (diameter, 6
mm) that had not been identified on MDCT. Thus, 28 subjects were correctly
classified as free of pulmonary metastases when interpretation was based on
HASTE MRI findings.
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Fig. 1D. —39-year-old man with melanoma. MDCT scan obtained at same
level as C shows same lesion (arrow). Metastasis was confirmed
on follow-up MDCT scan obtained 3 months later that revealed increase in
size.
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Analysis based on chest radiography revealed metastases in 19 of 32
subjects with MDCT-confirmed lesions. Chest radiography failed to show
confirmed lesions in 13 patients (Figs.
1A,
1B,
1C,
1D and
2A,
2B,
2C,
2D). The maximum diameter of
the lesions missed on chest radiography was 2.4 cm. Findings on chest
radiography were correctly judged as not suspicious in 27 patients. In two
patients, pulmonary nodules that were suspected on the basis of chest
radiography were not visualized on MDCT.
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Fig. 2C. —62-year-old man with renal adenocarcinoma. Solitary
metastasis with a maximum diameter of 1.9 cm (small arrow) is seen
close to pericardium on both MDCT scan (C) and HASTE MR image
(D). Note residual pneumonia in right lower lobe (large arrow)
which is visible on both images. Third density (arrowhead) with
diameter smaller than 5 mm can be seen in lingula on MDCT scan and MR
image.
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Fig. 2D. —62-year-old man with renal adenocarcinoma. Solitary
metastasis with a maximum diameter of 1.9 cm (small arrow) is seen
close to pericardium on both MDCT scan (C) and HASTE MR image
(D). Note residual pneumonia in right lower lobe (large arrow)
which is visible on both images. Third density (arrowhead) with
diameter smaller than 5 mm can be seen in lingula on MDCT scan and MR
image.
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Table 1 summarizes the
results of the analysis of 122 hemithoraces assessed in this study. When
hemithoraces that were classified as grades 1 and 2 (definitely affected and
probably affected) were combined for purposes of analysis, chest radiography
revealed 30 affected hemithoraces, whereas MRI revealed 43 hemithoraces as
affected (Table 2). The
resulting sensitivity of chest radiography for the detection of affected
hemithoraces was thus 55.8% and the specificity was 92.4%. The corresponding
positive and negative predictive values were 80% and 79.3%, respectively. For
MRI, sensitivity and specificity were calculated to be 93.0% and 96.2%, with
corresponding positive and negative predictive values of 93.0% and 96.2%,
respectively. The overall conspicuity index produced an ROC area of 0.8 for
chest radiography, whereas the area under the ROC curve was 0.96 for MRI
(Fig. 3).
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TABLE 1 Number of Hemithoraces Affected by Pulmonary Nodules as Seen on Chest
Radiography and HASTE MRI Based on the Grade Assigned on 4-Point Conspicuity
Scale
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TABLE 2 Number of Hemithoraces Affected by Pulmonary Nodules as Seen on Chest
Radiology and HASTE MRI Compared with MDCT Findings as Reference
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Lesion-to-Lesion Comparison
Of the 226 nodules detected on MDCT in 32 patients, 179 lesions showed
diameters of between 5 and 10 mm, 39 had diameters that ranged between 11 and
30 mm, and eight had diameters that exceeded 30 mm. Of the 227 lesions
revealed on HASTE MRI in 30 patients, 178 nodules showed diameters that ranged
between 5 and 10 mm, 41 had diameters between 11 and 30 mm, and eight had
diameters larger than 30 mm (Fig.
4A,
4B,
4C,
4D).
MRI interpretations produced 10 false-negative findings. The diameters of
nine of the nodules missed on MRI ranged between 5 and 10 mm (Fig.
5A,
5B,
5C,
5D,
5E), and one lesion measured
13 mm in diameter. Most of the missed lesions were either located close to the
pericardium or the pleura (n = 5), obscured by hypostasis in the
posterior part of the lungs (n = 2), or misinterpreted as vessels
(n = 3).
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Fig. 5C. —57-year-old man with testicular carcinoma. Lesion-to-lesion
comparison with MDCT scan reveals metastasis (diameter, 5 mm) (arrow)
in anterior segment of upper lobe of right lung close to subsegmental
vessel.
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The number of false-positive findings (n =11) on MRI increased as
lesion size decreased. Among lesions with diameters of between 5 and 10 mm,
eight had false-positive interpretations: Six misinterpretations were caused
by nonspecific artifacts, and in two cases, a subpleural scar was suspected to
be a metastasis. Among lesions with diameters that ranged between 11 and 30
mm, two false-positive findings occurred: One lesion was found to be a
conglomerate of two smaller lesions on MDCT, and the size of the second lesion
was overestimated on MRI; MDCT revealed a diameter of less than 11 mm. No
false-positive findings were found in the pulmonary lesions larger than 30
mm.
Accordingly, the sensitivity values for HASTE MRI were 94.9% for lesions
between 5 and 10 mm, 97.4% for lesions between 11 and 30 mm, and 100% for
lesions exceeding 30 mm. The overall sensitivity for the detection of all
pulmonary lesions was 95.6% (Table
3). On the basis of these data, a positive predictive value for
MRI of 94.9% was calculated.
Discussion
ECG-triggered breath-hold HASTE MRI of the lung combined with dedicated
surface coils represents a quick and robust method to reliably detect
pulmonary nodules exceeding 5 mm in diameter. With MDCT as the standard of
reference for the detection of pulmonary nodules, MRI proved significantly
more accurate than conventional chest radiography. Both lesion-by-lesion and
hemithorax-based analysis showed that MRI reliably revealed noncalcified
metastatic nodules with sensitivity and specificity values exceeding 93%.
