MRI quality assurance using the ACR phantom in a multi-unit imaging center

Figures & data

Table I. Imaging parameters of the ACR sequences [16].

Sequence	TR (ms)	TE (ms)	FOV (cm)	Matrix	Averages	Number of slices	Slice thickness (mm)
Sagittal locator	200	20	25	256 × 256	1	1	20
Axial T1	500	20	25	256 × 256	1	11	5
Axial T2	2000	20/80	25	256 × 256	1	11	5

TR, repetition time; TE, echo time; FOV, field of view.

Table II. Imaging parameters of site T1-weighted sequences of different systems.

System #	Sequence	TR (ms)	TE (ms)	FOV (cm)	Matrix	Averages	BW (Hz/pixel)	Pixel size (mm)
1	SE	500	10	23 × 23	256 × 205	1	207	0.9 × 1.1
2^a	SE	500	8.4	23 × 20	256 × 218	1	201	0.9 × 0.9
2^b	SE	500	8.4	21 × 22	256 × 218	1	201	0.9 × 0.9
3	SE	491	14	23 × 20	256 × 224	2	130	0.9 × 0.9
4	SE	550	12	23 × 23	256 × 256	1	90	0.9 × 0.9
5	SE	550	8.7	23 × 23	256 × 256	1	150	0.9 × 0.9
6	SE	500	7.7	23 × 20	256 × 168	2	140	0.9 × 1.2
7	SE	475	14	23 × 23	240 × 180	2	122	1.0 × 1.3
8	SE	475	14	23 × 23	240 × 180	2	122	1.0 × 1.3
9	SE	180	14	24 × 24	256 × 224	2	61	0.9 × 1.1
10	SE	460	20	25 × 25	320 × 224	1	61	0.8 × 1.1
11	SE	297	15	23 × 23	256 × 205	2	100	0.9 × 1.1

TR, repetition time; TE, echo time; FOV, field of view; BW, bandwidth; SE, spin echo.

In FOV, matrix and pixel size, the first number refers to anterior-posterior direction and the second number to right-left direction.

^a,bThe first measurement was performed just after the installation of the system and the parameters were changed by the time of the second measurement.

Table III. Imaging parameters of site T2-weighted sequences of different systems.

System #	Sequence	TR (ms)	TE (ms)	FOV (cm)	Matrix	Averages	ETL	BW (Hz/pixel)	Pixel size (mm)
1	TSE	4000	80	24 × 24	400 × 316	1	13	213	0.6 × 0.8
2^a	TSE	6000	96	23 × 22	320 × 320	1	18	220	0.7 × 0.7
2^b	TSE	5120	94	22 × 22	448 × 314	3	13	223	0.5 × 0.7
3	TSE	4000	96	23 × 20	448 × 293	2	11	101	0.5 × 0.7
4	motion corrected TSE	4000	94	23 × 23	320 × 320	1	30	365	0.7 × 0.7
5	motion corrected TSE	4000	106	23 × 23	320 × 320	1	35	365	0.7 × 0.7
6	TSE	4000	99	23 × 20	256 × 244	2	11	100	0.9 × 0.8
7	TSE	2217	100	23 × 23	384 × 299	3	17	168	0.6 × 0.8
8	TSE	2217	100	23 × 23	384 × 299	3	17	168	0.6 × 0.8
9	FLAIR	8802	126	22 × 22	320 × 224	1	N/A	98	0.7 × 1.0
10	TSE	5200	101	25 × 25	448 × 320	2	16	122	0.6 × 0.8
11	TSE	2135	96	23 × 23	352 × 278	3	13	100	0.7 × 0.8

TR, repetition time; TE, echo time; FOV, field of view; ETL, echo train length; BW, bandwidth; TSE, turbo spin echo; FLAIR, fluid-attenuated inversion recovery.

The motion corrected TSE refers to BLADE/PROPELLER/MultiVane techniques. In FOV, matrix and pixel size, the first number refers to anterior-posterior direction and the second number to right-left direction. Inversion time of sequence of system #9 was 2200 ms.

^a,bThe first measurement was performed just after the installation of the system and the parameters were changed by the time of the second measurement.

Figure 1. Examples of ACR phantom images. In slice 1 the hole-array pairs are used for high-contrast spatial resolution and the ramps in the middle for slice thickness accuracy. Slice 5 together with measurements from slice 1 and the sagittal image are used for the geometric accuracy determination. Image intensity uniformity is determined from slice 7 and slices 8 to 11 are used for low-contrast object detectability measurement.

Figure 2. Image intensity percent integral uniformity of a. ACR T1, b. ACR T2, c. site T1 and d. site T2 sequences. The dash lines indicate the ACR recommended acceptance values for 1.5 T (87.5%) and 3.0 T (82%).

Figure 3. Slice thickness accuracy; the nominal value is 5 mm with ±0.7 mm tolerance, limits indicated by dash lines. a. ACR T1, b. ACR T2, c. site T1 and d. site T2 sequences.

Figure 4. Low contrast detectability of measurements 1 and 2 for a. T1-weighted sequences and b. T2-weighted sequences. The dash lines indicate the ACR recommended acceptance values for 1.5 T (9 objects) and 3.0 T (37 objects).

Table IV. High contrast spatial resolution of site sequences.

	T1		T2
system #	site, 1^st	site, 2^nd	site, 1^st	site, 2^nd
1	1.1	1.1	0.9	0.9
2	1.0	1.0	0.9	0.9
3	0.9	1.0	0.9	0.9
4	0.9	0.9	1.0	1.0
5	0.9	0.9	1.0	0.9
6	>1.1	>1.1	0.9	0.9
7	>1.1	>1.1	0.9	0.9
8	>1.1	>1.1	0.9	0.9
9	>1.1	1.1	1.0	1.1
10	1.0	1.1	0.9	0.9
11	1.1	>1.1	0.9	0.9

1^st and 2^nd refer to the two measurements. The values in the table indicate the size of smallest holes that were resolved (0.9, 1.0 or 1.1 mm). >1.1 indicates that the largest holes of 1.1mm were not resolved.

Table V. Percentages of the systems that passed the ACR recommended acceptance criteria in each test.

Sequence (measurement number)	ACR (1)	ACR (2)	Site (1)	Site (2)
Geometric accuracy	100	91	100	91
High-contrast spatial resolution	100	82	36	36
Slice thickness accuracy	100	91	55	55
Slice position accuracy	100	100	100	100
Image intensity uniformity	91	91	91	91
Ghosting	100	100	100	100
Low contrast object detectability	100	100	91	82

The American College of Radiology. Site scanning instructions for use of the MR phantom for the ACR MRI accreditation program. Reston (VA), USA; 2004.

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