Therefore, HASTE MRI of the lungs should be considered as an addition to all
MRI examinations focusing on the heart and great vessels of the chest.
Furthermore, in countries in which screening with ionizing radiation is
prohibited, this radiation-free technique has potential for tumor staging
purposes and for lung screening programs.
Vast improvements in MRI hardware and software have resulted in a
considerable increase in the number of MRI examinations of the heart and great
vessels [15,
16]. MR angiography represents
the technique of choice for the assessment of chronic aortic disease, and
cardiac MRI is now routinely used for the assessment of myocardial function
and viability in patients with coronary artery disease
[17]. The addition of
breath-hold black blood–prepared HASTE imaging of the lungs,
accomplished in merely two additional breath-holds, could enhance the
diagnostic yield of thoracic MRI because risk factors predisposing patients to
arterial or cardiac disease are also associated with an increased incidence of
bronchogenic carcinoma. Thus, a 5% (65/1,326 patients) incidence of
noncalcified pulmonary nodules has been reported when evaluating electron-beam
tomographic scans of cardiac patients obtained to quantify coronary artery
calcification [18,
19].
The excellent sensitivity and specificity data suggest MRI could also be
used for dedicated pulmonary imaging performed for tumor staging. However, the
combination of the inability to reliably detect metastases smaller than 5 mm
[4,
9] and the inability to
properly assess the interstitium and its possible invasion by lymphangitic
tumor spread is likely to limit the clinical usefulness of MRI for this
indication. In addition, calcified metastases such as those from osteosarcoma
may be missed because low proton density causes them to appear dark. Despite
these limitations, pulmonary MRI may be used for tumor staging in young
patients with potentially curable primary tumors, such as testicular cancer or
lymphoma, to reduce the radiation exposure caused by multiple staging and
follow-up scans.
The ability to detect most lesions exceeding 5 mm in diameter, the lack of
exposure to ionizing radiation, and relatively short data acquisition and
in-room times combine to make pulmonary MRI a potentially attractive technique
for lung disease screening. Screening for bronchial carcinoma on CT has been
suggested to be cost-effective for high-risk patients
[20–22].
MDCT is accurate but exposes the patient to a considerable amount of ionizing
radiation. Although the effective dose can be reduced to approximately 1 mSv
using low-dose protocols [23],
radiation exposure will always remain a deterrent for screening. This concern
is reflected by European Union legislation that explicitly prohibits the use
of diagnostic radiographic techniques for the purpose of screening with the
exception of mammography
[24–26].
MRI of the lung is potentially hampered by several factors including low
proton density, limited spatial resolution, high susceptibility differences
between air spaces and the pulmonary interstitium, and the presence of
respiratory and cardiac motion
[9,
10,
27]. The technique we have
described overcomes most of these limitations. Breath-holding and
ECG-triggering eliminate respiration and flow-related artifacts. Beneficial
effects on image quality have been documented in a study analyzing
single-slice T2-weighted turbo spin-echo and turbo STIR sequences
[9]. Advantages inherent to
these sequences, including higher spatial resolution and excellent contrast
properties, are tempered by long acquisition times. On the other hand,
breath-hold and ECG-gated HASTE imaging provides rapid data acquisition with
complete coverage of the entire chest in contiguous 5-mm sections collected
within two breath-holds, each lasting less than 20 sec.
HASTE images are characterized by high signal intensity in water-rich
tissues. Thus, lung parenchymal lesions and vessels appear bright whereas
surrounding air-filled lung parenchyma display low signal intensity. The black
blood preparation assures flow voids with no apparent signal in pulmonary
vessels, thereby facilitating the differentiation of small lung nodules from
arteries and veins. In addition, the short echo spacing applied in conjunction
with several (180) refocusing pulses minimizes magnetic susceptibility. Hence,
excellent lesion contrast is achieved without IV contrast administration.
The technical approach we have outlined is not without its limitations. All
imaging was performed on a 1.5-T scanner equipped with the latest hardware and
software, resulting in excellent image quality and short scanning times.
However, MRI scanners with less powerful gradients or lower field strengths
would not necessarily produce a comparable image quality with short scanning
times.
Despite combining a torso phased array surface coil with the spine array
coil, we achieved an in-plane resolution in this study of 2.4 x 1.5
mm2, which remains poor and could result in a limited sensitivity
for lesions with diameters smaller than 5 mm. However, this limitation could
be overcome by the implementation of parallel acquisition techniques that
could enhance spatial resolution without prolonging the data acquisition time
[28].
No attempt was made to distinguish benign from malignant nodules.
Calcifications, which are easily depicted on CT, usually denote a benign
origin. Calcifications on MRI appear dark and hence cannot be distinguished
from the surrounding air-filled structures. For predominantly calcified
lesions, which are almost always benign, this difficulty in differentiation
causes no problems because these lesions cannot be detected on MRI. However,
small calcifications in a soft-tissue nodule that most likely indicate a
benign lesion may well be missed on MRI. CT cannot reliably distinguish
between benign and malignant noncalcified nodules, but dynamic MRI performed
with short TR and TE parameters may provide additional information.
Implementation of this procedure seems worthwhile in cases in which pulmonary
nodules are found incidentally on HASTE MRI data sets
[29–31].
Nevertheless, we would recommend a CT scan be obtained in all patients with
lung nodules incidentally detected on MRI.
We conclude that ECG-triggered black blood–prepared HASTE MRI is a
reliable technique for the detection of pulmonary nodules with diameters of 5
mm or larger and that the technique is significantly more accurate than
conventional chest radiography. The technique appears useful as an adjunct to
MRI of the heart or great vessels because it may increase the diagnostic yield
of these examinations. In addition, ECG-triggered black blood– prepared
HASTE MRI may be used for screening purposes.
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Abstract
Introduction
